The impact of biodiversity on initial soil erosion processes and nutrient fluxes in subtropical forest ecosystems
Steffen Seitz*, Philipp Goebes*, Peter Kuhn and Thomas Scholten
Department of Geosciences, Eberhard Karls University Tubingen, Germany steffen.seitz@uni-tuebingen.de, philipp.goebes@uni-tuebingen.de
In soil erosion research it is widely accepted that vegetation is a key factor for the type and intensity of erosion. Thus, scientists have long recognized the importance of forests for erosion control and afforestation is a common measure of soil protection. However, the
mechanisms how forests protect the soil remain debated and especially the role of biodiversity is unclear.
In the framework of the “Biodiversity and Ecosystem Functioning (BEF) China” project (funded by the German Research Foundation) several experiments have been carried out in subtropical China to investigate the role of biodiversity for soil erosion control. In this study, we present results of an experiment on the influence of tree diversity on initial soil erosion focusing on sediment discharge, runoff volume and nutrient as well as carbon fluxes.
The initial soil erosion has been quantified in the field using small scale runoff plots (MiniROPs, 40 cm x 40 cm). Within the BEF China project, 70 study plots have been equipped with 5 ROPs each (350 MiniROPs in total). The study plots represent different levels of
biodiversity ranging from 0 (bare plots) to 24 tree species mixtures. The measurements took place during the rainy season from May to July 2013 with rainfall events showing intensities up to 85 mm h-1. We measured sediment discharge, runoff volume, soil surface cover and leaf cover in the field. In addition organic carbon, nitrogen and phosphorous contents were analyzed in the lab.
The results show soil loss rates of 55 t ha-1 year-1. Compared to other studies from subtropical regions they are in the same range. This confirms that our MiniROPs are well suitable to measure initial soil loss and runoff in subtropical ecosystems. According to their small size, they are easy to handle in the field and a large number of replications can be applied. First analyses of runoff and sediment discharge data indicate a significant influence of tree diversity on initial soil erosion. Since our experimental forest is still young with 3 and 4 years old trees, not only LAI but also the size of the gap fraction controls soil loss greatly. Another important component in such initial forest ecosystems is biological soil crust (BSC) cover. We observed different BSC (mosses, lichen, algae and cyanobacteria) covering up to 55 % of the ground. In general, it can be shown that such BSC increase runoff. Regarding sediment discharge, runoff plots with high BSC cover show lower sediment loss. We assume that CNP fluxes follow the same pattern. These preliminary findings will now undergo a detailed statistical analysis to better understand the processes involved and to quantify the relationships between tree diversity and soil erosion and will be presented at the 20th WCSS in Jeju.
