Fire and plants have interacted, influencing each other and their surroundings, for millennia. Burn severity (ecological change following a fire) influences post-fire vegetation via differing levels of biomass removal by burning, soil heating, and nutrient deposition among other factors. Interactions between fire, plants, and climate have been of particular concern in northern boreal forests where there has been an increase in area burned at high severity, resulting in shifts in dominant vegetation. Previous studies have focused mainly on tree regeneration; therefore, only a few studies have examined how burn severity affects understory species assemblages. We examined the effects of burn severity (derived via remote sensing [dNBR]) on understory plant communities 12 years post-fire. We characterized understory species in unburned and high, moderate and low burn severity areas on the Taylor Complex fires in interior Alaskan boreal spruce forest that burned in summer 2004. Multivariate ordination analysis was used to examine the influence of burn severity, aspect, and elevation on plant communities, with multi-response permutation procedure to perform pairwise comparisons between the plant communities at sites burned at different severity levels. An indicator species analysis was also performed.
Results/Conclusions
Ordination analysis (cumulative R2=0.83) produced a primary axis (R2=0.52) positively correlated with transformed aspect (r=0.40) and dNBR (r=0.38) with a negative correlation with elevation (r=-0.28). Pairwise comparisons show that unburned plant community composition is significantly different (α=0.05) from all burned communities (p<0.02), while low and high severity communities are marginally significantly different (p=0.079). Several species were identified as significant indicators for unburned (e.g. Alnus viridis, Empetrum nigrum, Hylocomium splendens; all p<0.03), low severity (Calamagrostis canadensis; p=0.024), and high severity sites (Chamerion angustifolium, crustose lichen sp.; both p<0.03) respectively, per an indicator species analysis (p=0.005). While the overall plant community composition did not differ significantly between burn severity levels, it is important to note that even 12 years post-fire there are still significant indicator species differentiating between low and high severity sites. Because of the slow growth of dominant moss species, these sites would likely not recover for several decades. Our findings will help inform management and future research by furthering our understanding of the drivers of post-fire understory recovery patterns, with important implications for overall ecological knowledge of how burn severity and other variables interact in the long-term to affect understory species diversity and composition.