Thursday, August 6, 2009
Exhibit Hall NE & SE, Albuquerque Convention Center
Background/Question/Methods
Thousands of hectares of blackbrush (Coleogyne ramosissima) communities have been destroyed by wildfire over the past 20 years after droughts and increased fuel loads due to invasion by non-native cheatgrass (Bromus tectorum). Most of these burned blackbrush communities have become annual grasslands dominated by cheatgrass. Blackbrush communities develop on relatively old, 5,000 to 125,000 year-old aridisol surfaces with moderate to well-developed desert pavements in the intercanopy spaces, covering extensive areas in the northern Mojave Desert of southern Nevada at elevations of 1,000-2,000 m. Most blackbrush communities occur on Bureau of Land Management lands that are subject to grazing and often have low perennial diversity. My study site is dominated by blackbrush, Mormon tea (Ephedra nevadensis) and Yucca species with total cover ranging from 20-45 percent. I studied recruitment in 140 (.25 m^2 ) plots in spring 2009 after a landscape level fire in August 2008 that incinerated most of the above ground biomass.
Results/Conclusions
Burning destroyed all aboveground biomass, leaving a 3-10 mm thick layer of ash where shrubs previously occurred. Total recruitment, consisting of 11 winter annual species and blackbrush, was not affected by fire, but species diversity was. Recruitment in drainage sites was significantly greater than upland sites (246 versus 122 plants m^-2 ). Understory microsites had significantly greater recruitment than shrub interspaces (302 versus 84 plants m^-2 ). Burning, topography, microsite and their interactions significantly influenced blackbrush recruitment. Burned upland understory sites had significantly greater blackbrush recruitment (29 seedlings m^-2 ) than all other sites and no recruitment occurred in burned drainage understory, burned drainage interspace and unburned upland understory sites. Cheatgrass seeds were destroyed by the fire resulting in less 1 seedling m^-2 compared to unburned understory sites (223-254 seedlings m^-2 ), though cheatgrass recruitment in unburned shrub interspaces sites was also low, (<5 seedlings m^-2 ). Recruitment of the native annual grass, Vulpia octoflora, was significantly greatest in unburned upland understory, unburned drainage interspaces and burned upland interspaces (81-154 seedlings m^-2 ). Densities for the other 8 native annual forbs were generally low (0-12 seedling m^-2 ) and did not significantly differ by site except for blazing star (/Mentzelia albicaulis/) which dominated burned understory drainage sites (463 seedlings m^-2 ). These results indicate the inability of blackbrush communities to re-establish after burning is not always due to lack of seed germination, I will be monitoring their survival three years.
Thousands of hectares of blackbrush (Coleogyne ramosissima) communities have been destroyed by wildfire over the past 20 years after droughts and increased fuel loads due to invasion by non-native cheatgrass (Bromus tectorum). Most of these burned blackbrush communities have become annual grasslands dominated by cheatgrass. Blackbrush communities develop on relatively old, 5,000 to 125,000 year-old aridisol surfaces with moderate to well-developed desert pavements in the intercanopy spaces, covering extensive areas in the northern Mojave Desert of southern Nevada at elevations of 1,000-2,000 m. Most blackbrush communities occur on Bureau of Land Management lands that are subject to grazing and often have low perennial diversity. My study site is dominated by blackbrush, Mormon tea (Ephedra nevadensis) and Yucca species with total cover ranging from 20-45 percent. I studied recruitment in 140 (.25 m^2 ) plots in spring 2009 after a landscape level fire in August 2008 that incinerated most of the above ground biomass.
Results/Conclusions
Burning destroyed all aboveground biomass, leaving a 3-10 mm thick layer of ash where shrubs previously occurred. Total recruitment, consisting of 11 winter annual species and blackbrush, was not affected by fire, but species diversity was. Recruitment in drainage sites was significantly greater than upland sites (246 versus 122 plants m^-2 ). Understory microsites had significantly greater recruitment than shrub interspaces (302 versus 84 plants m^-2 ). Burning, topography, microsite and their interactions significantly influenced blackbrush recruitment. Burned upland understory sites had significantly greater blackbrush recruitment (29 seedlings m^-2 ) than all other sites and no recruitment occurred in burned drainage understory, burned drainage interspace and unburned upland understory sites. Cheatgrass seeds were destroyed by the fire resulting in less 1 seedling m^-2 compared to unburned understory sites (223-254 seedlings m^-2 ), though cheatgrass recruitment in unburned shrub interspaces sites was also low, (<5 seedlings m^-2 ). Recruitment of the native annual grass, Vulpia octoflora, was significantly greatest in unburned upland understory, unburned drainage interspaces and burned upland interspaces (81-154 seedlings m^-2 ). Densities for the other 8 native annual forbs were generally low (0-12 seedling m^-2 ) and did not significantly differ by site except for blazing star (/Mentzelia albicaulis/) which dominated burned understory drainage sites (463 seedlings m^-2 ). These results indicate the inability of blackbrush communities to re-establish after burning is not always due to lack of seed germination, I will be monitoring their survival three years.
