NDVI Time Series for Mapping Phenological Variability of Forests Across the Cerrado Biome in Minas Gerais, Brazil

Abstract

1.Introduction The constant threat that natural forests of the world have suffered over the years led to strategies that intend to prevent these from further losses in the near future. The tropical rain forest that exists in northern Brazil is the main concern of preservation, but other areas such as the " Mata Atlântica " have had losses over the years and almost 75 % of its remnants are under threat of deforestation. The main activities that lead to deforestation in the region are the expansion of agricultural frontiers, the extraction of coal and other minerals, timber exploitation, and other anthropogenic activities (Oliveira, 2004). Another area in Brazil that is under threat is the Cerrado Biome in Minas Gerais. The Cerrado biome of tropical South America covers about two million squared kilometres, representing almost 22% of the Brazilian territory. The biome was named due to its predominant vegetation type, a fairly dense woody savannah composed by shrubs and small trees. The term " cerrado " (Portuguese for closed or dense) was probably applied to this vegetation because of the difficulty of traversing it on horseback (Oliveira-Filho et al. 2002). The constant threat to the Brazilian Cerrado has led to the necessity of developing strategies and measures to promote the monitoring and mapping of this biome. The Cerrado has a rich biodiversity but its fragmentation throughout the years caused losses of a number of species from this biome (Oliveira 2004). The Cerrado has many types of phytophysiognomies, these include Semi-Deciduous Forests, Deciduous Forests, Cerradão (dense Savanna), Cerrado (Savanna), Floresta Ombrófila and other more specific types of vegetation. In order to prevent further deforestation of this biome, monitoring by means of remote sensing is regarded as an efficient tool. This technique can provide accurate mapping of the occurrence of each phytophysiognomy of the Cerrado Biome and promote efficient monitoring in order to detect changes so legal actions can be taken in due time. Mapping land cover using remotely sensed data has been an area of growing research interest throughout the past decades. Its complexity, peculiarities and state of the art concerning computational aids and processing routines differ a lot from past conventional cartographic tools. Developments in computer science have aided a better information www.intechopen.com Phenology and Climate Change 254 extraction from remotely sensed images, as well as an effective use of geographical information systems to store, analyse and present all sorts of land cover information (Carvalho 2001). The Statewide Vegetation Monitoring and Mapping of Minas Gerais was conducted by Carvalho (2007) with the use of multitemporal Landsat images. This project includes a dataset of images acquired in different seasons of a year so that the dry and wet seasons could be captured in order to characterize the phenological cycle of deciduous and semideciduous forests (Figure 1). Fig. 1. Visual Difference of phytophysiognomies (a) Deciduous forest, (b) semi-deciduous forest Source Oliveira (2004). Semi-deciduous forests loose less leaves in the dry season.