Abstract
Fire is one of the main modeling agents of savanna ecosystems, affecting their distribution, physiognomy and species diversity. Changes in the natural fire regime on savannas cause disturbances in the structural characteristics of vegetation. Theses disturbances can be effectively monitored by time series of remote sensing data in different terrestrial ecosystems such as savannas. This study used trend analysis in NDVI (Normalized Difference Vegetation Index)–MODIS (Moderate Resolution Imaging Spectroradiometer) time series to evaluate the influence of different fire recurrences on vegetation phenology of the Brazilian savanna in the period from 2001 to 2016. The trend analysis indicated several factors responsible for changes in vegetation: (a) The absence of fire in savanna phytophysiognomies causes a constant increase in MODIS–NDVI, ranging from 0.001 to 0.002 per year, the moderate presence of fire in these areas does not cause significant changes, while the high recurrence results in decreases of MODIS–NDVI, ranging from −0.002 to −0.008 per year; (b) Forest areas showed a high decrease in NDVI, reaching up to −0.009 MODIS–NDVI per year, but not related to fire recurrence, indicating the high degradation of these phytophysiognomies; (c) Changes in vegetation are highly connected to the protection status of the area, such as areas of integral protection or sustainable use, and consequently their conservation status. Areas with greater vegetation conservation had more than 70% of positive changes in pixels with significant tendencies. Absence or presence of fire are the main agents of vegetation change in areas with lower anthropic influence. These results reinforce the need for a suitable fire management policy for the different types of Cerrado phytophysiognomies, in addition to highlighting the efficiency of remote sensing time series for evaluation of vegetation phenology.
Highlights
Fire is a key agent in the ecological processes of biomes, changing the distribution and structure of vegetation, with the regulation of forest and savanna species, and modifying carbon-climate cycles at regional and global levels, as a result of greenhouse gases and aerosol emissions and the consequent alteration of the surface radiation balance [1,2]
This study aimed to characterize the influence of fire recurrence on the phenological pattern of vegetation, in different phytophysiognomies in the largest conservation area of Brazilian savanna, the Jalapão, from time series of Normalized Difference Vegetation Index (NDVI) derived from Moderate Resolution Imaging Spectroradiometer (MODIS) sensor, and reconstruction of fire history in the region based on Landsat satellite images
As previously indicated by several authors [14,15,44,69], the results presented in this study reinforce the need for a consistent fire management policy in the Brazilian Cerrado
Summary
Fire is a key agent in the ecological processes of biomes, changing the distribution and structure of vegetation, with the regulation of forest and savanna species, and modifying carbon-climate cycles at regional and global levels, as a result of greenhouse gases and aerosol emissions and the consequent alteration of the surface radiation balance [1,2]. Mosaics of forests and savannas, dependent on the absence or presence of fire to maintain their structure and plant diversity, were created from the result of fire in terrestrial ecosystems [3]. Interaction of fire with the biomes resulted in decrease of tree biomass, allowing the emergence of savanna ecosystems with high diversity, supported by domain of grass and shrub species, attenuation of competitive exclusion, expansion of landscape diversity and generation of new niches [4,5]. Cerrado species are adapted in different ways to long periods of drought and diverse physical conditions of the soil, resulting in a mosaic of phytophysiognomies from grassy fields, very resistant to high intensity fires, to closed forests, with high plant diversity in areas of nutrient-rich soils [11,12]
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