Wednesday, 19 November 2003: 10:30 AM
Effects of fuel treatments, post-fire rehabilitation treatments and wildfire on establishment of invasive species
Establishment and spread of invasive species following wildfires can pose threats to long-term native plant recovery. Disturbance severity and propagule pressure may influence the likelihood that invasives will establish in burned areas. In this study we examine the establishment of invasive species after wildfires in relation to native species diversity and cover, fire severity, and resource availability. In addition, we examined the effects of fuel treatments implemented prior to the wildfire and reseeding for post-fire erosion control. We analyzed post-fire effects at multiple scales within the Cerro Grande fire in Los Alamos, New Mexico. At the 1000 m2 plot scale we examined vegetation dynamics in relation to fuel treatments (thinned, prescribed burn, thinned + prescribed burn), aspect (north, south), vegetation type (ponderosa pine forests, mixed-conifer forests, pinyon-juniper woodlands), fire severity (high, moderate, low, none), percent slope, and total soil nitrogen content. At the 1 m2 plot scale we examined the relationship between cover of exotic species, dominant vegetation (perennial grasses), subdominant vegetation (native forbs), and seeded grasses (annual and perennial grasses). We hypothesize that invasive plants are more likely to establish in areas treated for fuels reduction because of the increased traffic and disturbance in such areas. We also suggest that exotic species are likely associated with seeded grasses used in erosion control efforts because they may be unintentionally introduced to burned areas with application of seed mixes. Exotic species typically make up a small percentage of seed mixes, yet when large amounts of seed are applied over broad areas, the small percentage of weedy species may be sufficient to establish populations across the landscape. The threat of establishment of invasive species should be weighed against the need for soil stabilization when applying seed mixes for purposes of erosion control. Areas treated for fuel hazard reduction also should be monitored, especially after severe wildfires that remove cover of dominant native species and provide colonization opportunities for invasive species.