Dryland feedbacks to climatic change: Results from a climate manipulation experiment on the Colorado Plateau

Abstract:

Arid and semiarid ecosystems cover ~40% of Earth’s terrestrial surface and make up ~35% of the U.S., yet we know surprisingly little about how climate change will affect these widespread landscapes. Like many dryland regions, the Colorado Plateau in the southwestern U.S. is predicted to experience climate change as elevated temperature and altered timing and amount of annual precipitation. We are using a long-term (>10 yr) factorial warming and supplemental rainfall experiment on the Colorado Plateau to explore how predicted changes in climate will affect vascular plant and biological soil crust community composition, biogeochemical cycling, and energy balance (biocrusts are a surface soil community of moss, lichen, and cyanobacteria that can make up as much as 70% of the living cover in drylands). While some of the responses we have observed were expected, many of the results are surprising. For example, we documented biocrust community composition shifts in response to altered climate that were significantly faster and more dramatic than considered likely for these soil communities that typically change over decadal and centennial timescales. Further, while we continue to observe important climate change effects on carbon cycling – including reduced net photosynthesis in vascular plants, increased CO₂ losses from biocrust soils during some seasons, and changes to the interactions between water and carbon cycles – we have also found marked treatment effects on the albedo and spectral signatures of dryland soils. In addition to demonstrating the effects of these treatments, the strong relationships we observed in our experiments between biota and climate provide a quantitative framework for improving our representation of dryland responses to climate change. In this talk we will cover a range of datasets that, taken together, show: (1) large climate-driven changes to dryland biogeochemical cycling may be the result of both effects on existing communities, as well of relatively rapid shifts in community composition; (2) drylands could provide feedbacks to future climate not only though altered carbon cycling but also via changes to surface albedo; and (3) models of dryland responses to climate change may need significant revision, but such a revision is well within reach.