Vegetation recovery in a desert landscape after wildfires: influences of community type, time since fire and contingency effects.
Theories of plant succession are poorly developed in arid lands, hindering our understanding of how long communities may take to recover after disturbances such as fire. In desert landscapes vulnerable to fire, information about vegetation recovery is important when deciding whether land managers should facilitate vegetation recovery. The deserts of the southwestern USA are increasingly subject to unprecedented fires, facilitated by fuel from exotic grasses, yet management strategies are unclear. We evaluated post-fire recovery patterns of perennial plant species richness and diversity, compared the rate and direction of succession between two major community types, and explored the relationship of time since fire (TSF) and other environmental factors with vegetation recovery. We sampled perennial plant communities and environmental variables (e.g. soil N) on 32 burns, ranging from 2 to 29 years TSF and each paired with their own unburned area, within a 1.8 million ha landscape in the Mojave Desert, USA. Species richness, diversity and composition exhibited different post-burn recovery patterns, and recovery rates differed between community types. Specifically, diversity in Coleogyne ramosissima communities was greater in burned than unburned areas, but diversity did not differ in Larrea tridentata communities. Species composition in Larrea communities exhibited trajectories that indicate convergence with unburned community composition after 19 years TSF. Conversely, burned and unburned Coleogyne communities lacked convergence irrespective of TSF. Environmental variables (e.g. soil texture and P) accounted for 79-83% of the variation in burned species composition, suggesting environmental characteristics in part control recovery patterns. Synthesis and applications. The results indicate that geographically similar vegetation types within the same landscape can have markedly different post-disturbance successional rates and trajectories. Furthermore, the persistence of fire effects varied depending on the community measure, with fire effects on species composition more long-lasting than the effects on species diversity. This work supports (i) the use of post-disturbance successional analyses for helping to prioritize management where it is most needed (e.g. communities not recovering naturally) and (ii) the need to assess whether persistent, early successional desert communities meet functional management objectives.