Theory of the greatest threat to drylands

There are many types of dryland ecosystems and many types of threats including overgrazing, nitrogen deposition, species invasions and climate-change driven alterations of temperature, precipitation amount and variability. We hypothesize that threats with the highest impact per unit of change are those that experience lowest level of natural variability. Consequently, the biggest threat for each dryland type will be that for which the ecosystem has experienced low natural variability and will experience moderate to large changes. Examples from drylands with low and high evolutionary grazing history and low and high precipitation variability support our theory.