Vegetation structure and species richness of the seasonally dry tropical forest
The data were collected in order to evaluate the different pathways through which the chronic disturbance determines the loss of species richness. The study was carried out in the seasonally dry tropical forest (SDTF) of southwestern Ecuador, specifically in Zapotillo County, Loja Province. Within an area of 12400 ha, we haphazardly located three grids of 4.2 x 2.2 km to have a reasonable variation of the forest diversity and heterogeneity in the region. Grids were separated at least 2.5 Km from each other and with a distance of 5 to 8 Km from Zapotillo town. Within each of these grids, we selected randomly 20 cells and located three transects of 50 x 2 m. In each transect, we registered all intercepted trees and shrubs with diameter at breast height (DBH) ≥ 1 cm and height > 1.30 m, and sub-shrubs with height ≥ 30 cm. Shrubs and sub-shrubs were only recorded in the central band of each transect, along 50 x 1 m. For each selected cell we defined a measure of anthropogenic disturbance based on the distance to populated centers, roads and farms. We adjusted a PCA with standardized values with all these variables and used the first component as a chronic disturbance intensity variable. We adjusted a PCA with standardized values with all these variables and used the first component as a chronic disturbance intensity variable. To characterize the forest structural complexity we used the square root index (SQRI) proposed by Barbeito et al. (2009). To calculate the plant productivity of each cell, we used the Normalized Differentiation of Vegetation Index (NDVI). The last variable was the density of large trees, considering all stems > 25 cm DBH in the three transects of each cell.