Dryland ecosystems such as deserts, semiarid areas, and some monsoonal regions are vulnerable to land degradation, where soil or climate changes starve vegetation of resources—like water or nutrients—and cause ongoing loss of fertility and vegetation cover.
Losing plant cover can worsen desertification. Without plant canopies covering the soil surface, rainfall can damage the soil structure, causing tough crusts to form. Instead of letting water infiltrate and reach plants’ roots, crusts shed water as surface runoff. Whether crusts that form in bare sites cause desertification or actually help to prevent it depends on the fate of that runoff.
In a new study, Assouline et al. analyze the role of soil crusts as driving or deterring desertification, as environmental factors such as vegetation cover, plant morphology, plant water requirements, and land surface slope change. The researchers looked at field data collected at a semiarid Long-Term Ecological Research site in Israel between 1978 and 2013 and analyzed the data with one- and two-dimensional numerical models.
Where a high fraction of the land was covered in vegetation, soil crusts intensified desertification for almost all environmental conditions.
Areas with intermediate plant coverage were more complex: If vegetation was effective at intercepting runoff or if the canopy was bigger than the root zone, soil crusts prevented desertification. For areas with low vegetation cover, soil crusts mitigated the effects of desertification.
The findings help explain why sometimes soil crusts accelerate desertification, whereas in other places crusts are essential for healthy functioning of dryland ecosystems. In 2015, the parties to the Convention to Combat Desertification agreed to achieve “land degradation neutrality”—to bring the net rate of land degradation to zero—by 2030. Strategically creating soil crusts through physical or biological soil treatments could provide a new approach to restoring desertified lands to meet this 2030 goal. (Journal of Geophysical Research: Biogeosciences, doi:10.1002/2015JG003185, 2015)
—Lily Strelich, Freelance Writer
Citation: Strelich, L. (2016), Soil crusts play a dual role in desertification, Eos, 97, doi:10.1029/2016EO045599. Published on 16 February 2016.