Climate is more influential to vegetation green-up than factors that contribute to erosion following high-severity wildfire

Background In the southwestern United States, post-fire vegetation
recovery is increasingly variable in forest burned at high-severity. Many
factors, including temperature, drought, and erosion, can reduce post-fire
vegetation recovery rates. Here, we examined how post-fire precipitation
variability, topography, and soils influenced post-fire vegetation
recovery in the southwestern United States as measured by greenness. We
modeled relationships between post-fire vegetation and these predictors
using Random Forest and examined changes in post-fire normalized burn
ratio across fires in Arizona and New Mexico. We incorporated growing
season climate to determine if year-of-fire effects were persistent during
the subsequent five years or if temperature, water deficit, and
precipitation in the years following fire were more influential for
vegetation greenness. Results We found reductions in post-fire greenness
in areas burned at high-severity when heavy and intense precipitation fell
on more erodible soils immediately post-fire. In highly
erodible scenarios, when accounting for growing season climate,
coefficient of variation for year-of-fire precipitation, total
precipitation, and soil erodibility decreased greenness in the fifth year.
While the effects of year-of-fire factors related to erosion were
significant, they were small, and the variability explained by growing
season vapor pressure deficit and growing season precipitation were
significantly greater. Conclusions Our results suggest that while the
factors that contribute to post-fire erosion and its effects on vegetation
recovery are important, at a regional scale, the majority of the
variability in post-fire greenness in high-severity burned areas in
southwestern forests is due to climatic drivers such as growing season
precipitation and vapor pressure deficit. Given the scale of area burned
at high-severity, the likelihood that high-severity burned area will
continue to increase, and the potential for more post-fire erosion that
can result in different vegetation trajectories, quantifying how these
factors alter the trajectory of greenness and what that means in terms of
ecosystem development is central to understanding how different ecosystem
types will be distributed across these landscapes with additional climate
change.