Identification of Pivotal Factors Influencing the Establishment of Green Port Governance Models: A Bibliometric Analysis, Content Analysis, and DPSIR Framework

Abstract

Green port governance is an emerging and recent port restructuring process influencing port authorities regarding adopting recurring sustainable governance practices within their business models. However, contemporary academic bias towards a particular aspect of port sustainable governance practice leads to publication results fragmentation and difficulty in a collective assessment of the conclusions. The lack of holistic research endeavors to port sustainable governance practices hinders the identification of organized, specific, and goal-oriented factors indispensable for coherently directing ports to sustainable and green transitions. In order to bridge the identified gap, this paper conducts a bibliometric analysis of 278 scientific articles on the emerging green port governance concept in the maritime industry, published in 113 academic outlets, authored by 695 scholars, and obtained from the world’s most reputable scientific database—ISI Web of Science. The conducted meta-analysis via HistCite software revealed the most prestigious academic institutions, the most prominent scientific journals, the most impactful scientific articles, and the most influential scholars. The bibliographic coupling methodology via Bibliometrix tool in R software indicated five concurrent research streams on the basis of the top 10% of the scientific articles: (1) Adoption of contextualized models of port governance reform as a consequence of port multi-scalar embeddedness forces and institutional stretching; (2) Fostering port sustainability competitiveness via extended resource pools in terms of dry ports coupling; (3) The digitalization role of information systems regarding the interaction between transport, infrastructure, and institutional management in ports; (4) Assessment and innovation in seaport competition policies for the integration of green and sustainable operations; and (5) Conceptual development and awareness raising of port management practices on account of CO₂ evidence-based policies regarding port terminals. The application of co-citation analysis methodology revealed future research directions within the five concurrent research streams on the basis of the top 5% trending scientific articles. The detailed content analysis assesses the scientific mapping of future research directions via the structural associations of the Driver-Pressure-State-Impact-Response (DPSIR) framework. The cause-and-effect relationships of the structural associations of the DPSIR framework possess the possibility of providing substantial insights into the most influential factor identification regarding the development of green port governance models and self-assessment toolkits.

1. Introduction

Governance constitutes a complex system of institutions, values, and policies utilized by civilizations in order to address economic, social, and ecological affairs between interactions of the state, civil society, and the private sector [1]. The contemporary scholarly approach toward the traditional concept of governance characterizes a disassociation of the term “governance” from the term “government” [2,3]. Pivotal factors contributing to the obsolescence of the traditional concept of governance stem from the fact that globalization enabled the emerging new concept of governance to occur beyond the retreating reach of government control. Thus, the resulting consequence manifests itself in agent-based approaches, specifically in terms of: (1) Expanding the role of civil society regarding directing and regulating the utilization of public resources; and (2) increasing reliance on deliberative, as opposed to representative, forms of democracy [4].

The most recent conceptualization of the emerging concept of governance states that governing authorities have become more dependent on societal actors (agents) to achieve their goals because of the increasing complexity of the governments’ challenges [5]. Thus, governance is a horizontal process of collaborative actions occurring within governance networks comprising complex webs of relationships between government, business, and civil society actors that are not necessarily equitable [6].

Modern seaports are nodes in global supply chains possessing attributes of strong maritime character coupled with functional and spatial clustering of seaport and land transport mode-related activities [7]. The respective statement concludes that seaports are complete opposites of homogenous environments, which creates the condition to perceive seaports as inherently complex and heterogenous environments that involve a wide diversity of market players and mutual interconnections [8]. Progressive globalization sustained by trade liberalization facilitates seaports concerning attracting water and land transport modes which inevitably results in the concentration of various seaport-related and transportation-mode related environmental externalities. The proceeding detrimental effects of anthropogenic-induced climate change place seaports under pressure for the stringent perception of seaport operations in order to improve their sustainable pathways [9]. The detrimental effects of climate change resulted in the international port community to begin addressing the global energy crisis and environmental degradation-related effects of seaports by proposing the green port concept.

Contemporary notions and definitions of the green port refer to a seaport comprised of a sustainable environment, fair use of resources, low energy usage, and low emissions [10]. Even though the maritime industry is responsible for the realization of approximately 80% of the world trade, the majority of the pollution originates from high energy intensity activities of port production and transport ships. The predominant occurrence of the world’s maritime trade emissions happens in the coastal areas of seaports, representing a value of 70%, whereas 60–90% occurs during the ship berthing period [11]. Furthermore, the interconnected vastness of diverse societal agents holding differing socio-economic interests, as well as constantly developing regulatory requirements, additionally create barriers in establishing the green port governance models as an important direction in the seaport evolution process of the upcoming decades.

The furthest extent of the knowledge regarding the green port concept within the maritime scientific literature reflects a bias toward a particular aspect of seaport sustainable governance practice, which indicates a lack of considering the cause-and-effect relationships of factors within the seaport as a complex ecosystem. The upcoming maritime scientific literature review serves as evidence that the majority of scholars address the green port concept mainly from policy-creation, technological, and operations research approaches, respectively.

Yang and Chang (2013) conduct a comparison analysis of cargo handling equipment in container terminals and container yards from the perspective of energy savings and CO₂ reduction. The study concludes that governing authorities may utilize the results as a basis for formulating appropriate regulations and incentive measures for terminal operators to adapt electric rubber-tired gantry cranes to upgrade their terminal handling equipment [12]. Chiu, Lin, and Ting (2014) formulate a Fuzzy Analytical Hierarchy Process for the 13 selected most crucial attributes of green port operation. The study pinpoints the top five attributes and proposes them as a good referral for policy creators in order to reform the port operations process between port actors toward a greener pathway [13].

Sawada et al. (2003) indicate how technological approaches in terms of rapid industrial growth negatively affect the environmental qualities of coastal zones and port-cities even though they highly stimulate economic growth and regional development. The scholars provide important insights regarding how green technological approaches can foster a desirable ecosystem where both the social and economic system would flourish while simultaneously preserving the coastal environment [14]. Peris-Mora et al. (2005) extensively address the indispensable role of information communication technologies and data management regarding the correct implementation of Environmental Management Systems in industrial seaports. The study highlights how stage diagrams, systemic models (material and energy flow charts), and Multi-Criteria Analysis techniques can further advance the impacts on ICT technologies and data management in directing ports toward green transitions [15].

Esmemr et al. (2010) examine the possibilities regarding how Turkish ports can consider both lean and green approaches in their business operations. The scholars apply a simulation modelling technique on a Turkish container terminal in order to find the optimal solution regarding the mitigation of environmental damage caused by container handling equipment during cargo operations [16]. Bergqvist and Egels-Zanden (2012) address the employment of Corporate Social Responsibility (CSR) strategies of both local and global logistic service providers. The study concludes that green port dues are a positive CSR strategy that can be utilized as a tool to internalize external costs in seaport hinterland logistics systems [17].

The aforementioned brief literature review indicates a scarcity of maritime scientific literature on green port governance. Simultaneously, most scholars adhere to one perspective regarding developing the green port concept. Contrarily, studies adhering holistically to identifying and implementing pivotal factors influencing the establishment of green port governance models are scarce in the maritime scientific literature, thus creating a substantial knowledge gap.

The scholars of this study aim to bridge the identified knowledge gap via scientific mapping methodology in order to create the quantitative structure of the emerging green port research domain and to reveal the dynamics of the emerging green port research domain. A bibliometric analysis is conducted to review the selected studies that assess the emerging green port concept within the maritime context under four main research objectives. The first research objective is to provide the general results of the bibliometric analysis regarding the independent existence of the emerging green port research domain. The second research objective is to provide the specific results of the bibliometric analysis by identifying the most influential scientific articles, journals, institutions, and scholars within the emerging green port research domain. The third research objective is to indicate five concurrent research streams on the basis of the top 10% of the scientific articles of the bibliometric study. The fourth and final research objective is to implement the DPSIR framework in order to conceptually depict the cause-and-effect relationships of the factors influencing the establishment of green port governance models via future research streams identification on the basis of the top 5% of the scientific articles.

The expected research results of the study may prove beneficial and advantageous both for the maritime industry and academia. Port authorities and the wider port community regarding shipping companies, logistics service providers, and other critical societal agents within the seaport ecosystem can utilize the results to better identify and coordinate their actions, lower energy usage and emissions, improve safety, and mitigate environmental externalities. Scholars and scientists will have at their convenience a thorough synopsis of research results from an emerging research domain that is characterized by scientific rigor, reproducibility, and transparency.

The forthcoming chapters of the study are presented concludingly. Section 2 contains information on the bibliometric analysis research methodology regarding the general and specific results of the emerging green port research domain. Section 3 reports the five concurrent research streams on the basis of the top 10% of the scientific articles. Section 4 elaborates the DPSIR framework cause-and-effect relationships between factors via future research streams identification on the basis of the top 5% of the scientific articles. Section 5 is a critical conclusion of the entire study.

2. Bibliometric Analysis Research Methodology

Bibliometric analysis is a quantitative and qualitative research methodology extensively utilized in the scientific field of information and library research domains in order to comprehensively evaluate academic studies [18]. The main feature of bibliometric analysis is measuring the impact of scientific literature and ascertaining the level of maturity in the inquired research domain via criteria such as output volume, scientific quality, interdisciplinarity, and network strength [19]. Bibliometric analysis is advantageous for knowledge generation because it enables the researcher to explore the structure of scientific fields and reveal the dynamics of scientific fields [20]. Thus, the researcher has the possibility of finding and evaluating the most impactful scientific literature studies with mitigated subjective bias within the inquired scientific field. Furthermore, bibliometric analysis applies statistical algorithms in order to provide better objective and reliable scientific analysis, rendering it indispensable for conducting a systematic, replicable, and transparent literature review [21].

Figure 1 represents the graphical depiction of the bibliometric analysis five-step methodological workflow of this study.

Figure 1 indicates that the first step consists of the ISI Web of Science scientific repository search of scientific studies. The search was conducted via Boolean search term utilization and resulted in 2586 scientific studies in total. The second step comprises of article critical filtering with adherence to green port governance literature. The application of the three exclusion criteria in terms of article as publication type, English language, and article manual screening for inquired relevance resulted in 278 articles in total. The third step contains the bibliometric citation analysis research methodology. The most impactful scientific articles, scientific journals, academic institutions, and scholar collaboration networks are presented and assessed within the aforementioned step. The fourth step consists of content analysis and is subdivided into two sub-steps. The first sub-step consists of key articles extraction which enabled the formation of research clusters on the basis of the revealed five research streams in adherence to the key bibliometric term criteria of Total Local Citation Score (TLCS) being higher or equal than three. The second sub-step consists of trending articles extraction in adherence to the key bibliometric term criteria Local Citation Score ending (LCSe) in the last three years of the bibliometric analysis, which enabled the identification of future research directions. The extraction of scientific information from the future research directions enabled the identification of pivotal factors influencing the establishment of green port governance models and their cause-and-effect analysis via the structural associations of the Driver-Pressure-State-Impact-Response (DPSIR) framework. The fifth and final step contains the summary of the explored bibliometric analysis results and concluding remarks.

2.1. General Results of the Bibliometric Analysis Research Methodology

The bibliometric analysis research methodology regarding the emerging green port research domain is conducted on the basis of the bibliography data set obtained from the ISI Web of Science (WoS)—the most renowned scientific database. The process of bibliography data collection in the WoS scientific repository begins on 31 March 2022 and is enabled using the Boolean Search Terms.

Table 1. ISI WoS research findings on the emerging green port research domain via Boolean Search Terms utilization.

Step	Keyword Search via Boolean Search Term	Number of Articles WoS
1.	“seaport *“ (Topic)	2586
2.	“seaport*” OR “green port*”	2829
3.	“seaport*” OR “green port*” OR “port community system*”	2869
4.	((“seaport*” OR “green port*” OR “port community system*”) AND (“port governance”))	36
5.	((“seaport*” OR “green port*” OR “port community system*”) AND (“port governance” OR “sustainable port*”))	66
6.	((“seaport*” OR “green port*” OR “port community system*”) AND (“port governance” OR “sustainable port*” OR “port sustainability”))	84
7.	((“seaport*” OR “green port*” OR “port community system*”) AND (“port governance” OR “sustainable port*” OR “port sustainability” OR “port cluster*”))	100
8.	((“seaport*” OR “green port*” OR “port community system*”) AND (“port governance” OR “sustainable port*” OR “port sustainability” OR “port cluster*” OR “socio-technical”))	104
9.	((“seaport*” OR “green port*” OR “port community system*”) AND (“port governance” OR “sustainable port*” OR “port sustainability” OR “port cluster*” OR “socio-technical” OR “distribution network”))	113
10.	((“seaport*” OR “green port*” OR “port community system*”) AND (“port governance” OR “sustainable port*” OR “port sustainability” OR “port cluster*” OR “socio-technical” OR “distribution network” OR “container terminal*”))	399
11.	Exclusion Criteria: Article	298
12.	Exclusion Criteria: English Language	294
13.	Exclusion Criteria: Article Manual Screening for Inquired Relevance	278

contains the guidelines for the detailed keyword search process via utilization of Boolean Search Terms.

Table 1 indicates that the last keyword search located in step 10 constitutes two subsets of Boolean Search Term strings. The first subset contains the keyword structure (“seaport*” OR “green port*” OR “port community system*”), which addresses articles regarding the greening of seaports and the application of big data and information communication technologies within seaports as complex systems comprising a wide plethora of societal agents with differing interests. The second subset contains the keyword structure (“port governance” OR “sustainable port*” OR “port sustainability” OR “port cluster*” OR “socio-technical” OR “distribution network” OR “container terminal*”), which addresses articles regarding the interconnectedness of the seaport’s sustainability-oriented operational and managemental strategies with stakeholders on several scales and in many spheres, from local to global and from business to government. The refinement process starts at step 11 via exclusion criteria application. The first exclusion criteria consist of incorporating journal articles only as the examined scientific publications. The second exclusion criteria consist of considering only English language in journal articles as the medium of knowledge exchange. The third and final exclusion criteria consist of the journal article manual screening for inquired relevance within the selected sample of the WoS scientific repository. Accordingly, articles representing the homonymy problem of keywords such as “port” belong to telecommunications and electronics research domains, which indicates a deviation from the emerging green port research domain, resulting in their exclusion from this study.

The final sum of journal articles after the Boolean Search Terms utilization and exclusion criteria application represents a value of 278 journal articles. The analytical and theoretical purpose of this study aims to elucidate and elaborate on the emerging green port governance concept in the maritime industry and thus analyze the selected 278 journal articles from the aspect of four primary meanings of governance within the scientific literature: (1) Governance as a structure; (2) Governance as a process; (3) Governance as a mechanism; and (4) Governance as a strategy. A thoughtful and clear elaboration of the four primary meanings of governance is necessary in order to distinguish them categorically for the upcoming analytical and theoretical purposes of this study. Governance as a structure signifies the architecture of formal and informal institutions; as a process, it signifies the dynamics and steering functions involved in lengthy and incessant processes of policy-making; as a mechanism, it signifies institutional procedures of decision making, compliance and control; and as a strategy, it signifies the societal actor’s efforts to govern and manipulate the design of institutions and mechanisms in order to shape choice and preferences [22,23,24,25].

Figure 2 is a statistical representation of the total scientific output of green port governance literature regarding the refined bibliography sample of 278 journal articles.

Figure 2 indicates the average number of articles published per year of approximately 13.9 articles per year within the selected timespan of 20 years, ranging from 2001 to 2021, respectively. Graph 1 is a statistical representation of the scientific impacts of the refined bibliography sample of 278 journal articles as it contains the key bibliometric terms Total Local Citation Score (TLCS) and Total Global Citation Score (TGCS). Total Local Citation Score represents the number of times an article is cited by any other articles within the sample of the study [26]. Total Global Citation Score represents the number of times an article is cited by any other articles that are available on the ISI WoS scientific repository [26]. The comparison analysis of the refined bibliography sample of 278 journal articles with the key bibliometric terms TLCS and TGCS allows for a detailed assessment of scholarly interest in the emerging green port research domain. The first five-year quartile of the bibliography sample ranging from 2001 to 2005 reveals that the first eight articles represent a TLCS value of 6 and a TGCS value of 185 citations. The second five-year quartile of the bibliography sample ranging from 2006 to 2010 reveals that the second 27 articles represent a TLCS value of 32 and a TGCS value of 461 citations. The third five-year quartile of the bibliography sample ranging from 2011 to 2015 reveals that the third 67 articles represent a TLCS value of 173 and a TGCS value of 1519 citations. The fourth five-year quartile of the bibliography sample ranging from 2016 to 2020 reveals that the last 170 articles represent a TLCS value of 90 and a TGCS value of 1347 citations. Even though the bibliography data in Graph 1 indicates stable growth, the most impactful articles for the emerging green port research domain belong to the third quartile because the ratio between the key bibliometric term of TLCS and published journal articles represents the highest value of 2.6 local citations per article within the entire interquartile range. The last three years of the selected bibliography sample indicate a downward trend of key bibliometric terms of TLCS and TGCS due to the necessary time required for the recently published journal articles to gain scientific interest and significance.

2.2. Specific Results of the Bibliometric Analysis Research Methodology

The specific results of the bibliometric analysis research methodology constitute the activity of evaluating the scientific output and the scientific impact of the most impactful academic institutions, scientific journals, scientific articles, and influential scholars regarding the emerging green port research domain. The detailed analysis of the ISI WoS major scientific discipline categories reveals that the refined bibliography sample of 278 journal articles belongs to the following top five categories: (1) Transportation (46.4%); (2) Economics (15.1%); (3) Environmental Studies (14.3%); (4) Environmental Sciences (14.0%); and (5) Green Sustainable Science Technology (8.1%). The remaining 2.2% accounts for a multitude of business, oceanography, water resources, and geography ISI WoS major scientific discipline categories.

2.2.1. The Most Prestigious Academic Institutions

The refined bibliography sample of 278 journal articles regarding the emerging green port research domain stems from 476 academic institutions.

Table 2. The top 10 prestigious academic institutions regarding the emerging green port research domain.

Ordinal Number	Academic Institution	Articles	Percentage	TLCS	TLCS/Article
1	University of Antwerp	17	6.1	74	4.35
2	Delf University of Technology	15	5.4	9	0.6
3	Shanghai Maritime University	12	4.3	8	0.6
4	Nanyang Technological University	10	3.6	48	4.8
5	University of Naples Parthenope	9	3.2	12	1.3
6	Erasmus University Rotterdam	8	2.9	17	2.1
7	University of Genoa	7	2.5	8	1.1
8	Antwerp Maritime Academy	6	2.2	50	8.3
9	University of Malaysia Terengganu	6	2.2	8	1.3
10	University of Rijeka	6	2.2	5	0.8

contains the top 10 most prestigious academic institutions in the emerging green port research domain.

Table 2 indicates that the top 10 most prestigious academic institutions generate more than one-third of the total output, representing 34.6% of the generated scientific articles. The top three academic institutions in terms of the total aggregate sum of generated scientific articles are the University of Antwerp with 17 articles, the Delft University of Technology with 15 articles, and the Shanghai Maritime University with 12 articles. The aforementioned three academic institutions are responsible for one-sixth of the total aggregate sum of generated scientific articles regarding the emerging green port research domain, representing 15.8% of the generated scientific articles. Even though certain prestigious academic institutions may have a higher generation rate, not all of the generated scientific articles have the same scientific impact. Thus, the adherence to the ratio between the key bibliometric term of TLCS and the generated scientific articles reveals that the Antwerp Maritime Academy holds first place with an 8.3 TLCS/Article ratio, and the Nanyang Technological University holds second place with a 4.8 TLCS/Article ratio. The University of Antwerp holds third place with a 4.35 TLCS/Article ratio. Concludingly, the top three most prestigious academic institutions regarding the emerging green port research domain belong to the Netherlands (Antwerp Maritime Academy and the University of Antwerp) and to China (Nanyang Technological University).

The application of the Bibliometrix tool in R software enables the evaluation of the network strength regarding the collaboration between the most prestigious academic institutions. Figure 3 graphically represents the most prestigious academic institutions’ collaboration network strength by combining the node-based and distance-based approaches.

The node-based approach in Figure 3 indicates 17 nodes in terms of the most prestigious academic institutions’ collaboration network strength. The distance-based approach indicates the strength of the relationship between the academic institutions. A total of five individual research clusters are identified, revealing that the maritime industry’s green port research domain is emergent and developing. The blue cluster is the most comprehensive and comprises seven academic institutions. The Antwerp Maritime Academy, the Nanyang Technological University, and the University of Antwerp, the most prestigious academic institutions, belong within the blue cluster. The red cluster holds second place in terms of prominence and is comprised of four academic institutions. The Delft University of Technology and the Erasmus University Rotterdam belong within the red cluster. The remainder of the clusters (purple, green, and orange) reveal research collaboration between two academic institutions.

2.2.2. The Most Prominent Scientific Journals

The refined bibliography sample of 278 journal articles regarding the emerging green port research domain is published in 113 scientific journals.

Table 3. The top 10 prominent scientific journals regarding the emerging green port research domain.

Ordinal Number	Scientific Journal	Articles	Percentage	TLCS	TLCS/t	TGCS	TGCS/t	TLCR
1	Sustainability	26	9.4	0	0.00	228	85.25	62
2	Maritime Policy and Management	25	9.0	15	3.88	244	54.31	29
3	Maritime Economics and Logistics	18	6.5	34	4.84	363	51.97	7
4	Journal of Transport Geography	13	4.7	38	4.38	394	52.02	14
5	International Journal of Shipping and Transport	8	2.9	9	1.80	99	14.64	7
6	Research in Transportation Business and Management	8	2.9	20	3.70	185	36.0	20
7	Asian Journal of Shipping and Logistics	6	2.2	14	2.22	84	15.93	5
8	International Journal of Transport Economics	6	2.2	3	0.37	39	5.75	11
9	Transport Policy	6	2.2	12	2.67	170	29.41	8
10	Transportation Research Record	6	2.2	9	0.73	57	4.54	1

contains the top 10 most prominent scientific journals in the emerging green port research domain.

Table 3 indicates that the top 10 most prominent scientific journals contain nearly half the total scholarly output regarding the emerging green port research domain, representing 44.2% of the generated scientific articles. The top three scientific journals in terms of the total aggregate sum of generated scientific articles are Sustainability with 26 articles, Maritime Policy and Management with 25 articles, and Maritime Economics and Logistics with 18 articles. The aforementioned three scientific journals are responsible for one-fourth of the total aggregate sum of the generated scientific articles regarding the green port research domain, representing 24.9% of the generated scientific articles. However, the adherence to the key bibliometric term of TLCS/t reveals that not all of the scientific journals have the same scientific impact in terms of scientific articles. TLCS/t represents the published scientific article average local citation count per year beginning at the designated article publication year and ending at the designated year of the conducted study. Thus, Maritime Economics and Logistics holds first place with a 4.84 TLCS/t score, Journal of Transport Geography holds second place with a 4.38 TLCS/t score, and Maritime Policy and Management holds third place with a 3.88 TLCS/t score. Concludingly, the aforementioned top three scientific journals most explicitly address the emerging green port research domain.

2.2.3. The Most Impactful Scientific Articles

The refined bibliography sample of 278 journal articles regarding the emerging green port research domain is explored and formed by 695 scholars. Scientific articles are measured by the key bibliometric terms TLCS, TLCS/t, TGCS, and TGCS/t regarding article impact and breakthrough within the inquired research domain.

Table 4. The top 10 impactful scientific articles regarding the emerging green port research domain.

Ordinal Number	Article	TLCS	TLCS/t	Article	TGCS	TGCS/t
1	Lam, J.S.L.; Notteboom, T. (2014) [27]	32	4.00	Lam, J.S.L.; Notteboom, T. (2014) [27]	160	20.00
2	Ng, A.K.Y.; Pallis, A.A. (2010) [28]	14	1.17	Veenstra, A. et al. (2012) [29]	105	10.50
3	Veenstra, A. et al. (2012) [29]	14	1.40	Ng, A.K.Y.; Pallis, A.A. (2010) [28]	95	7.92
4	Notteboom, T. et al. (2013) [30]	13	1.44	Notteboom, T. et al. (2013) [30]	85	9.44
5	Lirn, T.C. et al. (2013) [31]	11	1.22	Dooms, M. et al. (2013) [32]	75	8.33
6	Puig, M. et al. (2014) [33]	11	1.38	Ferrari, C. et al. (2011) [34]	73	6.64
7	Dooms, M. et al. (2013) [32]	10	1.11	Liu, C.I. et al. (2004) [35]	72	4.00
8	Carlan, V. et al. (2016) [36]	9	1.50	Puig, M. et al. (2014) [33]	70	8.75
9	Wan, C.P. et al. (2018) [37]	9	2.25	Iannone, F. (2012) [38]	69	6.90
10	Debrie, J. et al. (2013) [39]	8	0.89	Lirn, T.C. et al. (2013) [31]	64	7.11

contains the most impactful scientific articles in the emerging green port research domain.

Table 4 indicates that in accordance with the key bibliometric terms, the most impactful scientific article regarding the emerging green port research domain is authored by Lam and Notteboom (2014), representing a TLCS/t value of four and a TGCS value of 160 citations. Further application of the key bibliometric terms enables additional comparative analysis of the most impactful scientific articles substantially influencing the development of the emerging green port research domain. Concludingly, Wan et al. (2018) hold second place, representing a TLCS/t value of 2.25 and a TGCS value of 54 citations, Carlan et al. (2016) hold third place, representing a TLCS/t value of 1.50 and a TGCS value of 54 citations, Notteboom et al. (2013) hold fourth place, representing a TLCS/t value of 1.44 and a TGCS value of 85 citations, and Veenstra et al. (2012) hold fifth place, representing a TLCS/t value of 1.40 and a TGCS value of 105 citations.

2.2.4. The Most Influential Scholars

Scholarly endeavors are the most important component regarding the development and progression of any scientific and research domain.

Table 5. The top 10 influential scholars regarding the emerging green port research domain.

Ordinal Number	Scholar	Articles	Percentage	TLCS	TLCS/t	TGCS	TGCS/t
1	Jeevan, J.	8	2.9	15	3.13	100	22.95
2	Lam, J.S.L.	7	2.5	40	6.17	269	48.00
3	Notteboom, T.	6	2.2	50	6.38	362	57.96
4	Parola, F.	5	1.8	16	2.27	203	23.48
5	Vanelslander, T.	5	1.8	9	1.50	69	12.83
6	Chen, S. L.	4	1.4	10	2.19	66	15.42
7	Ferrari, C.	4	1.4	8	1.38	129	16.11
8	Haezendonck, E.	4	1.4	18	2.77	99	13.37
9	Monios, J.	4	1.4	2	0.33	45	13.33
10	Tijan, E.	4	1.4	5	1.05	23	5.55

contains the topmost influential scholars in the emerging green port research domain.

Table 5 indicates that the top 10 most influential scholars contribute nearly one-fifth of the total scholarly output regarding the emerging green port research domain, representing 18.2% of the generated scientific articles. The top three scholars in terms of aggregate sum of scholarly output are Jagan Jeevan, with eight scientific articles, Jasmine Lam with seven scientific articles, and Theo Notteboom with six articles. The prior mentioned three scholars contributed nearly one-tenth of the scientific articles regarding the emerging green port research domain, representing 7.6% of the published articles. Contrastingly, the key bibliometric term of TLCS/t reveals that scholarly contribution influences the development of the emerging green port research domain differently. Consequently, Theo Notteboom holds first place with a 6.38 TLCS/t score, Jasmine Lam holds second place with a 6.17 TLCS/t score, and Jagan Jeevan holds third place with a 3.13 TLCS/t score. The remainder of influential scholars such as Elvira Haezendonck hold fourth place with a 2.77 TLCS/t score and Francesco Parola hold fifth place with a 2.27 TLCS/t score. Thus, these scholars most significantly influence the development and progression of the emerging green port research domain. Additional information regarding the scholarly influence is presented in Appendix A [8,27,28,29,30,31,32,33,36,37,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58].

Further analysis of scholarly activity is possible with the three-fields plot supplement by applying the Bibliometrix tool in R software. The three-fields plot is a Sankey diagram that illustrates quantitative information about flows, their relationships, and their transformation. Sankey diagrams represent directed, weighted graphs with weight functions that satisfy flow conservation in terms of the sum of the incoming weights for each node being equal to its outgoing weights [59]. Figure 4 is a Sankey diagram that graphically represents the scholarly activity within the emerging green port research domain by indicating the interactions of the most influential scholars (left), scholar keywords (center), and countries (right).

Figure 4 reveals that the emerging green port research domain is most prevalent in Asia, Europe, and North America. The leading Asian countries are China and Korea, while the leading European countries are the Netherlands, Poland, Belgium, Italy, and Spain. The United States is the leading country in North America. The detailed analysis reveals that the Asian countries are focusing on: (1) Container terminals; (2) Green ports; (3) Sustainable ports; and (4) Data Envelopment Analysis. European countries are focusing on: (1) Container terminals; (2) Sustainable ports; and (3) Port governance; and (4) Competitiveness. The United States is focused on: (1) Container terminals; (2) Port governance; and (3) Port management. Concludingly, the Asian countries of China and Korea are the most active in the emerging green port research domain.

3. Research Streams Identification and Analysis

Research domains are a collective sum of individual research streams regardless of emergence or establishment. The bibliographic coupling methodology is a bibliometric method that links documents that reference the same set of cited documents, thus enabling the formation of document clusters due to the indication that a probability exists that the linked documents treat a related subject matter, i.e., research stream [60]. The bibliographic coupling methodology via Bibliometrix tool in R software indicated five concurrent research streams on the basis of the top 10% of the scientific articles. Even though certain scientific disciplines such as medicine require higher thresholds regarding the establishment of the cut-off criteria (TLCS ≥ 5), the emerging green port research domain suffices to TLCS ≥ 3 as the cut-off criteria [61].

The selected 30 scientific articles from the refined bibliography sample of 278 scientific articles are thoroughly evaluated via content analysis in the form of the matrix method of literature review. Appendix A contains the selected and clustered 30 scientific articles belonging to each research stream. Content analysis is a critical literature review of each article’s title, author, journal, research question(s), theory, data sources, variables, category, and key findings [62]. The matrix method of the literature review conducted via MS Excel is a formal guidance and provides a means to systematize the process of the literature review. This means that the literature review does not become a subjective process characterized by a bias toward preferred references that supports only the view of the researcher, while ignoring references that present contrary points of view [63]. Figure 5 graphically represents the intellectual structure of the emerging green port research domain regarding the five concurrent research streams on the basis of the top 10% of the scientific articles.

Figure 5 reveals the citation networks of the selected 30 scientific articles represented as nodes. The bibliometric coupling methodology enables the utilization of the critical path method, indicating that the closer and more connected the node is to another node, the higher the likelihood of the individual research stream occurrence [64]. The iterative process of the selected 30 scientific articles’ content analysis resulted in identifying five independent yet interconnected research streams and sub-research streams. The five independent research streams with their respective sub-research streams are:

(1) Port Governance Reforms: Adoption of contextualized models of port governance reform as a consequence of port multi-scalar embeddedness forces and institutional stretching;

(1.1) Port Management Tools; (1.2) Path Dependence; (1.3) Diversified Institutional Frameworks; (1.4) Institutional Plasticity; (1.5) Environmental Performance Indicators; (1.6) Stakeholder Management; (1.7) Multi-Scalar Embeddedness; (1.8) Sustainable Growth Quantitative Assessment;

(2) Port Hinterland Integration: Fostering port sustainability competitiveness via extended resource pools in terms of dry ports coupling;

(2.1) Extended Resource Pools; (2.2) Inland Freight Distribution System; (2.3) Dry Port Operations

(3) Port Digitalization Management: The digitalization role in information systems regarding the interaction between transport, infrastructure, and institutional management in ports;

(3.1) Electronic Data Interchange; (3.2) Information Systems; (3.3) Port Community Systems;

(4) Port Competition Strategies: Assessment and innovation in seaport competition policies for the integration of green and sustainable operations;

(4.1) Internal Competition; (4.2) External Competition; (4.3) Systems Integration;

(5) Port CO₂ Evidence-Based Policies: Conceptual development and raising awareness of port management practices on account of CO₂ evidence-based policies regarding port terminals;

(5.1) Electric Container Handling Equipment; (5.2) CO₂ Footprint Analysis; (5.3) Terminal Operating Models.

Further analysis of Figure 4 indicates that research streams significantly differ in proportion. Research stream 1, “Port Governance Reforms” holds first place with 18 articles representing 60% of the total selected articles. Research stream 2, “Port Hinterlands Integration” and research stream 3, “Port Digitalization Management” share second place with five articles belonging to each research stream, thus individually representing 16.6% and collectively representing 33.2% of the total selected articles. Research stream 4, “Port Competition Strategies” and research stream 5, “Port CO₂ evidence-based policies share third place, with one article belonging to each research stream, thus individually representing 3.3% and collectively representing 6.6% of the total selected articles. Figure 6 is a schematic view of the five concurrent research streams with their respective sub-streams that constitute the emerging green port research domain.

Figure 6 reveals that Research stream 1, “Port Governance Reforms” holds first place, containing eight research sub-streams. The principal reason for such an occurrence is that most of the articles belong to the aforementioned research stream, thus indicating that port governance reforms are receiving a lot of scholarly interest within the emerging green port research domain. The remainder of the research streams share second place because they contain the same amount of research sub-streams, representing a value of three research sub-streams per each research stream. This indicates that more scholarly interest is required for developing the aforementioned research streams and their respective sub-streams. The upcoming section is a thorough analysis and discussion of the selected 30 articles belonging to each research stream and sub-stream in order to critically assess the emerging green port research domain.

3.1. Port Governance Reforms

The high price associated with global warming and climate change is shifting attention to the port authorities by highlighting how their changing role is manifesting with the reinforcement of their centrality in contemporary port management [65]. In addition, the rising scrutiny of environmental regulatory compliance is subjecting the port ecosystem under evident evolving circumstances by emerging trends such as the coordination of societal agents across supply chains, port cooperation, port clusters, and green port governance. Thus, adoption of contextualized models of port governance reform as a consequence of port multi-scalar embeddedness forces and institutional stretching is gaining the most scholarly support within this research stream.

Lam and Notteboom (2014) analyze the port management tools utilized by the port authorities and public regulators of the selected leading ports in Asia (Singapore and Shanghai) and Europe (Antwerp and Rotterdam) in order to steer the functional activities of the ports toward greenness [27]. The five functional activities of the four ports are: (1) Ship traffic; (2) Cargo handling and storage; (3) Port expansion; (4) Intermodal connections; and (5) Port industrial activities; and are assessed by the three port management tools: (1) Pricing policies; (2) Monitoring and measuring; and (3) Market access control and environmental standard regulation. The overall conclusion is that the aforementioned port management tools are indispensable for the proper institutional arrangement of the port ecosystem in order to reinforce green port governance effectiveness.

Ng and Pallis (2010) address the neo-institutional perspectives of the recent corporatization process of ports in Asia and Europe by revealing that institutions structure the relationships between societal agents within various units of polity and economy with the help of cultural political analysis of the economy [28]. The scholars analyze that port private–public partnerships are greatly influenced by the cultural political economy in terms that different countries or regions perceive similar developmental concepts differently. Thus, port governance is associated with institutional legacy and tradition in terms of implementation processes dependent on the path established by the broader institutional frameworks in which the economy where the ports are located develops. Ports must be studied within the context of the cultural political economy because they follow reforms based on divergent trajectories in different regions where the cultural and political traditions serve as causal factors of institutional framework establishment.

Notteboom et al. (2013) explore the concepts of: (1) Institutional plasticity; and (2) Path dependence in seaports, as a consequence of the interactions between various institutions, port authority routines, and port governance reforms [30]. The scholars reimagine the deterministic concept of path dependence by developing the concept of institutional plasticity. Institutional plasticity is the consequence of societal agent actions to purposefully transform institutions to different contexts via conversion and reinterpretation of the societal agents’ new business objectives. The analysis of the governance structures of the landlord port authorities of Rotterdam and Antwerp reveals that the existing path of development can be retained by adding new societal agent business arrangements with the following four institutional plasticity tools: (1) Conversion; (2) Layering; (3) Stretching; and (4) Displacement.

Lirn et al. (2012) assess the green performance criteria of three major container ports in the Greater China region [31]. The scholars conduct an Analytical Hierarchy Process (AHP) with the selected 17 green indicators calculated by the obtained data from the ports’ survey respondents. The 17 indicators are grouped into the following 5 dimensions: (1) Air pollution management; (2) Aesthetic and noise pollution management; (3) Solid waste pollution management; (4) Liquid pollution management; and (5) Marine biology preservation. Results revealed that the dimension (1) Air pollution management requires the most adherence in all the three container ports. Thus, ports must develop green port strategies that mitigate air pollution by: (1) Encouraging the use of low-sulfur fuel, and (2) Implementation of electrically powered equipment.

Puig et al. (2014) emphasize the fact that port authorities—regardless of size, activity profile, administration structure, and geographical surroundings—share the same contemporary requirements of the societal pressure to satisfy economic demands and industrial activity with: (1) Sustainable development; (2) Stakeholder compliance with legislation; and (3) Stakeholder compliance with cost and risk reduction [33]. The scholars develop a user-friendly methodology to assist port authorities in calculating and reporting the 12 selected Environmental Performance Indicators (EPI) belonging to 3 distinct categories: (1) Management performance indicators; (2) Operational performance indicators; and (3) Environmental performance indicators. Results indicate that environmental performance indicators require the most attention and adherence.

Dooms et al. (2013) contribute to port governance reforms by providing a stimulus to policy makers to engage on a path of continuous reflection on who and what matters in decision-making in terms of the effective implementation of new, large-scale seaport infrastructure projects [32]. The scholars analyze the general economic and infrastructural evolution of the port of Antwerp and its impacts on stakeholders and on port governance changes during the period of 1960 to 2010 in the Netherlands. The scholarly contribution is that port path dependence must adhere to temporal dynamics: (1) Stakeholder-based analysis of temporal dynamics; and (2) Long-term, strategic port planning based on real stakeholder inclusion acts as a driver for governance change in the broader region or port ecosystem.

Parola et al. (2016) identify the gap that conventional studies on port governance reform mostly propose de-contextualized models that ignore the embeddedness forces of ports in specific economic and institutional areas [43]. The scholars address the identified gap by contextualizing port governance developmental trajectories under local territorial contexts by proposing the concepts of: (1) Multi-scalar embeddedness; and (2) Institutional divergence. Multi-scalar embeddedness represents the vertical interconnectedness of key societal agents, namely from the aspects of: (1) The complexity and heterogeneity of the institutional framework; (2) The multi-layered decisional chain; (3) The geo-economic dimension; and (4) The socio-cultural environment. Institutional divergence is the consequence of temporally changing objectives between the vertical interconnectedness of national, regional, and local societal agents. The magnitude of institutional divergence creates the four following types of ports in terms of business objective proactivity: (1) Path follower port; (2) Path adaptor port; (3) Path resistant port; and (4) Path leader/ pioneer port.

Schipper et al. (2017) evaluate and interpret the port–city planning documents in 10 major container ports by adherence to the perspective of the triple bottom line (3BL) principle of People, Planet, and Prosperity [41]. The highest SICI (Sustainable Integrated Condition Index) scores regarding port–city cooperation are, respectively, KPIs for: (1) Port employment; (2) Citizen wellbeing; (3) Air quality; (4) Greenhouse gas emissions; (5) Cargo growth; and (6) Cruise tourism. The presented assessment methodology allows for a retrospective approach to learn by comparing older long-term port and recent port–city plans to the situation actually achieved within the time span of both plans. The method can better cross-link port plans and city plans with conditions using the economic, environmental, and social data exploration of publicly available data.

Hollen et al. (2015) highlight the fact that continuously evolving market circumstances in terms of environmental regulation and competitiveness require an active role of port authorities in fostering the development of industrial ecosystems in their port-industrial complex [47]. The incorporation of industrial ecosystems in port governance structures is beneficial for the port greening process because standalone societal agents in the port ecosystem can: (1) Create added value; (2) Become more energy efficient; (3) Reduce their feedstock costs; and (4) Lower their emissions and waste disposal. The scholars reveal the two most important generic policy instruments for port authorities to foster industrial ecosystems: (1) Investments in physical and knowledge infrastructure; and (2) Land allocation. Concluding remarks indicate that land lease contracts regarding their environmental clauses are the building block for further formation and development of industrial ecosystems in seaports. The main reason for such claims is that this will enable the provision of organizational and legal frameworks for the societal agents to utilize one another’s residual resources such as: (1) Energy effluents; and (2) Chemical effluents, for their own production process. However, the scholars stress that port authorities must endeavor in management innovation research because the industrial ecosystem implementation requires adopting strategies beyond the traditional landlord function of port authorities.

Verhoeven and Vanoutrive (2012) apply a factor analysis data reduction technique in order to reveal the relations between governance practices of port authorities in Europe and explain port governance diversity [42]. The scholars fill the research gap by providing a quantitative analysis of port governance in Europe via categorizing the factors into seven distinct port governance dimensions: (1) Devolution; (2) Corporate governance; (3) Operational profile; (4) Functional autonomy; (5) Functional pro-activeness; (6) Investment responsibility; and (7) Financial autonomy. Research results indicate that regional characteristics constitute an important factor that explains port governance diversity in Europe by subdivision into four main port geographical categories: (1) Hanseatic; (2) Anglo-Saxon; (3) Latin; and (4) New Member State. The combination of the geographical categories with the three hypothetical typologies of port authority governance structures: (1) Conservator; (2) Facilitator; (3) Entrepreneur, reveals the duality of the North (Hanseatic and Anglo-Saxon)–South (Latin and New Member State) port authority governance structures by discovering that the North port authorities enjoy greater functional and financial autonomy than the South port authorities.

Vieira et al. (2014) conduct a systematic method of scientific literature review spanning from 1992 to 2013 in order to identify, select, and critically evaluate governance models and their relationships with port performance [46]. An in-depth analysis of the 63 selected studies reveals that ports are facing an extension of their activities beyond the traditional limits of the port by taking into notion inland transport, and favoring the emergence of logistics hubs and transport corridors. The scholars defined the aforementioned new phase of port logistics systems development as a regionalization of ports and identified that it constitutes the following factors: (1) Port devolution; (2) Port reform process; (3) Institutional structure or port logistics chains; (4) Roles of PA’s; (5) Stakeholders conflict management; and (6) Port performance. Furthermore, five specific governance models are identified which the port authorities exercise in order to be actively emerged into port regionalization; (1) Matching framework; (2) Modular governance model; (3) Firm–government relationship model; (4) Model for implementing port reforms; and (5) Port authority renaissance. Further research is encouraged by proposing in-depth studies between the interaction of port performance in terms of port regionalization and the aforementioned five governance models.

3.2. Port Hinterland Integration

Fostering port sustainability competitiveness via extended resource pools in terms of dry ports coupling is receiving the most scholarly attention within this research stream. Haezendonck and Langenus (2018) conduct a linear regression and factor analysis in order to determine the port of Antwerp’s strategic response to retaining the competitive advantage in the port’s hinterland [53]. The scholars stipulate that ports are pressured to develop strategic partnerships in their hinterlands due to: (1) Increased scale of carriers and ship sizes; (2) Stakeholder opposition to port expansion; and (3) Heavy environmental regulation. Their concluding remarks indicate that the port’s hinterland network area must be recognized as an extended resource pool and be addressed from the resource-based view (RBV) perspective.

Veenstra et al. (2012) investigate the operational mechanisms of inland freight distribution systems in the hinterlands of the ports of Rotterdam and Amsterdam [29]. The scholars argue that the extended gate concept must be perceived as a business network innovation to the constantly increasing hinterland transport complexities and that the correct implementation of the extended gate concept leads to sizeable benefits in terms of: (1) Port logistics performance; (2) Regional development; and (3) Modal shift. The extended gate concept is further addressed by indicating the main barriers to its full implementation and adoption: (1) Smart business network development; (2) Trimodal transport connections balance; (3) Risk and reward management; and (4) Legal framework for hinterland multimodal transport.

Jeevan et al. (2017) address port hinterland integration by enhancing dry port performance by adapting a process benchmarking strategy among the Malaysian dry ports [52]. The benchmarking process is conducted via grounded theory among the key societal agents of the Malaysian container seaport system. The scholars reveal that dry ports must keep the seaport ecosystem competitive with the following operations: (1) High-capacity railway tracks; (2) Express clearance lane at terminals; (3) Increase schedule integrity of seaports; and (4) Expose dry ports credibility to other societal agents in the seaport ecosystem. Jeevan et al. (2015) explore the challenges of Malaysian dry ports development by conducting 11 face-to-face interviews with dry port stakeholders [50]. The scholars conclude the following challenges that the dry ports are facing: (1) Insufficient railway tracks; (2) Unorganized planning on the rail deck; (3) High dependence on transport unimodality; (4) Poor recognition from the seaport ecosystem community; and (5) Localized seaports inter-competition. Jeevan et al. (2018) highlight the interdependence between dry ports and seaports by investigating the impact of dry port operations on container seaport competitiveness [51]. The scholars conduct an exploratory factor analysis (EFA) on basis of 120 key dry port societal agent online surveys. Research findings indicate that dry ports create several beneficial development strategies for maritime policy makers: (1) Enhancing seaport competitiveness; (2) Enhancing seaport performance; (3) Enhancing seaport capacity; (4) Increasing variety of seaport services; (5) Improving seaport-hinterland proximity; and (6) Accelerating the volume of container trade.

3.3. Port Digitalization Management

The digitalization role in information systems regarding the interaction between transport, infrastructure, and institutional management in ports is gaining the most interest within this research stream. Gustafsson (2007) highlights that maritime supply chains contain a multiplicity of societal agents and that high quality data interchange between them has a positive impact on the overall supply chain performance [55]. The scholar conducts a semi structured interview as a pre-study for the Port of Gothenburg’s stance on port community system adaptation. The leading remarks are that the PCS would improve the port ecosystem under the condition of the collaboration agreement among its key societal agents: (1) The shipping industry (reporting is obligatory); (2) The authorities (possess the legal right to demand reporting); and (3) The port (acts as a broker or mediator).

Heilig and Voß (2017) conduct a state-of-the-art categorization and overview of information systems in seaports [54]. The scholars classify the following 10 most important information systems for facilitating port competitiveness, visibility, and communication: (1) National single window; (2) Port community systems; (3) Vessel traffic services; (4) Port river information systems; (5) Terminal operating systems; (6) Port road and traffic control Systems; (7) Intelligent transport systems; (8) Port hinterland intermodal information systems; (9) Automated yard systems; (10) Automated gate systems. The aforementioned information systems mainly rely on enabling technologies such as RFID, GPS, EDI, and mobile devices.

Carlan et al. (2015) emphasize the trend toward collaborative innovation in the maritime supply chain by implying that a good understanding of the actors and their roles and an efficient exchange of information with the different stakeholders are indispensable [36]. The scholars develop a comprehensive cost-benefit framework for every societal agent adhering to the port community system within the port ecosystem. Tsamboulas et al. (2012) propose a methodology to assess to which extent the introduction of a port community system generates added value to the port and its stakeholders [57]. Key performance indicators are established for the port authority and the stakeholders on the basis of five categories: (1) Financial; (2) Operational; (3) Production; (4) Supply chain; and (5) Functional. The results of the study conclude that the establishment of the port community system has a positive impact on the port ecosystem and that it complements conventional methods of port stakeholder management. Tijan et al. (2012) conduct a document analysis and simulation of ICT-enabled administrative processes in Croatian seaports in order to prove the positive aspects of the port community system for the ports [56]. The scholars conclude that the port community system implementation in the Croatian seaports will have the following eight aspects of stakeholder satisfaction in terms of optimized port services provision: (1) Access to services; (2) Booking; (3) Shipping instructions; (4) Vessel operations; (5) Cargo documents; (6) Cargo operations; (7) Inland logistics; and (8) Integrated track and trace.

3.4. Port Competition Strategies

Scholarly interest is mainly focused on the assessment and innovation in seaport competition policies for the integration of green and sustainable operations within this research stream. Musso et al. (2013) provide ample evidence that ports are no longer homogenous entities that compete with each other at different operational levels but rather complex and heterogenous entities with many interconnected societal agents [8]. The scholars revisit the concept of port competition from the aspect of: (1) Internal competition; (2) External competition; and (3) Systems integration. Internal competition constitutes the interaction and interconnectedness of crucial port ecosystem societal agents with differing economic objectives such as: (1) Shippers; (2) Goods owners; (3) Forwarders; (4) Shipping companies; (5) Port authorities; (6) Terminal operating companies; and (7) Hinterland operators. External competition constitutes the role of the port authorities in regulating the objectives of the port societal agents by considering their most important governing instruments: (1) Negotiating power; (2) Goods flow rates; (3) Cost control; (4) Port dues; (5) Concession policy; (6) Capital investments; (7) Handling fees; and (8) Technological choice adaptation. Systems integration refers to the interaction of the internal competition aspect and external competition aspect [8]. Ports must accept the fact of being complex logistics nodes within larger supply chain networks relying on exogenous and endogenous competition factors. Thus, the successfulness of port competition strategies depends critically on the competitiveness of the supply chain to which the port is systemically integrated.

3.5. Port CO₂ Evidence-Based Policies

Conceptual development and raising awareness of port management practices on account of CO₂ evidence-based policies regarding port terminals is the most addressed topic within this research stream. Yang (2015) investigates the environmental feasibility of container handling equipment in order to determine energy saving and CO₂ reduction strategies for terminal operators in order to comply with green port requirements [58]. The scholar evaluates the CO₂ emissions produced by two different container terminal operating models such as tire transtainers and rail transtainers on the basis of the green port assessment criteria: (1) Working time; (2) Efficiency; (3) Energy consumption; (4) CO₂ emissions. Grey relational analysis is utilized to determine the ranking order of different container operating models, concluding that rail transtainers and electric tire transtainers can be considered green cargo handling equipment because of their significant contributions to: (1) Working efficiency; (2) Energy savings; and (3) CO₂ footprint reduction. Additional research is implied regarding the terminal operating models in terms of the container terminal layout. Green container terminals should be designed to reconfigure the container terminal layout and operations in spatial harmony with the ecological environment in order to obtain and equilibrium of: (1) Economic aspects; (2) Infrastructure; and (3) Provision of business links to the rest of the port community.

4. Future Research Directions and DPSIR Framework Structural Associations

Identifying future research directions within the individual research streams of the emerging green port research domain is essential in order to indicate the possible trajectories of the research domain’s development. The co-citation analysis methodology via HistCite software revealed future research directions within the five concurrent research streams on the basis of the key bibliometric term of LCSe utilized to indicate the trending scientific articles within the emerging green port research domain. The key bibliometric term of LCSe (Local Citation Score ending) presents the local citation frequency inside the bibliography data collection, starting with an arbitrary cut-off year and including the last year of the time interval for which the bibliography data collection has been compiled [64]. The arbitrary cut-off years of this study are the last three years since the bibliography data has been compiled. Thus, the most trending papers regarding the emerging green port research domain stem from 2019, 2020, and 2021, respectively, representing 15 scientific articles or the top 5% of the scientific articles within the entire bibliography. Appendix B contains the selected trending 15 scientific articles in each respective year.

Content analysis in the form of the matrix method of literature review is conducted in order to thoroughly evaluate the selected trending 15 scientific articles from the refined bibliography sample of 278 scientific articles.

Table 6. Future research directions identified from the selected trending 15 scientific articles.

Research Stream	Future Research Directions
Port Governance Reforms (1), (3), (4), (6), (7), (8), (9), (11), (13), (14)	Remove barriers that challenge the implementation of environmental policies in ports (autonomy of government departments, weak sectoral connections, inefficient cross—sectoral procedures, institutional fluidity, unguided evolution of administrative frameworks) [1,4,6,13,14] Develop novel concession contract policies (CO2 performance—based agreements of terminal operators, ecological preservation regarding port terminal expansion, punishment mechanisms for stakeholders disobeying environmental clauses) [1,3,4] Implement activity—based Environmental Management Systems for port greening baselines (Air quality, water quality, soil quality, sediment quality, noise quality, ecosystem and habitat quality) [1,3,9,11] Integrate Environmental Ship Index as benchmark for port fees and surcharges in order to stimulate shipping company green marine fuel utilization (encourage use of low Sulphur fuels, bio—fuels and LNG) [1,4,11] Develop strategic infrastructural stakeholder management models on basis of internalization of external costs (cold ironing facilities feasibility, deployment of electrically powered equipment on terminals, encourage reuse of recyclable resources, renewable energies facilities, carbon capture and storage facilities) [4,7,9]
Port Hinterland Integration (2), (15)	Contextualization and specification of port—city relationship integrated plans (improving port employees working conditions and safety, citizen wellbeing, enhanced city competitiveness via strategic environmental investments) [8] Investigate market positions (SWOT analysis) of small and medium sized hinterland forwarder firms due to inclination of novel sustainability—oriented business models implementation (corporate social and ecological responsibility in the port ecosystem) [8,9] Develop mathematical simulation—based models regarding the involvement and interconnectedness of terminal operators with end points in the maritime supply chains [2,15] Research seaport ecosystem membership selection in terms of sustainable goal setting for implementing green hinterland network corridors on basis of energy consumption and transport modality—efficiency [2] Cost—benefit assessment of seaport—dry port operational infrastructure requirements (container yard, rail access track, rail siding, express clearance lane, customs office) [15]
Port Digitalization Management (5), (12)	Develop a comprehensive framework for quantifying the costs and benefits of PCS implementation in the port ecosystem [5] Assess competitive advantages of PCS regarding better access to business information, reduced transaction costs, less illegal transactions, decreased error occurrence, efficient resource use [5] Research and reveal IT/IS implementation and interaction maturity levels between societal agents of the port ecosystems to enhance value—creating maritime logistics chains [12] Increase port business credibility image via cyber—security information technologies in guidelines with major international security initiatives (ISPS Code) [12] Foster intelligent context—aware management decisions by monitoring port physical and environmental conditions such as temperature, humidity, air quality and water quality on basis of RFID, WSN and mobile technologies [12]
Port Competition Policies (10)	Expand the understanding of ports as complex heterogenous systems from the aspects of exogenous and endogenous competition factors within maritime supply chains [10] Sustainable assessment of value—adding services of ports as a chain of interlinking functions of port societal agents (shipping companies, forwarders, terminal operating companies and port authorities) [10] Investigate the instances of collusion and cartelization in ports in relation to the price competition to equilibrate supplier quantity [10] Research technological innovation as a strategic variable from the aspect of supply chain sustainability (lower average costs, organizational advantages, lower pollution) [10] Mitigate the limited degrees of freedom the ports are facing in terms of capacity constraints (market share cap, lack of expansion zones)
Port CO2 Evidence—Based Policies	Investigate the relationship between the spatial layout of container terminals (horizontal, vertical) with the CO2 output of the container terminal equipment [3,4] Provide a quantitative and comparison analysis of automatic, semi—automatic and manual container handling equipment in terms of CO2 footprint on container terminals [3] Develop comprehensive energy—saving strategies for port terminal greening on basis of container handling equipment workload, operating efficiency and output [4,8] Assess specific patterns of container terminal equipment technological behavior at different container terminal sites (gate area, container yard, berth area) [3,8] Determine energy costs per movement of container handling equipment in order to create CO2 evidence—based policy frameworks for the internalization of external costs of container throughput in port concession contracts [4]

contains the future research directions stemming from the 5 concurrent research streams, which are identified from the selected trending 15 scientific articles. The article ordinal number located in Appendix B is a reference point regarding the identified future research directions in Table 6.

Table 6 indicates that the most common factors influencing the future success of the port greening process stem from the combination of the following three green port developmental trajectories: (1) Decarbonization; (2) Digitalization; and (3) Multimodality. The application of the aforementioned three green port developmental trajectories will differ in each port due to being a unique node within the maritime supply chain because of differing competencies in the port area, the share of transport modality, type of cargo handled, hinterland connections, energy sectors, industrial sectors, and geographical location and circumstances [29,33,36]. Grasping the green governance and competence of port authorities is essential when preparing their pathways to a green future, and is also beneficial to every port societal agent within the port ecosystem along with maritime policymakers.

The application of the detailed content analysis on the future research directions resulted in the identification of 16 pivotal factors influencing the establishment of green port governance models. The factors are assessed via the structural associations of the DPSIR framework. The DPSIR framework is a flexible system thinking methodology initially developed by the Organization for Economic Co-operation and Development (OECD) in 1994, and utilized for assisting decision makers in complex systems decision processes [66].

Table 7. Elaboration of the 16 pivotal factors influencing the establishment of green port governance models.

Factors Belonging to the Drivers Category
Factor	Green port governance factor elaboration
GDP Growth Rate	Economic growth is highly associated with GDP growth. However, Incessant GDP growth rate can adversely influence ports in terms of higher levels of pollution, increased consumption of non—renewable resources, and potential loss of environmental habitats due to lack of market—based mechanisms for external costs internalization [8,37,54].
Container Port Throughput	Ports are important hubs within global supply chains due to expansion of industrial activities such as cargo handling, cargo value—added strategies, and freight forwarding. Container port throughput reflects port efficiency, productivity and overall service capability [8,37,54].
Competitive Forces	Competitive forces consist predominantly of critical transport infrastructure, geographical characteristics, and political factors. The amalgamation of the three competitive forces significantly affects ports in terms of port capacity and demand, hinterland market access, market share strength, and stakeholder loss absorption via subsidies [8,37,54].
Factors Belonging to the Pressures Category
Factor	Green port governance factor elaboration
Operational Profile—Shipping Companies	Constant rising market demand for goods compared with limited supply in terms of ship size adversely affects shipping companies regarding their interaction with the environment. The interaction can be categorized as intentional in terms of ship chemical and oil spills due to lack of environmental legislation compliance, and as accidental in terms of shipwrecks and groundings resulting in container damage, theft, and delays [27,40,50].
Operational Profile—Terminal Operators	The overall market activity influenced by containership cargo volume shifts raises terminal operators’ cost pressures due to increased volatility and demand. Adverse impacts on the port environment may reflect as supply chain failures, environmental compliance failures, worker strikes, ageing terminal handling assets, and business disruption due to adaptation of emerging advanced technologies [27,40,50].
Operational Profile—Hinterland Operators	Market pressures significantly influence the strategies of hinterland operators and their overall performance. Overperforming hinterland operators are more willing to adopt green corporate strategies than underperforming hinterland operators. However, the proactivity of both operator types within the seaport ecosystem is impacted negatively by the gate waiting time, idling time, lack of designated parking spaces, limited access to road and rail systems, and cumbersome cargo bureaucratic procedures [27,40,50].
Factors Belonging to the States Category
Factor	Green port governance factor elaboration
Port Air, Water, Soil Quality	Contemporary seaports are nodes in global supply chains characterized by high energy transport and value—added activities. Excessive utilization of such activities results in port air, water and soil quality environmental degradation. Port air pollution refers to hydrocarbon fuel utilization such as heavy vehicle traffic, railway traffic, ship hoteling, and bunkering. Port water pollution refers to accidental discharge of oils and other chemicals in the sea during terminal operations, bunkering operations, ship demolitions, dry docks operations, dredging operations and storm water runoffs. Port soil pollution refers to accidental discharges and spills of oils and chemicals during cargo handling equipment operations, refueling activities, ship demolition spills, and pipeline damages [27,37,43].
Factors Belonging to the States Category
Factor	Green port governance factor elaboration
Port—Related Supply Chain Disruptions	Fixed and predefined shipping schedules are the cornerstone of adequate container shipping services because they enable the planning of vessel turnaround at each of the ports of call on the shipping route within the designated ship hoteling time in ports. Market demand volatility can prompt underperformance in one port which can disrupt the shipping schedule and transport flows for every port ecosystem stakeholder in the entire port network. Adverse results manifest themselves as reduction of port competitiveness on the waterfront and the hinterland, increase in export and import costs, impediments to trade, economic growth slowdown, and inhibition of poverty reduction [27,37,43].
Port Worker Safety Conditions	The recurrent port governance restructuring process of the landlord port governance model has dramatically affected port labor and workforce because the terminal management and commercial activities are left to private companies. The free market law of supply and demand of labor allowed private companies the organization and management of terminals through authorizations and administrative concessions, which resulted in the elimination of the market reserve of port worker pools. Over capacitated workforce terminal operations can result in cargo damage, worker safety compromise and working conditions deterioration [27,37,43].
Factors Belonging to the Impacts Category
Factor	Green port governance factor elaboration
Additional Port Waste Generation	Over capacitated port supply chains and logistics networks stimulate port ecosystem stakeholder additional port waste generation due to requirements of meeting unregulated market demand. Adverse effects of overcapacity result in residual energy loss in terms of waste heat and steam from electricity, chemical effluents generation in terms of processed hydrocarbons, further distribution challenges of industrial water and CO2 emissions treatment [28,41,43].
Port—City Relationship Tensions	The predominance of globalization and containerization is causing divergence in the relationship between ports and their respective host cities. The principal reason for the occurrence of divergence manifests itself in the fact that ports construct strategies primarily on economic growth in terms of container throughput and adoption of financial investments in highly advanced port technology. Such activities can be cumbersome for host cities due to the demand for additional scarce space and dredging operations. Highly automatized equipment reduces the quantity of necessary labor, thus ending the necessity to employ the city population. Container ships hotel in ports in less than 24 h, resulting in the reduction of shore leave opportunities which stimulate the city economy [28,41,43].
Port Revenue Decline	The volatility of economic conditions and circumstances places strain on seaport ecosystem agents in supply chain networks which can result in port revenue decline due to the halting of the agents’ business activities. The spatial—temporal functions of the port ecosystem are in constant change which if not timely adhered to by the seaport ecosystem agents, may result in tensions and conflicts between the agents. Seaport ecosystem agent orchestration in order to mitigate conflicts and foster port revenue growth requires the evaluation of economic, social and physical advantages of each agent by specialized public institutions or consulting companies [28,41,43].
Factors Belonging to the Responses Category
Factor	Green port governance factor elaboration
Green Marketing Strategies	The clustering of water—based, port—related, and hinterland—based activities within the seaport ecosystem possess the possibility of exerting strong environmental advantages.The adherence to green marketing strategies such as: (1) Pricing strategies, (2) Monitoring and measuring; and (3) Market access control and environmental standard regulation via mutually binding agreements between the port authorities and the seaport ecosystem stakeholders creates a constructive dialogue for greener and sustainable transitions of the seaport ecosystem. Pricing strategies promote environmental awareness in transportation sectors via utilization of penalty pricing (fines) for pollution reduction. Monitoring and measuring refer to quantifiable and detailed information on the impacts of port operations on the adjacent environment in order to take timely and corrective actions. Market access control and environmental standard regulation are mandatory and indispensable tools utilized to restrict market access control and stipulate environmental standards to stakeholders who do not meet and comply with regulatory requirements in order to change stakeholder market behavior towards sustainability [8,27,40,41,54].
Stakeholder Legislation Compliance—Environmental	The baseline for the greening of seaport activities requires the adherence to IMO international conventions such as MARPOL, ISPS and ISM because it enables each signatory nation to effectively enact domestic laws via compliance with the guidelines set in the conventions. However, it is important to indicate that at the present stage of the port greening process, shipping traffic receives the most attention and focus regarding decarbonization. Port area activities and port hinterland activities require adherence as well in terms of national and local legislation creation regarding port greening such as imposing sulfur fuel caps on heavy cargo handling vehicles, and meeting environmentally friendly modal splits. Such legislation creation is slow and relatively weak in enforcement due to conflicting interests of seaport ecosystem stakeholders, market volatility, and a lack of GHG evidence—based solutions [8,27,40,41,54].
IT/IS Monitoring and Measuring	Modern value creating logistics chains are a collective effort requiring an alignment and coordination of societal agents and business processes in all aspects. The efficient governance and management of the seaport ecosystem in terms of equipment behavior, terminal operations and facility maintenance requires advanced planning, monitoring, and measuring activities supported by Information Technologies and Information Systems. The information—centric point of view is favorable for the seaport operations greening process because it enables the collection, exchange, analysis, evaluation, and dissemination of crucial economic, social and environmental information among port ecosystem stakeholders. Thus, port—related Information Technologies and Information Systems are indispensable for enabling smarter and greener port operations because they promote better short—term and long—term decision making via creation of process—related knowledge [8,27,40,41,54].
Port Environmental Remediation Facilities	Port facilities in general are associated with positive benefits for the port ecosystem in terms of improved freight services, improved labor supply, and technical and technological diffusion and dissemination. The prevalent notion of sustainability prompts seaport ecosystems to adopt and install port facilities and accompanying instruments that benefit the frequent climate change targets by mitigating the amount of CO2 generated by societal agents within the seaport ecosystem. Seaports are developing great interest in installing port environmental remediation facilities in terms of Carbon Capture and Utilization facilities, Carbon Capture and Storage facilities, onshore power supply facilities, renewable energies facilities, and circular economy facilities. Even though the aforementioned facilities possess the possibility of lowering costs, reducing additional waste creation, and lowering GHG emissions, further feasibility studies are required for their proper operations [8,27,40,41,54].

elaborates on the 16 pivotal factors influencing the establishment of green port governance models identified via detailed content analysis from the selected trending 15 scientific articles on the basis of the DPSIR framework.

Table 7 indicates that the development and evaluation of green port governance models must take into consideration the embeddedness and interconnectedness of the aforementioned 16 pivotal factors with an end result of achieving and maintaining sustainable competitiveness of seaports in the world maritime trade. The recurring global port governance reforms must consider the developmental pathways of green port governance in a dynamic manner of seaport evolution with adherence to end goals such as rational usage of various seaport resources, low energy consumption, low pollution, ecological protection, and environmental health preservation [10,58].

However, the absence of comparative empirical studies devoted to green port governance developmental pathways results in the recurring port governance reforms being characterized by partiality and inadequacy regarding the full incorporation of the 16 identified factors. Thus, significant scholarly endeavors are required via the blending of academic research with the input of maritime and seaport professional expert opinions with adherence to the following operations research and advanced statistical techniques in order to explicitly evaluate the factor weights and factor interconnections to aid seaport governance decision-making to green and sustainable pathways [67,68,69,70,71]:

(1)

Analytic Hierarchy Process (AHP): A Multiple Criteria Decision Making (MCDM) technique that aids stakeholder decision consensus effectiveness via construction of a hierarchical structure enabling the consolidation of quantitative and qualitative variables (factors). The main specialty of AHP is its flexibility in being integrated with different techniques such as fuzzy logic, linear programming, and quality function deployment, resulting in achieving the desired goal in a better way;

(2)

Analytic Network Process (ANP): The analytic network process (ANP) technique is a generic form of AHP that allows for more complex, interdependent, relationships, and feedback among elements in the hierarchy. AHP does not account for dependencies and interrelations among factors, even though real world problems usually consist of synergistic dependence and feedback between factors. This concludes that the ANP method is better regarding the provision of a flexible model to solve real world situations as compared to the AHP models because it enables the measurement of inter-factor dependencies;

(3)

Data Envelopment Analysis (DEA): DEA is a mathematical programming approach used to provide a relative efficiency assessment and benchmarking for a group of decision-making units (stakeholders) with multiple number of factor inputs and outputs. The method utilizes the production function in order to calculate and assess the production frontier of the DMU. The DEA methods and models are utilized for comprehensive description of the DMU production frontier. Therefore, DEA is also recognized as a non-parametric statistical estimation method;

(4)

Stochastic Frontier Analysis (SFA): Unlike the DEA technique that admits the assumption that DMUs are efficient, the SFA technique takes into account the fact of DMU inefficiencies in real world scenarios. Thus, the SFA technique stems from the theoretical idea that no economic agent can exceed the ideal production frontier, and deviations from this ideal extreme represent economic agent individual inefficiencies. Inefficiencies represent themselves as asymmetric information in terms of incomplete markets, different business cultures of DMUs, etc. The inefficiencies in the SFA technique are accounted for in statistical error estimation derived from likelihood-based regression methods;

(5)

Structural Equation Modeling (SEM): SEM is a multivariate quantitative statistical technique utilized to interpret, clarify, test, and evaluate the relationships of multiple cause-and-effect connections between observed factors to validate a theoretical model in terms of theory testing and extension. The SEM technique conducts this in three consecutive steps: (1) EFA; (2) CFA; (3) SM. Exploratory Factor Analysis (EFA) reveals the underlying structure of large sets of observable items of the selected factors via Kaiser–Meyer–Olkin and Cronbach’s Alpha equations. Confirmatory Factor Analysis (CFA) confirms the identified factor structure via absolute fit, incremental fit, and parsimony fit formulaic indices. Structural Model (SM) is the final step, which includes the utilization of multiple linear regression equations on the selected factor structure in order to estimate the validity of the cause-and-effect relationships of the structural associations (factors).

Seaports are heterogenous and complex business environments that result in constant changes in addressing and evaluating their governance structures [8]. The vast majority of individual seaport ecosystem societal agents further amplifies the complex issue of seaport governance which results in the necessity to address seaport governance from different perspectives. The aforementioned five scientific-research methodologies provide the possibility to mitigate the ambiguity of the recurring port governance restructuring process by better understanding the formalization approach of stakeholder management. Accordingly, the research agenda regarding the recurring port governance restructuring process towards greenness and sustainability should be addressed in the following aspects [46]:

(1)

Develop and conduct in-depth studies of the relationship between green port governance model factors and seaport performance;

(2)

Further detail the identified green port governance model factors by linking them to topics related to seaport governance;

(3)

Discussion of seaport governance actions, particularly with regard to the design and implementation of such actions in the context of port strategy;

(4)

Analysis of the identified green port governance model factors, primarily from the seaport logistics flows and relationships between the societal agents belonging to the seaport logistics chain.

Addressing the interdependencies among the factors will require the development of the dynamic capabilities of both the industry and the academia in order to select, evaluate, and validate the factors that are acceptable and feasible to the maritime and port sector, and which are practicable in their application and implementation [33].

Figure 7 is a graphical depiction of the cause-and-effect relationships of the structural associations (factors) of the DPSIR framework regarding the establishment of green port governance models.

Figure 7 reveals that the establishment of green port governance models requires a complex systems thinking methodological framework consisting of diverse port factors. The DPSIR framework allows for the incorporation of diverse and essential port factors stemming from economic, social, and environmental circumstances, into green port governance models. “Driver” is utilized for delineating the factors fostering port economic activities and industrial development, of which the overutilization can cause a strain on the port socio-environmental aspects. Recurring trends such as global trade growth (GDP growth rate), increasing vessel sizes (container port throughput), and port facilities modernization race (competitive forces) belong to the “Driver” category [8,37,54]. “Pressure” is utilized for representing the factors stressing the activities of crucial port ecosystem societal agents. The activities of shipping companies, terminal operators, and hinterland operators belong to the “Pressure” category [27,40,50]. “State” is utilized for describing the factors that reflect the changing circumstances of the port ecosystem. Port air quality, port water quality, port soil quality along with port-related supply chain disruptions, and port worker safety conditions belong to the “State” category [27,37,43]. “Impact” is utilized for elaborating the factors that emphasize the necessity of the port to address its activities via societal obligations along with respecting its economic and financial objectives. Port–city relationship tensions, additional waste generation, and port revenue decline belong to the “Impact” category [28,41,43]. “Response” is utilized to distinguish the set of actions at the disposal of the port authorities in order to foster the sustainable development of ports and the greening of ports. Green marketing strategies in terms of modal split targets, port infrastructure charges, green discounts, green fuel utilization encouraging, and environmental clauses in lease contracts or concessions belong to the “Response—Driver” category [27]. Stakeholder environmental compliance in terms of adhering to international and national environmental legislation, and punishment mechanisms for stakeholders disobeying environmental clauses belong to the “Response—Pressure” category [8,27]. IT/IS monitoring and measuring in terms of applying RFID, GPS, RTLS, WSN, and EDI enabling technologies in combination with big data analytics, decision analytics, and optimization methods belong to the “Response—State” category [54]. Port environmental remediation facilities in terms of cold ironing facilities, renewable energies facilities, circular economies facilities, and carbon capture and storage facilities belong to the “Response—Impact” category [40,41]. The DPSIR framework cause-and-effect relationships of the factors possess the possibility of steering ports towards a greening pathway by outlining the competencies of port authorities, port ecosystem societal agents, and the local community regarding their economic, social, and environmental agendas and ambitions.

5. Conclusions

This study conducted a bibliometric analysis research methodology in addition to guided content analysis in order to quantitatively comprehend the intellectual structure of the emerging green port research domain in the maritime industry. The process of obtaining the bibliography data collection in the WoS scientific repository was enabled by using the Boolean Search Terms along with the exclusion criteria, and resulted in: (1) Identification of 278 scientific articles; (2) Authored by 695 scholars; and (3) Published in 113 academic outlets. The obtained bibliography data collection was further anatomized in accordance with the four research objectives stated in this study’s Section 1.

The general results of the total scientific output of the emerging green port research domain literature regarding the refined bibliography sample of 278 journal articles indicate stable growth with a yearly publication growth rate of approximately 13.9 articles per year within the selected timespan of 20 years, ranging from 2001 to 2021, respectively. Further segmentation of the selected 20-year period into 5-year quartiles reveals that the most impactful articles for the emerging green port research domain belong to the third quartile (2011 to 2015) because the ratio between the key bibliometric term of TLCS and published journal articles represents the highest value of 2.6 local citations per article within the entire interquartile range. Scientific article analysis is advised from the aspect of the four primary meanings of governance in the scientific literature: (1) Governance as a structure; (2) Governance as a process; (3) Governance as a mechanism; and (4) Governance as a strategy.

The emerging green port research domain predominantly stems from the following ISI WoS major scientific discipline categories: (1) Transportation (46.4%); (2) Economics (15.1%); and (3) Environmental Studies (14.3%). The most prestigious academic institutions with adherence to the TLCS/Article ratio are: (1) Antwerp Maritime Academy (The Netherlands); (2) Nanyang Technological University (China); and (3) The University of Antwerp (The Netherlands). The aforementioned most prestigious academic institutions characterize a strong collaboration network strength. The most prominent scientific journals most explicitly addressing the emerging green port research domain on the basis of the TLCS/t score are: (1) Maritime Economics and Logistics; (2) Journal of Transport Geography; and (3) Maritime Policy and Management. The most impactful scientific articles substantially influencing the development of the emerging green port research domain on basis of TLCS/t and TGCS scores are: (1) Lam and Notteboom (2014); (2) Wan et al. (2018); and (3) Carlan et al. (2016). The most influential scholars intellectually shaping the development of the emerging green port research domain on the basis of the TLCS/t score are: (1) Theo Notteboom; (2) Jasmine Lam; and (3) Jagan Jeevan. Further analysis of scholarly activity via the Sankey diagram revealed that the Asian countries of China and Korea are the most active in the emerging green port research domain.

The application of the bibliometric coupling methodology in conjunction with the TLCS ≥ 3 as the cut-off criteria further refined the bibliography sample of 278 articles down to 30 articles. The iterative process of the selected 30 scientific articles’ content analysis resulted in identifying 5 independent yet interconnected research streams and sub-research streams constituting the emerging green port research domain. The five independent research streams are: (1) Port Governance Reforms, addressing the adoption of contextualized models of port governance reform as a consequence of port multi-scalar embeddedness forces and institutional stretching; (2) Port Hinterland Integration, exploring fostering port sustainability competitiveness via extended resource pools in terms of dry ports coupling; (3) Port Digitalization Management, highlighting the digitalization role in information systems regarding the interaction between transport, infrastructure, and institutional management in ports; (4) Port Competition Strategies, emphasizing the assessment and innovation in seaport competition policies for integration of green and sustainable operations; and (5) Port CO₂ evidence-based policies, investigating the conceptual development and awareness raising of port management practices on account of CO₂ evidence-based policies regarding port terminals.

The first independent research stream of Port Governance Reforms contributes to the seaport greening process by highlighting that seaports are complex and heterogenous environments consisting of a multi-layered decisional stakeholder chain; and that the analysis of the recurring port governance structures of landlord port authorities must adhere to institutional divergence via a path following the three green port developmental trajectories: decarbonization, digitalization, and multimodality. The second independent research stream of Port Hinterland Integration highlights the seaports’ efforts to develop efficient sustainable competitive operational mechanisms such as dry ports coupling for achieving and retaining competitive advantages in their hinterlands due to the growing pressures of increasing ship sizes, stakeholder opposition to port expansion, and heavy environmental regulation. The third independent research stream of Port Digitalization Management emphasizes the necessity of implementing key enabling information technologies and information systems in order to improve the seaport ecosystem through high quality data interchange between seaport stakeholders in order to boost the sustainable competitiveness of the entire maritime supply chain. The fourth independent research stream of Port Competition Strategies provides insight into seaport supply chain integration regarding seaport adherence to systems integration in terms of considering both the endogenous and exogenous competition aspects between seaport ecosystem stakeholders in competition policy creation. The fifth independent research stream of port CO₂ evidence-based policies indicates the necessity of spatial harmony by developing and incorporating environmentally friendly container terminal layouts in order to lower the working time, energy consumption, and CO₂ emissions; and to increase container handling equipment efficiency for achieving greener and sustainable terminal operations that take into account the ecological environment.

The application of the co-citation analysis methodology in conjunction with the LCSe for 2019, 2020, and 2021 as the cut-off criteria further refined the bibliography sample of 278 articles down to the top 15 trending articles or the top 5% of the articles of the emerging green port research domain. The iterative process of the selected 15 trending articles’ content analysis resulted in identifying 5 research directions within each research stream, representing a total of 20 future research directions. Further content analysis of the 20 future research directions resulted in the identification of 16 pivotal factors influencing the establishment of green port governance models. All of the factors influencing the future success of the port greening process stem from a combination of: (1) Decarbonization; (2) Digitalization; and (3) Multimodality as the main green port developmental trajectories. A DSPIR model is introduced in order to establish the cause-and-effect relationships of the 16 factors influencing the establishment of green port governance models in order to steer ports towards green transitions via coordination of sustainability-oriented objectives of the port authorities, port ecosystem societal agents, and the local community. Future research endeavors should encompass ports other than the container ports, and apply advanced quantification models capable of systematically organizing the interdependencies of factors such as structural equation modeling, exploratory factor analysis, and confirmatory factor analysis; and multicriteria decision-making models in order to give weight to the factors, such as the analytic hierarchy process and the analytic network process.