Decreased species richness along bare patch gradient in the degradation of Kobresia pasture on the Tibetan Plateau

The Kobresia pasture in the Tibetan Plateau, as the world's largest and most unique pastoral alpine ecosystem, is undergoing severe degradation, visible in the formation of bare patches. Characteristics of bare patches in Kobresia pastures are regarded as indicators of the fragmentation and degradation of the alpine landscapes. Here, we used unmanned aerial vehicles (UAV)-based low-elevation remote sensing to monitor 72 study sites in the eastern Tibetan Plateau for identifying the spatial patterns of bare patches of Kobresia pasture degradation on regional scale. We conducted field surveys of species composition, quantified fragmentation caused by bare patches using four landscape indices (patch area, total edge length, shape index and splitting index, representing the patch area, length of the edge, shape, and dispersion of the bare patches, respectively), then modeled the response of plant species richness and productivity at the scale of 50 × 50 m to the Kobresia pasture fragmentation process. Our results indicated that species richness and biomass production decreased significantly with each increasing bare patch index. The total edge length of bare patches increased the spatial turnover of plant species. Although bare patch area significantly decreased the species richness of plant communities, it led to a decrease in forb richness and an increase in grass richness along the degradation of Kobresia pastures. Bare patch areas, as the most easily accessible and highly accurate parameter by UAV-based low-elevation remote sensing, significantly related to the decrease in species richness and productivity, and mainly explained the changes in functional group composition. For assessing the ecological integrity of grassland functionality (plant species diversity and above-ground productivity), bare patch area can be used as an important indicator of Kobresia pasture degradation.