# Temporal Changes in Land Use, Vegetation, and Productivity in Southwest China
## 1 Introduction  
The ecological environment of karst landforms in southwest China is fragile and has been significantly affected by climate and human activities in recent decades [1; 2; 3]. Changes in vegetation, LULC, and GPP affect biogeochemical cycles, and social effects in this region impact the area range of influence [4; 5; 6; 7]. However, the spatial and temporal characteristics of LULC, vegetation, and carbon storage are not clear. This has a significant impact on ecological evolution and regional social development [8; 9]. Therefore, there is a need to clarify the temporal change characteristics of LULC, vegetation, and carbon storage in southwest China. Southwest China has a large number of karst ecosystems, which are hypersensitive and fragile. First, this area is one of the largest exposed areas of carbonate rock salts in the world [10], and in these environments, the soil formation rate is low, and the permeability is high due to the presence of interstitial fractures. Furthermore, it has unique and fragile geomorphological and hydrogeological features [11]. In recent decades, long-term and severe climate change and human activities have brought enormous pressure to the ecosystem in this area [12; 13; 14]. Rocky desertification has become one of the most serious environmental problems in karst areas [15; 16]. Terrestrial vegetation types and compositions have changed due to climatic conditions, carbon dioxide fertilization effects, and LULC [17; 18]. Second, under the background of population pressure and urbanization, the intensity of human activities has increased rapidly, and the land cover has undergone drastic changes [19]. Third, since the end of the 20 th century, China has implemented a large number of ecologicalengineering constructions, which have achieved an increase in vegetation coverage and carbon storage through ecological restoration and improved ecosystem services [20; 21; 22]. In addition, the southwest region is an important ecological barrier and ecologically fragile, with extensive potential for various ecosystem services, such as soil and water conservation, climate regulation, and carbon balance [23; 24; 25], providing a huge contribution to social development, ecosystem balance and carbon sequestration [24; 26; 27]. At present, the spatial and temporal changes in LULC, vegetation cover, and gross primary productivity (GPP) in southwest China are not clear. Vegetation is an important factor affecting the ecological balance and is usually considered as a direct and obvious indicator to analyze the impact of natural seasonal changes and human activities on the ecological environment [28; 29]. Gross primary productivity (GPP) is an important indicator reflecting vegetation status, ecosystem structure, and function [30] and plays a key role in carbon cycling in terrestrial ecosystems [31], and is an important factor in measuring the regional ecological value [32; 33]. Therefore, clarifying temporal and spatial evolution processes is of great significance for understanding the value and sustainable development of ecosystems. Studies have found that China's vegetation has shown an overall greening trend in the past 30 years [24]. However, due to the vast heterogeneity of climate, topography, and human activities in the southwest, the spatial and temporal distributions of LULC, vegetation dynamics, and gross primary productivity (GPP) are significantly different [2; 14; 34]. Since 2000, the LULC change in southwest China has been mainly manifested in the expansion of forest land and the reduction in cropland [4; 35]. The study found that NDVI increased significantly in low- to mid-altitude areas < 3400 m due to improved afforestation and agricultural productivity [36]. In the afforestation and grassland restoration areas, the direct contribution of forest land to the annual growth rate of GPP is 24.64% [37].