The authors found that distance to seed source was the most important predictor of ponderosa pine regeneration after high severity fire in this study, although, climate also was significant, suggesting that areas that are more affected by drought-stress are less likely to regenerate naturally or regenerate slowly. Combined with future climate change, large patches of high severity fire may not regenerate to forest stands for decades to centuries or may shift toward novel ecosystems such as herbaceous and/or shrub- and grass- dominated communities.

Spikes in regeneration of aspen often correspond to years where high-severity fire was common across the greater landscape.

The authors found high variation of ponderosa pine regeneration and seedling survival after high severity fire. Seedling density in planted plots was generally higher than in unplanted plots, but still only half of the planted plots met restoration targets. Seedling density did, however, increase as time since fire increased.

Fire severity has also increased by four times that of previous large fires, resulting in high tree mortality and low regeneration in burn scars.

A previous study by Savage et al. (1996) found that moisture conditions during the year of germination highly influence ponderosa pine regeneration. This article builds on this prior research to find that sites burned at high severity fire may have reduced microclimatic water availability and extreme temperature conditions of the soil thereby limiting seedling regeneration and establishment.

The authors found that in areas burned at high severity understory plant cover was greater than in low-severity burned areas, likely due to the increases in resources made available after the death of mature, overstory trees. Areas that had been treated prior to the wildfire had significantly higher ponderosa pine regeneration. The difference between regeneration in treated versus untreated areas was larger for areas burned at high severity. The authors suggest this is due to the greater heterogeneity of patch sizes of high severity fire that were created due to the treatments, allowing for a shorter distance to seed source to facilitate regeneration.

The authors also found that after severe fires, over half of the sites lacked any ponderosa pine regeneration and was more likely to be dominated by sprouting species, although one site did have hyperdense pine regeneration. The authors suggest that these sites may go decades as shrublands or grasslands, and it remains to be seen if they return to a forested state.

The authors found that large, mixed-severity fires can result in greater heterogeneity of spatial patterns of fire. High-severity patch size varied considerably across both fires in the study. Regeneration also varied considerably within high-severity patches with most seedlings establishing and surviving after 5-10 years post-fire.

Despite subsequent management and other disturbance, including fire, on these study sites, the authors found that the spatial pattern of fire severity was still significantly tied to ponderosa pine regeneration patterns and still impacted the sites decades after the fire. Regenerating seedling density of ponderosa pine decreased with increasing distance to seed source in the high severity patches of fire. Though long-distance dispersal did occur, the rate of recovery was slower with increasing distance to seed source in the larger high-severity patches.

In high severity patches, cover of woody vegetation that regenerates via seeds were more abundant at shorter distances to unburned edges, which acted as refuge seed sources. Pre-fire vegetation composition and structure influenced the post-fire distribution of sprouting species in high-severity burns.

Regeneration success was not tied to fire severity, but favored fire-susceptible species, typically resprouting species.

The authors found that tree regeneration was abundant after, and even enhanced by, high severity fire.

Chihuahua pine is one of the few pine species that can resprout from its base after a disturbance. In the Rodeo-Chediski fire, Chihuahua pine resprouted post-fire, but the ability to resprout was negatively influenced by increasing fire intensity. Smaller trees had greater mortality due to fire, however, of the survivors at any age class, these younger trees were more likely to resprout from their base.

Despite issues with pseudoreplication and the limited sample size, the authors found that post-fire conditions moved toward range of natural variation conditions after intense burning. Small trees and fire-susceptible understory trees were preferentially killed by fire and forest floor woody debris was within desired conditions. The sites had adequate regeneration of seedlings with no evidence of any landscape conversion to a non-forest vegetation type.

The author found that the stand of ponderosa pine they studied was fairly heterogeneous and did not regenerate in large, even-aged groups following large patches of mortality. They hypothesize that patches of additional fuel surrounding single or small groups of trees likely led to smaller patches of mortality during low-severity surface fires, which would create openings and seedbeds for new seedlings.