Understanding and Combating the Fire-Enhancing Impact of Non-Native Annuals in Desert Scrub through the Tools of Population and Landscape Ecology - SI-1721
Claus Holzapfel & Kirk Moloney
Jennifer L. Schafer, Erika L. Mudrak, 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. While changes in vegetation pattern that cause increased fire frequencies have been amply documented, a mechanistic understanding of how non-native plants are changing desert communities and landscapes is lacking.
Traditionally, annual plants were patchily distributed, were restricted to nutrient-rich areas under desert shrubs, and avoided open areas between shrubs (source-focus strategy). This new 4 year project (that started in March 2010) examines the hypothesis that some of the now dominant and problematic non-native plants are able to spread into the areas between the shrubs by employing population strategies (source-sink strategies) that sharply contrast with those of native species. It also explores how soil disturbances and changes in moisture availability related to climate change influence these effects. The environmental consequences of this new strategy are that the formerly open inter-shrub areas are filling with plant biomass. This biomass, especially after the growing season, can greatly increase the fuel load in the matrix, which has historically produced a natural firebreak between shrubs.
Inflammable desert: invaded by red brome and splitgrass (top left) and Sahara mustard (right)
The objectives of this project are to
(1) gain an understanding of the landscape-scale population dynamics of fire-promoting and fire-retarding plant species;
(2) test whether, once fire becomes prevalent, naturally formed islands of fertility break down and a negative feedback enhances fire even further;
(3) apply the results to aid management practices that will help restore the original environmental pattern of islands of fertility in a low-nutrient matrix and therefore prevent future wildfires;
(4) understand the effects of non-native plant species on fire regimes and their interdependence with future climate scenarios as predicted by current General Circulation Models;
(5) determine how disturbances impacting soils may change the response to fire.
Through the experimental studies, demographic data will be obtained under different environmental conditions for several target species, both invasive and native. Spatial patterns of fertility and soil moisture availability will be characterized using data from the experimental studies. We will parameterize detailed, landscape-scale, spatially explicit population models using field observations and controlled experimental studies examining the impacts of soil disturbance, fire and altered rainfall patterns in two contrasting desert sites on military installations (the Mojave Desert and the Sonoran Desert).
• Fire: burned vs. unburned
• Hydrology: 0.5x, 1x and 2x average precipitation using irrigation and rain-out shelters
• Soil disturbance: soil turbation vs. control
• Seed limitation: seed addition of non-native species (already present in the area) vs. control
Landscape-scale, spatially explicit simulation models of the spread of invasive species in matrix habitat will be 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. The models developed by this project will be used to explore the causes and consequences, at a landscape scale, of increased fire frequency and intensity under projected scenarios of climate change and disturbance and further examine the efficacy of different management strategies.
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.