Abstract
The Pampa biome is an important ecosystem in Brazil that is highly relevant to livestock production. The objective of this study was to analyze the potential use of vegetation indices to discriminate grazing intensities on natural grasslands in the Pampa biome. Moderate Resolution Imaging Spectroradiometer (MODIS) Normalized Difference Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI) images from Jan to Dec, 2000 to 2013 series, were analyzed for natural grassland experimental units managed under high (forage allowance of 5 ± 2 % live weight – LW), moderate (13 ± 5 % LW) and low grazing intensity (19 ± 7 % LW). Regardless of intensity, the temporal profiles showed lower NDVI and EVI during winter, increased values in spring because of summer species regrowth, slightly decreased values in summer, especially in years when there is a water deficit, and increased values in the fall associated with the beginning of winter forage development. The average temporal profiles of moderate grazing intensity exhibited greater vegetation index values compared with low and high grazing intensities. The temporal profiles of less vegetation index were associated with lower green biomass accumulation caused by the negative impact of stocking rates on the leaf area index under high grazing intensity and a floristic composition with a predominance of tussocks under low grazing intensity. Vegetation indices can be used for distinguishing moderate grazing intensity from low and high intensities. The average EVI values can discriminate moderate grazing intensity during any season, and the NDVI values can discriminate moderate grazing intensity during spring and winter.
Highlights
The Pampa biome is an important ecosystem in Brazil which has great relevance to livestock production
The ability to discriminate moderate grazing intensity becomes important for monitoring natural grasslands in the Pampa biome because management is necessary for the sustainability of these grasslands
The lowest Normalized Difference Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI) values occurred in winter because of reduced available solar radiation and air temperature which reduce the impact on plant biomass growth and accumulation; winter is considered the most limiting period for animal production on native grasslands in southern Brazil (Mezzalira et al, 2012)
Summary
The Pampa biome is an important ecosystem in Brazil which has great relevance to livestock production. With the growing impact of overgrazing, this natural resource has become seriously threatened (Carvalho and Batello, 2009). The sustainable use of grassland areas has high environmental and socio-economic relevance because animal production on degraded grasslands is less than that on restored or well-managed grasslands. In production systems, adjusting grazing intensity according to the forage allowance is vital for achieving sustainability; this process is subjective and depends on the evaluator’s experience. Rapid and effective grazing intensity monitoring over large areas is central to the conservation of natural grasslands in the Pampa biome. Satellite imagery provides an important data source for monitoring vegetation cover dynamics because it generates objective information with adequate spatial and temporal characteristics (Li et al, 2012). The Normalized Difference Vegetation Index (NDVI) and the Enhanced Vegetation Index (EVI) are considered indicators of plant growth and can be employed in the determination of correlated biophysical variables, such as the leaf area index (LAI), biomass, photosynthetic activity and grain yields (Xavier et al, 2006; Fernandes et al, 2011; Monteiro et al, 2012)
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