Petri Martikainen

Species richness of Coleoptera in mature managed and old-growth boreal forests in southern Finland

The beetle (Coleoptera) fauna of old-growth spruce (Picea abies) forest was compared with that from managed mature and overmature forests in southern Finland. Samples were collected from 9–11 sample plots in each case using 10 window-flight traps in each stand. These yielded a total of 43,289 beetles and 553 species of which 232 were associated with dead wood. The species richness of these saproxylic species was significantly higher in old-growth forests than in managed forests, and had very significant positive correlations with most dead-wood variables. Seventy eight percent of the saproxylic species were more abundant in old-growth than in mature managed forests, and their assemblages in managed and old-growth forests were distinctive with almost no overlap. On the other hand, species richness and assemblages of non-saproxylic species did not differ between the managed and old-growth forests. Obviously these species do not require as much attention as saproxylic species when conservation measures are planned in managed forests. An increase in the general level of decaying wood would improve the situation of many declining saproxylic species. Although the species richness of Coleoptera as a whole was higher in overmature than in mature managed stands, the value of long-rotation stands in preserving species assemblages typical of old-growth forests may be limited.

Forest Fragmentation in Fennoscandia: Linking Habitat Requirements of Wood-associated Threatened Species to Landscape and Habitat Changes

Fragmentation may occur simultaneously in different spatial and temporal scales. The ecological importance of fragmentation depends both on the scale of fragmentation and on the habitat requirements of the species. The fragmentation of old-growth forests is regarded as one of the most important causes for the recent decline of several forest-dwelling species in Fennoscandia. In Fennoscandia landscape-level fragmentation has proceeded differently in various areas. For example, in eastern Finland mature forest fragmentation was evident very early. By the 1800s, only one third of the landscape was covered by 150 yr old forests. This early fragmentation resulted mostly from the slash-and-burn cultivation practised widely in these areas. In the northern Fennoscandia, however, no such landscape changes have been found before the 1900s. During the 1900s fragmentation has accelerated. Recent results suggest that biological impacts of current landscape-level fragmentation of mature forests may have been overestimated, especially among invertebrate species. Specific habitat requirements of these groups are still poorly known. Instead of requiring mature forests, several wood-associated threatened species may require only dead wood that can occur in any successional stage, in both managed and protected areas. Such variability in the habitat requirements allows good opportunities for preservation of the threatened species. Results from current research indicate the need to restore and recreate natural fire-originated early successional stages where the amount of coarse woody debris is high. Promotion of coarse woody debris in young managed forests is potentially a very effective way to sustain populations of several threatened wood-associated species.

Dead trees left in clear-cuts benefit saproxylic Coleoptera adapted to natural disturbances in boreal forest

Forest management alters the pattern of forest dynamics from that in natural conditions in the boreal region. In order to examine how certain forestry measures matching natural dynamics affect forest insects, we compared assemblages of saproxylic Coleoptera on dead, standing birch trunks left behind in eight clear-cut areas with corresponding assemblages in seven mature forests in southern and eastern Finland. We used trunk-window traps for sampling. Distinct beetle assemblages were associated with the different habitats. Median numbers of species or specimens caught did not differ between closed forests and clear-cuts, but individual beetle species occurred unevenly among the habitats. Several beetle species associated with open forest habitat, e.g. burned forests or storm-damage areas, including species regarded as threatened in Finland, were found almost exclusively, in clear-cuts. Correspondingly, a number of beetle species occurring frequently in closed forests were not found in clear-cuts. We conclude that dead trunks left in the clear-cut areas may host not only generalist saproxylic species but also many beetle species specialized to warm, sun-exposed environments, and such species may not be able to survive in closed forests. Management measures matching suppressed natural disturbances are found useful in preserving diversity in managed forests.

Occurrence of rare and threatened insects living on decaying Populus tremula: a comparison between Finnish and Russian Karelia

Beetles and flat bugs living on the decaying wood of aspen (mainly under bark) were collected during expeditions to Finnish and Russian Karelia. Similar searching methods were used, and a comparable number of sites and trees (about 120) were examined on both sides of the border. The fauna on aspen in Russian Karelia was considerably rich. A total of 21 and 5 rare species were found in Russian Karelia and Finnish Karelia, respectively. Within about twenty working hours in Russ. Karelia we encountered two species considered extinct in Finland (Hylochares cruentatus and Cyllodes ater) and five considered endangered or vulnerable (Acritus minutus, Rhacopus attenuatus, Uleiota planata, Cucujus cinnuberinus and Anidus truncatus). We suggest that the high number of rare species at the sites studied in Russian Karelia is attributable to the different management history of the forests, particularly to the abundance and continuity of large, dead aspens. Disturbance caused by logging and leaving the non‐marketable t...

Saproxylic beetles in managed and seminatural Scots pine forests: quality of dead wood matters

Habitats of saproxylic species (species that are dependent on decaying wood) have been greatly changed during the last few decades. Due to intensive forest management, volume of dead wood has decreased and its quality is less diverse in managed than in naturally disturbed forests. There is an urgent need to develop and apply guidelines for forest management so that they also facilitate the survival of saproxylic species and mimic the natural dynamics of forests. This requires detailed information about how the differences in forest structure between managed and natural forests affect the occurrence of species and what are the real habitat requirements of species. Thus, we explored the richness of saproxylic beetles, composition of species assemblages and relationship between saproxylic beetles and their substrate in managed and seminatural pine dominated forests. Richness of saproxylic species tended to be higher in seminatural than in managed forests but the difference was not statistically significant. However, species assemblages in managed forests had differentiated from those on seminatural sites. Our results suggest that for the survival of saproxylic beetles, increasing the total volume of dead wood is an important task but more important one is to improve the diversity and continuity of dead wood in managed forests. This requires that the continuous production of dead wood is allowed also in managed forests to improve the continuity of dead wood and availability of recently dead wood. In green tree retention the main stress should be laid on the trees of large diameter to maintain the potential for large decaying wood.

Sampling the rarest: threatened beetles in boreal forest biodiversity inventories

Presence or absence of threatened species in samples is information that is widely used in designing and implementing conservation actions. We explored the effectiveness of beetle (Coleoptera) inventories and contribution of different sampling methods in revealing occurrences of threatened and near threatened species in boreal forests. The number of species caught using traps in a particular area proved to be a useful indicator of the representativeness of data, the relationship between total number of species and the number of threatened and near threatened species being almost exponential. Samples containing less than 200 trapped species (or 2000 individuals) are almost useless in surveying threatened and near threatened species. The probability of finding such species increases considerably when the number of trapped species exceeds 400. Window traps attached directly on the trunks of dead trees proved to be the most efficient sampling method in trapping threatened beetles, whereas many other standard methods gave relatively poor results. We suggest that the best alternative in surveying threatened species in boreal forests is a combination of intensive direct searching and trunk window traps. Finding threatened beetles with rigorous probability requires very large sample sizes, even if the most effective sampling methods are used. For example, ranking 10 boreal forest areas to be protected according to the occurrence of threatened species with some reliability may require trapping of over 100000 beetle individuals. Collecting and identifying these large samples routinely in conservation actions is not feasible, which means that shortcuts (indicators etc.) are necessary. However, a lot of good-quality inventories with appropriate sampling efforts are needed before these shortcuts can be identified and elaborated. Such inventories are also crucial for the improvement of the classification of threatened species and full assessment on how past forest management has eventually affected the biota.

Prescribed fires and retention trees help to conserve beetle diversity in managed boreal forests despite their transient negative effects on some beetle groups.

Abstract. 1 Controlled burning and green‐tree retention have been suggested to alleviate the negative effects of forestry on species diversity in boreal forests, but the ecological impacts of these measures are poorly known. 2 We studied experimentally the response of four ecological groups of beetles – saproxylics, herbivores, species on ephemeral resources, and litter‐dwelling species – to different harvesting intensities and controlled burning in Scots pine‐dominated forests. The study included four levels of green‐tree retention (0, 10, 50 m3 ha−1, and no harvesting) with burning on 12 of the 24 study sites, covering ~4 ha each. A beetle data of 153 334 individuals representing 1142 species were collected during one pre‐treatment (2000) and two post‐treatment years (2001–2002), using window traps. 3 Species richness increased in all four groups after harvesting, with and without burning, and there were major community‐level changes. The species richness of saproxylics and herbivores continued to increase in the second post‐treatment year on burned sites, whereas it decreased on many unburned sites. The assemblages were strongly affected by the treatments, but higher volumes of green‐tree retention maintained them closer to the pre‐treatment structure. 4 Although some ecological groups, such as species on ephemeral resources, experienced substantial turnover as a result of burning, populations of species that initially declined recovered. Since the increase in the saproxylics was evident, and the population reductions of other species were transient, we recommend the controlled burning with reasonable volumes of green‐tree retention to reduce negative effects of forestry on insect diversity.

Fallen retention aspen trees on clear-cuts can be important habitats for red-listed polypores: a case study in Finland

Green-tree retention is a relatively new forestry application, which aims at decreasing the negative effects of clear-cut logging on forest biodiversity. In this study, the value of retained aspens in maintaining diverse assemblages of wood-decaying fungi (polypores; Basidiomycota) on clear-cuts was investigated, after the retention trees had died, fallen and started to decay. A total of 110 fallen aspen trunks were investigated on clear-cuts and within old-growth forests in eastern Finland, southern boreal zone; and 499 records of polypores belonging to 46 species were made. The intermediately decayed trunks on a clear-cut area hosted more species and more red-listed species than did trunks within forests. Most of the polypore species with more than two records were found in both habitats. These results suggest that many aspen-associated polypores are able to live and reproduce in sun-exposed habitats, if the quality and quantity of dead wood fulfill the species-specific requirements. This unexpected result, however, may be partly due to the exceptionally great abundance of aspen in the study area. Furthermore, in the long term, the local benefits of fallen retention trees can be limited, unless the local continuity of large aspens, both living and dead, is ensured.

Intensity of forest management and bark beetles in non-epidemic conditions: a comparison between Finnish and Russian Karelia

Abstract: The population levels of bark beetles in non‐epidemic conditions were compared between intensively managed forests in Finnish Karelia and extensively managed forests in Russian Karelia. Thirty randomly chosen sample plots with five window flight traps in each were established in both countries. The numbers of species and individuals of bark beetles did not differ between the countries. This indicates that extensive forest management has not increased the general level of bark beetle populations. Species assemblages were, however, different between the countries and between the forest site types. Hylastes brunneus and Pityogenes bidentatus, which are common in stumps or in logging residue of Scots pine, were more abundant in Finland. Crypturgus subcribrosus, Polygraphus punctifrons, and Hylurgops glabratus, which prefer dead spruce trees in shady conditions, and Trypodendron signatum, which live in dead deciduous trees, were more common in Russia. Bark beetles were most abundant in old mesic forests. The amount of decaying wood on the ground did not correlate with the numbers of bark beetles caught.

Prescribed burning is an effective and quick method to conserve rare pyrophilous forest‐dwelling flat bugs

Fire suppression and reduced volumes of dead wood have led to a major decline in pyrophilous and saproxylic insects in Fennoscandian boreal forests. As a consequence, several species are currently seriously threatened. Flat bugs (Heteroptera, Aradidae) is an important invertebrate group that includes several pyrophilous species, including many threatened ones. We explored whether specific conservation measures – prescribed burning and retention forestry – can facilitate the survival of flat bugs in managed forests. The large‐scale field experiment consisted of a burning treatment (yes/no) and four levels of logging intensity (clear‐cut, retention levels of 10 and 50 m3 ha−1, and unharvested controls). The data included 1224 individuals of 12 species, sampled over a 4‐year period. Burning increased the species richness and abundance of the pyrophilous species. Two Red‐Listed and very rare pyrophilous species, Aradus angularis J. Sahlberg (Vulnerable) and A. laeviusculus Reuter (Near Threatened), were abundant after burning. The number of non‐pyrophilous flat bugs collapsed after burning but they re‐colonised the stands quickly, becoming as abundant as at the unburned stands. Logging increased the abundance of flat bugs only when retention forestry was applied. This study shows that pyrophilous flat bugs are quickly able to locate recently burned forests and that these forests are important for their survival. The effect of fire is, however, transient at the stand level and pyrophilous species disappear almost completely quickly after fire. To maintain these species, recently burned forests with a sufficient volume of retention trees should be available continuously at the landscape level.