Relationships among biological soil crusts, environment, and vascular plants in Ozark sandstone glades

Background/Question/Methods

Biological soil crusts play important ecological roles in communities where they occur, but factors that control their distribution as well as their effects on vascular plant community assembly processes remain poorly understood. Biological soil crusts are known to have both positive and negative effects on vascular plant establishment, and effects may vary among soil crust functional groups and among ecosystems. Here, we present results from an observational study of biological soil crusts in sandstone glades in the Ozarks region of Missouri and Arkansas. We investigated whether soil crust abundance is related to environmental factors, and assessed relationships between the abundance of several soil crust morphological groups and vascular plant species richness. We hypothesized that biological soil crusts would be more abundant in glades with lower heat load and poorer soils, and that soil crust cover would be negatively correlated with vascular plant species richness.

Results/Conclusions

Our results indicate that biological soil crust abundance responds strongly to environmental gradients in sandstone glades. Total soil crust cover was negatively correlated with heat load, indicating that soil crusts prefer more mesic environments. Biological soil crusts were also more abundant in glades with less fertile soils. Vascular plant species richness was negatively correlated with total soil crust cover, and with cover of most soil crust functional groups. However, the few plots with high cyanolichen cover also had unusually high vascular plant cover, suggesting positive influences of these nitrogen-fixing lichens on vascular plant species richness. Our results suggest that biological soil crusts may play important roles in influencing vascular plant communities. Future research should investigate mechanisms by which biological soil crusts may limit or promote vascular plant establishment in sandstone glades.