2.1 Site selection
The sites were selected based on the normalized difference vegetation
index (NDVI), which estimates the biomass and productivity of the
vegetation by calculating: NDVI = (Infrared - Red) / (Infrared + Red),
using the ArcGIS 10.2. desktop software program. We used three images
captured by the Landsat-8 satellite between September to October 2017
(earthexplorer.usgs.gov) so that the entire length of the Cariri
ParaĆbano was covered. This period was chosen because it is the drought
season, and the vegetation cover images may change in the rainy season
due to the herbaceous stratum established at this time. The calculations
were performed using composite images combining bands 4 (Red,
wave-length 0.64-0.67) and 5 (Near Infrared, wave-length 0.85-0.88) of
the satellite, which is satisfactory for describing vegetation cover.
NDVI values can range from -1 to +1, with values close to 0
corresponding to regions with little vegetation and higher values
corresponding to areas with denser vegetation cover. A total of 12 plots
were established, divided into two areas: a) six plots in sites of NDVI
values between 0.15 and 0.37, hereafter referred to as Area I, which
corresponds to the lowest vegetation cover, and; b) six plots in sites
of NDVI values between 0.44 to 0.66, hereafter referred to as Area II,
which comprises environments with higher vegetation cover levels (Figure
1). We first identified all of the sampling sites through the satellite
images, and we later visited the areas to confirm. All collections were
carried out from November 2018 to July 2019.
Note : Here figure 1 will be inserted