1. Introduction
People have a key role in shaping, forming, and preserving green areas, since inadequate maintenance and design can lead to the deterioration of the plants represented in the green infrastructure [
1]. Plant species as a major element contribute individual and collective aesthetic qualitative value, with trees being not merely decorative elements but essential components of urban ecosystems. Their functions extend beyond aesthetics to encompass various ecological, environmental, and socio-economic services [
2,
3].
The concept of green infrastructure involves the use of multidisciplinary and interdisciplinary methodologies, including biological, agricultural, social, and other branches of science, to provide a better approach to planning and managing green areas [
4]. Green infrastructure emphasizes the quality and quantity of urban and suburban green spaces, promoting biodiversity enrichment and conservation since urban greenery is comprised of different annual, bi-annual, and perennial species, including flowering species, evergreen, and deciduous trees and shrubs. Environmentally aware citizens see this natural capital as the one not inherited from the ancestors, but borrowed from future generations. However, this capital’s valorization often ends with marks for vitality and ornamental value (decorativeness), including marks for the presence of phytopathological, entomological, and mechanical damage [
5,
6,
7,
8]. Users’ scorings and appreciation for trees and greenery can vary based on individual preferences, cultural backgrounds, current residence, and specific needs. Urban planners, environmental advocates, and policymakers need to recognize and consider these values when making decisions about urban development and green space preservation, respecting the basic principles of climate justice [
9]. Broadly considered, people value trees and greenery in their surroundings for various reasons, and these values can be both intrinsic and instrumental [
10]. Exposure to green areas and trees improves mental health and facilitates children’s learning and cognitive abilities, as well as focus and attention [
11,
12].
In the scientific realm of ecosystem services, monetary valuation methods have garnered greater attention compared to alternative valuation approaches [
13,
14], but such exclusive emphasis on monetary evaluation places a spotlight on instrumental values, potentially overlooking the intrinsic and relational values associated with ecosystem services [
15]. Landscape tree appraisal, also referred to as tree evaluation or tree monetization, is a systematic process employed to assess the monetary value of trees within a specific landscape or urban setting. This form of appraisal holds significance for diverse applications, including property assessment, insurance claims, litigation, and establishing compensation for instances involving tree removal or damage [
16]. However, this value is far from being only monetary, as it includes several factors taken into account when appraising the value of a tree (tree species, its size, health, condition, location, and the ecosystem services it provides—shade, air purification, aesthetics).
Tree appraisal is a valuable tool in urban and suburban planning, which provides local governments, professionals, and researchers with an effective tool to determine the monetary value of both public and private urban trees or can be an instrument in resolving disputes and making fair compensations [
17]. Urban environments are rapidly expanding worldwide, with more than half of the global population residing in cities and urban areas [
18]. This ongoing urbanization presents a unique set of challenges, including increased demands for sustainable, livable, and environmentally friendly urban spaces. In this context, the role of trees in the urban core has gained significant attention due to their multifaceted contributions to the well-being of cities and their residents. Facing limited resources and competing urban development interests, efficient tree appraisal is essential for informed decision-making and the sustainable management of urban forests [
19]. The existence of the value possessed by a good and service (including natural and environmental resources) will, in turn, direct the decision-making behavior performed by individuals, communities, or organizations [
20].
With the challenging urbanization and climate change era, policy and decision-makers are striving towards the implementation of nature-based solutions (NBSs) and alignment with sustainable development goals to mitigate the devastating influence that urban development has caused. Both the theory and practice teach us that blue and green infrastructures, like bioretention gardens, green walls, and green roofs, can mitigate but cannot significantly reduce the detrimental effects of meteorological events like heavy rain, storms, hail, and heat waves. The primary concern that has arisen is that urban green infrastructure might become prone to natural hazards [
21]. Although devastating winds and tornadoes are not associated with European land, their emergence in the last decade has been prominent [
22].
Similarly, the novelty in the last decade on the territory of Serbia is supercell storms, which first occurred in June 2013 as a consequence of a heat wave that struck Europe [
23]. At the end of the period characterized by extremely high temperatures, the development of a storm along with supercell high precipitation convection took place in Serbia, producing tennis ball-sized hailstones and wind with speeds exceeding 35 m/s. Similarly, in 2023, two consecutive supercell storms hit Northern Serbia on July 19th and 21st. At first glance, understandably, the government and public focused their attention on human and material losses related to infrastructure, buildings, and personal assets, such as houses and cars, scarcely mentioning the number of fallen trees (around 3000 on the urban area of Novi Sad). Such an approach can neglect the true extent of the events’ impact; thus, a damage appraisal included in the greenery cadaster is of the utmost importance [
24].
Generally, urban green infrastructure planning in Serbia, as a developing country, is often neglected and taken for granted, while potential risks are overlooked. In a previous study regarding vulnerable populations, poisonous and allergenic plant species were identified in eight primary schools and six preschools located in Novi Sad, Serbia, and a total of 22 poisonous plant species and 21 allergenic plant species were identified [
25]. Contemporary studies on environmental justice are focused on agricultural losses as drought or flooding consequences [
26], air pollution due to wildfires [
27], and green space quality [
28], but there are no investigations dealing with the climate justice impaired by climate change resulting in extreme weather events, such as supercell storms. Implementing appropriate urban greenery to mitigate climate and other societal challenges is an essential element in sustainable cities.
Due to the urban green infrastructure values stated above, inappropriate greenery choice as well as the lack of information regarding the causes of and greenery losses after supercell storm events, this paper aims to (i) assess the monetary loss according to the tree appraisal method in public green spaces of Futog (Serbia) affected by the supercell storm; (ii) estimate the trees’ characteristics that influence wind-caused damage, especially canopy-driven uprooting risks; (iii) address the species-specific responses to wind-caused damage; and (iv) propose measures and highlight recommendations for the prevention of similar damage when faced with windstorms and trees’ uprooting, advocating for mutual action towards green infrastructure resilient planning aligned with climate justice principles.
4. Discussion
The main purpose of this research was to assess trees’ monetary loss in the public green spaces in Futog, one of the towns most affected by the supercell storm that hit the territory of Northern Serbia in the summer of 2023, concomitantly highlighting permanent social, environmental, and economic losses. The three investigated public green areas (two educational areas and one park), comprising less than 5 ha (44,588 m2), experienced a total loss of almost half a million Euros (EUR 495,864) when expressed in the national nursery prices as well as more than 1.5 million Euros according to the European price levels (EUR 1,528,481). While this monetary value is understandable to both highly and lower-educated citizens, regardless of gender, race, religion, minority dependence, seniority, or any other discriminating element, there are much greater losses about which there is a need for raised awareness among engineers, practitioners, and users.
Considering that economic losses are only one of the three pillars, social and environmental irreversibility must be taken into account. Total canopy volumes (calculated from the crown heights and widths) of the uprooted trees amounted to 30,333 m
3, indicating that 0.7 cubic meters of green mass were lost per one square meter of the investigated public spaces. This implies that some of the most important ecosystem services, corresponding to the mentioned social, economic, and environmental pillars, were irretrievably lost. Provisioning, regulating, cultural, and supporting services affected by the uprooted trees are presented in
Figure 7.
From the analysis of dozens of publications, it was determined that all types of ecosystem services are significantly influenced by factors such as leaf area and morphology, as well as crown dimensions, diameter at breast height, and tree height [
37], investigated in the present study. At the same time, these features are crucial for wind resistance. The influence of the canopy shape and size on the uprooting of trees due to wind blows is a multifaceted interaction, involving various factors that have been explored in the field of tree biomechanics and urban forestry. Canopy characteristics play a pivotal role in determining a tree’s vulnerability to uprooting during high winds [
38,
39]. Larger canopies expose a greater surface area to the wind, increasing aerodynamic forces and the risk of uprooting. The weight distribution within the canopy is crucial, with symmetrical canopies generally offering better aerodynamic properties [
40]. The species-specific characteristics of trees also contribute significantly to their wind resistance [
41]. Different tree species have evolved specific adaptations to environmental conditions, influencing their aerodynamic properties and resilience [
42]. However, species that were noted for the highest or medium–high wind resistance to the several hurricanes in the United States coastal areas (such as
Acer,
Betula,
Fraxinus, and others) by Duryea et al. [
38] were not confirmed as wind-resistant in the present study, implying that this criterion cannot be solely taken into account. Furthermore, trees belonging to one species did not perform in the same way in all three investigated areas (for instance, birch trees fell in two out of three investigated green spaces, while Serbian spruce trees fell in one out of three spaces). Frankly, understanding the complex relationship between wind forces and tree stability requires considering the overall health of the tree, its canopy characteristics, and the surrounding environmental conditions. Based on the available literature survey, Salisbury et al. [
43] classified those influences as biotic, abiotic, and management factors, with diameter at breast height (DBH) as the most frequently studied factor, while species influence was positioned as the second. In this review, root properties have shown significance only in rural studies. On the contrary, among 21 critical variables when estimating green space vulnerability to typhoons, Nguyen et al. [
44] considered both the canopy characteristics and root–soil interaction in the prediction of uprooting damage. Exploring tree failure following a windstorm that occurred in Brewster (Massachusetts, USA), Kane [
45] noted that the species, height, DBH, the presence of defects, and whether the trees had undergone pruning or if nearby trees had been removed affected tree uprooting. According to the same author, a critical wind speed (>30 m/s) is usually coupled with other factors such as precipitation, soil properties, and tree characteristics. Additionally, the health of a tree, including well-developed root systems and sturdy trunks, enhances its ability to withstand wind forces. It is clear that, besides the aboveground properties, the belowground characteristics (root spread, root architecture, soil type, and root-plate development) also influence wind resistance [
46].
Soil conditions, such as type and compaction, also play a crucial role in tree stability during windy conditions [
47]. Loose or waterlogged soils may increase the risk of uprooting, even for trees with well-designed canopies. This might be one of the major uprooting causes in the present study. As noted in the field survey after the supercell storm, documented in
Figure 2b, although generally described as species with tap and heart root systems, the majority of the fallen trees had developed shallow roots, not balanced with their canopy sizes. As noted by Gardiner et al. [
42] and Krišāns et al. [
48], fatal tree failures under extreme wind loads are primarily determined by tree anchorage, especially the characteristics of the soil–root plate interface. As shown by Gardiner et al. [
42], the very limited depth of the roots induced the uprooting of edge-standing Sitka spruce trees on wet soil. Due to the proximity to the Danube River and its inundation-prone nature, the town of Futog represents an area with a high level of underground water. We combined the available literature data on root system properties and obtained canopy measures to underline the possible uprooting causes. Notably, larger canopies (frontal areas > 200 m
2) are required for the uprooting of species characterized by a heart root system, characteristic of
Q. robur,
P. occidentalis, and
T. tomentosa, placed close to the linear correlation line in the scatterplot. On the contrary, segregated from the correlation line are species with an intrinsic tap root system, such as
S. japonica,
F. americana, and
P. cerasifera ‘Pissardii’, impeded by high underground water levels, where even small canopy frontal areas were enough to exhibit more than 50% of uprooted trees. Smaller but still significant percentages of uprooted trees (30–50%), with variable canopy areas (10–150 m
2), also indicate that the expected intrinsic root system architecture was not achieved and that there was a significant misbalance between above and below ground biomass, enabling a ‘shovel’ effect and canopy failures.
In our study,
P. nigra,
B. alba,
T. tomentosa,
F. excelsior,
A. saccharinum,
P. occidentalis, and
P. cerasifera were the species that showed a lower resistance to hurricane-strength wind, with both a significant number and percentage of uprooted trees. However, among these,
P. nigra,
B. alba,
F. excelsior, and
P. cerasifera are considered resistant according to the official catalog description. Mixed results related to the trees’ characteristics and uprooting correlation might ultimately be a result of the wind speed, direction, and duration, which unfortunately was not predicted to happen and thus not investigated and recorded in the given three areas (only in general, >30 m/s). As stated by Duryea et al. [
38], the percentage of urban trees loss is directly correlated with the wind speed. The same authors noted that their lists should be used with some reservations, bearing in mind that no species or individual tree is entirely immune to wind damage. Similarly, in our study, even the most adaptive and so-called ‘climate trees’ experienced more than 50% of uprooting (
C. bignonioides,
G. triacanthos,
A. negundo,
F. americana, and
S. japonica). On the contrary, it can be noted that mainly young trees of the most invasive alien species in the continental climate,
C. occidentalis,
M. nigra,
R. pseudoacacia,
R. pseudoacacia ‘Globosa’,
T. occidentalis, and
U. pumila, were not affected by the storm event. Thus, with a developed protocol for their maintenance (obligatory generative potential exclusion and vegetative mass preservation), these species might be of the importance in future planning activities [
49].
Proper greenery management supports successful thriving in altered urban ecosystems. Adequate pruning practices can influence canopy structure and reduce wind resistance area. Maintaining a tree by removing dead or weak branches can enhance its ability to withstand wind loads, which, in the cases analyzed in this paper, could partly be entrusted to the specialized teachers in the Agricultural High School and serve for horticultural educational purposes in their own schoolyard, supported by specialists from academia. As noted by Rolleston et al. [
50] in 2023 there was a notable increase in climate-related catastrophes worldwide, thus proposed higher education institutions’ involvement towards significant advancement of Climate justice through their research, education, community involvement, and public outreach. Besides teachers and pupils, engagement could consider other citizens, since investigated green areas have significant importance for all residents [
51]. With such an approach, multiple sustainable development goals (SDGs) could be addressed simultaneously [
52]. Education and involvement of all related groups—citizens, nursery producers, entrepreneurs, planners, and policy-makers—are some of the most important prerequisites towards upgrading green public areas to more sustainable and resilient ones (SDG11), concurrently ensuring the healthier life of citizens (SDG3) and biodiversity protection (SDG15), as well as the efficient use of natural resources (SDG12).
Due to climate change, the strong storms that hit Futog and the entire Vojvodina area in July 2023, which caused significant damage, will become more frequent. In this regard, it is necessary to enhance plants’ adaptability by maintaining their health and condition at a higher level. The recent findings of Nguyen et al. [
44] suggest the importance of appropriately managing urban trees to alleviate the impacts of climate change, especially typhoons’ influence on urban green spaces. The prevention of losses rather than costly sanitation must be prioritized. In many cases, plants considered inadequate in urban green spaces must be replaced, especially those that generate more disservices than benefits [
53]. In December of 2005, a devastating windstorm struck a limited area of Cape Cod in Massachusetts, USA, where, despite the relatively confined scope of the storm, wind speeds reaching approximately 45 m/s led to thousands of tree failures, incurring cleanup costs exceeding USD 1 million [
33]. Similarly, in the present study, damage caused by a single storm in an area of less than 5ha, induced losses of 98 trees and EUR 495,864 (local prices) or more than three-fold (EUR 1,528,481) in international prices, with ongoing cleanup and costs that remain to be calculated. Although economic valuation will remain a crucial piece of evidence to support investments in urban tree planting and management, its practical application in landscape planning and design will necessitate further investigation into how it integrates with frameworks for making decisions [
54].
In the face of climate change, in addition to protection and enhancement, we also need to consider insuring trees, given the losses that occurred during just one storm, and the estimated value of the currently thriving trees (EUR 396,480; 565,133; and 265,876 in the national and EUR 1,330,345; 1,697,561; and 875,148 in the international prices for the each of the three investigated areas). Due to the green area’s significance (i.e., high school yard accompanying the Chotek Castle as valuable cultural heritage) as well as the presence of the currently undamaged 140-year-old
P. occidentalis specimen under protection as a natural monument of the III category (The decision on protection ‘Official Gazette of the City of Novi Sad’ number 2/95 named ‘American Sycamore in Futog’), tree appraisal should be considered as a basis for insurance in the case of future storm damage. The estimated value of this tree alone is EUR 31,647 (national prices) and EUR 91,575 (international prices) due to the impressive state and size (condition class of 0.8, tree height of 28 m, trunk height of 6 m, trunk circumference of 4.20 m and crown diameter of 24 m), urging its unequivocal preservation. A better understanding of the risk factors associated with tree species’ susceptibility to severe storms is key to predicting and ensuring the future of forest ecosystems under climate warming [
41].
Climate and environmental justice issues in Novi Sad and its adjusted settlements in the past few transitioning years were successfully recognized and significantly addressed, Including poisonous and allergenic specimens’ assessment and management recommendation in preschools and schoolyards; invasive alien specimens’ determination and management recommendation in highly visited streets and parks; public and private urban fruit production using disease- and pest-resistant cultivars; revitalization of neglected urban spaces through accessible pocket gardens; rain gardens [
55] and green roof at the Special Education School ‘Milan Petrović’ [
56] complemented with the current amenity tree appraisal, preservation, and insurance. Local governments must continuously monitor the indicators of urban greenery value and provide financial resources for maintaining the ecosystem services for all vulnerable groups of the population. Implementing NBS that can mitigate multiple challenges and correspond to vulnerable users’ needs leads to a resilient and sustainable city green infrastructure [
57]. Providing a ‘peace of nature’ in the dense urbanized areas to each resident regardless of gender, race, religion, minority dependence, seniority, or any other discriminating element supports climate justice basic principles [
58,
59].
5. Conclusions
Understanding the complex interplay between canopy characteristics, tree and root structure, and environmental conditions is essential for assessing the risk of uprooting during windy conditions. Arborists and urban planners must consider these factors when selecting tree species for urban environments and implementing measures to enhance tree stability, such as pruning and proper soil management. Additionally, the importance of a thoughtful approach to planning and designing the outdoor spaces of educational institutions, including the careful selection of plant species, due to their users’ vulnerability, is undeniable.
The total appraised monetary loss as a consequence of the supercell storm according to the tree appraisal method in a territory of less than 5 ha amounted to almost half a million Euros (EUR 495,864) when expressed in the national nursery prices as well as more than 1.5 million Euros according to European price levels (EUR 1,528,481). The correlation analyses showed that no single tree’s characteristic could explain the uprooting incidence alone, but indicated that both belowground and aboveground biotic (morphological and physiological), abiotic (environmental), and artificial (root and canopy maintenance) factors, to be further investigated, might influence the wind-caused losses. Since no species-specific responses to the wind-caused damage could be observed, except for the invasive ones (C. occidentalis, M. nigra, R. pseudoacacia, R. pseudoacacia ‘Globosa’ T. occidentalis, and U. pumila), root system and canopy maintenance measures applied towards preventing uprooting are of the utmost importance. Advocating for mutual action towards resilient planning aligned with climate justice principles, this study convokes all interested parties (teachers, parents, citizens, landscape architects, horticulturalists, biologists, socialists, and environmental economists) to take part and co-create institutional green areas on the scientific and practical foundations provided by academia.
Prevention due to the direct economic, as well as indirect ecological and social, losses considering the safety of the greenery users, especially the most vulnerable part of the population, must be highlighted. Invaluable human losses in this study were avoided since the storm occurred during the summer school vacation, making this study an alarming warning for both canopy and root health inspection and proper management. From an economic and environmental point of view, the insurance of the currently unaffected solitary specimens of an excellent appearance and ecosystem services provision should be initiated and promoted, taking into account and monetizing all possible services, be they present or future.