Snag Density Research Articles

Model Predictions of Postwildfire Woody Fuel Succession and Fire Behavior Are Sensitive to Fuel Dynamics Parameters

Abstract Computer models used to predict forest and fuels dynamics and wildfire behavior inform decisionmaking in contexts such as postdisturbance management. It is imperative to understand possible uncertainty in model predictions. We evaluated sensitivity of the Fire and Fuels Extension to the Forest Vegetation Simulator predictions to parameters that determine dynamics of standing dead trees (snags) and surface woody fuels. Predicted peak coarse and fine woody fuels were not sensitive to the decomposition rate of snags but were sensitive to decomposition rate of surface fuels regardless of initial snag density. Predictions of coarse woody fuel were sensitive to the snag fall rate when there was a higher initial density of snags. Fire behavior predictions were most sensitive to whether stylized fuel models or modeled fuels were used in calculations. When modeled fuels were used, fire behavior predictions were sensitive to the decomposition rate of surface fuels. Although this analysis does not inform the accuracy of model predictions, it does show where there is potential uncertainty in predictions of woody fuels succession and associated fire behavior. It is likely that any model that predicts postdisturbance fuel succession will also be sensitive to parameters that control snag dynamics and fuel decomposition.

Black-Backed Woodpecker Nest Density in the Sierra Nevada, California

In the western U.S., the black-backed woodpecker has been found to be associated with dense montane conifer forests with high snag densities, typically resulting from moderate- to high-severity wildland fires. However, black-backed woodpeckers are occasionally also detected nesting in unburned forests, raising questions about the type of habitat in which they nest and the potential abundance of such habitat. We conducted intensive black-backed woodpecker nest density surveys in large plots within the middle/upper-montane conifer forests of the Sierra Nevada, California, within general (undisturbed) forests, snag forest habitat from moderate/high-severity wildland fire, and unburned snag forest habitat from drought and native bark beetles. We found black-backed woodpeckers nesting only in the two snag forest conditions, mostly in burned snag forest, and their preferential selection of burned snag forest was statistically significant. No nest was found in general forests. Our spatial analysis indicates that snag forest is rare in the forests of the Sierra Nevada due to fire suppression and logging, raising concerns regarding small population size, which we estimate to be only 461 to 772 pairs in the Sierra Nevada.

Fuel Dynamics Following Wildfire in US Northern Rockies Forests

Accumulation of dead woody material is a critical management concern following wildfires, especially given the possibility of subsequent wildfires. Forest structure and fuel accumulation are largely driven by site climatic conditions, so variability in site conditions is important to consider in management beyond the one-size fits all model for post-fire fuel dynamics. Moreover, dead woody material provides important ecological functions for forested ecosystems. Understanding when surface fuels biomass is highest following wildfires and how these dynamics change after repeated fires affords land management agencies opportunities to adjust fuel reduction strategies without removing large quantities of dead trees that are important in these post-fire landscapes for a variety of ecosystem services, including wildlife, water and nutrient retention, and soil stabilization. Here, we examined how surface fuels and standing dead trees change over time, by burn severity, site climate, and with repeated fires at seven different years since- fire (1-24 years) across 182 sites from ten wildfires in central Idaho. Downed woody fuel loads were higher on moister and cooler sites. Large-diameter woody fuels saw significant increases after about 14 years post-fire while smaller woody fuels had the highest loads at 20 years post-fire. Surface fuel loads varied by burn severity and years since fires, with the highest loadings at longer years since fire and sites burned in stand replacing fire. Litter and duff had not sufficiently accumulated to compensate for continued decomposition, resulting in lower forest floor biomass through 24 years post fire. Density of snags of all sizes generally declined after 7-9 years, but large diameter snags were still standing 24 years post fire. Repeated fires resulted in >40% reduction in both surface fuels and standing trees compared to once-burned areas at the same years since fire. Burned landscapes can serve a great ecological benefit by providing an infusion of both standing and downed dead woody debris. Additionally, though some sites burned in stand replacing fires exceed recommended surface fuel loadings, these ecological considerations should be weighed against concerns about reburning potential and fire fighter hazards.

Effects of post-fire management on dead woody fuel dynamics and stand structure in a severely burned mixed-conifer forest, in northeastern Washington State, USA

The increasing amount of high-severity wildfire in historical low and mixed-severity fire regimes in western US forests has created a need to better understand the ecological effects of different post fire management approaches. For three different salvage prescriptions, we quantified change in stand structural metrics (snag densities and snag basal areas), dead woody fuel loadings, tree regeneration survival, and percentage change in vegetation cover before and after post-fire logging 1 year after the 2015 Stickpin Wildfire on the Colville National Forest in northeastern Washington State, USA. In a generalized randomized block design three salvage logging prescriptions were randomly assigned within each block: no treatment control (C); standard salvage retention (SSR; thin to 3.4 m2/ha basal area); and mimic green tree thinning (GTR; thin to 10.3 m2/ha basal area). SSR reduced average snag basal area 73–83% to 4.1–8.8 m2/ha (68–674 trees ha−1). GTR reduced average snag (standing dead trees) basal area 41–71% to 6.5–15.9 m2/ha (90–794 trees ha−1). There were mixed results for the change in dead woody fuel loadings depending on fuel size class. In general, fine (FWD) and coarse woody (CWD) debris tended to increase immediately post-treatment in logged areas relative to the controls but did not exceed management loading threshold for providing acceptable risk of fire hazard. Treated stands had a significant increase in FWD relative to controls, including the individual 1-, 10-, and 100-hr fuel size classes. The treatment effect differed by experimental block. The 1000-hr sound class did not have a significant treatment effect. Changes in surface fuel loading were inconsequential to modeled wildfire behavior metrics (rate-of-spread, flame lengths). The Fire and Fuels Extension to Forest Vegetation Simulator (FFE-FVS) modeling projected CWD accumulation in the controls exceeded total accumulation in both treatments. Future fuel loadings may affect reburn severity as our simulated wildfire 20 years after harvesting caused significant mortality (89%) to regenerating forest. Almost all blocks showed a decrease in seedling counts pre and post-logging, including the control plots. This study provides empirical data on the effects of different post-fire management strategies that can inform environmental analyses for future post-fire management decision and address social concerns associated with this often-controversial practice (Roccaforte et al., 2012).

Combining conservation value with conservation filters to guide forest management for avian biodiversity

Maintaining richness and diversity of bird species on forest landscapes has long been a major theme in sustainable forest management. However, effects of management decisions on species diversity are uncertain because of difficulties in accounting for all species simultaneously. Utilizing a diversity contribution approach, we applied an integrated coarse filter-mesofilter conservation strategy to inform avian biodiversity conservation in the western Upper Peninsula of Michigan, USA. Diversity contribution is a measure of relative contribution of a given area to regional species diversity based on species richness and distinctiveness, with region defined according to the study design. At the coarse filter level, we compared and ranked forest types by bird conservation value based on proportional representation of high-contribution sampling plots (sampling plots in the top 25% of diversity contribution) relative to proportional representation in the dataset. At the mesofilter level, we identified how plot-level compositional and structural attributes affected diversity contribution within forest types. We found that forest types less common in the dataset, such as cedar and upland conifer, had the highest bird conservation value, while the most common forest type (northern hardwoods) provided the greatest number of high-contribution plots. Stand-level attributes that increased structural complexity, such as higher densities of large trees, saplings, and snags, or lower basal area, tended to increase the likelihood of being a high-contribution plot within a given forest type. However, the importance and effect of different attributes varied among forest types. Our novel application of the conservation filter strategy provides a way to identify high priority forest types for avian conservation, and create stand-level prescriptions for increasing avian conservation value. Given data on forest inventory and bird community composition, managers can use this application as a planning tool in the face of uncertainty about how management decisions affect larger-scale avian biodiversity.

Fuel dynamics and reburn severity following high-severity fire in a Sierra Nevada, USA, mixed-conifer forest

BackgroundHigh-severity fire in forested landscapes often produces a post-fire condition of high shrub cover and large loads of dead wood. Given the increasing patch size of high-severity fire and the tendency for these areas to reburn at high severity in subsequent wildfires, post-fire management often targets restoration of these areas. However, these areas are challenging to manage, in part due to limited knowledge of post-fire fuel dynamics over space and time and uncertainties in how specific fuel components such as snags and logs influence future fire severity. In this study, we used high-resolution aerial imagery collected nine years after a wildfire to measure snags, logs, and shrub cover within high-severity patches, and to assess how fuel development influenced reburn severity in a subsequent wildfire.ResultsThe abundance of snags, logs, and shrubs following high-severity fire varied with elevation and slope steepness; however, generalized additive models explained only 6 to 21% of their variation over the post-fire landscape. High densities of both snags and logs were associated with high reburn severity in a subsequent fire, while shrub cover had a marginally insignificant (P = 0.0515) effect on subsequent fire severity.ConclusionsOur results demonstrate that high levels of large dead wood, which is often not considered in fire behavior modeling, corresponded with repeated high-severity fire effects. Future research should leverage the increasing availability of high-resolution imagery to improve our understanding of fuel load patterns in space and time and how they may impact landscape resilience to facilitate management planning for post-fire forest landscapes.

Barred Owl Effects on Spotted Owl Resource Selection: A Meta‐Analysis

ABSTRACTWe quantified the effects of barred owls (Strix varia) on fine‐scale (~2 ha), spatially explicit selection of putative foraging habitat by 175 radio‐tagged northern spotted owls (Strix occidentalis caurina) from 1998 to 2012 in western Oregon and northern California, USA. We constructed annual nighttime discrete‐choice resource selection functions (RSFs) for northern spotted owls in 8 study areas. We compared RSFs from pooled data from 4 study areas where barred owls were absent or rare (≤14% of spotted owl territories potentially influenced by barred owls) with RSFs from 4 study areas where barred owls were abundant (≥89% of spotted owl territories potentially influenced by barred owls), and we conducted a meta‐analysis of all 8 study areas. Top‐ranked RSFs for individual study areas indicated that the relative probability a forest patch was selected by northern spotted owls for foraging was most strongly associated with basal area of large coniferous trees (≥66 cm diameter at breast height [dbh]) or quadratic mean diameter (QMD, the diameter of trees of average basal area) of all coniferous trees. The influence of such trees was non‐linear, usually quadratic, in 7 study areas, suggesting that an optimal basal area of large‐diameter trees or QMD may be associated with selection of foraging patches. The relative probability of selection of such trees decreased nonlinearly with increasing distance from nest sites in ≥4 study areas. Basal area of all or specific hardwood tree species was linearly associated with increases in the relative probability of a patch being used for foraging in 7 of 8 study areas. The relative probability of selection was also positively associated with densities of large snags (>50 cm dbh), coarse woody debris, and undergrowth shrubs in most study areas where we estimated those covariates. The relative probability that a patch was selected decreased nonlinearly with increasing distance from streams (7 study areas), increasing elevation (5 study areas), and decreasing slope (5 study areas). Barred owls exerted strong effects on habitat selection by spotted owls, which may have attempted to minimize interference competition via spatial segregation. Spotted owls occupying study areas where barred owls were abundant used foraging patches at greater distances from streams, at greater distances from nest sites, and on steeper and warmer slopes than those occupying areas with few or no barred owls. In addition, northern spotted owls in areas where barred owls were abundant exhibited reduced selection for large‐diameter trees close to nest sites but may have compensated by increasing use of large trees in home‐range locations distant from nest sites. Programs that seek to improve the link between spotted owl demographic performance or occupancy rate and habitat conditions should account for the influences of fine‐scale variation in vegetation composition and structure and physiographic conditions. Forest managers may contribute to spotted owl conservation via silvicultural prescriptions that retain coarse woody debris and large snags, promote undergrowth shrubs, and retain intermediate to high densities of large, old shade‐intolerant early‐seral trees and riparian hardwoods within and beyond core areas surrounding nest sites. © 2019 The Wildlife Society.

Black-backed woodpecker occupancy in burned and beetle-killed forests: Disturbance agent matters

In the western United States, the black-backed woodpecker (Picoides arcticus) is a “snag specialist”, found predominantly in burned montane forests. While fire is a key disturbance agent in this system, recently, unprecedented large tracts of drought-stressed forest in the Sierra Nevada and Southern Cascades of California have succumbed to bark beetle outbreaks. Although this tree mortality could potentially be a boon for snag-dependent species, it is unclear whether the resulting snag forests provide sufficiently high-quality habitat for black-backed woodpeckers and other wildlife that are regionally associated with burned forests. We tested for differences in black-backed woodpecker occupancy between fire- and beetle-killed forests, and whether key environmental relationships driving woodpecker occupancy differed between stands affected by the two disturbance agents. Between 2016 and 2018, we surveyed for black-backed woodpeckers during 4448 surveys at 75 burned and 113 beetle-killed forest stands throughout the black-backed woodpecker’s range in California, detecting at least one black-backed woodpecker on 448 surveys (16.2%) in burned forests and 115 surveys (6.8%) in beetle-killed forests. Controlling for a suite of environmental variables that can affect habitat quality, the odds of black-backed woodpeckers occurring in burned forests were predicted to be 12.6 times higher than in beetle-killed forest. Occupancy declined with time-since-disturbance in fire-killed but not beetle-killed forests, but occupancy increased similarly with snag density resulting from either disturbance agent. Across our broad study region, black-backed woodpeckers were more likely to occur in burned forests at higher latitudes and elevations; these patterns were even stronger in beetle-killed forests, where we found woodpeckers only at the more northerly and higher elevation sites. Our results demonstrate that for this disturbed-habitat specialist, disturbance agent matters; black-backed woodpeckers do not use habitat created by bark beetle outbreaks as readily as habitat created by fire. Given the likely increased magnitude and extent of bark beetle outbreaks in the future, further work is needed to assess the role of beetle-killed forests in longer-term population dynamics of black-backed woodpeckers beyond the first decade after disturbance, and to investigate whether these results can be generalized to other fire-associated wildlife species in the region.

Nest site selection and nest survival of Black-backed Woodpeckers after wildfire

Abstract Recently burned coniferous forests host wildlife communities that respond to variation in burn severity, post-fire habitat structure, and patch configuration. Habitat selection theory predicts that birds inhabiting these variable post-fire landscapes will select nesting locations that confer an adaptive advantage through increased fitness and reproductive success. Understanding the effect of post-fire habitat on avian nesting ecology can provide valuable information to guide restoration and management after wildfire. The Black-backed Woodpecker (Picoides arcticus) is strongly associated with recently burned forests in the western United States, where it is used as an indicator species for the effects of post-fire forest management. Between 2011 and 2018, we located and monitored 118 Black-backed Woodpecker nests in burned forests of northern California. We evaluated the influence of habitat and nest characteristics on nest site selection and daily nest survival. Our results demonstrate a pattern of neutral congruence between habitat selection and fitness. Black-backed Woodpeckers showed strong selection for each of the nest habitat variables that we measured: woodpeckers selected moderately sized trees in areas of high snag density burned at high severity, but also in areas relatively close to low-severity or unburned edges. However, only nest initiation date affected nest survival, with decreased survival in late-season nests. Our results suggest that management actions aimed at maintaining breeding habitat for Black-backed Woodpeckers should prioritize retention and creation of pyrodiverse landscapes that include dense stands of snags (>5 snags per 100 m2) within ~500 m of forest that burned at low severity or remained unburned.

An integration framework for linking avifauna niche and forest landscape models.

Avian cavity nesters (ACN) are viable indicators of forest structure, composition, and diversity. Utilizing these species responses in multi-disciplinary climate-avian-forest modeling can improve climate adaptive management. We propose a framework for integrating and evaluating climate-avian-forest models by linking two ACN niche models with a forest landscape model (FLM), LANDIS-II. The framework facilitates the selection of available ACN models for integration, evaluation of model transferability, and evaluation of successful integration of ACN models with a FLM. We found selecting a model for integration depended on its transferability to the study area (Northern Rockies Ecoregion of Idaho in the United States), which limited the species and model types available for transfer. However, transfer evaluation of the tested ACN models indicated a good fit for the study area. Several niche model variables (canopy cover, snag density, and forest cover type) were not directly informed by the LANDIS-II model, which required secondary modeling (Random Forest) to derive values from the FLM outputs. In instances where the Random Forest models performed with a moderate classification accuracy, the overall effect on niche predictions was negligible. Predictions based on LANDIS-II simulations performed similarly to predictions based on the niche model’s original training input types. This supported the conclusion that the proposed framework is viable for informing avian niche models with FLM simulations. Even models that poorly approximate habitat suitability, due to the inherent constraints of predicting spatial niche use of irruptive species produced informative results by identifying areas of management focus. This is primarily because LANDIS-II estimates spatially explicit variables that were unavailable over large spatial extents from alternative datasets. Thus, without integration, one of the ACN niche models was not applicable to the study area. The framework will be useful for integrating avifauna niche and forest ecosystem models, which can inform management of contemporary and future landscapes under differing management and climate scenarios.

Spanning the habitat gradient: Red-headed woodpecker nest-site selection in three distinct cover types

Understanding species habitat relationships is fundamental to ecology and underpins conservation-based management. Species with broad habitat preferences and wide geographic ranges are capable of fulfilling breeding requirements in different habitat contexts. Habitat selection in these species may vary in a context-specific way, so determining the factors driving habitat selection requires spanning the habitat gradient. Complex landscapes offer a unique opportunity to compare habitat selection across habitat gradients within a single study site. Here, we used a comparative approach to model scale-dependent nest-site selection of the red-headed woodpecker (Melanerpes erythrocephalus) in three distinct cover types at Fort A.P. Hill military installation, Virginia. We found that nest preferences varied among cover types for several patch-scale habitat features. In closed forests, red-headed woodpeckers selected patches with an open canopy characteristic that lacked holly (Ilex opaca) in the understory and contained large pines. In open forests, patches with a high percentage of canopy cover were also avoided. In wetlands, patches with low percent stem cover were preferred. We also found a single variable, medium/large snag density, was highly influential in models for all cover types at the patch scale, indicating the importance of suitable snags for nesting, irrespective of cover type. Models at the tree scale showed similar results for all cover types: red-headed woodpeckers consistently preferred large snags with less bark. Our results demonstrate the value of comparing habitat selection across a habitat gradient. Managers charged with promoting red-headed woodpecker populations would do well to manage for large, partially decayed snags while also considering context-specific habitat needs.

Relationships between Wildfire Burn Severity, Cavity-Nesting Bird Assemblages, and Habitat in an Eastern Ponderosa Pine Forest

Historically, eastern ponderosa pine (Pinus ponderosa) forests were described as sparse patches of old-growth trees maintained by frequent, low-severity fires; however, in recent decades, there have been a number of large mixed-severity wildfires throughout the range of these forests. Wildlife responses to severe fire disturbance in eastern ponderosa pine forests are not well understood. Our study investigates how cavity-nesting bird species in an eastern ponderosa pine forest are impacted by burn severity. The objectives of our study were to: (1) identify the community composition of cavity-nesting birds in a 27 y old burn of mixed severity, (2) assess how habitat variables important to cavity-nesting birds differ in the mixed-severity fire, and (3) determine what habitat variables best predict bird occurrence 27 y after mixed-severity fire. We surveyed 56 sites across four burn severity classes, ranging from unburned to severely burned forest, in the Pine Ridge region of Nebraska. We measured multiple habitat characteristics (tree and snag diameter at breast height (DBH), coarse woody debris (CWD), tree and snag density, shrub height, and shrub cover) in May–August 2016 and conducted bird count surveys between 25 May and 8 June 2016. Cavity-nesting bird species' occurrence varied among the burn severity variables. Burn severity class (unburned, low severity, moderate severity, high severity) was a significant predictor of habitat characteristics for cavity-nesting birds, including tree density, snag density, mean snag DBH, variance in DBH, and CWD, which also was the best indicator of cavity-nesting bird community composition. We report evidence that mixed-severity wildfires in eastern ponderosa pine forests create variation in habitat characteristics and cavity-nesting bird occurrence.

Structure, diversity and health of Sierra Nevada red fir forests with reestablished fire regimes

The reestablishment of natural fire regimes may benefit forest ecosystems by restoring their fundamental structural, compositional or functional attributes. We examined the influence of fire on the structure, understorey diversity and health of red fir (Abies magnifica) forests by comparing burned and unburned stands in 22 separate, paired fires of Yosemite, Sequoia and Kings Canyon National Parks and the Giant Sequoia National Monument. Burned red fir plots were characterised by lower tree densities and canopy cover, restored spatial heterogeneity and higher understorey species richness than unburned plots. Densities of large trees and large snags and red fir regeneration were similar between burned and unburned sites. Forest health indicators were similar between burned and unburned sites, and red fir crown loss ratings were primarily associated with topographic variables indicative of increased moisture stress or reduced soil moisture availability (i.e. lower elevations, south-facing slopes). Our results suggest that fire does not improve the health of red fir trees especially in areas of greater moisture stress, but it can restore red fir forest structure, increase understorey diversity and enhance adaptive capacity in landscapes with reestablished fire regimes.

Environmental, Structural, and Disturbance Influences over Forest Floor Components in Interior Douglas-Fir Forests of the Intermountain West, USA

Downed woody material (DWM) is a key component in forest ecosystems with age, structure, and disturbance described as primary factors that influence DWM dynamics. In particular, much emphasis is placed on large coarse woody debris (CWD). Fine woody debris (FWD) (less than 7.62 cm diameter), duff, and litter also contribute to carbon stocks, provide habitat, add to nutrient cycling, and are often the most available fuels for fire, yet are regularly overlooked in studies describing the forest floor. Throughout the middle montane zone within the Intermountain West region USA, interior Douglas-fir (Pseudotsuga menziesii var. glauca Mirb. Franco) is a predominant forest type, yet little is known about the forest floor complex in these forests. We used a chronosequence approach to compare DWM patterns over the course of stand development among stands with different disturbance histories. Using classification and regression trees, we also evaluated an assemblage of environmental, structural, and disturbance variables to determine factors of most importance for estimating loading for DWM, duff, and litter. We found CWD resembled a U-shaped pattern of buildup while FWD components remained stable over the course of stand development regardless of disturbance history. Our results indicate that large DWM components are most closely associated with the amount of standing dead material in a stand, primarily the density and basal area of snags. Fine woody material was more aligned with live stand components, while duff and litter were more influenced by disturbance.

Fuel mass and stand structure 13 years after logging of a severely burned ponderosa pine forest in northeastern Oregon, U.S.A

Stand structure and fuel mass were measured in 2011, 13 years after logging of a seasonally dry, ponderosa pine-dominated forest that had burned severely in the 1996 Summit Wildfire, Malheur National Forest, northeastern Oregon, U.S.A. Data are compared to those taken one year after post-fire logging (1999), and analyzed in the context of a second fire (Sunshine Fire) that burned through one of the four treatment blocks in 2008. Three treatments were evaluated in a randomized block experiment: unlogged control, commercial harvest (most dead merchantable trees removed), and fuel reduction harvest (most dead merchantable trees removed plus most dead trees >10 cm diameter). Density and basal area of live trees trended downward between 1999 and 2011, but this delayed mortality was limited to smaller diameter stems. Dead tree basal area (snags) in unlogged stands declined over 12 years by 74%, compared to an 84% decline in logged stands over the same period. Higher snag fall rate in logged stands over time, combined with snag removal during logging in 1998, resulted in snag densities that were 22% of unlogged stands by 2011. In unlogged mixed-species stands, Douglas-fir snags fell at the same rate as did ponderosa pine snags, but fir snags fell at a faster rate in logged stands. Slash fuel tripled over twelve years in unlogged stands, such that mean slash mass levels became equal for all treatments. Unlogged stands accumulated nearly double the mass of coarse woody debris as logged stands, with most of the difference observed in the sound component of coarse woody fuel. By 13 years after logging (2011), density of regeneration averaged higher overall for unlogged stands, but was highly variable and patchy across all study units. Finally, the Sunshine Fire burned through nearly one complete block of the experiment in 2008, and erased most of the effects of the 1998 logging operation: snags were reduced to <0.5 ha−1 for all treatments, forest floor and slash fuel mass declined to near zero, log mass declined to about 25% that observed in stands unburned by the Sunshine Fire, and shrubs, seedlings, and saplings were nearly eliminated. While the intermediate-term effects of the 1998 logging were still evident in 2011, the 1996 Summit Fire remained the most dominant recent disturbance evident on the landscape.

Spruce Beetle outbreaks guide American Three‐toed Woodpecker Picoides dorsalis occupancy patterns in subalpine forests

American Three‐toed Woodpeckers Picoides dorsalis are considered a sensitive species by the United States Bureau of Land Management and are on the United States Fish and Wildlife Service's Watch List. In Idaho, Oregon and Washington, they are of conservation concern due to low abundance and an apparent reliance on disturbed, old‐growth forests. This species is strongly associated with Spruce Beetle Dendroctonous rufipennis epidemics, yet their occupancy relation with epidemic conditions have not been described. We studied Three‐toed Woodpecker occupancy patterns in spruce–fir forests experiencing varying degrees of beetle infestation between 2013 and 2016. Accounting for detection probability, we found a strong positive relationship between occupancy and the density of currently infested trees. Estimated occupancy was 0.57 (Bayesian credible interval 0.49, 0.64) for 75‐m‐radius survey points with zero infested spruce trees vs. 0.99 (Bayesian credible interval 0.99, 1) for points with 235 recently infested stems per ha. In contrast, we found no relationships with density of trees infested at least 3 years prior to sampling, density of older snags (i.e. &gt; 10 years dead) or quadratic mean diameter of healthy or recently infested trees. These results provide evidence of the importance of active Spruce Beetle infestation for Three‐toed Woodpecker habitat. Conserving Spruce Beetle‐infested trees for at least 3 years following the onset of a beetle epidemic would benefit Three‐toed Woodpecker populations and other species that depend on woodpecker‐excavated cavities. We suggest managers consider these results when planning logging activities aimed at Spruce Beetle mitigation.

Overstory Structure and Surface Cover Dynamics in the Decade Following the Hayman Fire, Colorado

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.

Den-site selection of eastern spotted skunks in the southern Appalachian Mountains

The eastern spotted skunk (Spilogale putorius) is a small, nocturnal omnivore that was once common throughout the eastern United States, but has declined over the last 75 years. We examined den-site selection of eastern spotted skunks in the southern Appalachian Mountains of Alabama from December 2014 to February 2016. We compared the local habitat characteristics of 97 den sites from 8 individual skunks with paired random sites. Dens were most frequently located in burrows, but were also found under uprooted trees, between rocks, in tree stumps, and in tree cavities. Skunks never communally denned and individuals frequently reused the same den. Den sites were located in densely forested areas with greater woody understory cover, midstory cover, and snag density and less overstory density than nearby random sites. Dense understory and midstory around skunk den sites likely provided protective cover from predators, particularly owls. Snags may provide additional cover for spotted skunks while offering possible denning or foraging habitat. Habitat management for eastern spotted skunks in the southern Appalachian Mountains should include retention and promotion of dense understory and midstory cover.

Wildlife implications across snag treatment types in jack pine stands of Upper Michigan

Abstract Standing dead trees, or snags, represent post-disturbance biological legacies in forest ecosystems, and intentional creation of new snags is increasingly common during forest treatments. The abundance, volume, size, and distribution of snags can affect wildlife communities and stand-level biological diversity. Characteristics such as the wood properties of different tree species, environmental conditions, and cause of tree death (e.g., insects, disease, senescence, wind, fire) can influence decomposition and subsequent use of snags by wildlife. The objectives of this study were to characterize decay patterns in jack pine (Pinus banksiana) snags that had been killed by prescribed fire, topping, and girdling and determine the effects of these treatments on subsequent snag use by subcortical insects and primary cavity-nesting birds. The prescribed fire, topping, and girdling treatments were implemented in 2003, 2004, and 2007, respectively; bird excavations were quantified in 2014 and insect activity was measured in 2016. One-way analysis of variance tests were used to examine any differences among treatments in snag characteristics, decay characteristics, past insect activity, and past use by birds. An information theoretic approach to model selection was then used to rank potential predictors of bird foraging activity and cavities. The topping treatment had unique decay characteristics relative to the other two treatments; topped snags had the highest levels of past insect colonization, were softer, and had higher proportions of loose bark remaining on the boles. Trees killed by prescribed fire had the greatest number of foraging excavations and cavities. Girdled snags had the lowest evidence of past insect colonization and showed different levels of decay and insect use at different vertical positions on the snag bole. Comparison of candidate models showed that a model containing treatment type alone was the highest ranked when predicting foraging by birds, while snag diameter was the highest ranked when predicting the presence of cavities. A model containing treatment and snag density was also a highly ranked for predicting cavity presence. Our findings suggest that different jack pine snag treatments result in unique decay trajectories that may influence snag use by an array of wildlife taxa. Our characterization of three snag creation treatments can also inform options for generating snags, depending on the desired outcome, when management for biological legacies and wildlife habitat is of interest within mixed-pine forests of the Great Lakes region.

Fine‐scale forest variability and biodiversity in the boreal mixedwood forest

Local spatial variation in species distributions is driven by a mix of abiotic and biotic factors, and understanding such hierarchical variation is important for conservation of biodiversity across larger scales. We sought to understand how variation in species composition of understory vascular plants, spiders, and carabid beetles is associated with concomitant spatial variation in forest structure on a 1‐ha permanent plot in a never‐cut mixedwood forest in central Alberta (Canada). Using correlations among dendrograms produced by cluster analysis we associated data about mapped distribution of all living and dead stems &gt; 1 cm diameter at breast height with distributions of the three focal taxa sampled from regular grids across the plot. Variation in each of these species assemblages were significantly associated with several forest structure variables at various spatial scales, but the scale of the associations varied among assemblages. Variation in species richness and abundance was explained mostly by changes in basal area of trees across the plot; however, other variables (e.g. snag density and tree density) were also important, depending on assemblage. We conclude that fine‐scale habitat variation is important in structuring spatial distribution of the species of the forest floor, even within a relatively homogeneous natural forest. Thus, assessments that ignore within‐stand heterogeneity and management that ignores its maintenance will have limited utility as conservation measures for these taxa, which are major elements of forest biodiversity.