Kinetic Energy of Throughfall in Subtropical Forests of SE China – Effects of Tree Canopy Structure, Functional Traits, and Biodiversity Christian Geißler 1 *, Karin Nadrowski 2 , Peter Ku ¨ hn 1 , Martin Baruffol 3 , Helge Bruelheide 4 , Bernhard Schmid 3 , Thomas Scholten 1 1 Institute of Geography, University of Tu ¨ bingen, Tu ¨ bingen, Germany, 2 Special Botany and Functional Ecology, University of Leipzig, Leipzig, Germany, 3 Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Zurich, Switzerland, 4 Institute of Biology/Geobotany and Botanical Garden, University of Halle, Halle, Germany Abstract Throughfall kinetic energy (TKE) plays an important role in soil erosion in forests. We studied TKE as a function of biodiversity, functional diversity as well as structural stand variables in a secondary subtropical broad-leaved forest in the Gutianshan National Nature Reserve (GNNR) in south-east China, a biodiversity hotspot in the northern hemisphere with more than 250 woody species present. Using a mixed model approach we could identify significant effects of all these variables on TKE: TKE increased with rarefied tree species richness and decreased with increasing proportion of needle- leaved species and increasing leaf area index (LAI). Furthermore, for average rainfall amounts TKE was decreasing with tree canopy height whereas for high rainfall amounts this was not the case. The spatial pattern of throughfall was stable across several rain events. The temporal variation of TKE decreased with rainfall intensity and increased with tree diversity. Our results show that more diverse forest stands over the season have to cope with higher cumulative raindrop energy than less diverse stands. However, the kinetic energy (KE) of one single raindrop is less predictable in diverse stands since the variability in KE is higher. This paper is the first to contribute to the understanding of the ecosystem function of soil erosion prevention in diverse subtropical forests. Citation: Geißler C, Nadrowski K, Ku ¨ hn P, Baruffol M, Bruelheide H, et al. (2013) Kinetic Energy of Throughfall in Subtropical Forests of SE China – Effects of Tree Canopy Structure, Functional Traits, and Biodiversity. PLoS ONE 8(2): e49618. doi:10.1371/journal.pone.0049618 Editor: Gil Bohrer, The Ohio State University, United States of America Received March 15, 2012; Accepted October 11, 2012; Published February 15, 2013 Copyright: ß 2013 Geißler et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: The funding by the German Research Foundation (DFG FOR 891/1) and by the National Science Foundation of China (NSFC 30710103907 and 309300005), as well as various travel grants to prepare the project financed by DFG, NSFC and the Sino-German Centre for Research Promotion in Beijing (GZ 524, 592, 698 and 699) are highly acknowledged. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: christian.geissler@uni-tuebingen.de Introduction Biodiversity, ecosystem functioning and soil erosion The term ‘‘Biodiversity and Ecosystem Functioning’’ (BEF) emerged in the beginning of the 1990ies due to growing concern about a global loss of biodiversity [1]. The basic question in functional biodiversity research is if and how biodiversity affects various ecosystem functions and services. Especially in forest ecosystems, regulating and supporting services like primary production, nutrient cycling, species conservation, soil formation, climate regulation and the prevention of soil erosion are of major interest [2,3]. Some of these functions have already been shown to respond to gradients of biodiversity in the tree layer [4]. Soil erosion and its prevention is a central topic in the subtropics, in particular in SE China [5,6]. Here, highly erosive rainfall causes severe and continuous soil losses, which can cause enormous economic costs [7–9]. Forest ecosystems may prevent erosion by water via three main mechanisms [10–12]: (1) interception of raindrops by leaves and branches; (2) high infiltration rates of forest soils due to low bulk densities and high pore volumes; (3) plant root systems securing the soil. Although soil erosion is generally reduced under forests [13], high sediment loads of rivers from forested catchments, especially in subtropical regions with high rainfall intensities, are often reported [14,15]. It can be assumed that mechanisms controlling soil erosion under forest are dynamic in space. In particular, it is conceivable that mechanism (1) can increase kinetic energy (KE) of raindrops on the soil surface due to leaf arrangements channeling small drops into larger ones [16]. A substantial increase in KE with canopy height has been found in monocultures such as beech forests in New Zealand [17], acacia forests in Indonesia [18], tropical rain forests in Colombia [19] and in Brazil [20], forest plantations in Japan [21] and secondary subtropical forests in China [22]. Variables considered to describe the amount and variation of KE in forests or throughfall redistribution under forest in general mainly refer to the characteristics of the rainfall event [21,23], the age or height of the forest studied [24,25], total plant cover or leaf area index (LAI) [26] and to leaf traits [21,27]. A potentially important factor neglected so far is tree diversity, even though the relations between erosion processes and PLOS ONE | www.plosone.org 1 February 2013 | Volume 8 | Issue 2 | e49618