Abstract
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.
Highlights
Tropical dry forests (TDF) cover about 46% of tropical forests worldwide and they are one of the most threatened ecosystems due to anthropogenic disturbance [1,2]
A major finding major finding of this research is that spectral bands, vegetation indices, spectral unmixing fractions, of this research is that spectral bands, vegetation indices, spectral unmixing fractions, and texture andfrom texture metrics from high-resolution imagery are good of predictors of treedeciduousness species deciduousness metrics high-resolution imagery are good predictors tree species of tropical of tropical dry forests along an environmental gradient that covers the most important forest dry forests along an environmental gradient that covers the most important forest ecosystems in ecosystems in the Yucatan Peninsula
In the semi-evergreen forest site (Figure 5c), there are homogeneous 1 ha areas dominated by green canopy forest, where texture measures of homogeneity were negatively correlated with deciduousness. These results reveal the importance of using texture metrics for estimating deciduousness
Summary
Tropical dry forests (TDF) cover about 46% of tropical forests worldwide and they are one of the most threatened ecosystems due to anthropogenic disturbance [1,2]. Forests 2020, 11, 1234 these forests is a pronounced dry season lasting 4 to 6 months when mean monthly precipitation is less than 100 mm, resulting in seasonal drought [3]. This seasonal water shortage has a significant impact on the structure and function of these ecosystems and determines the growth patterns and the phenological and physiological behavior of the vegetation [4]. There is a wide range of phenological strategies of species from the deciduous to evergreen plants with some intermediate strategies, such as brevi-deciduous, semi-deciduous, or tardily deciduous [7]
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