Cross-Scale Interactions and Ecosystem Resilience in Drylands.

Dryland ecosystems are often assumed to be highly resilient to periodic drought, and much less resilient to most other types of disturbance. The “desertification” paradigm reflects the widespread assumptions that (a) drylands are particularly susceptible to degradation, often resulting perennial grass losses and woody plant increases, (b) degradation is relatively persistent, and (c) abiotic forces dominate shifts towards desertified systems. The past 100 years of research at the Jornada Experimental Range USDA-LTER site in the northern Chihuahuan Desert has provided some support for the first two assumptions. Long-term research has also shown that avoiding degradation, and promoting perennial grass recovery, requires a more nuanced understanding of ecosystem dynamics at multiple spatial and temporal scales, and that multi-scale interactions between patterns and processes are important to long-term, large-scale dynamics. In this presentation we focus on how vegetation structure is both a short-term response to, and a long-term driver of, geomorphology at patch to landscape and even regional scales. We begin with relatively short-term relationships between soil moisture availability, and plant community composition and structure, and show how changing spatial structure can trigger changes in resource redistribution by wind and water. We then explore the consequences of these changes, in the form of relatively persistent shifts between plant communities, for landscape-scale changes in soil redistribution and pedogenesis. These changes eventually result in a shift in the potential of the system to support the establishment and growth of different plant communities in different parts of the landscape. We conclude with a brief discussion of conceptual and technological tools that are increasingly being used to contextualize and communicate to managers this multiple, interacting scales approach to ecosystem resilience to ensure that the information is relevant to both the current (soil and vegetation) state of their land, and the long-term (soil, topography, climate) potential.