High-severity Forest Fires Research Articles

Post-fire regeneration of oak-pine forest across a chronosequence in western Mexico: key species for forest restoration

Background: High-severity fires are serious anthropogenic threats to forests, as they can cause forest degradation on unrecoverable scales. Therefore, understanding the patterns and drivers of post-fire regeneration is essential to designing restoration proposals.
 Hypotheses: After a high-severity fire, we expected greater species richness and abundance of individuals in flat sites than in hillside sites since seeds, nutrients, and organic matter accumulate in flat landforms. Compared to some Pinus species, Quercus species are more drought-tolerant after a forest fire and, therefore, they are expected to dominate post-fire chronosequences.
 Study site: The study was conducted in the “La Primavera” Flora and Fauna Protection Area.
 Methods: We sampled vegetation and microenvironmental variables from 2021 to 2022 at 18 sites located on flat and hillside areas, at 3, 9, and ≥ 20 years since the last high-severity forest fires (TSF).
 Results: The richness of woody and herbaceous species was higher at 3 TSF and 9 TSF. The topographic condition did not significantly drive the richness and abundance of woody species, but richness and abundance of herbaceous species were significantly greater in flat sites. The oak tree Quercus resinosa Liebm. was the dominant species throughout the chronosequence.
 Conclusions: Quercus resinosa represents a foundational species for recovering forest structure and composition. Flat sites may act as regeneration nuclei, but hillside sites require greater restoration efforts.

Simulation of Soil Organic Carbon Dynamics in Postfire Boreal Forests of China by Incorporating High-Resolution Remote Sensing Data and Field Measurement

Soil organic carbon (SOC) is an important component of the ecosystem carbon pool, and fire is one of the important disturbances in forest ecosystems. With global warming, there has been a gradual increase in boreal forest fires, which has a nonnegligible impact on the SOC dynamics in forests. The CENTURY model was employed in our study to simulate the changes in SOC stocks in boreal forests of the Great Xing’an Mountains, China under different fire severity conditions. Fire severity was represented by the metric of difference normalized burn ratio (dNBR) derived from 30-m Landsat-8 imageries. Changes in forest SOC stocks following fire disturbance were predicted under four future Representative Concentration Pathway (RCP) scenarios (RCP2.6, RCP4.5, RCP6.0, and RCP8.5). We found that the CENTURY model had good results in simulating the SOC stocks in the postfire of China’s boreal forests. Forest SOC dynamics responded differently to fire severities and the larger SOC loss was associated with increasing fire severity. Importantly, a feedback mechanism was found between climate change and SOC stocks, which reduces SOC stocks with increasing temperatures. High-severity forest fires tended to cause serious damage to the SOC pool and delay forest SOC recovery time; after such events, forest SOC stocks cannot be fully recovered to the prefire levels (6.74% loss). In addition, higher CO2 emissions and warmer temperatures significantly affected the recovery of SOC stocks after fire disturbance, resulting in larger SOC losses. Overall, we projected losses of 10.14%, 12.06%, 12.41%, and 15.70% of SOC stocks after high-severity fires in four RCP scenarios, respectively. Our findings emphasize the importance of fire disturbance and climate change on future dynamics of SOC stocks in China’s boreal forests, providing a scientific basis for future boreal forest management and fire management.

Dynamics of carbon stocks of different pools in Huzhong National Nature Reserve, Northeast China under the disturbance of various severity fires.

In this study, the FireBGCv2 model was used to simulate the dynamics of forest carbon pools of Huzhong Nature Reserve within the next 100 years under various forest fire severity scena-rios. The aim of this study was to explore the responses of different forest carbon pools to fire disturbance, and to provide scientific basis for forest fuel management. The results showed that forest fire significantly reduced forest carbon storage, with the greatest reduction under the scenario of high-severity forest fire. Fire disturbance affected carbon storage in different pools, and relocated carbon among those pools. Forest fire disturbance reduced carbon storage of living trees and duff, increased that of coarse woody debris in the early and middle stages of simulation, and decreased that in late stage. The carbon storage of shrub and herb strata increased significantly in the late simulation period. The higher the fire severity, the lower the carbon storage of living tree and shrub-herb carbon pools, with snag and coarse woody debris showing the opposite trend. The impact of forest fire disturbance on the total carbon pool distribution was as follows: forest fire increased the proportion of shrub and herb strata, snag, coarse woody debris and soil carbon pool, and reduced the proportion of living tree and duff. The higher severity forest fire was, the lower the proportion of carbon pool of shrub-herb, and the higher the proportion of carbon pool of coarse wood debris. The severity of forest fire had less impact on the proportion of other carbon pools. In addition, our results demonstrated periodic change of litter carbon that reached a high value within 20 years and then dropped to a low value within 10 years. Our results could provide sound basis for determining the forest fuel treatment interval. We suggested performing prescribed burning every 20 years in the Great Xing'an Mountains area to protect forest resources.

Limits to Ponderosa Pine Regeneration following Large High-Severity Forest Fires in the United States Southwest

High-severity fires in dry conifer forests of the United States Southwest have created large (>1000 ha) treeless areas that are unprecedented in the regional historical record. These fires have reset extensive portions of Southwestern ponderosa pine (Pinus ponderosa Lawson & C. Lawson var. scopulorum Engelm.) forest landscapes. At least two recovery options following high-severity fire are emerging. One option is for post-fire successional pathways to move toward a return to the pre-fire forest type. Alternatively, an area may transition to persistent non-forested ecosystems. We studied regeneration patterns of ponderosa pine following eight fires in Arizona and New Mexico, USA, that burned in dry conifer forests dominated by ponderosa pine during a recent 18-year regional drought period, 1996 to 2013. Our a priori hypotheses were: 1) the most xeric areas within these severely burned dry conifer forests are least likely to regenerate to the pre-fire forest type due to persistent post-fire moisture stress; and 2) areas farther away from conifer seed sources have a lower likelihood of regeneration, even if these areas are climatically favorable for post-fire ponderosa pine establishment. We evaluated our hypotheses using empirical data and generalized linear mixed-effects models. We found that low-elevation, xeric sites are more limiting to conifer regeneration than higher-elevation mesic sites. Areas >150 m from a seed source are much less likely to have ponderosa pine regeneration. Spatial interpolations of modeled post-fire regeneration of ponderosa pine across the study landscapes indicate expansive areas with low likelihood of pine regeneration following high-severity fire. We discuss multiple post-fire successional pathways following high-severity fire, including potentially stable transitions to non-forest vegetation types that may represent long-term type conversions. These findings regarding landscape changes in Southwest forests in response to fires and post-fire regeneration patterns during early-stage climate warming contribute to the development of better-informed ecosystem management strategies for forest adaptation or mitigation under projected hotter droughts in this region.

Response of Lizards to High-Severity Wildfires in a Southern United States Mixed Pine/Hardwood Forest

High-severity forest fires are increasing in large areas of the southern and western United States as the climate becomes warmer and drier. Natural resource managers need a better understanding of the short- and long-term effects of wildfires on lizard populations, but there is a paucity of studies focused on lizard-wildfire relationships. We used a before-after, control-impact (BACI) sample design to assess the response of three lizard species—Six-lined Racerunner (Aspidoscelis sexlineata), Prairie Lizard (Sceloporus consobrinus), and Little Brown Skink (Scincella lateralis)—to high-severity wildfires that occurred in the Lost Pines Ecoregion, Texas, USA. Specifically, we analyzed monitoring data collected across 17 trapping sessions from spring 2008 to spring 2013 using stratified N-mixture models to estimate trends in lizard abundances, while accounting for environmental parameters that might influence lizard detectability. We found no evidence of a fire-induced change in abundance for any of the lizar...

Short-term changes in summer and winter resident bird communities following a high severity wildfire in a southern USA mixed pine/hardwood forest

High severity forest fires are increasing in large areas of the southern and western United States as the climate becomes warmer and drier. Given their strong roles in ecosystem dynamics, documenting the response of bird communities to wildfires is important for improving our understanding and management of post-wildfire ecosystems. However, because wildfires are unplanned events, relatively few studies have been conducted to assess local-scale impacts on forest bird communities. In this study, we had the opportunity to use a before-after, control-impact (BACI) approach to assess the response of resident birds to high severity wildfires that occurred in the Lost Pines ecoregion of Texas in September and October 2011. We replicated a previous study using point count surveys to assess summer and winter bird community changes ca. 1year after the wildfires. We found that total number of detected individuals did not change following the wildfires, but winter bird species richness increased in burned habitat. Changes were apparent at the foraging guild-level for the winter bird community, with an increase in aerial insectivores and decrease in bark insectivores. Summer and winter bird community composition changes were apparent at the species-level and generally agreed with species-specific habitat preferences. For example, species such as eastern bluebirds and chipping sparrows that prefer open woodlands were positively associated with burned habitat. Our results provide quantitative evidence that high severity forest fires increased habitat suitability for many resident bird species. At the landscape-scale, fire-induced increases in habitat heterogeneity could result in higher bird diversity in the Lost Pines ecoregion. We expect bird community composition will be dynamic in the Lost Pines ecoregion over the next few decades as the burned habitat continues to change through successional processes and post-fire management actions.

Occupancy of California Spotted Owl sites following a large fire in the Sierra Nevada, California

High-severity forest fire often is presumed to adversely affect the occupancy of territories by California Spotted Owls (Strix occidentalis occidentalis) because these owls are associated with mature and old-growth forests. We used single-season, multi-state occupancy statistics to estimate site occupancy probability for Spotted Owls at 45 historically occupied sites during the breeding season immediately following the 2013 Rim Fire, which was one of the largest forest fires on record in California. We quantified how occupancy probability was influenced by the amount of high-severity fire occurring in mature forested habitat within Protected Activity Centers (PACs). The model-averaged estimate of site-occupancy probability for at least a single owl was 0.922 (±SE = 0.073), which was higher than other published occupancy probability estimates for this subspecies in either burned or long-unburned sites in the Sierra Nevada. Mean site-occupancy probability for pairs was 0.866 (±0.093), and most sites (33) were occupied by pairs. The amount of high-severity fire in the PAC did not affect pair occupancy. Occupancy probability by at least a single bird was negatively correlated with the amount of high severity fire in the PAC but remained >0.89 in 100% high-severity burned PACs. These data add to observations that California Spotted Owls continue to use post-fire landscapes, even when the fires were large and where large areas burned at high severity, suggesting that owls are not generally negatively impacted by high-severity fire. Based on this and other studies of Spotted Owls, fire, and logging, we suggest land managers consider burned forest within and surrounding PACs as potentially suitable California Spotted Owl foraging habitat when planning and implementing management activities, and we recommend against logging burned forest within at least 1.5 km of nests or roosts for the conservation and recovery of this declining subspecies.

Wildfire and Postfire Restoration Action Effects on Microclimate and Seedling Pine Tree Survivorship

AbstractThrough modification of structural characteristics, ecological processes such as fire can affect microhabitat parameters, which in turn can influence community composition dynamics. The prevalence of high-severity forest fires is increasing in the southern and western United States, creating the necessity to better understand effects of high-severity fire, and subsequent postfire management actions, on forest ecosystems. In this study we used a recent high-severity wildfire in the Lost Pines ecoregion of Texas to assess effects of the wildfire and postfire clearcutting on six microclimate parameters: air temperature, absolute humidity, mean wind speed, maximum wind speed, soil temperature, and soil moisture. We also assessed differences between burned areas and burned and subsequently clearcut areas for short-term survivorship of loblolly pine Pinus taeda seedling trees. We found that during the summer months approximately 2 y after the wildfire, mean and maximum wind speed differed between unburned and burned areas, as well as burned and burned and subsequently clearcut areas. Our results indicated air temperature, absolute humidity, soil temperature, and soil moisture did not differ between unburned and burned areas, or burned and burned and subsequently clearcut areas, during the study period. We found that short-term survivorship of loblolly pine seedling trees was influenced primarily by soil type, but was also lower in clearcut habitat compared with habitat containing dead standing trees. Ultimately, however, the outcome of the reforestation initiative will likely depend primarily on whether or not the trees can survive drought conditions in the future, and this study indicates there is flexibility in postfire management options prior to reseeding. Further, concerns about negative wildfire effects on microclimate parameters important to the endangered Houston toad Bufo (Anaxyrus) houstonensis were not supported in this study.

Adapting Habitat Equivalency Analysis (HEA) to assess environmental loss and compensatory restoration following severe forest fires

Over the past few decades, there has been a substantial increase in the number of large, high-severity forest fires in the western United States. The habitat loss caused by these fires can have broad ecological and economic consequences. Federal courts have acknowledged the legitimacy of damages claims based on state laws and regulations for habitat and ecological service losses resulting from high-severity fires, with some claims placing higher economic value on ecosystem services than traditional forest products (e.g., timber). This has created a need to adapt or develop new tools for quantifying the value of lost ecosystem services in the absence of well-defined regulatory or other generally accepted guidance.Habitat Equivalency Analysis (HEA), borrowed from a common Natural Resource Damage Assessment (NRDA) approach for quantifying environmental harm and restoration, is a tool that has been used to quantify forest fire habitat damages. HEA involves determining a baseline for habitat services that would have occurred in the absence of the fire, and determining the lost services from the time of the incident until ecosystem functions have been recovered to baseline conditions. Depending on the habitat being evaluated, recovery may take a century or more for old growth forests. This paper reviews and identifies critical issues that may affect the estimate of lost services following high- severity fires, including potential approaches for dealing with uncertainty. Some items discussed can be addressed in the short-term while others represent research and tool development opportunities.

Starting points for small mammal population recovery after wildfire: recolonisation or residual populations?

Wildfire is a major driver of spatio‐temporal variation in terrestrial ecosystems. Large wildfires are predicted to occur more frequently due to climate change. The mechanisms by which post‐fire recovery proceeds are influenced by the abundance of survivors, and their distribution in relation to habitat variability and refugia. Thus, characterising early post‐fire demographic processes is critical to understanding the demographic and community‐level responses of ecosystems to fire. The Black Saturday fires of February 2009 burnt an area of approximately 3500 km2 in Victoria, Australia. We quantified the effects of this high severity forest fire on the habitat, abundance, sex ratio and body mass of two small mammal species, the agile antechinus Antechinus agilis and bush rat Rattus fuscipes. We developed a hypothetical framework to distinguish in situ survival and rapid recolonisation as the processes underlying short‐term post‐fire distributions. These hypotheses were based on expected patterns of abundance over increasing distances from unburnt sources, and the estimated recolonisation capabilities of each species and sex. The agile antechinus and bush rat were present in burnt sites at 30% and 12% of the density observed in unburnt sites. In situ survival, and not recolonisation, was the most plausible explanation for our findings. Abundance and body mass data indicated a greater effect of fire on the bush rat than the agile antechinus. The bush rat showed a shift in topographic association, whereby drainage lines acted as post‐fire refugia. Our findings suggest these species do not depend on recolonisation for recovery, and that the bush rat will follow a nucleated recovery, expanding from topographic refugia. Thus, connectivity‐reducing management activities, such as salvage logging and firebreak and road construction, may not affect the early stages of population recovery in remaining stands of burnt forest. Rather, ongoing recovery is likely to be limited by demographic rates and resource availability.

Quantitative Evidence for Increasing Forest Fire Severity in the Sierra Nevada and Southern Cascade Mountains, California and Nevada, USA

Recent research has concluded that forest wildfires in the western United States are becoming larger and more frequent. A more significant question may be whether the ecosystem impacts of wildfire are also increasing. We show that a large area (approximately 120000 km2) of California and western Nevada experienced a notable increase in the extent of forest stand-replacing (“high severity”) fire between 1984 and 2006. High severity forest fire is closely linked to forest fragmentation, wildlife habitat availability, erosion rates and sedimentation, post-fire seedling recruitment, carbon sequestration, and various other ecosystem properties and processes. Mean and maximum fire size, and the area burned annually have also all risen substantially since the beginning of the 1980s, and are now at or above values from the decades preceding the 1940s, when fire suppression became national policy. These trends are occurring in concert with a regional rise in temperature and a long-term increase in annual precipitation. A close examination of the climate–fire relationship and other evidence suggests that forest fuels are no longer limiting fire occurrence and behavior across much of the study region. We conclude that current trends in forest fire severity necessitate a re-examination of the implications of all-out fire suppression and its ecological impacts.

Spatial distribution and properties of ash and thermally altered soils after high-severity forest fire, southern California

After a century of fire suppression, dense forests in California have fueled high-severity fires. We surveyed mixed conifer forest with 995–1178 trees ha−1 (stems > 10 cm diameter at breast height), and nearby pine–oak woodland having 175–230 trees ha−1, 51 days after a severe burn, to contrast the spatial extent and properties of thermally altered soil at sites with different tree densities. Water-repellent soils were more extensive in forest than woodland. Deposits of white ash, composed largely of calicite, covered at most ~25% of the land surface, in places where large fuel items (e.g. logs, branches, exfoliated oak bark) had thoroughly combusted. At least 1690 kg ha−1 of CaCO3 in ash was deposited over the forest, and at least 700 kg ha−1 was added to the woodland. Combustion of logs and large branches also reddened the underlying yellow-brown soil as deep as 60 mm (average 8 mm), and over ~1–12% of the land surface. The reddened soils have magnetic susceptibilities that are three to seven times greater than surrounding unreddened soils within the burn, indicating thermal production of maghemite. Such fire-altered conditions persist over spatial and temporal scales that influence soil genesis in Mediterranean-type climate regions.