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The 2002 Hayman Fire burned with mixed-severity across a 400-ha dry conifer study site in Colorado, USA, where overstory tree and surface cover attributes had been recently measured on 20 0.1-ha permanent plots. We remeasured these plots repeatedly during the first post-fire decade to examine how the attributes changed through time and whether changes were influenced by fire severity. We found that most attributes were temporally dynamic and that fire severity shaped their dynamics. For example, low-severity plots experienced a modest reduction in live overstory density due to both immediate and delayed tree mortality, and no change in live overstory basal area through time; in contrast, high-severity plots experienced an immediate and total loss of live overstory density and basal area. Large snag density in low-severity plots did not vary temporally because snag recruitment balanced snag loss; however, in high-severity plots large snag density increased markedly immediately post-fire and then declined by about half by post-fire year ten as snags fell. Mineral soil cover increased modestly immediately post-fire in low-severity plots and substantially immediately post-fire in high-severity plots, but changed little in ensuing years for either severity class. By incorporating pre-fire and repeatedly-measured post-fire data for a range of severities, our study uniquely contributes to the current understanding of wildfire effects in dry conifer forests and should be of interest to managers, researchers, and others. [ABSTRACT FROM AUTHOR]

• Limited studies have explored effects of forest management and fire disturbance on pollinator communities. • Bee species richness and diversity were highest in high-severity wildfire sites; abundances were unaffected by disturbance type. • Habitat structure varied by disturbance type, with differences in tree density, floral resources, and woody debris. • Bee community composition differed between habitat types. • We recommend maintaining a mosaic of disturbances on the landscape to promote bee habitat, maximizing bee biodiversity. In fire-adapted ponderosa pine forests of western North America, fire suppression policies during much of the 19th century gradually resulted in high stem densities undesirable for fire risk management. To restore desirable forest structures, regional ecosystem management efforts often focus on reducing stand densities and re-introducing fire disturbances. However, it remains unclear whether these practices benefit insect species important for ecosystem function, including native bees. Bee community assemblages were sampled across the growing season in 39 ponderosa pine stands for two years in central Colorado to model effects of fire and thinning disturbances on bee populations. Four key findings emerged: (1) overall native bee diversity consisted of 5 families (Andrenidae, Apidae, Colletidae, Halictidae, and Megachilidae), 30 genera, and at least 70 unique bee species. Predominant genera were bumblebees (Bombus spp.), mason bees (Osmia spp.), and digger bees (Anthophora spp.), accounting for 50%, 9%, and 5 % of all captures, respectively. (2) Average bee abundance did not vary among burned, thinned, or non-treated control stands, though bee species richness and diversity were highest in stands affected by high severity wildfire. (3) Bee community composition differed among disturbance types, and there was turnover in the ratios of Bombus : Osmia species between control and burned stands. (4) Representation of bee nesting strategies at sample sites also differed due to fire and thinning disturbances, but these effects were moderated by seasonality. We link variation in forest structure to bee assemblages using linear models and show that presence of coarse woody debris has positive effects on overall forest bee abundance, richness, and diversity. Ponderosa pine forests in central Colorado provide habitat for a diverse assemblage of native bee species, and thinning operations are not associated with reductions in bee diversity, and fire disturbances were associated with enhanced bee foraging and nesting habitats. Bee community composition and associated life histories vary across disturbance types and unique bee assemblages are associated with different disturbance histories. Accordingly, maintaining a mosaic of thinning treatments and promoting wildland fire use that results in a gradient of burn severities may increase floral resources and nesting opportunities and can help to maximize overall bee biodiversity at a landscape scale. [ABSTRACT FROM AUTHOR]

Abstract: Severe wildfires across the western US have lead to concerns about heavy surface fuel loading and the potential for high-intensity reburning. Ponderosa pine (Pinus ponderosa) forests, often overly dense from a century of fire suppression, are increasingly susceptible to large and severe wildfires especially given warmer and drier climate projections for the future. However, the majority of research on fuel dynamics after wildfires has focused on high-severity burned areas in more productive forest types. We sampled fuel loadings in 2009 and 2010 across a range of tree mortality on two high-severity wildfires that occurred in 2000: the Pumpkin Fire in Arizona, and the Jasper Fire in South Dakota. We established 60 plots per fire, 10 in each of five post-fire mortality classes: 0–20%, 21–40%, 41–60%, 61–80%, and 81–100% mortality, based on percentage of trees killed, plus unburned control areas. We measured height, diameter, status (alive or dead) and crown base height of each tree, plus fuel loading by size class, litter and duff depth, and herbaceous biomass. Ten years after wildfire, low mortality (0–40%) plots resembled unburned plots in almost every fuels attribute. Basal area in low-mortality plots exceeded reconstructed historical ranges and fire hazard reduction targets by up to 130%. However, coarse woody debris (CWD; woody material >7.62cm) loadings fell below a recommended “optimum” range and herbaceous fuels were sparse. Mid-mortality (41–80%) plots were characterized by more open stands and increased surface fuel loadings, basal area was close to target ranges and CWD loadings were within the recommended range. High mortality (81–100%) plots had few trees but CWD loadings exceeded recommended levels by up to 28%, and herbaceous fuels were adequate to carry a surface fire. These findings suggest that post-fire management should be targeted to the level of mortality. Low mortality and unburned areas should be targeted for reducing stand densities and promoting understory growth, to minimize crown fire hazard and increase site potential. Burned areas with >80% tree mortality have the lowest crown fire hazard, but may benefit from fuel reduction efforts such as low intensity prescribed burning to reduce both fine fuels and some of the CWD. Stand structures and surface fuel loads in mid-mortality plots most resembled historical targets and met numerous restoration objectives for ponderosa pine-dominated forests, especially given predicted climate changes. These areas can be maintained through low-intensity prescribed burning to prevent them from becoming overly dense and thus enhance their longer-term resiliency to future disturbances. [Copyright &y& Elsevier]

• Recently-burned area in southwestern US forests is increasing. • Landscape context, values, and future trajectories of change can inform management. • Postfire forest patches can be managed for resilience to future fires. • Novel reforestation practices may help adapt to future climate and fire in some areas. The increasing incidence of wildfires across the southwestern United States (US) is altering the contemporary forest management template within historically frequent-fire conifer forests. An increasing fraction of southwestern conifer forests have recently burned, and many of these burned landscapes contain complex mosaics of surviving forest and severely burned patches without surviving conifer trees. These heterogeneous burned landscapes present unique social and ecological challenges. Severely burned patches can present numerous barriers to successful conifer regeneration, and often contain heavy downed fuels which have cascading effects on future fire behavior and conifer regeneration. Conversely, surviving forest patches are increasingly recognized for their value in postfire reforestation but often are overlooked from a management perspective. Here we present a decision-making framework for landscape-scale management of complex postfire landscapes that allows for adaptation to a warming climate and future fire. We focus specifically on historically frequent-fire forests of the southwestern US but make connections to other forest types and other regions. Our framework depends on a spatially-explicit assessment of the mosaic of conifer forest and severely burned patches in the postfire landscape, evaluates likely vegetation trajectories, and identifies critical decision points to direct vegetation change via manipulations of fuels and live vegetation. This framework includes detailed considerations for postfire fuels management (e.g., edge hardening within live forest patches and repeat burning) and for reforestation (e.g., balancing tradeoffs between intensive and extensive planting strategies, establishing patches of seed trees, spatial planning to optimize reforestation success, and improving nursery capacity). In a future of increasing fire activity in forests where repeated low- to moderate-severity fire is essential to ecosystem resilience, the decision-making framework developed here can easily be integrated with existing postfire management strategies to optimize allocation of limited resources and more actively manage burned landscapes. [ABSTRACT FROM AUTHOR]

In temperate coniferous forests, biotic disturbances such as bark beetle outbreaks can result in widespread tree mortality. The characteristics of individual trees and stands, such as tree diameter and stand density, often influence the probability of tree mortality during a bark beetle outbreak. However, it is unclear if these relationships are mediated by climate. To test this, we assembled tree mortality data for over 3800 ponderosa pine trees from Forest Inventory and Analysis (FIA) plots measured before and after a mountain pine beetle outbreak in the Black Hills, South Dakota, USA. Logistic models were used to determine which tree, stand, and climate characteristics were associated with the probability of mortality. Interactions were tested between significant climate variables and significant tree/stand variables. Our analysis revealed that mortality rates were lower in trees with higher live crown ratios. Mortality rates rose in response to increasing tree diameter, stand basal area (both from ponderosa pine and non-ponderosa pine), and elevation. Below 1500 m, the mortality rate was ~1%, while above 1700 m, the rate increased to ~30%. However, the association between elevation and mortality risk was buffered by precipitation, such that relatively moist high-elevation stands experienced less mortality than relatively dry high-elevation stands. Tree diameter, crown ratio, and stand density affected tree mortality independent of precipitation. This study demonstrates that while stand characteristics affect tree susceptibility to bark beetles, these relationships may be mediated by climate. Thus, both site and stand level characteristics should be considered when implementing management treatments to reduce bark beetle susceptibility. [ABSTRACT FROM AUTHOR]

• We conducted a review to synthesize factors driving post-fire ponderosa pine regeneration. • Three of the 21 synthesized factors emerged as strong drivers of regeneration. • Areas closer to seed sources commonly have more regeneration than areas further away. • Higher elevations generally harbor more regeneration than lower elevations. • Low climatic stress areas tend to have higher regeneration than high stress areas. Ponderosa pine (Pinus ponderosa Lawson & C. Lawson) is a prominent tree species in forests of the western United States. Wildfire activity in ponderosa pine dominated or co-dominated forests has increased dramatically in recent decades, with these recent wildfires often burning in an uncharacteristic manner due to past land management activities and changing climate. The structure and function of vegetative communities that develop following recent wildfires are highly contingent on ponderosa pine regeneration, making it important that the factors influencing this regeneration be thoroughly understood. In this evidence-based review, we qualitatively synthesized publications that examined how the post-fire abundance of ponderosa pine regeneration was related to such factors. We identified 33 relevant publications, from which we synthesized relationships for 21 factors. Numerous publications indicated that distance to seed source (e.g., distance to nearest live overstory tree or group of trees) was a factor that clearly affected post-fire ponderosa pine regeneration abundance; with few exceptions, these publications demonstrated that as distance to seed source increased, the amount of regeneration decreased. Climatic stress (e.g., Palmer Drought Severity Index, actual evapotranspiration, climatic moisture deficit) and elevation also emerged as well-studied factors with a clear relationship to post-fire regeneration abundance. Specifically, areas with lower climatic stress and/or at higher elevations generally harbored more regeneration than areas with higher climatic stress and/or at lower elevations; together, these factors highlight that cooler, moister environments enhance regeneration. The other 18 factors were either well studied but did not have consistent relationships with regeneration abundance, or were not well studied, highlighting research areas that could benefit from further attention. Overall, the strong influence of distance to seed source, climatic stress, and elevation on post-fire ponderosa pine regeneration abundance has important implications for post-fire vegetative recovery and management, particularly in light of recent and predicted changes in wildfire activity and climate. [ABSTRACT FROM AUTHOR]