2024-04-18
The water and vegetation growth of terrestrial ecosystems are fundamental biophysical processes for material cycling and energy exchange in terrestrial systems. Human activities have significantly impacted water and vegetation development, leading to the emergence of two main global environmental issues: water scarcity and global climate change. Research efforts are focused on saving water resources while improving carbon sequestration and sink capacity. To holistically manage these processes at various scales, the concept of vegetation–climate coupling was introduced.
In the arid region, the oasis is characterized by a desert substance and a mosaic of vegetation. The biophysical processes and interactions between vegetation and the local climate in this kind of region are determined by the macroscopic structure of the ecosystems, i.e. landscape patterns. To understand how these landscape patterns impact regional hydro-heat coupling across space and evolve over time, the research team utilized remote sensing observational data and methods to examine the relationships among these factors. In this case, the team focused on the oasis along the upstream of the Hotan River Basin in the Taklamakan Desert in Xinjiang of western China and employed the satellite imagery datasets of Landsat from 1993 to 2019 to investigate the dynamics of vegetation–climate factors. Based on the land use and cover change datasets, the landscape pattern metrics, including patch density (PD), contagion index (CONTAG), fractal dimension (FRAC), were calculated to measure the landscape features on the different aspects, i.e. the fragmentation, the connectivity, and the complexity. With the algorithm of land surface energy balance, the land surface indicators, including the soil-adjusted vegetation index (SAVI), albedo, surface irradiance temperature (Ts), and evapotranspiration (ET), were calculated to represent the key process in the interaction of vegetation–climate. The temporal-spatial dynamics of the landscape patterns and the vegetation–climate metrics were mapped and demonstrated in a quantitative manner. The statistical results revealed that during the past decades, the agricultural land in the study area had significantly increased by 17 %. Grassland and shrubs had also expanded, while the desert area decreased from 82.57 % to 78.82 % of the total area, with an overall reduction rate of 1.4 %/10a. It was found the study area was getting warmer and dryer based on the general trends of Ts and ET observed during the period of 1993–2019. The agricultural land had the highest PD and CONTAG, and the lowest FRAC. The agricultural land had the lowest Ts and the highest ET. The results of structural equation model identified the decoupling effects of PD and CONTAG on the regional hydro-heat environment, while confirmed that FRAC had positive impact on the coupling between Ts and ET. The study bridged the landscape pattern with the regional vegetation–climate interaction and provided the suggestions for the landscape planning and management for a more sustainable arid region.
The study reveals that the accelerated urbanization process and population growth in the region have led to intensified human activities, resulting in a significant expansion of reclaimed agricultural land, which has altered the local environment to become colder and more humid. At the same time, the changes in hydrothermal conditions and the impact of human activities have also significantly increased the surrounding grassland and shrub areas. From a macro perspective, the quantitative analysis results explain the changes in the climate regulation function of the ecosystem caused by the dynamic landscape pattern which was driven by urbanization in this region. The process of subsequent decline in the ecosystem has affected the albedo, which exhibits a “V”-shaped change trend. The irradiation temperature of the regional underlying surface has been increasing, and the evapotranspiration flux showed a trend of fluctuation increasing. The agricultural land had the highest PD and CONTAG, and the lowest FRAC, while the agricultural land had the lowest Ts and the highest ET. The analysis on the relationships between the landscape patterns and the regional vegetation–climate interaction factors shed light on how the macroscopic ecosystem structure at landscape level impacted on the regional biophysical process. The results of structural equation model identified the decoupling effects of PD and CONTAG on the regional hydro-heat environment, while confirmed that FRAC promoted the coupling between Ts and ET. It required the local land planner and management department to reflect on the way of land development in the oasis in the context of the arid region sustainability. By considering the regional waters and wetland area decline and grassland fragmentation, the hydrothermal environment in this region is in a trend of warming and drying. It is crucial to further optimize the landscape spatial pattern of artificial and natural vegetation landscape to promote a healthy and sustainable eco-hydrological cycle in the region.
The research outcome was published in Ecological Modelling (IF=3.1) in the title of "The landscape altered the interaction between vegetation and climate in the desert oasis of Hotan River Basin, Xinjiang, China" with Cai Yimeng, Wu Jiaxin and Tudi Yimiti from the School of Grassland Science as the first authors, Li Zhouyuan from the same school is the corresponding author. Besides, Professor Yang Xiuchun and Professor Dong Shikui also provide guidance to the research.
This work was financially supported by the Third Xinjiang Scientific Expedition Program (2022xjkk0402), the Second Tibetan Plateau Scientific Expedition and Research Program (2019QZKK0307), the National Natural Science Foundation of China (32101324), the National Key R&D Program of China (2023YFF1304305), and the College Students' Innovation and Entrepreneurship Training Program (S202110022170, 202310022126).
Paper Link: https://doi.org/10.1016/j.ecolmodel.2024.110687
