Patterns of post-fire vegetation recovery in a Mojave Desert springs complex

Background/Question/Methods

Although desert springs occur infrequently they are a major source of surface water in arid regions.  These literal oases provide resources for a diverse array of aquatic and terrestrial plants and animals. The isolated nature of these unique ecosystems also makes them prone to high rates of endemism.  However, little is known about the ecological role of fire in desert springs.  The primary objective of this study was to examine how different desert springs plant communities respond to fire of varying severity and to repeated burning within a five year time period.  We identify the conditions associated with high recovery of native species, which will aid restoration practitioners in allocating resources to those areas where growth is likely to be slowest.  An intensive vegetation sampling study was conducted in Ash Meadows National Wildlife Refuge, a desert springs complex located in the Mojave Desert region of southern Nevada.  Plant community composition and environmental data were collected in eighty 0.08 ha plots located in or near areas burned in five recent wildfires (2000-2005).  Topographic data were interpreted from a LiDAR dataset, while anthropogenic alteration was characterized from photo-interpretation of false color-infrared imagery.
Results/Conclusions

Fire regimes in these unique ecosystems are not likely to be ignition limited, as both weather related and human induced sources of ignition are abundant.  Instead, fire regimes in desert springs are more likely fuel driven, with more fires occurring in wetland areas with greater understory herbaceous vegetation to be used as fuel.  The presence of fire and repeated burning within a five year time span reduced the cover of native woody vegetation relative to nearby unburned areas, while increasing cover of native herbaceous species.  Time since last fire did not have a significant effect on the cover of plant functional groups.  Screwbean mesquite (Prosopis pubescens) was most likely among native tree species to be entirely killed by fire, while velvet ash (Fraxinus velutina) was the most likely to experience top-kill, as indicated by resprouting from the root crown.  Screwbean mesquite was also most likely of the native trees to establish from seed following fire.  Native trees were less affected by fire than native shrubs, primarily due to their ability to resprout following top-kill by fire.  The lack of competition from slow-recovering shrubs presents opportunity for increased establishment of Tamarix sp. and exotic herbaceous plants.