Abstract
The oasis-desert transition zone, the boundary between the desert and oasis, has special significance in maintaining oasis stability and indicating ecosystem health. The width of the boundary is one of the critical indicators to determine the sampling design and restrict findings scaling in the study of the desert oasis transition zone. Buffer analyze and focal analyze were conducted to determine the width among oasis-desert transition zone and oasis artificial sand fixation zone in Hexi corridor China. Focal analyses indicate that TCImax and TCImin can constrain NDVI of trend variation, and the effect increases with the analysis scale. On the same spatial scale, NDVI and TCI have opposite trends and have intersections. The intersection of the sandy desert transition zone is between 30–90 m, and the oasis artificial sand-fixaion zone is between 90–150 m. The width of the sandy desert transition zone is between 220–300 m, and the width increases with the increase of analysis scale. The oasis artificial sand-fixation zone is between 420 and 540 m, which decreases with the increase of the analysis scale. NDVI shows a trend of decreasing from the oasis boundary to the desert, the trend of TCI is different from that of NDVI, showing an increase from the edge of oasis to the interior of desert. The differences in the spatial distribution of NDVI and TCI can be clearly expressed, and different types of transition zones and analysis scales have their own characteristics.
Highlights
The oasis-desert transition zone, the boundary between the desert and oasis, has special significance in maintaining oasis stability and indicating ecosystem health
The core conclusion of these findings was that Vegetation Condition Index (VCI) and TCI could be used to calculate surface vegetation conditions and temperature[5,7], and VCI and TCI interactions were used to construct a Vegetation Temperature Condition Index (VTCI)[8]
According to the results of Normalized difference vegetation index (NDVI) and TCI analysis on different scales (Fig. 2), NDVI shows a decreasing trend from the oasis boundary to the desert, which trend is more obvious with the analysis scale from 90 m to 330 m (Fig. 2a,b)
Summary
The oasis-desert transition zone, the boundary between the desert and oasis, has special significance in maintaining oasis stability and indicating ecosystem health. From the perspective of the spatial attributes of the oasis-desert transition zone, the inner boundary of the farmland and woodland is easy to identify, but the outer boundary is different in various scales and regional studies[3,4]. This difference comes from the spatial heterogeneity of vegetation types and the diversity of oasis boundary pattern. Because this study is the first to use the NDVI and TCI trends to determine the width of the oasis-desert transition zone, the natural boundary between the oasis and sandy desert boundary types (no artificial sand-fixation, yellow line in Fig. 1) and artificial interference boundaries are selected.
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