Changes in rainfall interception along a secondary forest succession gradient in lowland Panama

B Zimmermann,M Van Breugel,T Schmid,A Zimmermann,J S Hall,H L Scheckenbach

doi:10.5194/hess-17-4659-2013

Abstract

Abstract. Secondary forests are rapidly expanding in tropical regions. Yet, despite the importance of understanding the hydrological consequences of land-cover dynamics, the relationship 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 modeling 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 comprised 20 forest patches 3 to 130 yr old. We sampled each patch with a minimum of 20 funnel-type throughfall collectors over a continuous 2-month period that had nearly 900 mm of rain. During the same period, 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 had the strongest influence on the variation of canopy interception. Our analyses yielded three main findings. First, canopy interception changed rapidly during forest succession. After only a decade, throughfall volumes approached 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 fragmented landscapes might be detectable only in regions with a substantial fraction of young forests. Our results suggest that where entire catchments undergo forest regrowth, initial stages of succession may be associated with a substantial decrease of streamflow generation. Our results further highlight the need to study hydrological processes in all forest succession stages, including early ones.

Highlights

Across the tropics, large parts of mature forests have been cleared and converted into agricultural land
A parsimonious model based on the ratio of the basal area of small stems to the total basal area outperformed more complex multivariate models (BMA approach)
At a montane cloud forest site in Mexico, for instance, canopy interception loss of a 20 yr old secondary forest amounted to only 50 % of the value estimated for an adjacent mature forest, which was explained by the slow recovery of the epiphyte biomass (Holwerda et al, 2010)

Summary

Introduction

Large parts of mature forests have been cleared and converted into agricultural land. Secondary forests are rapidly expanding in tropical regions (Chazdon, 2008; Perz and Skole, 2003). Most often, regrowing forests are found alongside patches of mature forest, pastures, farmland, settlements, etc., and they are part of fragmented landscapes, which are a typical feature of many tropical regions worldwide (Laurance and Bierregaard, 1997). Given the extent of secondary forests, their effect on hydrological processes as well as their role within the hydrological cycle of fragmented landscapes merits attention (Giambelluca, 2002). Mature forests, which provide the baseline for evaluating secondary forest hydrology, differ from

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Discussion

Conclusion