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

Abstract

AbstractBiological 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 shrubArtemisia tridentata.At the smaller scale of individual shrubs and the open matrices between shrubs, biocrusts were negatively associated withArtemisia. Juveniles ofArtemisiawere 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 ofFestucaand the photosynthetic rates ofArtemisia.Festucaplanted underArtemisiawere also at least twice as large as those planted in open sites without crusts or whereArtemisiawere 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.