Large Snags Research Articles

Snag characteristics and dynamics following natural and artificially induced mortality in a managed loblolly pine forest

A 14-year study of snag characteristics was established in 41- to 44-year-old loblolly pine (Pinus taeda L.) stands in southeastern USA. During the initial 5.5 years, no stand manipulation or unusually high-mortality events occurred. Afterwards, three treatments were applied consisting of trees thinned and removed, trees felled and not removed, and artificial creation of snags produced by girdling and herbicide injection. The thinned treatments were designed to maintain the same live canopy density as the snag-created treatment, disregarding snags that remained standing. We monitored snag height, diameter, density, volume, and bark percentage; the number of cavities was monitored in natural snags only. During the first 5.5 years, recruitment and loss rates were stable, resulting in a stable snag population. Large snags (≥25 cm diameter) were common, but subcanopy small snags (10 to <25 cm diameter) dominated numerically. Large natural snags survived (90% quantile) significantly longer (6.0–9.4 years) than smaller snags (4.4–6.9 years). Large artificial snags persisted the longest (11.8 years). Cavities in natural snags developed within 3 years following tree death. The mean number of cavities per snag was five times greater in large versus small snags and large snags were more likely to have multiple cavities, emphasizing the importance of mature pine stands for cavity-dependent wildlife species.

Comparison of snag densities among regeneration treatments in mixed pine–hardwood forests

Standing dead trees (snags) are an important component of forest ecosystems, providing foraging, nesting, and roosting substrate for a variety of vertebrates. We examined the effects of four forest regeneration treatments on residual snag density and compared those with densities found in unharvested, naturally regenerated forests (controls) during the second, fourth, and sixth year after timber harvest in mixed pine–hardwood forests of Arkansas and Oklahoma. Regeneration treatments were clearcut with snag creation, shelterwood, single-tree selection, and group selection. Density of large snags (≥25.0 cm DBH) differed only during the sixth year after harvest, with shelterwoods having a lower density of large snags (1.0 snags/ha) than the control or group selection stands (4.0 and 4.2 snags/ha, respectively). Density of small snags (10.0–24.9 cm DBH) mirrored residual basal area, with controls and group-selection stands having the greatest snag densities. Creation of snags in clearcuts by injection with herbicides caused initial snag density in these areas to be greater than other treatments, but density in clearcuts declined sharply by 6 years after harvest. In the absence of snag creation, treatments such as shelterwoods that remove most trees may have snag densities below that required to address some management objectives without additional snag creation.

Night Crawlers

Night Crawlers Kathryn Wilder (bio) A dark shadow crosses my face and my heart jumps. Standing over me, Tyler says, “I’m ready to go.” “So soon?” I say, shaking something away from me, something that buzzes around my head like a fly. The sun holds steady above the canyon wall but the air has cooled. I startle at how long I may have dozed. As my mind clears on the drive home I ask Tyler, my nine-year-old son, if he had a good day. “No,” he says. The road, like most in this county, traces the course of a river. I look at Tyler as I round a bend. He glances at me and quickly away, but not so fast that I miss the tears in his eyes. “What is it?” I say. We have just gone fishing for the first time this spring, which means Tyler fished and I lay beside the river in the sun, having dug out a sandy bed between the rocks like the dogs. Clouds coasted across the sky high above the canyon walls, the sun’s warmth pushing through their thin layers and into my skin. This alluvial flat of land, made eons ago by tributaries flooded with snowmelt, rain, and mud, is connected to the highway by a bridge just downriver. A few years back that bridge [End Page 77] was access to one of seven busy lumber mills; today the abandoned mill rests in pieces. The lone mill continuing to operate in this Sierra Nevada county of a single stoplight and no fast-food drive-thru is near my house, near one of the few tiny towns, all of which are peopled by generations of loggers and ranchers, hunters and fishermen. I have hunted—with Tyler’s father—but never fished. In the earlier part of his life Tyler was raised by his father the hunter as well as by me; now that he wants to fish he has to learn on his own, no man to guide him. I have thought this would be good for him, help build his confidence and independence. Besides, I am tired. Always tired—too tired to learn how to help him learn to fish, too tired to even think about finding a man to replace his father. I won’t know for some years that this fatigue is due to more than single motherhood, that I’ve got a life-threatening disease, which I will later defeat, which in the end will not take my life. In the meantime, I find myself asleep at wrong times, unable to fight it—even teaching, I have to go into the bathroom and put my head down for two or five quick minutes of slumber. Doctors say I’m healthy—apparently they don’t know how to read the blood tests that say I’m not—so I continue to live an active, albeit randomly sleep-filled, life. We were the only people at the river this morning and when we got there Tyler settled himself near a low rock wall made by winter water, prepared his hook, cast his line. At that bend the river pulls itself together to make what might be a Class I rapid. I’ll call it a riffle. There are no obstacles, no jutting rocks, no holes, just a slim wave train that would splash enough water over my whitewater raft to make us laugh and want to run it again. If the water were warm and lifejackets available, it might be a good riffle to float through boatless, but today the river still has enough power in its current to carry us into the waiting arms of dead ponderosa pines downriver, where large snags brought down by winter’s floodwaters hug the supports of the bridge—those branches, worn smooth by the weight of rocks and water, could reach out and grab, holding a body tight in their grip until more floodwaters came, or summer’s low water exposed the victim. Someone told me once about spotting an arm flapping above the [End Page 78] current in a snag on a southwestern river—a Navajo boy had gone...

Snag distributions in relation to human access in ponderosa pine forests

Ponderosa pine (Pinus ponderosa) forests in western North America provide habitat for numerous cavity-using wildlife species that often select large-diameter snags for nesting and roosting. Yet large snags are often removed for their commercial and firewood values. Consequently we evaluated effects of human access on snag densities and diameter-class distributions at nine locations in ponderosa pine forests throughout the interior western United States. We found no relationship between small-diameter (23–50 cm diam breast ht [dbh]) snags and human access measures (i.e., road density, distance to nearest town, and topography). However, large-snag (≥50 cm dbh) density was best predicted by road density, which suggested a decline, on average, of 0.7 large snags/ha for every km of road/km2. Most locations had relatively high densities of small-diameter snags (<23 cm dbh) and diminishing density as diameter class increased. Idaho and Colorado study locations had higher snag densities in the largest diameter classes compared with remaining locations. These locations experienced minimal commercial timber harvest, were situated far from towns, and had few or no roads. Persistence of large-diameter snags and adequate snag densities for wildlife requires consideration of human access characteristics at coarse spatial scales. Snag management guidelines may need to incorporate these measures and focus more on retention of large-diameter snags than minimum density targets. © 2013 The Wildlife Society.

Using reference conditions in ecosystem restoration: an example for riparian conifer forests in the Pacific Northwest

Quantifying the attributes of reference sites is a crucial problem in the restoration of ecosystems, driving both the evaluation of current conditions and the setting of management targets for specific points in the future. Restoration of riparian ecosystems, particularly those dominated by conifers, has become a priority because of the numerous ecosystem services they provide, including a high number of vertebrate species in population decline that utilize these structurally complex forests. By way of example, we illustrate a three‐step process to assess the effects of proposed riparian ecosystem restoration efforts: (1) identify reference sites (2) quantify metrics that describe the reference sites, and (3) use models to predict the likely effects of restoration actions relative to reference conditions. To this end, we identified 117 natural, late‐successional conifer dominated stands from existing forest inventories in the Pacific Northwest for the purpose of establishing reference conditions. We did this to establish quantitative metrics for structural attributes essential to the maintenance of biodiversity in these forests, and to assess whether there were any important quantitative differences between upland and riparian forests or whether upland and riparian forest reference sites could be used interchangeably. Both forest types were generally similar, but riparian stands had higher average live tree wood volumes and basal areas, suggesting they may be growing on sites that are more productive. Both riparian and upland forests had abundant large diameter (&gt;50 cm) live trees and snags. Collectively, our data suggest that mature, late‐successional conifer dominated forests have well developed structural characteristics in terms of abundant large trees in the overstory, abundant large snags, and a well‐developed understory of shade‐tolerant trees. We modeled the growth of young conifer stands to assess whether a common restoration treatment would accelerate development of structural characteristics typical of reference conditions. We found that left untreated, the stands followed a trajectory towards developing forest structure similar to the average reference condition. In contrast, the restoration treatment followed a developmental trajectory along the outside range of reference conditions.

Artificial roosts for tree‐roosting bats in northern Arizona

AbstractBats use large (69 cm mean diameter) ponderosa pine (Pinus ponderosa) snags for maternity roosts in northern Arizona. Anthropogenic causes have altered forest structure, decreasing density of large snags. To examine use of artificial roosts for bats in these forests, we selected 26 sites and 2 treatments (clustered, single) using 1 type of roost (resin or wood) per site. At each site, we installed 4 roosts on ponderosa pine trees with a cluster of 3 roosts (south‐, east‐, or west‐facing; &lt;20 m apart) and a single roost (south‐facing) 250–350 m away. We checked roosts every 2 weeks for use (guano or bats) and monitored internal temperatures every 2 hours from May through September in 2009 and 2010. Bats used 52% of roosts (19 roosts in 2009, 49 in 2010) at least once and colonized resin roosts sooner than wood roosts. Sites with clustered resin roosts were used more than single roosts. Bats used south‐ and east‐facing resin roosts more and these had warmer average temperatures than west‐facing roosts. We captured 47 bats of 5 species using artificial roosts. We only captured male bats from roosts in 2009, juveniles and females were also captured in 2010 but no maternity roosts were documented. We recommend that resin roosts placed in clusters on live trees be used to supplement natural roosts in ponderosa pine forests. Because use increased with time we suspect artificial roosts may be used for several years before establishment of maternity colonies. Artificial roosts require annual maintenance (e.g., waterproofing) to maintain function and can be expensive to install and maintain. © 2012 The Wildlife Society.

Experimental effects of structural enrichment on avian nest survival

Managers of landscapes dedicated to commodity production require information about how alternative practices can promote retention of native biological diversity. Retaining or creating structural features (e.g., snags or downed logs) needed to fulfill life history requirements may benefit populations and communities. However, demographic responses of species to alternative practices have received little research attention. We tested nest survival of cavity-dependent birds in response to experimental structural enrichment by creating snags on 28 plots, Oregon, USA, 2008–2010. Each plot represented one of six combinations of created snag density (0.5, 1, and 2snags/ha) and spatial dispersion (clumps of 5–7 snags or dispersed individual snags). We monitored 506 nests built by 10 species; three species nested in sufficient numbers for analysis. Chestnut-backed chickadee Poecile rufescens nest success was highest in the medium density clumped created snag treatment (average proportion of successful nests=0.76; 95% CI=0.61–0.87) and lowest in the low density clumped treatment (average proportion of successful nests=0.39; 95% CI=0.20–0.62). We did not find a response of either house wren Troglodytes aedon or northern flicker Colaptes auratus nest success to the experimental treatments. Period survival rates were 0.57 (95% CL: 0.39–0.72) for CBCH; 0.71 (95% CL: 0.51–0.84) for HOWR; and 0.59 (95% CL: 0.34–0.77) for NOFL. Our study suggests that creating snags in commercial harvest units is an effective practice for increasing structural complexity and supporting nesting communities of cavity-dependent birds. While leaving either clumped or dispersed created snags at a density of ∼1ha should support nest survival rates that are similar to those reported from unmanaged forests, we emphasize that this type of structural enrichment is not a panacea for species that require very large snags or snags that occur under complex forest canopies. Retention of existing structural features in reserve areas may be an appropriate practice for conserving species with nesting requirements that differ from those we evaluated in our study.

Topographic Variation in Structure of Mixed-Conifer Forests Under an Active-Fire Regime

Management efforts to promote forest resiliency as climate changes have often used historical forest structure and composition to provide general guidance for fuels reduction and forest restoration treatments. However, it has been difficult to identify what stand conditions might be fire and drought resilient because historical data and reconstruction studies are generally limited to accurate estimates only of large, live tree density and composition. Other stand features such as smaller tree densities, dead wood, understory structure, regeneration, and fuel loads have been difficult to quantify, estimate how they may vary across a landscape, or assess how they would be affected by fire under current climate conditions. We sampled old-growth, mixed-conifer forests with at least two low-intensity fires within the last 65 years in 150 plots at 48 sample sites ranging over 400 km of the Sierra Nevada. Recent fire history had the strongest influence on understory conditions with small tree density decreasing and shrub cover increasing with the increased intensity and frequency of fire associated with upper-slope and ridge-top locations. In contrast, stand structures associated with large, overstory trees such as total basal area, canopy cover, and the abundance of large snags and logs increased in topographic locations associated with more mesic, productive sites regardless of fire history. In forests with restored fire regimes, topography, fire and their interaction influence productivity and burn intensity, creating the structural heterogeneity characteristic of frequent-fire forests.

Nest Site Characteristics and Nest Tree use by Northern Flying Squirrels (Glaucomys sabrinus) in Southwestern Alberta, Canada

Abstract Nests are used by many species for rearing offspring, thermoregulation and predator avoidance, and are thus critical resources, especially in cold climates. I examined the nest tree and nest site use by a population of northern flying squirrels (Glaucomys sabrinus), a secondary cavity nester and species of management interest, along the Rocky Mountain foothills in Sheep River Provincial Park, Alberta, Canada. Northern flying squirrels in this study area nested most often in tree cavities (∼63%) located in large snags and aspens (Populus tremuloides). Northern flying squirrels selected nest sites surrounded by less canopy cover and more large snags than random sites. As such, northern flying squirrel populations in cold climates may be constrained by specific habitat characteristics.

Temporal dynamics and decay of coarse wood in early seral habitats of dry-mixed conifer forests in Oregon’s Eastern Cascades

Early seral forest habitats are increasingly valued for the unique structural resources they provide in many western US forests. Coarse woody detritus (CWD) are a significant feature of this developmental stage and are highly dynamic, suggesting these environments exhibit temporally diverse structural conditions prior to forest canopy closure. In dry-mixed conifer forests, snags are hypothesized to decay slower than logs making long-term dynamics in these forests dependent on snag fall, breakage and the decay rates of both standing and surface CWD. We estimated snag fall and breakage rates for Pinus ponderosa, Abies sp., P. menziesii and P. contorta snags in three diameter classes (<23cm, 23–41cm and >41cm) from 6057 snags across a 24-year chronosequence of early seral environments. Snag and log decay rates were estimated by felling 60 Abies sp. and 60 P. ponderosa snags, and sampling 40 P. ponderosa logs. Half-life estimates for snags <23cm, 23–41cm, and >41cm were 7, 12, and 17years for Pinus sp., 10, 15, and 20years for Abies sp., and 11, 17, and 23years for P. menziesii. Breakage rates were lowest for small snags and not significantly different for medium and large snags, but did vary across species. We estimated an Abies sp. snag decomposition loss-rate constant of k=0.0179yr−1 (SE=0.00533, p-value=0.0014) but P. ponderosa snags did not exhibit statistically significant decay (k=0.0024yr−1, SE=0.00518, p-value=0.6414). P. ponderosa logs had an estimated decomposition loss-rate constant of k=0.0243yr−1 (SE=0.0073, p-value=0.0023), confirming reduced decay rates in snags and variation among species. Following high-severity fire, dry-mixed conifer stands experience relatively rapid temporal changes in CWD resources largely dependent on snag species and diameter-at-breast-height (DBH). Variation in fall, breakage and decay rates among species and DBH suggests maintaining a diverse selection of snag species and diameters would meet multiple ecological needs across a broader temporal scale. Additionally, given the rapid temporal changes in CWD, defining early seral habitat as the period immediately following disturbance until canopy closure may not adequately account for the diversity in habitat structures and resources available over time.

Implications of spatially extensive historical data from surveys for restoring dry forests of Oregon's eastern Cascades

Dry western forests (e.g., ponderosa pine and mixed conifer) were thought to have been historically old and park‐like, maintained by low‐severity fires, and to have become denser and more prone to high‐severity fire. In the Pacific Northwest, early aerial photos (primarily in Washington), showed that dry forests instead had variable‐severity fires and forest structure, but more detail is needed. Here I used pre‐1900 General Land Office Surveys, with new methods that allow accurate reconstruction of detailed forest structure, to test eight hypotheses about historical structure and fire across about 400,000 ha of dry forests in Oregon's eastern Cascades. The reconstructions show that only about 13.5% of these forests had low tree density. Forests instead were generally dense (mean = 249 trees/ha), but density varied by a factor of 2–4 across about 25,000‐ha areas. Shade‐tolerant firs historically were 17% of trees, dominated about 12% of forest area, and were common in forest understories. Understory trees and shrubs dominated on 83.5%, and were dense across 44.8% of forest area. Small trees (10–40 cm dbh) were &gt;50% of trees across 72.3% of forest area. Low‐severity fire dominated on only 23.5%, mixed‐severity fire on 50.2%, and high‐severity fire on 26.2% of forest area. Historical fire included modest‐rotation (29–78 years) low‐severity and long‐rotation (435 years) high‐severity fire. Given historical variability in fire and forest structure, an ecological approach to restoration would restore fuels and manage for variable‐severity fires, rather than reduce fuels to lower fire risk. Modest reduction in white fir/grand fir and an increase in large snags, down wood, and large trees would enhance recovery from past extensive logging and increase resiliency to future global change. These forests can be maintained by wildland fire use, coupled, near infrastructure, with prescribed fires that mimic historical low‐severity fires.

Early responses to thinning treatments designed to accelerate late successional forest structure in young coniferous stands of western Oregon, USA

The loss of critical habitat provided by late successional forests has prompted the search for management options that can accelerate the development of late successional forest structure in young stands. We examined operational-scale commercial thinning treatments at seven sites to evaluate if thinning could accelerate development of late successional forest structures in 40–60 year old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forests. Thinning treatments included an untreated control, high density, moderate density, and variable density retention. All thinning treatments had leave islands, and moderate density and variable density included harvest-created gaps. Thinned units, especially moderate density and variable density, had greater spatial variability in tree density, supported lower live branches, had greater tree regeneration and growth, and had slightly lower mortality relative to the control. Canopy gaps extended the range of stand densities and increased growth of trees immediately along gap edges. However, thinning had little effect on growth of the largest Douglas-fir trees and did little to provide large snags or coarse woody debris. These results suggest that thinning treatments can accelerate some aspects, e.g., spatial variability, of late successional forest structures. Other attributes, such as large trees and snags, may prove less responsive to thinning treatments, at least in the short term. Including tree retention levels lower than typical management applications and formation of canopy gaps provide the wide range of conditions that appears beneficial for developing late successional forest structure.

Community occupancy responses of small mammals to restoration treatments in ponderosa pine forests, northern Arizona, USA

In western North American conifer forests, wildfires are increasing in frequency and severity due to heavy fuel loads that have accumulated after a century of fire suppression. Forest restoration treatments (e.g., thinning and/or burning) are being designed and implemented at large spatial and temporal scales in an effort to reduce fire risk and restore forest structure and function. In ponderosa pine (Pinus ponderosa) forests, predominantly open forest structure and a frequent, low-severity fire regime constituted the evolutionary environment for wildlife that persisted for thousands of years. Small mammals are important in forest ecosystems as prey and in affecting primary production and decomposition. During 2006-2009, we trapped eight species of small mammals at 294 sites in northern Arizona and used occupancy modeling to determine community responses to thinning and habitat features. The most important covariates in predicting small mammal occupancy were understory vegetation cover, large snags, and treatment. Our analysis identified two generalist species found at relatively high occupancy rates across all sites, four open-forest species that responded positively to treatment, and two dense-forest species that responded negatively to treatment unless specific habitat features were retained. Our results indicate that all eight small mammal species can benefit from restoration treatments, particularly if aspects of their evolutionary environment (e.g., large trees, snags, woody debris) are restored. The occupancy modeling approach we used resulted in precise species-level estimates of occupancy in response to habitat attributes for a greater number of small mammal species than in other comparable studies. We recommend our approach for other studies faced with high variability and broad spatial and temporal scales in assessing impacts of treatments or habitat alteration on wildlife species. Moreover, since forest planning efforts are increasingly focusing on progressively larger treatment implementation, better and more efficiently obtained ecological information is needed to inform these efforts.

Habitat requirements of the Black Woodpecker, Dryocopus martius, in Hyrcanian forests, Iran

The relationships between the Black Woodpecker (Dryocopus martius (Linnaeus, 1758)) abundance and forest characteristics and the role of coarse woody debris for habitat selection were assessed. One hundred point counts were conducted 250 m apart in Hyrcanian forest in northern Iran from 21 April to 21 May 2009. There was a noticeable difference in forest structure between areas where the Black Woodpecker was present and absent, with the species preferring the later stages of forest succession. Tall and large diameter trees, high volumes of coarse woody debris, especially large snags, and dense canopy cover, all of which characterise mature forests, are significantly higher in areas where the Black Woodpecker occurs. Altogether, the conservation of the Black Woodpecker depends to a large extent on how the forests they inhabit are managed.

Flying Squirrel Demography Varies between Island Communities with and without Red Squirrels

Recent studies in Southeast Alaska suggest the ecology of Glaucomys sabrinus differs from populations in the Pacific Northwest. In Southeast Alaska, densities were the highest reported for the species, populations were not as closely linked to old-forest attributes, and individuals had a more diverse diet that was less dependent on mycophagy. Pacific Northwest communities are comprised of several arboreal rodents; Southeast Alaska has a depauperate mammal fauna. I hypothesized that Southeast Alaska populations had a broader realized niche because of competitive release. The red squirrel (Tamiasciurus hudsonicus) is the only other arboreal squirrel and it is absent from the southern outer islands of Southeast Alaska's Alexander Archipelago. I compared demography and body mass of G. sabrinus on Prince of Wales Island to a population in sympatry with T. hudsonicus on a separate island (Mitkof). Home ranges were larger and population density, breeding female density, and juvenile recruitment of G. sabrinus were all lower in sympatry with T. hudsonicus. In a companion study, G. sabrinus on Prince of Wales Island used cavities for denning relatively more frequently than in sympatry with T. hudsonicus on Mitkof Island. Female G. sabrinus depend on cavities for natal dens, and breeding female and population densities are positively correlated with large snag or tree density. The presence of T. hudsonicus may influence G. sabrinus populations by limiting availability of cavities. Furthermore, variation in vertebrate assemblages among islands may influence realized niches of resident species, which manifest unique demographic profiles compared to populations of different ecological communities.

A comparison of selected parametric and imputation methods for estimating snag density and snag quality attributes

Snags (standing dead trees) are an essential structural component of forests. Because wildlife use of snags depends on size and decay stage, snag density estimation without any information about snag quality attributes is of little value for wildlife management decision makers. Little work has been done to develop models that allow multivariate estimation of snag density by snag quality class. Using climate, topography, Landsat TM data, stand age and forest type collected for 2356 forested Forest Inventory and Analysis plots in western Washington and western Oregon, we evaluated two multivariate techniques for their abilities to estimate density of snags by three decay classes. The density of live trees and snags in three decay classes (D1: recently dead, little decay; D2: decay, without top, some branches and bark missing; D3: extensive decay, missing bark and most branches) with diameter at breast height (DBH)⩾12.7cm was estimated using a nonparametric random forest nearest neighbor imputation technique (RF) and a parametric two-stage model (QPORD), for which the number of trees per hectare was estimated with a Quasipoisson model in the first stage and the probability of belonging to a tree status class (live, D1, D2, D3) was estimated with an ordinal regression model in the second stage. The presence of large snags with DBH⩾50cm was predicted using a logistic regression and RF imputation. Because of the more homogenous conditions on private forest lands, snag density by decay class was predicted with higher accuracies on private forest lands than on public lands, while presence of large snags was more accurately predicted on public lands, owing to the higher prevalence of large snags on public lands. RF outperformed the QPORD model in terms of percent accurate predictions, while QPORD provided smaller root mean square errors in predicting snag density by decay class. The logistic regression model achieved more accurate presence/absence classification of large snags than the RF imputation approach. Adjusting the decision threshold to account for unequal size for presence and absence classes is more straightforward for the logistic regression than for the RF imputation approach. Overall, model accuracies were poor in this study, which can be attributed to the poor predictive quality of the explanatory variables and the large range of forest types and geographic conditions observed in the data.

Effect of deadwood position on saproxylic beetles in temperate forests and conservation interest of oak snags

Abstract.1. Intensive forestry has drastically reduced the volume of standing deadwood, even more than total deadwood volume. It has been demonstrated in boreal forests that snags have a high conservation value for many saproxylic species and that the lying or standing aspect of the deadwood makes a difference. The conservation of saproxylic beetles in the changing deadwood landscape of temperate managed forests depends on a deeper understanding of the ecological value of forest stand legacies.2. Our study questioned whether the retention of oak snags is an important conservation concern in European temperate forests. We analysed the differences in saproxylic beetle fauna between oak snags and logs and explored the diameter effect on log–snag differences. We compared the species composition and richness of saproxylic beetle assemblages in a temperate deciduous forest. Emergence traps were set in a balanced sampling design of 22 ground‐lying logs and 22 oak snags with a range of intermediate decay stages and 2 diameter classes.3. Oak snags yielded more individuals per volume unit and supported more species than logs, and exhibited significantly dissimilar assemblages from logs and hosted original species. Snags, especially large snags, were more interesting for rare beetle species conservation than logs. The feeding guild structure slightly differed between snags and logs. Overall, log–snag differences depended on the diameter class.4. We confirm that saproxylic biodiversity would significantly benefit from forestry measures favouring oak snag retention (especially large snags), even though further multi‐scale studies are necessary to develop quantitative retention guidelines.

Pre-fire forest conditions and fire severity as determinants of the quality of burned forests for deadwood-dependent species: the case of the black-backed woodpecker

Burned forests represent high-quality habitats for many deadwood-dependent species. Yet, post-fire conditions may vary greatly within and among burns and thereby may affect habitat suitability for these species. We studied habitat selection of nesting black-backed woodpeckers ( Picoides arcticus Swainson) in recently burned spruce-dominated boreal forests. Our objectives were to (i) identify factors involved in snag selection for both nesting and foraging and (ii) examine selection of nest sites within the burned landscape. A total of 92 nests and 1612 foraging observations were used to investigate snag selection. Our results show that both pre-fire forest conditions and fire severity are important in determining the quality of burned forests for black-backed woodpeckers. This species selected large snags for both nesting (&gt;20 cm DBH) and foraging (&gt;15 cm DBH). Woodpeckers selected deciduous and degraded “pre-fire” snags for nesting whereas black spruce snags that had been created by fire and that were moderately burned were preferred for foraging. Nest sites were concentrated in burned mature stands and supported higher densities of large snags (e.g., &gt;15 cm DBH). Our results suggest that burned forest patches of at least 20 ha and composed mainly of burned mature and old-growth forests should be maintained during post-fire harvesting. The decrease in the amount of late seral stands in managed forest landscapes raises concerns about the future availability of high-quality burned forests for this species.

Structural changes and potential vertebrate responses following simulated partial harvesting of boreal mixedwood stands

Partial harvesting, where different numbers and arrangements of live trees are retained in forest stands, has been proposed for maintaining late-successional structure and associated vertebrate species within managed boreal forests. Using the stand dynamics model SORTIE-ND, we examined 80-year patterns of structural change in response to different intensities (30–70% basal area removal) and spatial patterns (22–273 m 2 mean patch size) of harvesting. We also applied habitat models for seven late-successional vertebrates to the structural conditions present after harvesting to assess potential species responses. Partial harvesting increased understory and downed woody debris (DWD) cover and decreased overstory structure for the first 25 years after harvest, in comparison to unharvested stands, with this effect subsequently reversing as harvest-induced regeneration reached the canopy. Although harvesting enhanced long-term structural development in this regard, large trees, large snags, and large DWD all remained below unharvested levels throughout the simulation period. Harvesting also produced transient increases in early-decay DWD and ground exposure. Most changes in structural attributes increased in proportion to harvest intensity, but structural differences among harvest patterns were generally small. Dispersed harvesting induced somewhat less pronounced decreases in vertical structure, and produced more post-harvest slash, than aggregated harvesting. All seven vertebrate species decreased in abundance as harvest intensity increased from 30 to 70%. In comparison to their pre-harvest abundances in old stands, vertebrates associated with DWD (redback salamander, marten, red-backed vole) showed neutral or positive responses at one or more harvest intensities, whereas those associated with large trees and snags (brown creeper, flying squirrel) consistently exhibited substantial adverse impacts.

Snag characteristics and cavity-nesting birds in the unmanaged post-fire northeastern Canadian boreal forest

We studied the availability and characteristics of snags and their use by cavity-nesting birds in the northeastern part of the Canadian boreal forest. We built up two long-term (&gt; 200 years) chronosequences following time since the last fire in the unmanaged boreal forest of northeastern Québec, one in the balsam fir-white birch domain (southern region) and one in the spruce-mosses domain (northern region). We then sampled and characterized snags and live trees in 30 stands from each of these two chronosequences. We also looked for nest cavities on all sampled snags, performed bird inventories by point counts, and calculated tree mortality rate from permanent sample plots. Results show that mortality rates follow a U-shaped pattern, with more snags of large diameter (&gt; 20 cm DBH) in young (&lt; 50 years) and in old (&gt; 200 years) forests. In the latter, we also found more nest cavities than in any other age classes. Although abundance of primary cavity nesters (excavating species) did not vary among age classes, secondary cavity nesters (using cavities already available) tend to be more numerous in older forests. Our results highlight the capacity for young and old-growth forests to provide quality habitat for species that are dependent on large snags. Proper forest management should maintain a mosaic of different age forest stands, including snags, to promote biodiversity and provide important resources for resident bird species.