**1. Introduction**

The environment is the basis of human survival and development, comprising the sum of various natural factors within and around human society [1]. At present, China is committed to conserving natural ecosystems, focusing on strengthening the protection of the environment in large river basins [2]. Guizhou Province is located in the southwest karst area of China—the largest continuous karst landform region in the world [3]—which spans the Yangtze River and the Pearl River. It is an important ecological barrier in the upper reaches of the "two rivers". The entire ecological quality of this region is in good

**Citation:** Wu, Y.; Gu, L.; Li, S.; Guo, C.; Yang, X.; Xu, Y.; Yue, F.; Peng, H.; Chen, Y.; Yang, J.; et al. Responses of NDVI to Climate Change and LUCC along Large-Scale Transportation Projects in Fragile Karst Areas, SW China. *Land* **2022**, *11*, 1771. https:// doi.org/10.3390/land11101771

Academic Editor: Xiaoyong Bai

Received: 31 August 2022 Accepted: 9 October 2022 Published: 12 October 2022

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condition [4]; however, its ecosystems are vulnerable due to their significant sensitivity to external disturbances (including human activities and climate change) in this zone [5]. The Chinese government completed built numerous transportation infrastructure projects in Southwest China in recent years. As a consequence, the depth of highway access, road quality and network level in Guizhou been significantly improved. However, road construction projects are often in conflict with ecological protection. The rapid expansion of road traffic has brought unprecedented challenges to the local environment, and the construction or expansion of various types of roads may (directly or indirectly) leads to serious degradation of the natural environment, as well as increased local plant mortality. Therefore, a primary ecological problem to be addressed is to determine the current situation and change trend of vegetation along highways in karst region.

Highway construction and other large-scale construction activities can directly affect the environment by changing the surface vegetation cover. A construction project may greatly change the topography of the original slope conditions, geological conditions and natural stability, leading to increased vulnerability of the surrounding environment. Furthermore, with the promotion of large-scale projects, economic activities along the project will be activated, potentially including unreasonable human cultivation, excessive reclamation, overgrazing and urban expansion, all of which can lead to a decrease in vegetation coverage [6–8]. Therefore, large-scale artificial engineering activities have a significant impact on the growth and distribution of land surface vegetation [9,10], and can even change the distribution of vegetation coverage at the regional scale [11]. In contrast, reasonable project construction planning and ecological protection measures, such as afforestation, mountain closure afforestation and the improvement of agricultural technology, can facilitate the recovery vegetation [12,13].

Vegetation is one of the key components of the terrestrial ecosystem playing a fundamental role in regulating energy exchange and material cycling [14], especially in the process of karst rocky desertification control and ecological restoration [15,16]. Evidence has shown that, climate change is an important environmental factor having a significant impact on vegetation dynamics [17,18]. It influences the function and structure of the ecosystem by acting on the growth and adaptation characteristics of plants [19]. Temperature and precipitation are the most direct and important factors for vegetation growth and phenology [20,21]. At present, the normalized vegetation index (NDVI) is widely used to monitor vegetation and explore its response to climate change [22]. NDVI is an effective indicator of vegetation growth status and vegetation coverage, and it has a good linear relationship with surface vegetation. In a study on the correlation between global climate factors and NDVI changes, it has been found that NDVI presented an increasing trend with the increase in temperature in the middle high latitudes of the Northern Hemisphere [23]. In a regional study, it has been found that the seasonal variation of NDVI in different years were also responsive to land processes [24]. A spatial–temporal variation trend has been observed to vegetation degradation along with its response to climate change and anthropogenic stress [25]. Temperature may be an important driving force limiting forest greening in mountainous areas due to recent climate warming [26]. The NDVI of Guizhou karst area has been found to be more affected by temperature than precipitation and was one of the provinces with the most obvious environmental improvement [27,28]. In karst areas, a significant increase in vegetation NDVI is has been closely related to climate warming, but weakly related to precipitation [27,29]. Climate change in karst regions typically presents a cold-dry trend, while vegetation NDVI presents a recovery trend [30].

Although many scholars have studied the response of vegetation to human activities and climate factors, few have studied the impact of large engineering construction on the environment in karst areas. Relevant studies have revealed the spatial and temporal response relationship between NDVI and climate factors along the Qinghai–Tibet (QT) railway, as well as human activities, indicating that the influence of construction and operation of the QT railway on NDVI tended to weaken outward from the QT railway, while temperature and precipitation were positively correlated with NDVI [31,32]. Human

activities have contributed to the response relationship between regional vegetation change and climate change [33,34]. In karst areas, human activities tend to have a stronger role in vegetation improvement and degradation than climate change [35].

The Guiyang–Huangguoshu highway (GH highway) is the first highway built in the karst area. Over a long times scale (35 a), the construction and operation activities of this large project and the subsequent enhancement of human activities along the line were sufficient to change the original land-cover and affect the surrounding environment, resulting in the destruction of habitats along the line. Therefore, GH highway is an ideal research area. In this study, we take the earliest GH highway in the karst region as the research object. High-resolution NDVI data from 1986 to 2020 are used. The trend of NDVI in the area within 8 km of the GH highway route is analyzed. The impacts of temperature, climate, land use and land-cover change (LUCC) on the vegetation along the highway are comprehensively considered. We explored the long-term impact of road traffic engineering on vegetation, in order to provide guidance for future road traffic route planning and industrial layout in fragile karst regions.

#### **2. Materials and Methods**

*2.1. Study Area*

The GH highway is the first high-grade highway in the karst region [36]. It started construction in August 1986 and opened to traffic in May 1991. GH highway starts from Guiyang and finally reaches Huangguoshu, with a total length of 137 km (Figure 1). The average elevation of the road is about 1200 to 1300 m, low in the middle and high around the ends. The climate is subtropical monsoon with a mean annual temperature (MAT) of 15.3 ◦C. The mean annual precipitation (MAP) is about 1100 mm. The GH highway is located in a typical karst landform area, within karst landforms accounting for 76.5% [37].

**Figure 1.** Location and elevation of the study area.
