Dismantling the dryland monolith myth: Plant communities respond to fire differentially across five North American deserts

Background/Question/Methods

Desert ecosystems occupy expansive land area in western North America and face significant threats to their structure and function under future climate scenarios. Current research predicts reductions in precipitation and humidity and increases in surface temperature, all of which have been correlated with increased fire frequency and extent across many western North America ecosystems. Historically North American deserts have been less fire prone than other ecosystems, however, increased invasion by exotic annual plants have combined with drier fuels drying to result in increased desert wildland fire. Fire can induce major changes to ecosystem structure through whole-plant mortality, canopy dieback, and the removal of coarse woody debris and leaf litter. Fire disturbance in the North American southwestern deserts is less well studied than other ecosystems despite predictions of a hotter, drier climate that may lead to increased fire risk. Examining and understanding the difference between how these systems respond to changes in fire regimes would have substantial benefits to restoration and management efforts. Here, we examine broad level post-fire plant succession by assessing plant community composition along a fire chronosequence (15 and 30 years post-fire) in the Sonoran, Mojave, Chihuahuan, Great Basin and Colorado Plateau deserts.

Results/Conclusions

Plant community composition was dependent on which desert with some significant relationships to fire age. Total plant richness was highest in the warmer deserts and lowest in the colder deserts. Fire age did not affect richness or composition of the plant communities in Chihuahuan and Sonoran. Richness was not significantly different between fire ages for all but the Great Basin and Mojave deserts. In the Mojave, richness was slightly lower in the recent fire but not different in the old fire and the Great Basin old fire reduced richness to less than half of control levels. Shannon diversity only differed between fire treatments in the Sonoran old fire where it actually increased following fire. Fire treatments created more divergent communities in the Great Basin and Colorado Plateau than those in the Mojave, Sonoran, and Chihuahuan. We found no evidence of convergence of plant communities to low-diversity annual assemblages following fire, treatment effects (6%) and treatment by desert interactions (22%) suggest that fire can restructure desert communities. These data lend insight into variable responses of desert plant communities to fire with important implications for predicting plant community change and improving restoration efforts.