2.3.1. Diversity Index Data

Based on sample data obtained from the field survey, tree species diversity for each plot was calculated using the three commonly used plant diversity indices, namely Shannon (*H* ), Simpson (*λ*) and Pielou (*J* ) (Table 1). Specifically, we first counted the species (*i*) and proportion (*Pi*) of trees in each plot, and then input the statistical parameters into the equations of diversity index to calculate diversity values of each plot (see Figure A2). Finally, the diversity values of each plot were used as dependent variables, and multivariables from remote sensing data corresponding to the plot location were used as the prediction variables for the next step.

**Table 1.** Three diversity indexes and corresponding equations were used in the study. Note: S is the total number of tree species in a plot; *Pi* is the proportional abundance of species i relative to the total abundance of all species S in a plot; *InPi* is the natural logarithm of this proportion.


#### 2.3.2. Sentinel-2 Images

Multi-temporal Sentinel-2 imagery was obtained from the Copernicus open access (COA) Hub [30]. We extracted 4 tiles of Sentinel-2 images which corresponded to different phenological phases and covered the study areas from May, June, September, and October in 2020. Using the Sen2Cor plug-in provided by the ESA [31], the Sentinel images were atmospherically corrected. In the sentinel application platform [32], bilinear interpolation method is used to resample all bands to 50 m, and then multiple vegetation indices were also calculated using Sentinel-2 bands (Table 2).

**Table 2.** Vegetation indices extracted from Sentinel-2 satellite imagery.

