Woody plant encroachment drivers in the brazilian cerrado

Abstract

Woody plant encroachment (WPE) is increasing woody cover and biomass across tropical savannas, changing the composition and structure of vegetation and converting open-canopy into closed-canopy vegetation. These changes affect ecosystem functioning and promote biodiversity loss by reducing the herbaceous layer and changing the fire regime. Studies suggest that WPE is occurring in the Brazilian savanna (Cerrado), although many of these studies have been conducted at a small spatial scale, making it difficult to evaluate the causes, extension, and impact of this phenomenon. We aimed to identify the occurrence of WPE in forests, grasslands, and savannas throughout the Cerrado using the trend analysis of the annual minimum enhanced vegetation index (EVI) of MODIS images. To evaluate which factors explain WPE, we modeled the EVI trend for each vegetation type as a function of climate variables, soil properties, and fire frequency. Our study provided evidence that WPE was widespread in the Cerrado and occurred at different rates, as grasslands and savannas had more areas affected by WPE than did forests, although some peripheral regions with transitional climates experienced biomass reduction. In general, WPE was positively influenced by precipitation and temperature and negatively influenced by the initial EVI and fire frequency. The results indicates that sandy soils were prone to WPE and factors related to soil fertility facilitated the encroachment of woody plants. Because of the importance of the Cerrado for Brazilian biodiversity, we urge the development of conservation policies for this biome to reduce the impact of WPE due to changes in climate and fire patterns to conserve the remaining areas of this biome and preserve its endemic species.