Erosion also occurs in forests

Soil loss is usually associated with agricultural land. However, even under closed forest canopies, considerable erosion rates can occur. In contrast to croplands such as vineyards or corn fields, the effects of diverse forest ecosystems have so far been insufficiently studied.

Vegetation as a key factor

Many raindrops do not reach the forest floor directly. They first hit leaves, needles, or branches. There they can break apart, accumulate, and fall again as new drops. Depending on drop height, size, and velocity, their kinetic energy changes. These processes within the vegetation can either amplify or reduce rainfall erosivity.

The challenge

Spatial variation in forests is very high – between tree species, but also within single stands. Point measurements of kinetic energy alone cannot capture this complexity. To reliably assess erosion processes, we need methods that provide spatially continuous information and identify areas with increased erosion potential.

The RAINER project

RAINER investigates how Central European forests influence rainfall energy. To this end, we will conduct a field campaign in the southern Hardt near Bruchhausen. It includes:

• measurements of rainfall kinetic energy using sand-filled splash cups,
• field surveys of relevant vegetation traits,
• and UAV-lidar flights providing high-resolution 3D data of vegetation structure.

A new modeling approach

The collected data feed into the Vegetation Splash Factor Model. This model identifies which vegetation surfaces effectively protect the soil and where raindrops pass through without interception. It enables spatially continuous predictions of vegetation effects and can replace the strongly simplified crop factor values commonly used in erosion models.

Relevance

In the context of changing rainfall patterns and vegetation compositions, RAINER provides an important contribution to improving erosion models and increasing their predictive power.

Senn, J. A., Fassnacht, F. E., Eichel, J., Seitz, S., and Schmidtlein, S. (2020). A new concept for estimating the influence of vegetation on throughfall kinetic energy using aerial laser scanning. Earth Surface Processes and Landforms, esp.4820. https://doi.org/10.1002/esp.4820

Senn, J. A., Schäfer, J., Hosseini, Z., and Seitz, S. (2025 in press). Predicting rainfall kinetic energy under forest canopies – a pilot study using ULS. Earth Surface Processes and Landforms. https://onlinelibrary.wiley.com/doi/10.1002/esp.70150