University of Tübingen: Biological soil crusts slow down erosion

Every year billions of tons of valuable soil are lost worldwide through erosion, much of it is deposited in bodies of water that silt up or silt up as a result. The soil losses measured in Germany range from 1.4 to 3.2 tons per hectare and year, in extreme weather it can be up to fifty tons. Biological soil crusts provide a protective shield against erosion, as a research project by geoscientists at the University of Tübingen shows. These natural “carpets” consist of bacteria, mosses, lichens, fungi and other organisms that combine earth particles into coherent layers.

Biocrusts are only a few millimeters thick, but they stabilize the soil surface and protect it from being eroded by rain and wind. So far they have mainly been researched in dry regions, where they are particularly important because of their storage capacity for the water balance and as protection against wind erosion and as dust catchers. Under the direction of Dr. Steffen Seitz from the Chair of Soil Science and Geomorphology, the Tübingen scientists investigated the development of biological soil crusts on “back lanes” that were recently used in the Schönbuch Nature Park in Baden-Württemberg.

Moss mats with a type of moss grown in the greenhouse
Moss mats with a type of moss grown in the greenhouse: This can be used to stabilize soil surfaces.
Such aisles, which are created by wood harvesting machines, together with forest roads and deforested areas form preferred habitats for biocrusts. Although they cause a disturbance of the forest floor, they have the advantage that the forest management interventions concentrate on predetermined routes and the forest areas in between are protected.

For a year at different times of the year, the Tübingen team measured the soil composition in the back alleys and at other points in the terrain and carried out experiments with rain simulators. The results show how important biocrusts are for the preservation of the soil: “The soil erosion in the back alleys is on average thirteen times higher than in the undisturbed forest soil over all locations and measurement times”, says Professor Thomas Scholten, who runs the project at the Chair of Soil Science and Supervised geomorphology. But at the same time it became clear what protective mechanisms the forest floor had. “So soon after they were no longer used, biological soil crusts settled in the back lanes, which reduce erosion.”

These developed very differently depending on the location, especially the mosses, which play a particularly important role in erosion protection: their share in the crustal communities was between five and fifty percent, depending on the measuring point. The diversity of the moss species involved also fluctuated greatly, mainly due to differences in soil chemistry. In general, the greater the diversity of the species involved, the better the erosion protection that the biocrusts offered. It was also shown that they represent a basis for further plant growth: In the summer months, many biocrusts on the back alleys were replaced by higher vegetation such as rushes, grasses or tree seedlings, which also provide good protection against erosion.

Rain simulator
In the Schönbuch Nature Park, a rain simulator was used to measure how much the soil was eroded in the back alleys.
In a further experiment in cooperation with the Stuttgart company Reinhold Hummel, the scientists applied moss mats from a type of moss grown in the greenhouse in some back alleys. Not only can it store a lot of water, but it also proved to be the most vigorous and resilient of the 24 types of moss tested. Since it can also be applied like turf, it is particularly suitable for practical environmental protection. Most of these moss mats in the Schönbuch Nature Park have now taken root after a year. “Our research results obtained so far show that biocrusts are well suited for repairing and stabilizing surfaces. This not only applies to forest soils, mining landscapes or embankments are also possible areas of application, ”says Thomas Scholten.