Using UAVs to assess the relationship between alpine meadow bare patches and disturbance by pikas in the source region of Yellow River on the Qinghai-Tibetan Plateau

Degradation of the alpine meadow has received increasing attention recently, and plateau pika (Ochotona curzoniae, hereafter pika) disturbance is considered as an important cause. Bare patches are the most obvious features indicating the degree of degradation. Previous studies mainly focus on bare patches' overall status, i.e., the fractional bare patches (or fractional vegetation cover). However, our understanding of individual bare patches' change rates and their relationship with pika disturbances is insufficient. In this study, aerial photos were taken by an unmanned aerial vehicle (UAV) within a typical alpine meadow ecosystem, over four monitoring sites with different area fraction of bare patches: almost no bare patches (NBP, < 5%), low bare patches (LBP, 5% -20%), moderate bare patches (MBP, 20% -60%) and high bare patches (HBP, > 60%) during 2015 and 2018. The relationship between the changes of pika disturbances and bare patches were analyzed based on these aerial photos. Results showed that: 1) changes of pika holes and bare patches were not significant (P > 0.05) at MBP and HBP, while they increased significantly (P < 0.05) at NBP, which suggested that the increase of bare patches could be ascribed to increase of pika holes. However, both pika holes and bare patches almost disappeared at LBP in three years, implying a high resilience of this site; 2) the differences in correlations between the pika hole density and the area fraction of bare patches were remarkable among different sites. Specifically, there were significant linear correlation at NBP (y = 642.01x + 506.52, R-2 = 0.91; P < 0.05) and HBP (y =-29.036x + 2983.9, R-2 = 0.72, P < 0.01), and a significant negative correlation in exponential form at MBP (y = 2632.3e-0.022x, R-2 = 0.50, P < 0.05), while no significant correlation was observed between the two at LBP. We concluded that the changes in bare patches and their relationship with pika disturbances were diverse over a short period. Therefore, long-term repeated aerial photographing over grasslands at different stages of degradation is required for further research, and UAV is a feasible tool to fulfill the task. (C) 2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).