A realized facilitation cascade mediated by biological soil crusts in a sagebrush steppe community

Biological soil crusts can have strong effects on vascular plant communities which have been inferred from short-term germination and early establishment responses. However, biocrusts are often assumed to function as an organizing principle in communities because their effects can cascade to interactions among crust-associated plant species. We conducted surveys and experiments to explore these cascades and found that biocrusts were positively associated with large patches (> 10 m diameter) of a dominant shrub Artemisia tridentata. At the smaller scale of individual shrubs and the open matrices between shrubs, biocrusts were negatively associated with Artemisia. Juveniles of Artemisia were found only in biocrusts in intershrub spaces and never under shrubs or in soil without biocrusts. In two-year field experiments, biocrusts increased the growth of Festuca and the photosynthetic rates of Artemisia. Festuca planted under Artemisia were also at least twice as large as those planted in open sites without crusts or where Artemisia were removed. Thus, biocrusts can facilitate vascular plants over long time periods and can contribute to a realized cascade with nested negative and positive interactions for a range of species, but unusual among documented cascades in that it includes only autotrophs.

Automated summary

Biological soil crusts have significant effects on vascular plant communities, as their effects can cascade to interactions among crust-associated plant species. Surveys and experiments show that biocrusts are positively associated with large patches of dominant shrubs, but negatively associated with individual shrubs. Biocrusts enhance the growth of Festuca and the photosynthetic rates of Artemisia, resulting in a cascade of positive and negative interactions among autotrophs.