Land use and forest regrowth influences on soil hydraulic properties in a semi-arid environment in Brazil

Abstract:

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. The caatinga shrublands in northeastern Brazil, for example, are dry tropical forests undergoing rapid change because of conversion to cultivated crops and pasture lands, which are often abandoned after exhausted, allowing forests to regrow. In this study we evaluate soil hydraulic properties and soil erosion on caatinga landscapes of different ages, including a recently abandoned degraded pasture (DP), a young, 7 years secondary forest (YF), a 35 years intermediate secondary forest (IF), and an older forest with more than 50 years (OF). Rainfall simulation was used to assess infiltrability and susceptibility to soil erosion. In addition we determined hydrological conductivity in the field using the using the Beerkan method (Kfs) and collected samples for laboratory-determined measurements (Ks). We found that infiltrability and Kfs values were progressively higher with time since land abandonment, while Ks values were not significantly different across sites. Infiltrability was approximately 2 times smaller than Ks and Kfs - possibly due to the formation of soil crusts from raindrop impact. Soil erosion did not show a progressive improvement with forest’s age, and was better explained by site characteristics like herbaceous cover and slope. In general our results suggest that at least 50 years are required for the recovery of soil hydraulic properties in caatinga landscapes, following land abandonment.