Post-fire Climate Research Articles

Effects of fire severity and post-fire climate on short-term vegetation recovery of mixed-conifer and red fir forests in the Sierra Nevada Mountains of California

Abstract Forest ecosystems in the Sierra Nevada Mountains of California are greatly influenced by wildfire as a natural disturbance, and increased fire severity and drought occurrence may alter the course of post-fire recovery in these ecosystems. We examined effects of fire severity, post-fire climate, and topographic factors on short-term ( 405 ha) between 1999 and 2006 were examined. According to the modeling results provided by ordinary least squares (OLS) regressions including spatial variation coefficients, fire severity, post-fire wet eason precipitation, post-fire January minimum temperature, and topographic factors explain variations in short-term post-fire NDVI values (adjusted R-squared = [0.680, 0.688] for red fir forests; adjusted R-squared = [0.671, 0.678] for mixed-conifer forests). The modeling results indicated that burned mixed-conifer forest was sensitive to post-fire drought, while burned red fir forest, with higher summer soil moisture availability, was sensitive to post-fire temperature. We also found that differences in recovery related to fire severity disappeared more quickly in burned mixed-conifer forest than in burned red fir forest. Future efforts should focus on long-term recovery, including competition between forest and shrub species in previously burned areas.

Fire legacies impact conifer regeneration across environmental gradients in the U.S. northern Rockies

An increase in the incidence of large wildfires worldwide has prompted concerns about the resilience of forest ecosystems, particularly in the western U.S., where recent changes are linked with climate warming and 20th-century land management practices. To study forest resilience to recent wildfires, we examined relationships among fire legacies, landscape features, ecological conditions, and patterns of post-fire conifer regeneration. We quantified regeneration across 182 sites in 21 recent large fires in dry mixed-conifer forests of the U.S. northern Rockies. We used logistic and negative binomial regression to predict the probability of establishment and abundance of conifers 5–13 years post-fire. Seedling densities varied widely across all sites (0–127,500 seedlings ha−1) and were best explained by variability in distance to live seed sources (β = −0.014, p = 0.002) and pre-fire tree basal area (β = 0.072, p = 0.008). Beyond 95 m from the nearest live seed source, the probability of seedling establishment was low. Across all the fires we studied, 75 % of the burned area with high tree mortality was within this 95-m threshold, suggesting the presence of live seed trees to facilitate natural regeneration. Combined with the mix of species present within the burn mosaic, dry mixed-conifer forests will be resilient to large fires across our study region, provided that seedlings survive, fire do not become more frequent, high-severity patches do not get significantly larger, and post-fire climate conditions remain suitable for seedling establishment and survival.