Towards quantifying the increase of rainfall interception during secondary forest succession

Abstract

Large scale forest regrowth is one aspect of modern land-cover change. Yet, despite the importance of understanding the hydrological consequences of land cover dynamics, the relation between forest succession and canopy interception is poorly understood. This lack of knowledge is unfortunate because rainfall interception plays an important role in regional water cycles and needs to be quantified for many modelling purposes. To help close this knowledge gap, we designed a throughfall monitoring study along a secondary succession gradient in a tropical forest region of Panama. The investigated gradient comprises 20 natural forest patches regrowing for 3 up to about 130 yr.We sampled each patch with a minimum of 20 funnel-type throughfall collectors over a continuous two-month period that had nearly 900mm of rain. At the same time and locations, we acquired forest inventory data and derived several forest structural attributes. We then applied simple and multiple regression models (Bayesian Model Averaging, BMA) and identified those vegetation parameters that have the strongest influence on the variation of canopy interception. Our analyses provide three main findings. First, canopy interception changes rapidly during forest succession. After only a decade, throughfall volumes approach levels that are typical for mature forests. Second, a parsimonious (simple linear regression) model based on the ratio of the basal area of small stems to the total basal area outperformed more complex multivariate models (BMA approach). Third, based on complementary forest inventory data we show that the influence of young secondary forests on interception in real-world frag- mented landscapes might be detectable only in regions with a substantial fraction of very young forests. In case entire catchments are subject to forest regrowth, initial stages may be associated with undesirable effects on streamflow generation. Our results further highlight the need to study all forest succession stages, including early ones.