Cut logs and high stumps of spruce, birch, aspen and oak - nine years of saproxylic fungi succession

Managed stands generally contain little coarse woody debris compared to natural forests. This study addresses the potential of retained cut wood to increase the amount of substrate available for a variety of saproxylic fungi.Fruit bodies of fungi were recorded from 270 cut high stumps and logs of spruce, birch, aspen and oak over nine years of initial succession. A total of 1565 occurrences of 148 species, seven of which were red-listed, were found. Numbers of species were significantly higher on logs than on stumps. Annual diversity peaked four to seven years after logging, sooner on logs than on stumps. Numbers of species were positively related to substrate diameter, but not to the level of shade/sun-exposure, while the presence of some individual species were significantly affected by one or both of these factors. Comparisons with data from the literature indicated no fundamental differences between fungal communities on cut wood and on naturally dead substrates. We conclude that cut wood left on site, especially logs, may mimic dead wood from trees that die swiftly from natural causes and support diverse fungal communities, both in shaded stands and in open logging sites. Substrates generated by slow self-thinning processes in natural forests however, are probably difficult to mimic in managed stands.     

Habitat suitability models of saproxylic red-listed boreal forest species in long-term matrix management: Cost-effective measures for multi-species conservation

Understanding of how a large landscape or network of conservation areas and habitats of red-listed species change in time is an important topic when addressing the temporal interplay between protected areas and matrix. We developed models of habitat suitability indices (HSI) for saproxylic red-listed invertebrate and fungal species, accounting for roughly 70% of all red-listed boreal forest species of the study area in eastern Finland. By using a forestry planning program that incorporates various optimisation methods we analysed trade-offs between timber production and amount of habitats of saproxylic red-listed species within a 60-year period. We also produced production possibility frontiers that show how to increase quality of the matrix with least costs. Moreover, we analysed how habitat suitability criteria used in optimisations affect the area of different habitat quality classes.

Our analysis shows that by adopting HSI models in long-term matrix management, it is possible to increase habitats for several red-listed species without substantial losses in timber production. The increase in habitat area is achieved mainly by decreasing the area that is thinned compared to intensive timber production plan. In the long term, this seems to be a novel cost-effective method to increase the quality of the matrix for red-listed saproxylic species. However, the selected optimisation method and the criteria or specification of the management objective for red-listed forest species have a strong effect on results when HSI models are used in conservation planning. Therefore any practical application must be performed with great care.     

Parasitoids (Hymenoptera, Ichneumonoidea) of Saproxylic beetles are affected by forest successional stage and dead wood characteristics in boreal spruce forest

The habitat requirements and effects of forest management on insects belonging to higher trophic levels are relatively unknown in forest ecosystems. We tested the effect of forest successional stage and dead wood characteristics on the saproxylic parasitoid (Hymenoptera, Ichneumonoidea) assemblage in boreal spruce-dominated forests in northern Sweden. Within each of nine areas, we selected three sites with different management histories: (1) a clear-cut (2) a mature managed forest and (3) an old-growth forest. Parasitoids were collected in 2003 using eclector traps mounted on fresh logs, which were either untreated (control), burned, inoculated with fungi, or naturally shaded, and on artificially-created snags.Both forest type and dead wood characteristics had a significant effect on parasitoid assemblages. Grouped idiobionts and some species, such as Bracon obscurator and Ontsira antica, preferred clear-cuts, while others, such as Cosmophorus regius (Hym., Braconidae) and other koinobionts, were associated with older successional forest stages. No single dead wood substrate was sufficient to support the entire community of parasitoids in any forest type, even when the regular host was present. In particular, snags hosted a different assemblage of species from other types of dead wood, with parasitoids of Tetropium spp. such as Rhimphoctona spp. (Hym., Ichneumonidae) and Helconidea dentator (Hym., Braconidae) being abundant. These results indicate that a diversity of dead wood habitats is necessary to support complete assemblages of beetle-associated parasitoids from early successional stages of dead wood and that parasitoids may be more sensitive to habitat change than their hosts.     

Learning from a “benign neglect strategy” in a national park: Response of saproxylic beetles to dead wood accumulation

Increasing demands for firewood owing to rising energy costs have accelerated discussions about the amount of dead wood needed for conservation. A sharp increase in dead wood caused by bark beetles in a German national park provides lessons for management of commercial and protected forests. We investigated the effects of dead wood due to bark beetle infestation as well as tree senility on abundance and richness of saproxylic species of beetles. Increasing amounts of spruce dead wood and opening of the canopy by bark beetles had positive effects on the abundance of host-generalist, conifer-specialist, and red-listed saproxylic beetles. Broadleaf specialists were positively associated with the amount of broadleaf dead wood and negatively associated with canopy openness. Gradient analysis of beetle assemblages revealed two major environmental axes: canopy openness and amount of dead wood. We found a threshold for community divergence at a canopy openness of 23% (confidence interval CI: 11-49) and at an amount of dead wood of 64 m³ ha⁻¹ (CI: 35-160). Critically endangered species served as indicators of dense and open forests, but only when the amount of dead wood was high. Our results suggest that, to maintain saproxylic beetle assemblages, the amount of dead wood in commercial montane forests (at present ≈15 m³ ha⁻¹) needs to be tripled, with a focus on broadleaf wood in dense stands and spruce wood in open stands. For large protected areas in Europe, our data suggest that bark beetle infestation and senescence without active forest management improves habitat conditions for saproxylic beetles.     

Diversity of dead wood inhabiting fungi and bryophytes in semi-natural beech forests in Europe

Saproxylic organisms are among the most threatened species in Europe and constitute a major conservation problem because they depend on the most important forestry product - dead wood. Diversity of fungal and bryophyte communities occurring on dead beech trees was analyzed in five European countries (Slovenia, Hungary, The Netherlands, Belgium and Denmark) considering tree level species richness (TLSR), country level species richness (CLSR), frequency distributions of species, occurrence of threatened species and relations between TLSR and decay stage, tree size and countries. Altogether 1009 trees were inventoried in 19 beech dominated forest reserves.The number of fungi in the full dataset was approximately three times larger (456 versus 161 species) and the proportion of low frequent species was higher than among bryophytes. The species richness of bryophytes and fungi was significantly different among countries considering both TLSR and CLSR. In addition the diversity patterns deviated considerably between the two groups of organisms. Slovenian sites appeared to be biodiversity hotspots for bryophytes characterized by high TLSR and CLSR and a high fraction of threatened species. Hungarian sites had somewhat lower bryophyte diversity, while the Atlantic region had deteriorated assemblages. Fungal species richness was very high in Denmark, but the Hungarian and Slovenian sites were richer in threatened and low frequency species. Tree size was better able to explain variation in TLSR in both organism groups than decay stage. TLSR was found to vary significantly between countries but the difference was most considerable in the case of bryophytes.The diversity patterns of both organism groups along the investigated geographical gradient appear to be influenced by both climatic and management related factors (forest history, dead wood availability and continuity, habitat fragmentation). There is no doubt that an increase in the abundance of dead wood in European beech forests will benefit diversity of saproxylic fungi and bryophytes, especially if a continuous presence of large diameter logs are secured within individual stands.     

Elephant- and human-induced changes to dung beetle (Coleoptera: Scarabaeidae) assemblages in the Maputaland Centre of Endemism

High African elephant stocking rates in nature reserves in southern Africa have been shown to have significant impacts on vegetation structure and diversity. However, the direct and indirect effects of elephants on fauna, particularly invertebrates, remain poorly known. The Maputaland Centre of Endemism, an area of southern Mozambique and northern KwaZulu-Natal in South Africa, is undergoing rapid rates of habitat conversion. Sand Forest, the rarest vegetation type in the Centre, is threatened by human disturbance outside of protected areas and by elephant browsing pressure in Tembe Elephant Park, one of the few protected areas for Sand Forest. Here we examine the effects of elephant- and human-induced disturbance to Sand Forest on a functionally important component of invertebrate diversity, i.e. the dung beetle fauna. The dung beetle assemblage associated with elephant-disturbed Sand Forest was transitional between undisturbed Sand Forest and Mixed Woodland, whereas that associated with human disturbance was markedly different to either habitat type. Differences are attributed to a change in habitat structure under both disturbance types, as well as to changes in the quality and distribution of dung under human disturbance. Therefore, grazing impacts by elephant not only affect plant diversity, but also implement changes in invertebrate fauna. The maintenance of the integrity of the Sand Forest–Mixed Woodland matrix is considered critical for biodiversity conservation in the Maputaland Centre of Endemism. Management of elephant populations, as well as the protection of sufficient Sand Forest inside conservation areas must, therefore, necessarily form part of the conservation strategy for the Centre.