Pioneer biocrust communities prevent soil erosion in temperate forests after disturbances

Abstract

Abstract. Soil erosion continues to be one of the most serious environmental problems of our time, which is exacerbated by progressive climate change. Until now, forests have been considered an ideal erosion control in this regard. However, even minor disturbances of the forest floor for example from heavy vehicle used for timber harvesting can cause substantial sediment transport. An important countermeasure is the quick restoration of the uncovered soil surface by vegetation. In this context, biological soil crusts (biocrusts) can play a vital role, as they are known for their soil-protective effect. This study examined the natural succession of pioneer vegetation in skid trails on four soil substrates in a central European temperate forest and investigated their influence on surface runoff and sediment discharge. We applied rainfall simulation experiments on small-scale runoff plots and continuously surveyed vegetation during the same period, primarily to map biocrust development. Skid trails on clayey substrates showed considerably higher biocrust cover and species richness. Biocrust cover was higher in center tracks than in wheel tracks, while there was no clear difference for biocrust species richness with regard to track position. Although biocrusts were quickly overtopped by vascular plants, they managed to coexist until their growth was restricted due to leaf litter fall. Brachythecium rutabulum and Oxyrrhynchium hians were the most important and persistent pioneer biocrust species, while Dicranella schreberiana and Pohlia lutescens were volatile and quickly disappeared after spreading in summer. Soil erosion was reduced with pioneer biocrust vegetation in summer, and again increased in winter. Total amount of sediment discharge was clearly site-dependent, indicating a high relevance of underlying substrates. Sediment discharge was 13.2 times higher in wheel tracks compared to undisturbed forest soil, and bare soil runoff plots produced 22-fold sediment discharge compared to undisturbed forest soil. Overall, bryophyte-dominated biocrusts contributed more to mitigating soil erosion than vascular plants. When soil coverage exceeded 50 %, biocrusts resulted in an average of 18 times less sediment loss compared to vascular plants.

Biocrusts: Overlooked hotspots of managed soils in mesic environments

“…As a result, soil is directly exposed to sunlight and biocrusts can rapidly colonize within a few weeks (Seitz et al, 2017). Recent work has described biocrusts in forests (Baumann et al, 2017;Gall et al, 2022;Glaser et al, 2018;Kurth et al, 2021;Ngosong et al, 2020) and on agricultural fields (Nevins et al, 2020(Nevins et al, , 2021(Nevins et al, , 2022. In these environments, biocrusts are ephemeral and do not usually persist unless the disturbance is permanent (Szyja et al, 2018).…”

“…In disturbed areas, biocrusts have great potential to reduce soil erosion (Seitz et al., 2017), and in some cases are even more effective than vascular plant cover (Bu et al., 2015; Gall et al., 2022). In particular, pioneer biocrust cover can protect against erosion as early as a few weeks following timber harvest (Gall et al., 2022), a very vulnerable stage for soils. Three main erosion‐reducing mechanisms in biocrusts have been described.…”

“…Biocrusts can be found in both coniferous and deciduous forests of mesic environments, and are visible in the field as green cover (Baumann et al., 2017; Glaser, Albrecht, et al., 2022; Kurth et al., 2021) (Figure 1). While they can quickly establish in disturbed areas such as skid trails, their biocrust characteristics rapidly disappear with succession of vascular vegetation (Gall et al., 2022). Other cryptogamic communities that host a large part of their biomass above the soil's surface (such as thick moss mats, which are common in coniferous forests) are not always classified as biocrusts.…”

“…These regions are largely characterized by adequate water availability and unrestricted vascular plant growth, which can also be colonized by biocrusts. Recent studies have also found biocrusts at mesic, managed sites, which are anthropogenically impacted, such as monospecific pine forests, broadleaf-mixed forests, and agricultural fields (Baumann et al, 2017;Gall et al, 2022;Glaser et al, 2018;Kurth et al, 2021;Nevins et al, 2020Nevins et al, , 2021Ngosong et al, 2020). As the study of biocrusts on managed soils in mesic environments is still in its infancy, herein, we will elaborate on their dynamics, distribution, and potential impacts on ecosystem services.…”