Objective

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. This project examines 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. It will also explore 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.

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 important, 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; and (5) determine how disturbances impacting soils may change the response to fire.