Soil biodiversity and soil erosion
The relationship between soil erosion and biodiversity is extremely multifaceted. Erosion is widely recognized as one of the main threats to soil. Globally, about 2.8 tonnes of soil are lost per hectare annually. Given this, soil loss surely has an impact on the organisms populating this ecosystem. At the same time, the enormous variety of species living in the soil influences both its aggregate stability and water infiltration through their moving and feeding activities. Therefore, soil biodiversity certainly plays a role in soil loss processes. Large‐scale assessments of both soil erosion and biodiversity distribution are currently available. Nonetheless, the causal relationships between the distribution of belowground diversity and soil displacement, in both directions, have been poorly explored.
In this context, we identified three possible areas of research that, in our opinion, require advances in the coming years:
- Comprehension and quantification of the interactions between soil biodiversity and erosion;
- Development and integration of a “biodiversity factor” into the models used to assess soil erosion;
- Assessment of the ecological impact of soil erosion on soil‐living communities.
According to the current (limited) knowledge, earthworms can play a key role in reducing soil erosion, mainly due to their burrowing activity that increase soil porosity. Based available pan-European (11 countries) maps of earthworm richness and abundance, we developed an “Earthworm factor” (Et-factor) to be integrated into soil erodibility (K-factor) calculation. Due to uncertainty on the potential impact of earthworm communities on soil loss, two Et-factors were generated, one including richness and abundance (EtAR-factor), the other only abundance data (EtA-factor). Both factors were then included into K-factor to obtain revised soil erodibility values (KEt-factor).
Effects of soil organisms on soil erosion by water and wind. Red triangles depict a increasing (positive) effect on soil erosion, whereas green triangles describe a reducing (negative) influence on soil loss due to biodiversity. Patterns are similar for soil erosion by water and wind, except for the influence of earthworms, ants and termites. These three groups of organisms show a dual effect (both green and red triangles) on soil runoff by water. Their presence and activities can either increase or reduce soil loss depending on the community structure (i.e. functional group types, habits and abundance). In the case of wind erosion, they lead to only a negative effect, as the positive one (water infiltration due to burrowing activity) is null. Microorganisms (bacteria and fungi) tend to improve soil aggregate stability, therefore reducing both wind and water erosion. The main mechanisms driving this effect are metabolite production and hyphal binding. Soil-living mammals (megafauna) positively affect soil erosion, as they promote soil disaggregation through their moving and feeding activities. Yellow triangles represent unknown effects. These are associated with soil organisms, mainly micro- and mesofauna (nematodes, collembolans and mites), whose impact on erosion requires further investigation.
The result of this research are four datasets available for public users (Earthworm factors considering both richness and abundance data EtAR-factor, Modified soil erodiblity including EtAR-factor, Earthworm factors calculated considering only abundance data EtA-factor, modified erodibility including only EtA-factor).
Orgiazzi, A., Panagos, P. 2018. Soil biodiversity and soil erosion: It is time to get married: Adding an earthworm factor to soil erosion modelling. Global Ecology and Biogeography, 27(10): 1155-1167.
Panagos, P., Meusburger, K., Ballabio, C., Borrelli, P., Alewell, C. 2014. Soil erodibility in Europe: A high-resolution dataset based on LUCAS. Science of Total Environment, 479–480: 189–200