Grassland degradation by shrub encroachment: Mapping patterns and drivers of encroachment in Kyrgyzstan

摘要

Shrub encroachment is one of the major phenomena of grassland degradation throughout the world. One of the largest grassland areas is found in Central Asia. This area is playing an important role for biodiversity and food security, especially in a context of climate change. While sustainable land management is critical to avoid shrub encroachment, the dynamics of such encroachment are often unclear, especially in remote areas. We assessed the spatial and temporal dynamics of shrub encroachment in Suusamyr valley in Kyrgyzstan and analysed how these patterns relate to abiotic and social factors. To assess the extent of shrub encroachment we performed a random forest classification with Google Earth Engine to depict shrub encroachment between 2000 and 2019. By using a combination of vegetation indices and digital elevation derivatives in the classification model, the overall classification accuracy reaches above 90. The mapping of temporal changes revealed an increase in shrub encroachment of 48 within the valley, adding up to an overall coverage of 2 of the grassland area. The spatial patterns of shrub encroachment are more strongly associated with anthropogenic factors, such as locations of roads and settlements, than with variations in precipitation and amount of organic carbon in soils. Around 45 of shrub encroachment occurs close to main roads and local paths, and within around 5 km distance from temporal settlements. This degradation is probably caused by overgrazing near settlements and the loss of grasslands in those areas puts additional pressure on local livestock farming, potentially leading to further degradation in neighboring areas. A shrub encroachment susceptibility map was created to identify areas vulnerable to further shrub expansion, affecting valuable grassland area. The identification of these areas at risk may inform sustainable grassland management by better allocating pastures according their capacity and reducing pressures on those places most susceptible to degradation.