SP 6: Soil erosion / Soil properties

Mechanisms of soil erosion as a function of species richness and species composition in subtropical forests

Principal investigator(s):

Co-Principal investigator(s):

Phd candidate(s):

Contact adress:

Institute of Geography / Laboratory for Soil Science and Geoecology, Eberhard Karls University Tübingen, Rümelinstr. 19-23, D-72070 Tübingen, Germany

Summary

The role of biodiversity for soil erosion in forest ecosystems is unknown. Since velocity and mass of raindrops change when passing through the canopy cover, species composition and richness is crucial for erosion control under forest. The same is true for the litter covering the forest floor.

Soil erosion research has for a long time mainly been focused agriculture. Except the general importance of forests for erosion control, only little is known about soil erosion in forest ecosystems. The control mechanisms underlying this connection remain debated. In particular, the role of biodiversity is unclear. This is the starting point of SP6. We assume that species richness and species composition,  in addition to factors such as erodibility of the soil, control soil erosion under forest. To test this hypothesis, we follow the trace of the raindrops coming in from the sky, passing through the canopy, splashing on the ground or on the litter cover and detaching particles from the soil surface. Each of these processes has its own rules and controlling factors in terms of the magnitude, dynamics and importance for soil loss. Further, overland flow of excess water from rainfall and suspended sediment contribute to element cycling and matter fluxes. All these processes and mechanisms are related to the vegetation cover and, most important in the vicinity of BEF-China, biodiversity might play a decisive role for their extent and direction in forest ecosystems.

For example, looking closely at raindrops falling down from larger leaves we see that their kinetic energy is much higher (about 3-times) compared to the rain drop falling from the sky. The leaves collect the original drops and form larger ones dripping down from the leaf tips. In contrast, branches not only detour falling raindrops to the stem and convert them to stemflow, but also blast them to a smaller size with lower mass and velocity. When continuing to fall down to the forest floor, they have less ability to remove soil particles or destroy soil aggregates. Despite the erosive power (erosivity) of the raindrops, the protection of the soil by litter affects soil erosion and is influences by biodiversity. Thus, two process systems are of major interest: (a) modification of kinetic energy of throughfall and (b) its absorption by the litter cover on the forest floor.

Based on newly developed field methods and our findings from the first phase of BEF-China on species specific rainfall erosivity under tree canopies in secondary natural forests, our investigations focus on manipulative approaches within the newly established Main Experiment of BEF-China. Measurements include runoff and sediment discharge under natural and simulated rainfall with varying litter cover as well as biodiversity levels, species composition and stand ages. Additionally, we will continue and extend our investigations on the role of stand age vs. biodiversity for modification of the kinetic energy of raindrops in natural forests aged 20 to 100 years.

In the framework of BEF-China as a whole, this project is also responsible for spatial and pedological aspects of soil genesis, substrate characteristics, landscape development, and land use history. We will contribute to the development of the Ecoscape approach of BEF-China and estimates on C cycling and C stocks.