Understanding and Combating the Fire-Enhancing Impact of Non-Native Annuals in Desert Scrub through the Tools of Population

and Landscape Ecology


poster at:  Partners in Environmental Technology -  Technical Symposium & Workshop, December 2011, Washington, DC









SERDP Project SI-1721



Dr. Claus Holzapfel, Rutgers, Newark &  Dr. Kirk A. Moloney, Iowa State University


Team Members:

Dr. Jennifer L. Schafer, Dr. Erika L. Mudrak, Dr. Marjolein Schat, Carolyn E. Haines, Hadas A. Parag, Andres Fuentes Ramirez



Biological invasion, the spread of non-native organisms, is occurring rapidly worldwide, and many desert areas currently show a dramatic increase in the arrival and spread of non-native Old World plant species. Among the detrimental effects are alterations in fire regimes and direct negative impacts on native plant species. Prior invasion annual plants were mostly restricted to nutrient-rich areas under desert shrubs, and avoided open areas between shrubs. We are examining the hypothesis that some of the now dominant and problematic non-native annuals are able to spread into the areas between the shrubs by employing population strategies that sharply contrast with those of native species thereby herby can greatly increase the fuel load in the matrix, which has historically produced a natural firebreak between shrubs. 


 In the initial year of the project we established permanent research sites in creosote bush communities in the Sonoran Desert (Barry M. Goldwater Range) and the Mojave Desert (Fort Irwin),  gathered spatially explicit density data for shrubs and herbaceous plants and explored how these spatial pattern of shrubs and native and non-native herbaceous plants can lead to desert wild fires. Our initial data on annual and perennial plant densities and their spatial distributions suggest that different processes have the potential to promote fire in the two contrasting desert sites. In the Mojave the rise of non-native species also occupying the areas between shrubs indeed has the potential to promote fire.  In the Sonoran Desert also native species occupy the areas between shrubs and potentially provide enough fuel to carry wild fires. Additionally, higher shrub densities and lesser shrub segregation in the Sonoran Desert might be the key factor for promoting wildfires;  even in the absence of non-native species.


  In the coming years we will further investigate through experimental studies whether these initial conclusions are holding and will elucidate the mechanism for this. These experiments will combine the effects of fire, disturbance and climate change on the demographics of native and non-native annual plants. Spatial patterns of fertility and soil moisture availability are being characterized using data from the experimental studies. Landscape-scale, spatially explicit simulation models of the spread of invasive species in matrix habitat are developed based on parameters obtained in the experimental studies. Simulation studies of fire spread and the efficacy of different management strategies will also be conducted.



Inflammable desert: invaded by red brome and splitgrass (top left) and Sahara mustard (right)




The hypothesized pathway to fire










Annual plants restricted to shrub sub-canopies                                                                                                 Schismus grassland between shrubs

Research Sites









































Site maps. Shown are all shrubs on the site and their relative sizes.

Colored transects are soil sample transects.






Shrub diagram with transects, plots, and a dotted line indicating the location of the Larrea canopy drip line. UC = Under Canopy; CD = Canopy Drip line; ON = Open Near shrub; OF = Open Far from shrub. (B) Transect diagram with plot sizes and distances between plots within a transect. DM = demography plot  SL = soil plot.






Shrub and Annual Plant Spatial Pattern




















Current Directions











We would like to thank Dave Housman, Ruth Sparks  & Alex Misiura (ITAM, Fort Irwin),

Richard K. Whittle & Teresa Walker (Luke AFB) for help in the field. 

Thanks to John A. Hall and the SERDP team for support.