Mapping Tree Species Deciduousness of Tropical Dry Forests Combining Reflectance, Spectral Unmixing, and Texture Data from High-Resolution Imagery

• Published in: Forests 2020-11, Vol.11 (11), p.1234
• Main Authors: Huechacona-Ruiz, Astrid Helena, Dupuy, Juan Manuel, Schwartz, Naomi B., Powers, Jennifer S., Reyes-García, Casandra, Tun-Dzul, Fernando, Hernández-Stefanoni, José Luis
• Format: Article
• Language: English
• Subjects: Carbon; Carbon fixation; Drought; Dry forests; Dry season; Error reduction; Forest ecosystems; Forests; Geographical distribution; Global positioning systems; GPS; High resolution; Image resolution; Independent variables; Normalized difference vegetative index; Phenology; Precipitation; Reflectance; Root-mean-square errors; Seasons; Spatial distribution; Spatial variations; Species; Spectra; Texture; Topography; Trees; Tropical forests; Variables; Vegetation; Vegetation index
• ISSN: 1999-4907; 1999-4907
• DOI: 10.3390/f11111234

In tropical dry forests, deciduousness (i.e., leaf shedding during the dry season) is an important adaptation of plants to cope with water limitation, which helps trees adjust to seasonal drought. Deciduousness is also a critical factor determining the timing and duration of carbon fixation rates, and affecting energy, water, and carbon balance. Therefore, quantifying deciduousness is vital to understand important ecosystem processes in tropical dry forests. The aim of this study was to map tree species deciduousness in three types of tropical dry forests along a precipitation gradient in the Yucatan Peninsula using Sentinel-2 imagery. We propose an approach that combines reflectance of visible and near-infrared bands, normalized difference vegetation index (NDVI), spectral unmixing deciduous fraction, and several texture metrics to estimate the spatial distribution of tree species deciduousness. Deciduousness in the study area was highly variable and decreased along the precipitation gradient, while the spatial variation in deciduousness among sites followed an inverse pattern, ranging from 91.5 to 43.3% and from 3.4 to 9.4% respectively from the northwest to the southeast of the peninsula. Most of the variation in deciduousness was predicted jointly by spectral variables and texture metrics, but texture metrics had a higher exclusive contribution. Moreover, including texture metrics as independent variables increased the variance of deciduousness explained by the models from R2 = 0.56 to R2 = 0.60 and the root mean square error (RMSE) was reduced from 16.9% to 16.2%. We present the first spatially continuous deciduousness map of the three most important vegetation types in the Yucatan Peninsula using high-resolution imagery.