Background: Plants play a pivotal role in soil stabilization, with above-ground vegetation and roots combining to physically protect soil against erosion. It is possible that diverse plant communities boost root biomass, with knock-on positive effects for soil stability, but these relationships are yet to be disentangled.
Question: We hypothesize that soil erosion rates fall with increased plant species richness, and test explicitly how closely root biomass is associated with plant diversity.
Methods: We tested this hypothesis in salt marsh grasslands, dynamic ecosystems with a key role in flood protection. Using step-wise regression, the influences of biotic (e.g. plant diversity) and abiotic variables on root biomass and soil stability were determined for salt marshes with two contrasting soil types: erosion-resistant clay (Essex, southeast UK) and erosion-prone sand (Morecambe Bay, northwest UK). A total of 132 (30-cm depth) cores of natural marsh were extracted and exposed to lateral erosion by water in a re-circulating flume.
Results: Soil erosion rates fell with increased plant species richness (R2 = 0.55), when richness was modelled as a single explanatory variable, but was more important in erosion-prone (R2 = 0.44) than erosion-resistant (R2 = 0.18) regions. As plant species richness increased from two to nine species·m-2, the coefficient of variation in soil erosion rate decreased significantly (R2 = 0.92). Plant species richness was a significant predictor of root biomass (R2 = 0.22). Step-wise regression showed that five key variables accounted for 80% of variation in soil erosion rate across regions. Clay-silt fraction and soil carbon stock were linked to lower rates, contributing 24% and 31%, respectively, to variation in erosion rate. In regional analysis, abiotic factors declined in importance, with root biomass explaining 25% of variation. Plant diversity explained 12% of variation in the erosion-prone sandy region.
Conclusion: Our study indicates that soil stabilization and root biomass are positively associated with plant diversity. Diversity effects are more pronounced in biogeographical contexts where soils are erosion-prone (sandy, low organic content), suggesting that the pervasive influence of biodiversity on environmental processes also applies to the ecosystem service of erosion protection.
Keywords: Biodiversity–ecosystem–function; Ecosystem service; Erodibility; Erosion stabilization; Grassland; Plant species richness; Resilience; Root biomass; Salt marsh; Soil erosion.