Plant community response to the East Amarillo Complex wildfires in the Southern High Plains, USA

Abstract

Severe wildfires are increasing in extent in the western US. We used a matched-pairs design with plots in burned and non-burned areas to study effects of the East Amarillo Complex (EAC) wildfires on mixed grass prairie mean community composition and variability in composition. Species composition and ground cover data were collected at 5 study sites each year for three years following the EAC. Fire effects on mean species composition were analyzed with permutational analyses of variance; temporal patterns were analyzed with permutational anova and nonmetric multidimensional scaling; and an index of multivariate dispersion was used to assess variability in plant community composition. We found weak immediate impacts (year 1) of wildfire on mean species composition, but strong impacts by year three. Two general patterns of changes in mean species composition emerged: at 3 study sites, there was a progressive divergence in similarity between burned and non-burned areas following wildfire whereas at 2 study sites, wildfire effects lessened over time. In contrast, a trend of increased homogeneity in burned vegetation relative to non-burned vegetation was apparent at all 5 study sites 2 to 3 years post-fire; burned areas also had higher species diversity, higher evenness but similar species richness 3 years post-fire. Ground cover composition, which was immediately impacted by wildfire through removal of residual dry matter, was fully recovered to non-burned conditions 3 years after wildfire. We observed little seedling recruitment either of native or exotic species following wildfire. Community composition changes in burned areas were likely the result of changing dominance relationships among plants that survived the wildfires rather than the result of recruitment of new individuals in gaps created by dead plants. Given the growth form of perennial C4 grasses and the fact that these grasslands evolved in the context of repeated fire, it is likely that changes in mean species composition and compositional variability are short-term responses.