The habitat of Osmoderma eremita, a European endangered beetle species restricted to tree cavities, was examined in central Italy, at the southernmost limit of its distributional range. The occurrence of adults, larvae, and fragments was investigated in 170 and 151 living hollow trees by pitfall trapping and sampling of wood mould (i.e., loose material) in the hollow, respectively. Overall, O. eremita was present in 22% of the trees, which belonged to 4 different tree species (Ostrya carpinifolia, Quercus suber, Acer obtusatum, and Quercus pubescens). The frequency of presence was higher in cavities with more than 4 L of wood mould, in cavities with dry or half-moist wood mould rather than wet wood mould, and with wood mould with low soil contamination. A comparison with northern regions indicated that the warmer macro-climatic conditions in the south make the species independent of a warm microclimate. As most of the hollow trees contain only a small amount of wood mould (<4 L), the habitat quality is generally poorer than in oak pastures studied in northern Europe.

In cavity-nesting vertebrate species, reproduction is limited by the production and availability of tree cavities. Excavating species may create new cavities to exploit food resource pulses in novel habitats, but availability of nesting resources may be constrained with increases in population densities. Over a 15-y period, we monitored the reproduction of cavity nesters and a large-scale mountain pine beetle (Dendroctonus ponderosae) outbreak that killed all mature lodgepole pine (Pinus contorta var. latifolia), at 30 mixed coniferous—deciduous stands in interior British Columbia, Canada. We examined how the probability of excavation of a bark insectivorous, facultative cavity excavator, the red-breasted nuthatch (Sitta canadensis), was influenced by mountain pine beetle abundance and changes in population densities of conspecific individuals and a nest predator, red squirrel (Tamiasciurus hudsomcus). Nuthatches always chose trembling aspen (Populus tremuloides) for nesting regardless of densities of nuthatch nests and availability of beetle-decayed pine as alternate nest trees. The number of nuthatch nests increased in years of increasing densities of beetle-infected pine, and the proportion of freshly excavated nests varied annually, increasing with the beetle outbreak from 26% of all cavities used in 2001 to 70% in 2002 and then declining after the outbreak to 17% in 2009. For each unit increase in densities per hectare of both nuthatches and beetle-infected pine trees, the odds that individuals would excavate a new cavity rather than use an existing cavity increased by 147 times. With each 10 m farther into the coniferous forest interior, the odds of excavation increased by 10 times. These results suggest that facultative excavators are able to exploit novel habitats during insect outbreaks by adjusting their nest-site selection patterns and increasing excavation, but that resource pulses may lead to limitation of nesting resources.

Fire-generated mosaics of habitat legacies such as dead and dying trees are key structural components in boreal forest ecosystems that support diverse saproxylic beetles. Our study sought to elucidate the spatial pattern of community composition (beta diversity) of saproxylic beetles along gradients of post-fire habitat legacies (tree species composition, tree size [dbh], and burn severities) and geographical distance. For 2 y, we reared saproxylic beetles from 360 logs retrieved from 72 sites in burned forests. Tests were performed to explain the overall beta diversity (β_sor) by partitioning it into its 2 components: the “species spatial turnover” due to species replacement (β_sim) and the “richness-driven” beta diversity due to species richness differences (β_rich)- Variations in tree species, tree size, and burn severity had significant effects on overall beta diversity (β_sor) of saproxylic beetles; these effects varied according to the differential influence of these factors on the 2 distinct components of beta diversity. Tree composition had notable effects on species spatial turnover (β_sim), for which saproxylic species composition differed between jack pine and black spruce, and it was more variable between jack pine sites than between black spruce sites. On the other hand, variation in tree size was primarily responsible for the richness-driven beta diversity component (β_rich), which was highest between the smallest and largest dbh groups and lowest between largest and mid-sized trees. Similarly, richness-driven composition differed significantly across severity gradients and was highest across low to high severity and lowest between low-severity stands. Broader geographical distance per se did not affect compositional patterns of saproxylic beetles, yet the landscape context could have some effect. These results could have crucial implications for post-fire management, which also aims to efficiently conserve saproxylic beetles. The significant spatial turnover in saproxylic composition between black spruce and jack pine and the underlying host-tree specificity suggest that a mosaic of both tree species should be maintained in the landscape. The richness-driven beta diversity pattern along the tree size and severity gradients implies that it may be necessary to prioritize the most species-rich classes, such as larger trees with lower severity burns, but with qualifications to cater also for species displaying idiosyncratic distributions.

Early postfire habitats harbour numerous saproxylic species. Some are opportunistic feeders, while others are closely associated with burned forests. This distinction is important for developing sound postfire forest management aimed at conserving biodiversity, as concerns should be mostly directed towards burn-associated saproxylic beetles rather than opportunistic species. Here, we examine species-habitat associations, temporal dynamics, and community structure of saproxylic beetles in black spruce and jack pine stands disturbed by wildfire and by a “non-fire” disturbance generated by girdling trees to mimic the small-scale gap dynamics characterizing old-growth boreal forests in Canada. We used flightinterception traps and reared logs to compare abundance, species richness, and species composition of saproxylic beetles among treatments. We found that over 30% of saproxylic beetles had an affinity with jack pine or black spruce affected by either fire or girdling. Assemblages consistently differed between disturbance types over the 3 y of the study. We found that successional changes in species composition were more pronounced in burned sites than those with the girdling treatment, which indicates that the contribution of fire-generated habitats to regional diversity increases over time. While postfire forests are notable for their early-colonizing saproxylic species, our results show that they can also have substantial value for supporting mid-successional species such as Acmaeops pratensis, which is already on European red lists. This forewarns us about long-term negative consequences that postfire salvage logging could have for certain species.

In order to identify the distinctive traits of old-growth forests in a Mediterranean context, deadwood occurrence and forest stand structures were investigated in remote forests not subject to anthropogenic disturbance over the past few decades. Five study sites in south-central Italy were selected, and structural parameters were recorded in 1-ha plots. Living trees, deadwood, types, and decay stages were inventoried in the selected sites. Living tree volumes and amounts of deadwood indicated large variability among the investigated forest stands, ranging from 363 to 702 m^3·ha^_1 for living trees and from 17 to 143 m^3·ha^_1 for deadwood. Downed deadwood was the most abundant component, due to the natural mortality occurring in the stands. Stumps were the least common among the types of deadwood. All the decay classes were present in each study site. The main structural features useful for characterizing these old-growth forest stands included a multi-sized diameter distribution of living trees, the presence of small-scale gap dynamics, tree height heterogeneity, and high values of living volume and basal area. A ratio of dead to living wood not lower than 10%, downed deadwood much more abundant than standing deadwood, and a large range of deadwood size and decay classes across all the deadwood components are useful traits for tracking old-growth stages in these Mediterranean forests.

Wildland fire is the most important disturbance in Mediterranean ecosystems characterized by endemic yearly drought. Fires act on both the diversity and structure of plant communities. Because Aleppo pine (Pinus halepensis) is closely associated with wildfire, the dynamics of its population could regulate the load of woody debris (WD) during early decades before succession to oak-dominated vegetation (Quercus ilex, Q. pubescens). Here, we examine the effect of time since the last fire that affected the vegetation community on the load of WD. Pine dynamics should influence the structure of the WD, both fine and coarse. The sampling design is based on Mediterranean woodlands with different times since the last disturbance, enabling establishment of a proxy for a 130-y chronosequence. The density and biomass dynamics of Aleppo pine and WD were measured and the decay status of coarse WD assessed. The fire-date for each stand was determined on the basis of the structure of the pine population. The accumulation of WD load describes a U-shaped pattern. The high load of WD during the first 3 decades results from post-fire mortality and natural thinning of young trees; 100 y after fire, the WD load is the result of senescence of large, old Aleppo pines. These high loads of WD are concomitant with greater variation in the amount of WD and thus increased spatial heterogeneity within the ecosystem.

The flux of dissolved organic carbon (DOC) from aboveground litter into the soil is generally considered an important pathway for carbon transport. However, the extent to which dead wood, a highly concentrated source of carbon (C), may contribute not only to this flux but also to the accumulation of soil organic carbon (SOC) is still unknown. Here, concentrations and fluxes of DOC in solution beneath 5 logs of Fagus sylvatica were quantified using tension lysimeters. Soil samples beneath and adjacent to an additional 18 logs were analyzed for SOC. Concentrations of stable C isotopes were determined in wood of logs, DOC, and SOC to follow the fate of C from logs to the soil. Mean DOC concentrations in soil solution beneath logs were highly variable and ranged between 11.6 ± 5.8 mg·L^-1 (± SD) and 696 ± 654 mg·L^-1, while beneath litter without logs the DOC concentrations had an average value of 10 ± 3 mg·L^-1. Peak DOC concentrations beneath logs reached 4317 mg·L^-1. At 0–20 cm soil depth, SOC concentrations and SOC pools beneath logs were not higher than for control soils. The difference in the composition of stable C isotopes between wood (-25.5 ± 1.0‰) and litter (-28.4 ± 0.2‰) was maintained in DOC and SOC beneath respective substrates. A calculated amount of 20.5 ± 13.6% of the original SOC within 0–20 cm mineral soil was exchanged over a period of 17 ± 8 y by C from logs. However, despite the increased DOC fluxes, SOC pools beneath logs did not increase.

Fungi of woody debris are a diverse and functionally important component of forest ecosystems, but are potentially threatened by forest management activities. We used fruiting body and molecular sampling of the nrLSU gene to compare the composition and richness of fungal communities between 2 decay classes of conifer logs (classes 1 and 4) and among boreal mixedwood sites from 3 management histories (mechanized clearcutting, horse-based clearcutting, and unlogged). In 5 sites per management type, 5 logs per decay class were sampled for fruiting bodies. Wood samples for DNA extraction were collected from the logs at 3 mechanized logged and 3 unlogged forest sites. Fruiting body surveys yielded 116 species; 34 from decay class 1 logs, 65 from decay class 4 logs, and 17 from both. Molecular sampling, based on selection of 20 clones per log, yielded 304 operational taxonomic units (OTUs); 97 from decay class 1 logs, 184 from decay class 4 logs, and 23 from both. Community composition differed strongly between the 2 decay classes both for the fruiting body and OTU samples, with more species being recovered from decay class 4 than decay class 1 logs. Community composition also significantly varied according to log diameter and volume for fruiting bodies. The number of fruiting bodies on decay class1 logs was significantly greater in unlogged than logged sites and also was positively correlated with site-level volume of recently-decayed conifer woody debris. Dacrymyces chrysospermus and Fomitopsis rosea were significantly more frequently encountered in unlogged than logged stands. Despite relatively large volumes of woody debris in the logged stands that we sampled, we obtained evidence that logging in these forests resulted some 30–60 years later in a reduction in the amount and diameter of early-decay coniferous downed wood, with reductions in fungal fruiting body diversity as a result.

In the boreal forest, where tree cavities are mainly excavated by woodpeckers, many holes are incomplete excavations that are not suitable cavities for most other cavity users that form nest webs. We assessed cavity suitability for and use by a community of primary excavators and secondary users in managed and unmanaged landscapes in the boreal mixedwood forest of eastern Canada. We compared ground surveys of tree holes with direct inspections of the inside of potential cavities in remnant habitats surrounded by cutover areas and in large tracts of unharvested forest. We found that ground surveys overestimated suitable cavity abundance: only 38% of the potential cavities detected by ground surveys were suitable for nesting in both managed and unmanaged landscapes. Ground surveys of active nests correctly detected a greater proportion of primary (93%) than secondary cavity nesters (48%). In nest webs such as those of the boreal forest, where cavities are mainly created by woodpeckers, our results indicate that a large proportion of holes detected from the ground are not suitable for cavity nesters, thus overestimating the actual availability of nest sites. Furthermore, when nest cavities are active, ground surveys are satisfactory for detecting primary cavity nesters, but they are inadequate for detecting secondary cavity nesters.

Burned trees in the boreal forest are quickly colonized by wood-feeding beetles after fire. Roundheaded and flatheaded borers (Coleoptera: Cerambycidae, Buprestidae) are common wood-feeding beetles whose larvae feed on the phloem in the first instars before entering the xylem, where they excavate galleries several centimetres deep. These organisms cause significant damage to post-fire salvaged wood. Recent studies show that a variety of environmental factors may create heterogeneous patterns of damage throughout burned landscapes. We evaluated the relationship between fire intensity (measured as bole scorch height), tree size, elevation, and the landscape-scale distribution of beetle damage in black spruce in four 2-y-old fires in the central boreal forest of northern Quebec. Beetle damage significantly increased with char height and elevation but not with distance from unburned edge. With regard to tree diameter, the number of entry holes increased with fire intensity for large trees, whereas it declined with intensity for small trees. The most remarkable result was that while a very large sample size enabled us to detect these significant patterns, the difference in predicted beetle attack rates across a wide range of parameter values was quite muted. Thus, managers cannot use these results to dramatically improve either the way in which they salvage or the strategy for set-asides intended to benefit beetles and their subsequent avian predators.