Estrutura da vegetação e atributos químicos do solo 12 anos após uma restauração florestal

Abstract

With the current state of forest ecosystems degradation due to human activities, there has been an increase in water scarcity, greenhouse gases emissions, and a surprising reduction in biodiversity. With the loss of ecosystem services, there is a growing effort to restore forests worldwide. However, the efforts in the restoration of tropical forests can result in unpredictability of ecosystems functioning, so that a priority is the selection of appropriate ecological monitoring indicators. With the installation of the Small Hydroelectric Power Plant Anhanguera in 2007, in the northeast region of São Paulo state, a forest restoration project was carried out in the limits of Seasonal Semideciduous Forest. A total of 156,000 seedlings from 105 native tree species from the region were planted in an area of 70 hectares. The present study evaluated simultaneously the influence of the distance from the waterbody and soil moisture on the amount of accumulated litter and soil organic matter, mediated by the vegetation structure in the restoration area and in forest remnants (considered as reference sites) nearby. We also evaluated if there was an increase in soil organic matter 12 years after the restoration project was implemented, and whether the amount of organic matter was related with soil fertility. We collected data from vegetation structure (tree density, total basal area, mean diameter, mean trunk volume index, and forest stratification), litter, and soil samples 0-20 cm deep in 100 m2 plots. The results showed that the variation in tree density was due to the colonization of regenerating individuals, which decreased with increasing distance from the reservoir. Forest structure varied spatially when considering both the restored area and forest remnants, and when analyzing each separately. Plots nearer the reservoir had denser and more stratified forests, whereas more distant plots presented higher basal area values. More humid plots, with a denser and stratified vegetation, presented more litter and soil organic matter only when also considering the remnant forests in the analyses. Also, vegetation in plots with higher basal area weakly contributed with higher accumulated litter. There was a strong relationship between soil organic matter and fertility and, as vegetation structure developed, there was an increase in organic matter showing a partial recovery of soil fertility. Therefore, our study suggested that the trajectory and speed of restoration from some ecosystem aspects were determined by the distance from the waterbody and by soil moisture as influenced by the reservoir filling. Further, we found that a period of only 12 years after the implementation of the restoration project was enough to detect differences in litter accumulation and a substantial increase in soil organic matter.