Assessing biological soil crust recovery from drought and disturbance across three deserts of North America

Background/Question/Methods

Dryland regions are particularly sensitive to climate change and land degradation, which together diminish dryland ecosystem function. A fundamental community in dryland ecosystems is biological soil crusts (biocrusts) – assemblages of cyanobacteria, lichens, and bryophytes – that adhere and stabilize soil surfaces and have large effects on soil fertility and water availability. Early successional biocrust communities commonly contain lightly- pigmented cyanobacteria, whereas later successional communities typically contain darkly-pigmented cyanobacteria, lichens, and mosses. Biocrusts are shown to be highly vulnerable to changes in temperature and precipitation and to physical disturbance. This study aims to assess biocrust community and soil stability responses to drought and physical disturbance across a natural climatic gradient in three desert ecosystems: the Chihuahuan, Mojave, and Great Basin deserts. In each desert, we constructed 40 disturbed and droughted plots in a full-factorial design (n = 10 for each treatment). We surveyed biocrust communities and soil aggregate stability at three timepoints in each location: pre-treatment (T0), immediately following treatments (Tpost), and one year after treatments (Trecover). This experimental design allows us to assess how biocrust and soil stability are related, how they are altered by physical and climate disturbance, and their interactions, and to assess recovery after disturbance in ongoing droughted conditions.

Results/Conclusions

Biocrust community composition significantly differed at each desert site (PERMANOVA, P=0.001) such that the abundance of later-successional organisms declined with aridity. Prior to treatments there were no significant community differences among the plots at each site (PERMANOVA, P>0.05), however, immediately after the physical disturbance treatment (Tpost) the composition significantly changed in physically disturbed plots due to increased bare ground and litter (PERMANOVA, P<0.01). One year following treatments (Trecover), biocrust communities partially recovered in physically disturbed but not in drought x disturbed plots of the Great Basin and Chihuahuan. Soil stability followed similar patterns, with high stability in Chihuahuan and Great Basin sites at T0 and reduced stability at Trecover in all disturbed plots. The Mojave site had the lowest soil stability at T0, which is likely related to its low biocrust cover. Changes between T0 and Trecover of both biocrust community composition and soil stability in disturbed plots underscore the relationship between biocrust organisms and the stability of dryland ecosystems. Our findings emphasize that physical and climatic disturbances diminish the services provided by dryland biocrust communities and that climate change and physical disturbance will interact to drive lowered resilience in dryland biocrust communities.