Ecological Indicators (Feb 2023)
Watershed-level spatial pattern of degraded alpine meadow and its key influencing factors in the Yellow River Source Zone of West China
Abstract
This study aims to characterize the watershed-level distribution patterns of severely degraded alpine meadows commonly known as “heitutan” in the Yongqu River basin of the Source Zone of Yellow River. Topographic data were analyzed in ArcGIS to derive several variables and delineate multi-level watershed units. In addition, remotely sensed data were analyzed to map ground covers in two-level watershed units (i.e. first-level and second-level watershed units), including heitutan degraded grassland. The two sets of results were intersected to identify the correlation of land covers and spatial proximity with heitutan and their possible influences on it. The results show that the alpine meadow in the Yongqu watershed comprised 51.39 % of the total area, and shrub grassland accounted for 45.45 % of the total area. At the first-level tributary unit of the Yongqu watershed, heitutan-degraded grassland is the most common feature at 4.75 km2, accounting for 2.46 % of all alpine meadows. Heitutan patches on average have a minimal size of 1007 m2. Most heitutan patches are distributed on gentle, mainly sunny, and semi-sunny slopes of 7–18° in gradient. They are situated within 1000 m of roads, accounting for 90.53 % of total “heitutan”, while 96.56 % are distributed within 0–1500 m of settlements. At the second-level tributary unit of the Hallaqu and Chayangwa, heitutan is the most common at 1.23 and 0.41 km2, respectively, accounting for 0.79 % and 1.01 % of the total alpine meadows. However, the highest proportion in the Chayangwa River basin is in the 0–3° beach areas. The areas widely distributed with heitutan heavily overlap with those affected by overgrazing and rodent activities. Redundancy analysis and structural equation modeling indicate that slope exerts the greatest influence on the formation and distribution patterns of the heitutan degraded grassland, followed by slope aspect and distance to roads. In comparison, distance to river channels and settlements and the annual temperature has an insignificant influence on the heitutan degraded grassland.
