Abstract. This study investigated the development of biological soil crusts (biocrusts) in an early successional subtropical forest plantation and their impact on soil erosion. Within a biodiversity and ecosystem functioning experiment in southeast China (biodiversity and ecosystem functioning (BEF) China), the effect of these biocrusts on sediment delivery and runoff was assessed within micro-scale runoff plots under natural rainfall, and biocrust cover was surveyed over a 5-year period. Results showed that biocrusts occurred widely in the experimental forest ecosystem and developed from initial light cyanobacteria- and algae-dominated crusts to later-stage bryophyte-dominated crusts within only 3 years. Biocrust cover was still increasing after 6 years of tree growth. Within later-stage crusts, 25 bryophyte species were determined. Surrounding vegetation cover and terrain attributes significantly influenced the development of biocrusts. Besides high crown cover and leaf area index, the development of biocrusts was favoured by low slope gradients, slope orientations towards the incident sunlight and the altitude of the research plots. Measurements showed that bryophyte-dominated biocrusts strongly decreased soil erosion, being more effective than abiotic soil surface cover. Hence, their significant role in mitigating sediment delivery and runoff generation in mesic forest environments and their ability to quickly colonise soil surfaces after disturbance are of particular interest for soil erosion control in early-stage forest plantations.

This study investigated the development of biological soil crust (biocrust) covers in an early successional subtropical forest ecosystem and their impact on soil erosion. Within a biodiversity and ecosystem functioning experiment in Southeast China (BEF China), sediment discharge and runoff measurements were conducted with micro-scale runoff plots under natural rainfall and biocrust covers were surveyed over a five-year period. Results showed that biocrusts occurred widely in our experimental forest ecosystem and developed from initial light cyanobacteria- and algae-dominated crusts to later-stage bryophyte-dominated crusts in only three years. Biocrust covers were still increasing after six years of tree growth. Within later stage crusts, 25 bryophyte species were determined. The development of biocrusts was significantly influenced by the surrounding vegetation cover and terrain attributes. Besides high crown cover and leaf area index, the development of biocrusts was favoured by low slope gradients, slope orientations towards the incident sunlight and the altitude of the research plots. Our measurements showed, that bryophyte-dominated biocrusts were importantly decreasing soil erosion and more effective in erosion reduction than abiotic soil surface covers. Hence, their significant role to mitigate sediment discharge and runoff generation in mesic forest environments and their ability to quickly colonize gaps in higher vegetation layers are of particular interest for soil erosion control in early stage forest plantations. A detailed record of different biocrust species and their functional influence on soil erosion processes as well as a thorough monitoring of biocrust covers under closing tree canopy in subtropical forests is required in further studies

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<p>Biological Soil Crusts (biocrusts) are communities of algae, lichens, mosses, cyanobacteria, and other nonvascular organisms living in the soil surfaces. Biocrusts are a key factor in the protection of arid and semiarid ecosystems and, therefore, playing a major role against desertification. Biocrusts are also of profound importance in sand dune areas, as they are recognized as the first colonizers after environmental disturbances and can help preventing sediment remobilization. Moreover, biocrusts have shown to be of importance in soil protection against erosion, but also nutrient cycling in the Pampa biome in Brazil. Here, natural geomorphological processes and soil misuse led to the expansion of sediment remobilization areas, generating a severe problem - the difficulty of fixing field vegetation and crops. The present study investigates the behavior and interrelationships of biocrusts specifically in areas that suffer sandization in the Brazilian Pampa biome and verifies their relationship with soils and soil organisms. We analyzed biocrusts in three consecutive stages. Starting with a taxonomic exploration of the dominant component of cyanobacteria, proceeding to its characterization and finally determining its importance. We investigated two study sites in São Francisco de Assis and samples were collected in May 2016 and October 2019. The sites are characterized by sandy soils that suffer gullying, one without human intervention and the other one with artificially stabilized ravines. The analysis of biological material was carried out with microscopy, and it could be determined that the composition consists of 13 taxa of cyanobacteria and one filamentous species, <em>Stigonema </em>sp., could be specifically highlighted. These black to dark green spotty communities on the soil surface played an important role in particle aggregation, which can be granulated and show macroscopic forms. When analyzing the location of the biocrusts within the topography, it was observed that they occur in more humid places, occupying the same positions in all relief compartments. Biocrusts mostly develop on the top of the gullies or on upper and more stabilized slopes, especially when facing southern orientation. Taking into account the biocrust cover, we can identify different morphologies such as smooth, rolling and pinnacle blocks, which showed us different combinations according to the degree of evolution related to the micromorphology of the relief. We found that the presence of these biocrusts as an element of nutrient source and balance generator can lead to a reduction of soil erosion and was thus of outmost importance for the restoration of this biome.</p>

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