Abstract
Populus euphratica is an important tree species in desert ecosystems. The protection and restoration of natural Populus euphratica forests requires accurate positioning information. The use of Sentinel-2 images to map the Populus euphratica distribution at a large scale faces challenges associated with discriminating between Populus euphratica and Tamarix chinensis. To address this problem, this study selected the Daliyabuyi Oasis in the hinterland of the Taklimakan Desert as the study site and sought to distinguish Populus euphratica from Tamarix chinensis. First, we determined the peak spectral difference period (optimal time window) between Populus euphratica and Tamarix chinensis within monthly Sentinel-2 time-series images. Then, an appropriate vegetation index was selected to represent the spectral difference between Populus euphratica and Tamarix chinensis within the key phenological stage. Finally, the maximum entropy method was used to automatically determine the threshold to map the Populus euphratica distribution. The results indicated that the period from 22 April to 1 May was the optimal time window for mapping the Populus euphratica distribution in the Daliyabuyi Oasis. The combination of the inverted red-edge chlorophyll index (IRECI) and the maximum entropy method can effectively distinguish Populus euphratica from Tamarix chinensis. The user’s accuracy of the Populus euphratica distribution extraction from single-data Sentinel-2 images acquired within the optimal time window was 0.83, the producer’s accuracy was 0.72, and the F1-score was 0.77. This study verified the feasibility of mapping Populus euphratica distribution based on Sentinel-2 images, and analyzed the validity of exploiting spectral differences within the key phenological stage from a single-data image to distinguish between the two species. The results can be used to extract the distribution of Populus euphratica and serve as an auxiliary variable for other plant classification methods, providing a reference for the extraction and classification of desert plants.
Highlights
Populus euphratica is an important constructive tree species in the desert ecosystem, and is mainly distributed in Xinjiang, China
Spectral Reflectance Difference In Sentinel-2 images, the red-edge bands (0.65–0.793 μm) and near-infrared band (0.785–0.9 μm) are most useful to tree species classification [7,14]; we focused on the variation characteristics of the spectral reflectance of Populus euphratica pixels and Tamarix chinensis pixels in the red-edge bands and near-infrared band
Our results indicated that 22 April to 1 May is the optimal time window for separating Populus euphratica and Tamarix chinensis
Summary
Populus euphratica is an important constructive tree species in the desert ecosystem, and is mainly distributed in Xinjiang, China. It serves as a crucial barrier in protecting oases and maintaining the stability of the oasis ecosystem [1,2]. Habitat deterioration has resulted in a decline in natural Populus euphratica forests. The relevant watershed management agencies have repeatedly implemented ecological water conveyance to restore the natural Populus euphratica forests [3,4,5]. The protection of forest resources requires accurate positioning information as a basic premise [6,7]. Mapping the Populus euphratica distribution is essential for its protection and restoration
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