Uma análise do bioma caatinga no município de Gado Bravo - PB através do Índice Vegetação por Diferença Normalizada

Abstract

The present study examined the changes of the caatinga vegetation in response to climatic conditions in the municipality of Gado Bravo in the State of Paraíba, corresponding to the Agreste region. To this end, images from the MODIS sensor/land of the municipality, have been processed to obtain the Normalized Difference vegetation index-NDVI, rainy and dry periods during the years from 2011 to 2014. The use of historical data of precipitation rainfall of the Executive Agency for the Management of Waters of the State of Paraiba -EAWS, allowed to evaluate the wettest months of the year (April, may and June), the drought season months (september, october, november and december) and the months of low precipitation (january, february, march, august and july). In the years of study, the month of may was the wettest december and the drought season. Most plants in the drought season, has a typical adaptation, consisting of the miss of the leaves avoiding the dehydration through the process of transpiration, thus the caatinga biome appears to be a poor in biodiversity and/or high levels of degradation. However, during the rainy season, the plants respond quickly to rainfall, showing a biological regeneration. The NDVI is an index of the remote sensing that is directly connected the photosynthetic activity of vegetation, and is calculated by a normalized difference between two bands of the electromagnetic spectrum, the spectral band of red and near infrared band. The greater the difference between the spectral bands of red and near infrared vegetation is in full photosynthetic activity, and if the grass for some reason is having a stress where its components are vegetables at low photosynthetic activity, the differences between the reflectâncias of spectral bands decrease and with this the results of NDVI are smaller. In the study period, one can realize that there is a differentiation in the caatinga vegetation of the municipality of Gado Bravo-PB, in response to climate change that occurred in the annual cycle of precipitation and in the biological cycle of vegetation. The loss of leaves during the dry season, appears as adaptive process that can interfere directly on the results of the NDVI, because the vegetation without leaves presents significant photosynthetic activity and the results next to zero of the NDVI can be understood as an area degraded or severely degraded.