Post-wildfire Recovery of Riparian Vegetation during a Period of Water Scarcity in the Southwestern USA
Wildland fires occur with increasing frequency in southwestern riparian forests, yet little is known about the effects of fire on populations of native and exotic vegetation. From 2003 to 2006, we monitored recovering woody vegetation in wildfire sites in the bosque (riparian forest) along the Middle Rio Grande of central New Mexico, USA. To examine recovery potential, we estimated densities of native Rio Grande cottonwood (Populus deltoides ssp. wislizenii) and exotic saltcedar (Tamarix
... sima) in burned plots and estimated mortality rates of resprouts. Exotic vegetation density was higher in most burned sampling plots than in paired unburned plots. Native shrub density was lower in most burned sampling plots than in unburned plots, although the effect sizes were small. Native tree density did not differ between burned and unburned plots, despite relatively high mortality of cottonwood resprouts. All observed cottonwood mortality occurred between 2003 and 2004, following the hottest and driest summer of the study. Cottonwood resprouts had the lowest apparent mortality rate at the site with the lowest depth to groundwater. Saltcedar resprout mortality was low at all wildfire sites, consistent with previous studies showing that this species is less sensitive to drought and better adapted to wildfire than cottonwood and other native species. Our observations suggest that, in the absence of ideal hydrologic and climatic conditions, fire can reduce cottonwood density in the bosque and promote the spread of saltcedar. Increasingly xeric conditions predicted under most climate change scenarios could result in greater recovery of exotic saltcedar over native vegetation.