Deadwood-dependent Organisms Research Articles

Fungal inoculations and mechanical wounding of trees have limited efficacy for snag creation two decades after treatment

Standing dead trees (snags) support multiple functions within forest ecosystems by providing vertical structure, contributing to nutrient flows and carbon cycling, and serving as habitat elements for a diversity of organisms. In many forest landscapes, managers often use snag creation to enhance structural diversity, particularly in areas where snag loss is high and natural snag recruitment is low. Despite snag creation being used across a range of forest types on both private and public lands, a dearth of long-term studies has led to uncertainty about which techniques work best to create snags and support deadwood-dependent organisms over long (>15 y) timescales. In this study, I assessed the long-term consequences of varied snag creation treatments applied to live Douglas-fir (Pseudotsuga menziesii) trees in two study areas near Coos Bay, in southwestern Oregon, USA. Treatments included chainsaw topping, fungal inoculation, topping + inoculation, and mechanical wounding at the base. Trees were revisited 18–20 y after treatment and nearly all focal trees (97.6%, n = 809) remained standing when relocated. Markers of decay – including whether a tree was broken, cracked along the bole, had peeling bark, or harbored shelf fungi – were most pronounced on trees that had experienced one of two chainsaw topping treatments, differentiated by the number of retained branch whorls. In contrast, limited decay was observed on trees subjected to fungal inoculation and mechanical wounding treatments, likely due to the slow pace of decay processes in injured trees. The same pattern held for both bark cover and cavity cover, the latter an index of created snag use by woodpeckers, a keystone group within forest ecosystems. Finally, adding fungal inoculation to chainsaw topping of trees led to little additional decay relative to chainsaw topping alone. These findings indicate that managers should choose snag creation methods that align with the timeframe they require decaying trees to be available to deadwood-dependent organisms. They also show that combining different snag creation approaches that vary in timing of tree mortality and decay is likely to provide a longer window of use by wildlife and require lower implementation costs. Although snag creation is a widespread management tool, additional research is needed to ascertain the effectiveness of snag treatments across space and time, and to quantify the tradeoffs between the ecological benefits and financial costs that result from intentional snag creation.

Urbanization filters woodpecker assemblages: Habitat specialization limits population abundance of dead wood dependent organisms in the urban landscape

Although urban landscapes are regarded as unsuitable for dead wood dependent organisms, some species, including woodpeckers, commonly occur in cities. As the availability of trees and dead wood resources is a primary dimension of the habitat-niche for most woodpeckers, we hypothesized that increasing habitat specialization (decreasing habitat-niche-volume) would limit species abundance within an urban landscape. We surveyed the woodpecker assemblage in the urban landscape, and for seven species we quantified the habitat-niche relying on four dimensions (the availability of trees, snags, fallen logs and dead tree branches). Then, we analysed the habitat preferences and habitat-niche partitioning of the woodpecker assemblage. For each species, we calculated the habitat-niche-volume and tested whether this trait correlated with species abundance in the urban landscape. Woodpeckers selected habitats with a high availability of either trees or dead wood (especially dead tree branches). The habitat-niches partially overlapped, but varied between species in terms of the availability of trees, dead tree branches, snags or fallen logs. The habitat-niche-volume varied among species and was positively associated with species abundance in the urban landscape. The regional abundance of species, body size and relative brain size did not affect the abundance of urban woodpecker populations. Our study highlights that urbanization filters woodpecker assemblages by limiting habitat-specialists and promoting habitat-generalists. We suggest that the alteration of woodpecker assemblages in the urban landscape may have a cascading effect on entire assemblages of dead wood dependent organisms, including cavity-nesters, saproxylic insects and wood-decomposing fungi. Urban development, which limits dead wood resources, is therefore a serious threat to biodiversity, whereas sustainable management of urban green spaces, e.g. the preservation of dead wood, may mitigate biodiversity loss.

Ecological restoration for biodiversity conservation triggers response of bark beetle pests and their natural predators

Abstract The restoration of forest structure and function is increasingly being used in boreal forests in order to halt the loss of biodiversity. Often ecological restoration is aimed at increasing the volume of dead and dying trees to enhance the biodiversity of deadwood-dependent organisms, but it may also increase population sizes of pest bark beetle species, even several years following restoration. Herein, we used a large-scale restoration experiment in Northern Sweden to assess the 5 years post-restoration effects of restorative gap cutting and prescribed burning on the populations of a set of economically harmful pest bark beetles (Ips typographus, Polygraphus poligraphus, Tomicus piniperda and Pityogenes chalcographus) and the most important predators of bark beetles, Thanasimus spp. In addition, we assessed the effects of forest stand characteristics at stand and landscape scale on the abundance of I. typographus. Five years post-restoration, gap-cut stands supported the highest abundances of P. poligraphus and contained the highest count of spruce trees newly attacked by bark beetles. By contrast, prescribed burning generally sustained the lowest abundances of pest bark beetles, especially I. typographus and P. poligraphus, and the highest abundance of their natural predators Thanasimus spp. The population abundance of I. typographus was also positively affected by the area of clear cuts within a 500 m radius from the stand. In conclusion, prescribed burning appears to be a safer method for ecological restoration than gap cutting in the long-term. According to our results, a risk of a local bark beetle outbreak still remains 5 years following the initiation of ecological restoration treatments on spruce-dominated mature gap-cut stands.

Dispersal ecology of deadwood organisms and connectivity conservation.

Limited knowledge of dispersal for most organisms hampers effective connectivity conservation in fragmented landscapes. In forest ecosystems, deadwood-dependent organisms (i.e., saproxylics) are negatively affected by forest management and degradation globally. We reviewed empirically established dispersal ecology of saproxylic insects and fungi. We focused on direct studies (e.g., mark-recapture, radiotelemetry), field experiments, and population genetic analyses. We found 2 somewhat opposite results. Based on direct methods and experiments, dispersal is limited to within a few kilometers, whereas genetic studies showed little genetic structure over tens of kilometers, which indicates long-distance dispersal. The extent of direct dispersal studies and field experiments was small and thus these studies could not have detected long-distance dispersal. Particularly for fungi, more studies at management-relevant scales (1-10 km) are needed. Genetic researchers used outdated markers, investigated few loci, and faced the inherent difficulties of inferring dispersal from genetic population structure. Although there were systematic and species-specific differences in dispersal ability (fungi are better dispersers than insects), it seems that for both groups colonization and establishment, not dispersal per se, are limiting their occurrence at management-relevant scales. Because most studies were on forest landscapes in Europe, particularly the boreal region, more data are needed from nonforested landscapes in which fragmentation effects are likely to be more pronounced. Given the potential for long-distance dispersal and the logical necessity of habitat area being a more fundamental landscape attribute than the spatial arrangement of habitat patches (i.e., connectivity sensu strict), retaining high-quality deadwood habitat is more important for saproxylic insects and fungi than explicit connectivity conservation in many cases.

Consequences of bioenergy wood extraction for landscape-level availability of habitat for dead wood-dependent organisms

Stumps and slash resulting from forest clearcutting is used as a source of low-net-carbon energy, but there are concerns about the consequences of biofuel extraction on biodiversity. Logging residues constitute potentially important habitats, since a large part of forest biodiversity is dependent on dead wood. Here we used snapshot field data from a managed forest landscape (25 000 ha) to predict landscape scale population changes of dead wood dependent organisms after extraction of stumps and slash after clearcutting. We did this by estimating habitat availability for all observed dead wood-dependent beetles, macrofungi, and lichens (380 species) in the whole landscape. We found that 53% of species occurred in slash or stumps. For most species, population declines after moderate extraction (≤30%) were small (<10% decline) because they mainly occur on other dead wood types. However, some species were only recorded in slash and stumps. Red listed species were affected by slash and stump extraction (12 species), but less often than other species. Beetles and fungi were more affected by stump extraction, while lichens were more affected by slash extraction. For beetles and lichens, extraction of a combination of spruce, pine and birch resulted in larger negative effects than if only extracting spruce, while for fungi tree species had little effect. We conclude that extensive extraction decreases the amount of habitat to such extent that it may have negative consequences on species persistence at the landscape level. The negative consequences can be limited by extracting only slash, or only logging residues from spruce stands.

Dead wood quality influences species diversity of rare cryptogams in temperate broadleaved forests

Dead wood is one of the most important indicators of forest naturalness and the most important manageable habitat for biodiversity in forests. Standing and lying dead wood, and especially coarse woody debris, plays an important part in creating habitats for many highly specialized organisms, e.g., insects, fungi, lichens and bacteria. Temperate mixed deciduous forests, rich in species, have been studied only to a small extent from the point of view of the ecology of wood-related cryptogams. Our study aimed at the reduction of the gap in knowledge about the ecological characteristics of dead wood-dependent organisms by focusing on species of cryptogams developing on various dead wood structures typical of temperate non-beech forests. Studies were performed in forests located in Lithuania, Poland, Belarus and Russia. We recorded 48 species of cryptogams: 18 species of bryophytes, 24 species of fungi and 6 species of lichens developing on dead wood. Our study stresses the importance of all types of dead wood as a substrate for the development of rare cryptogam species. Logs were the most important substratum type for cryptogams, followed by snags, dead trees and stumps. The cryptogam species richness on logs was several times higher than on the three other types of substrata. Coarse logs of intermediate decay stages hosted the highest number of cryptogams, followed by freshly fallen logs and, finally, well decayed logs. Assessing the importance of dead wood quality for the studied cryptogams, we found that intermediate decay stages are extremely important for fungi, while bryophytes or lichens do not show a clear preference. The highest number of cryptogams was found on Fraxinus excelsior, Quercus robur and Picea abies, while other tree species had less than half cryptogam species.

Phenolic compounds in Scots pine heartwood: are kelo trees a unique woody substrate?

Deadwood quality can be a highly significant factor in determining the occurrence of deadwood-dependent organisms such as saproxylic fungi. Rare deadwood substrates that are produced only after a lengthy senescence such as kelo trees may have unique deadwood qualities. Using high-performance liquid chromatography, we compared the phenolic composition of six types of Scots pine (Pinus sylvestris L.) substrates: living mature trees with no fungal sporocarps, living mature trees with Phellinus pini sporocarps, fallen non-kelo trees, soon-to-be kelo (standing), standing kelo, and fallen kelo. The fungal-infected living trees and fallen kelos were found to have more similarities in their phenolic composition when compared with the living and fallen trees and the standing kelos, which gets further pronounced with increasing decay. The results also highlight the uniqueness of the fungal-infected living trees and the fallen kelos and illustrate a possible correlation between fungal infection and the heartwood phenolic composition of Scots pine. However, it remains unclear to what extent the differences in phenolic compositions are caused by fungal infection and fungal decomposition. We also observed a previously undocumented correlation between the phenolic groups and fire scars on the trunks of the trees. The variation in substrate quality warrants further consideration when deadwood restoration activities are planned, as the quality of the deadwood could be as equally important as the quantity.

Dead wood dependent organisms in one of the oldest protected forests of Europe: Investigating the contrasting effects of within-stand variation in a highly diversified environment

Old-growth forests are dynamic systems characterized by high levels of fine-scale structural variability. This variability is thought to support biodiversity by providing a range of environmental conditions within stands, such as canopy openness and dead wood abundance and quality. However, the response of many taxa, including those dependent on dead wood, to fine-scale habitat variability within old-growth stands remains under-studied in many temperate forests. We used saproxylic fungi and beetles as model groups to test the influence of within-stand variation in canopy openness and dead wood quantity and quality in an old-growth beech-dominated woodland left unmanaged in the Czech Republic since at least 1838 (Zofinsky prales and Hojna Voda). Responses to habitat variability differed both between and within taxa. Species composition was most influenced by canopy openness, with the beetle community responding positively to openness but the fungal community responding negatively. Species richness of beetles was also most influenced by canopy openness, while the number of red-listed beetle species was more associated with dead wood quantity. Fungi were significantly associated with high amounts of dead wood, with a critical threshold exceeding 300m3 per hectare. Overall, fungal responses were more complex than for beetles, with the former more associated with undisturbed (closed-canopy) patches, and the latter with disturbed/gapped patches. These results demonstrate the role of fine-scale habitat variability within old-growth forests and provide a potential model for managed forests. Perpetuating a full range of structural variability, including disturbance-generated gaps and dead-wood pockets, will help sustain a broader range of late-successional biodiversity.

Biodiversity of most dead wood-dependent organisms in thermophilic temperate oak woodlands thrives on diversity of open landscape structures

Oak and mixed deciduous forests with oaks are the most widespread woodland types in the central European lowlands. The aim of this study was to analyse how the biodiversity of saproxylic organisms (fungi, lichens, beetles, and ants, bees and wasps) in thermophilic temperate oak woodlands respond to the openness in landscape structure of tree habitats. We sampled 32 sites in a split-plot design in Krivoklatsko (Czech Republic), which were chosen to include spatial diversity, including dense forests, open forests, woodland edges and solitary trees. A canonical correspondence analyses (CCA) and generalized additive models (GAM) were used for analyses. The results indicated that the taxa studied showed differences in species composition among the studied landscape structures and most taxa preferred more open and light conditions of the woodland environment. We also observed positive effect of the heterogeneity in open landscape structures on biodiversity of saproxylic organisms. As it is recently showed by ecologists, most of the thermophilic oak woodlands are threatened by succession, saproxylic organisms are facing decline throughout the world and traditional forest management (e.g. game keeping, wood pasturing or coppicing) appears to be one solution to mitigate biodiversity loss.

Coarse woody debris in late-successional Picea abies forests in northern Europe: Variability in quantities and models of decay class dynamics

Coarse woody debris pools and their decay class dynamics were studied in three areas of unmanaged boreal forest in northern Finland, and in the Murmansk and Arkhangelsk provinces in northwestern Russia. The study areas had varying climatic and edaphic conditions, and disturbance histories. Living and dead trees (diameter at 1.3 m height ≥10 cm) were measured in five late-successional Picea abies-dominated stands in each of the three areas. Wood density and time since death were determined from randomly sampled dead P. abies, and their decay class dynamics were modeled using stage-based matrix models. Volumes and decay class distributions of coarse woody debris reflected each site's productivity and disturbance history. Volumes ranged from 41 to 170 m 3 ha −1, and as a proportion of total wood volume varied from 28% in an area with constant tree mortality, to 38% and 53% in areas with past episodic disturbances. Expected residence times (or half-lives) of snags varied from 12 to 27 years, and for down woody debris from 20 to 40 years, so that the residence times for both decreased from north to south. The results imply naturally variable quantities and residence times of coarse woody debris in late-successional European boreal forests. These data also indicate the role of a site's disturbance history as a determining factor for quantity and decay class distributions. The developed models for decay class dynamics are applicable for both assessing the habitat availability for deadwood-dependent organisms, and carbon dynamics.

Lakeside riparian forests support diversity of wood fungi in managed boreal forests

Riparian forests often have a more diverse tree species composition and more woody debris than neighboring upland forests, but little is known about their importance for the conservation of deadwood-dependent species. We studied the forest characteristics and the diversity of wood fungi (poroid Aphyllophorales) in lakeside riparian (flat and sloping topography) and upland boreal forests in eastern Finland. Riparian forests had a higher density of broadleaved trees and broadleaved debris than did upland forests. A total of 48 species of wood fungi were recorded, including eight red-listed or old-growth forest indicator species. Overall, more species and records and greater diversity were observed in the flat riparian sites than in the sloped riparian and upland sites. The mean species richness did not differ significantly among site categories, indicating greater β diversity among the flat riparian sites. Species composition was more similar between the two riparian categories than between the riparian and upland sites. Riparian sites also hosted more fungal species associated with broadleaved trees. The results show that riparian forests support the diversity of wood fungi in managed boreal forests. Diversity of deadwood-dependent organisms can be promoted by leaving wider and completely unharvested riparian buffer zones.

SPATIAL OCCURRENCE OF A HABITAT-TRACKING SAPROXYLIC BEETLE INHABITING A MANAGED FOREST LANDSCAPE

Because of the dynamic nature of many managed habitats, proper evaluation of conservation efforts calls for models that take into account both spatial and temporal habitat dynamics. We develop a metapopulation model for successional-type systems, in which habitat quality changes over time in a predictable fashion. The occupancy and recruitment of the predatory saproxylic (dependent on dead wood) beetle Harminius undulatus was studied in a managed boreal forest landscape, covering 24,449 ha, in central Sweden. In a first step, we analyzed the beetle's occupancy pattern in relation to stand characteristics, and the amounts of present and past habitat in the surrounding landscape. Managed forest is suitable habitat when > or =60 years old, and immediately after cutting, but not between the ages of 10 and 60 years. The observed occupancy of H. undulatus was positively correlated with the stand's age as habitat. We used a metapopulation model to predict the current probability of occurrence in each forest stand, given the spatiotemporal distribution of suitable forest stands during the last 50 years. Metapopulation parameters were estimated by matching predicted spatial distributions with observed spatial distributions. The model predicted observed spatial distributions better than a similar model that assumed constant habitat quality of each forest stand. Thus, metapopulation models for successional-type systems, such as dead wood dependent organisms in managed forest landscapes, should include habitat dynamics. An estimated 82% of the landscape-wide recruitment took place in managed stands, which covered 87% of the forest area, in comparison with 18% in unmanaged stands, which covered 13% of the forest area. Among the managed stand types, > or =60-year-old stands and 3-7-year-old clear-cuttings contributed to 79% of the total recruitment while 8-59-year-old stands only contributed 3%. The results suggest the following guidelines to improve conditions for H. undulatus and other species with similar habitat requirements: (1) the proportion of the landscape constituted by younger stands should not be allowed to grow too large, (2) the rotation period of managed stands should not be allowed to be too short, and (3) dead wood should be retained and created at final cutting.