Viability of Bell's Sage Sparrow (Amphispiza belli ssp. belli): Altered fire regimes

We modeled the viability of a Bell's Sage Sparrow (Amphispiza belli ssp. belli) metapopulation under different fire regimes in the foothills and mountains of San Diego County, California, USA. The approach integrates a landscape model, which predicts the vegetation composition and age under three fire regimes, a habitat model, which interprets the resulting landscape in terms of its suitability for the Sage Sparrow, and a metapopulation model, which predicts the viability of the species based on a dynamic spatial structure as determined by the landscape and the habitat models. Bell's Sage Sparrow depends on early-successional shrubland (chaparral) habitat, especially when the availability of preferred open coastal subshrub vegetation is limited. The three fire rotation intervals (FRI) used in the landscape model were "current" (30-yr), representing the effect of increased human ignitions; "natural" (90-yr), representing the historic shrubland fire regime at higher elevations without the effect of human ignitions; and "long" (150-yr), representing a hypothetical endpoint (very low fire frequency for southern California shrublands). The results indicated that the viability of the Sage Sparrow was highest under the "current" fire regime scenario, slightly lower (especially when population growth rate was low) under the "natural" scenario, and lowest under the "long" fire regime scenario.