The influence of forest regrowth on soil hydraulic properties and erosion in a semiarid region of Brazil

Dryland tropical forests are important but little-understood ecosystems. These landscapes are at risk globally because of accelerated deforestation and the consequent losses of hydrological functions. An example is the Caatinga shrublands in northeastern Brazil; these dry tropical forests are undergoing rapid change as the land is converted to cultivated cropland and pastureland and then often abandoned after the land is exhausted, allowing forests to regrow. In this study, we evaluated how these changes influence soil hydraulic properties and soil erosion in Caatinga landscapes, by examining four sites of different ages: a recently abandoned pasture, a young (7years of regrowth) secondary forest, an intermediate (35years of regrowth) secondary forest, and an older (more than 55years) forest. Rainfall simulation was used to assess soil infiltrability and susceptibility to erosion. In addition, we determined hydrological conductivity in the field using the Beerkan method (Kfs) and collected samples for laboratory-determined measurements (Ks). We found that infiltrability and Kfs values were progressively higher as time since land abandonment increased, whereas Ks values were not significantly different across sites. Infiltrability was approximately 2 times smaller than Ks and Kfspossibly owing to the formation of soil crusts from raindrop impact. Soil erosion did not show a progressive improvement with forest age and was better explained by site characteristics, such as herbaceous cover and slope. In general, our results suggest that in Caatinga landscapes, more than 35years is required for the recovery of soil hydraulic properties following land abandonment.