Abstract
Plateau pika (Ochotona curzoniae, hereafter pika) is considered to exert a profound impact on vegetation species diversity of alpine grasslands. Great efforts have been made at mound or quadrat scales; nevertheless, there is still controversy about the effect of pika. It is vital to monitor vegetation species composition in natural heterogeneous ecosystems at a large scale to accurately evaluate the real role of pika. In this study, we performed field survey at 55 alpine grassland sites across the Shule River Basin using combined methods of aerial photographing using an unmanned aerial vehicle (UAV) and traditional ground measurement. Based on our UAV operation system, Fragmentation Monitoring and Analysis with aerial Photography (FragMAP), aerial images were acquired. Plot-scale vegetation species were visually identified, and total pika burrow exits were automatically retrieved using the self-developed image processing software. We found that there were significant linear relationships between the vegetation species diversity indexes obtained by these two methods. Additionally, the total number of identified species by the UAV method was 71, which was higher than the Quadrat method recognition, with the quantity of 63. Our results indicate that the UAV was suitable for long-term repeated monitoring vegetation species composition of multiple alpine grasslands at plot scale. With the merits of UAV, it confirmed that pika’s disturbance belonged to the medium level, with the density ranging from 30.17 to 65.53 ha−1. Under this density level, pika had a positive effect on vegetation species diversity, particularly for the species richness of sedge and forb. These findings conclude that the UAV was an efficient and economic tool for species monitoring to reveal the role of pika in the alpine grasslands.
Highlights
The Qinghai-Tibetan Plateau (QTP) contains 83% of the earth’s terrain above 4000 m and has the largest alpine grasslands ecosystem globally [1]
It is reasonable to extract data directly from the aerial images as they were collected along the same method using the same type unmanned aerial vehicle (UAV), and it did not affect the processes of identifying species and pika burrows based on former studies [35,37]
The aerial image that was taken by the UAV at 2 m flight height covered ground area of 2.6 m × 3.5 m and the resolution of each single image was ~1 mm
Summary
The Qinghai-Tibetan Plateau (QTP) contains 83% of the earth’s terrain above 4000 m and has the largest alpine grasslands ecosystem globally [1]. It is necessary to test the feasibility of UAV for monitoring vegetation species composition of multiple types of alpine grasslands at a large scale, and it is vital to improve our understanding of the pika’s influence on vegetation species diversity in the real-world ecosystems. Our specific objectives were to (1) test the feasibility of the UAV for monitoring vegetation species composition in multiple types of alpine grasslands; (2) explore the relationship between pika density and vegetation species diversity in real-world ecosystems at the plot scale; and (3) reveal the role of pika in vegetation species diversity. It is reasonable to extract data directly (no referencing and rectification) from the aerial images as they were collected along the same method using the same type UAV, and it did not affect the processes of identifying species and pika burrows based on former studies [35,37]. The cover area of each aerial image is small (26 m × 35 m and 2.5 m × 3.5 m), meaning that it is hard and inefficient to rectify each one by setting ground reference points, but it meets the study accuracy requirements [28,35,37]
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