Jonas Hedin

Densities of large living and dead trees in old-growth temperate and boreal forests

We recorded and reviewed densities and basal areas of large living and dead trees in old-growth forest in Europe. Recorded densities were similar to those reported from old-growth forests in eastern North America, but lower than in northwestem North America. Based on our results we suggest that, 10-20 living trees per ha with dbh > 70 cm may have been typical values for many central European and south Scandinavian virgin forests. In boreal forests, it was probably common with at least 20 living trees per ha with dbh > 40 cm. Basal areas of living trees in mixed old-growth forests in central Europe and southern Sweden were 34-40 m 2 per ha on dry ground and about 60 m(2) per ha in wet alder-ash-spruce forests. Densities of large trees (dbh > 40 cm) were twice as high in the latter forest type than on dry ground in Bialowieza forest, Poland. Based on our results, we propose the following generalizations to be further tested in other old-growth temperate and boreal forests: 1. Among all standing trunks (including high stumps) about 10% are dead. but this proportion increases for the largest trees. The proportion of standing trees that are dead seem to be independent of total basal areas. Based on this, we suggest that the volume of dead wood is directly proportional to the productivity of old-growth forests. 2. Standing dead trees (snags) are on average larger than downed dead trees. Trees with dbh >40 cm often dominate the basal area and volume of standing dead trees and living trees. 3. About 30% (20-40%) of the basal area and volume of dead trees is standing in old-growth forests. This proportion seems to be independent of total volume of dead wood. Large disturbances by fire, strong winds and insects may temporarily change these proportions considerably in individual stands

Biodiversity and its assessment in boreal and nemoral forests

We review species richness in major organism groups, mainly using examples from northern Europe. A high proportion of these species is forest living, and large numbers are dependent on decaying wood. Biodiversity can be assessed at various scales using two different principles. One is to use features, such as ancient and dead trees, known to be important for a large number of species. The other method is to choose species or groups of species known to indicate high biodiversity or presence of many red-listed species. We argue that any serious biodiversity assessment method should include the most species rich organism groups, for example insects. In the present paper we point out the most important features for high biodiversity (old trees and large dead trees), and review the quantities of these features in near-virgin forests. The natural disturbance regime of a region should be the basis for defining a suitable scale and the appropriate features for biodiversity assessment. Possible indicator species for high biodiversity in northern Europe are suggested, based on previous investigations. Among epiphytic lichens and wood-living beetles there are many potentially useful species in addition to vascular plants in the nemoral forest. Among vertebrates, woodpeckers and grouses seem to be the most useful. Validation tests for indicator structures and species are largely lacking but urgently needed. The implications of possible delayed local extinctions are important to bear in mind when managing for sustainable forestry. The knowledge of forest history is useful when developing cost-efficient measures.

The dispersal rate of a beetle, Osmoderma eremita, living in tree hollows

The dispersal of an endangered beetle, Osmoderma eremita, that lives in tree hollows, was studied by mark-release-recapture with pitfall traps. As only a small proportion of all dispersals is observed by this method, a simulation model was constructed to estimate the dispersal rate per individual. The model results suggest that 15% of the adults leave the original tree for another hollow tree, and consequently most individuals remain in the same tree throughout their entire life. This suggests that each hollow tree sustains a local population with limited connection with the populations in surrounding trees. It supports the view that O. eremita has a metapopulation structure, with each tree possibly sustaining a local population, and with the population in an assemblage of trees forming a metapopulation. Low dispersal rate and range make the species vulnerable to habitat fragmentation, probably at a scale of only a few hundred meters.

Restricted dispersal in a flying beetle assessed by telemetry

Many insects living in ancient trees are assumed to be threatened as a result of habitat loss and fragmentation. It is generally expected that species in habitats with low temporal variability in carrying capacity have lower degree of dispersal in comparison to those in more ephemeral habitats. As hollow trees are long-lived, species in that habitat are expected to be sensitive to habitat fragmentation, due to a low capacity to establish new populations far from present ones. Using radio telemetry, we studied the dispersal for a beetle, Osmoderma eremita, living in hollow trees. O. eremita exhibited philopatry and only dispersed over short ranges. About 82–88% of the adults remained in the tree where they were caught. All observed dispersal movements ended up in nearby hollow trees and 62% in the neighbouring hollow tree. These results corroborate the suggestion that habitat fragmentation may be detrimental to insects living in temporally stable but spatially variable habitats. In order to preserve such species, we propose that conservation efforts should be focused on maintaining or increasing the number of suitable trees in and near presently occupied stands.

Using radio telemetry to study dispersal of the beetle Osmoderma eremita, an inhabitant of tree hollows

This paper describes a radio-tracking study of Osmoderma eremita, a large Scarabaeid beetle, living in hollow trees. The study seems to be the first in which radio telemetry has been used with a flying insect in the field. Some 74 adult beetles were tagged with radio transmitters weighing 0.48-0.52 1, and having a nominal battery life of 12-20 days. Transmissions were detected at ranges of up to 330 m, with 50-100 in obtained routinely. Contact was lost with 71% of the females and 20% of the males before the end of the nominal lifetime of the transmitters battery, probably because the transmitter ceased to function. Radio telemetry proved effective in this study and gave dispersal ranges and rates that were consistent with those from a concurrent mark-recapture study in the same area. However, further development of the technique is desirable. The antennas need to be more flexible and the transmitters smaller and lighter. Nevertheless, even the current form of the technique may be suitable for studying short-range dispersal in other large-bodied flight-capable insects. (Less)

Characteristic Odor of Osmoderma eremita Identified as a Male-Released Pheromone

Osmoderma eremita (Scopoli) is an endangered scarab beetle living in hollow trees. It has mainly been known for its characteristic odor, typically described as a fruity, peachlike or plumlike aroma. The odor emanating from a single beetle can sometimes be perceived from a distance of several meters. In this paper, we show that the characteristic odor from O. eremita is caused by the compound (R)-(+)-γ-decalactone, released in large quantities mainly or exclusively by male beetles. Antennae from male and female beetles responded in a similar way to (R)-(+)-γ-decalactone in electroantennographic recordings. Field trapping experiments showed that (R)-(+)-γ-decalactone is a pheromone attracting female beetles. Lactones similar to (R)-(+)-γ-decalactone are frequently used as female-released sex pheromones by phytophagous scarabs. This is, however, the first evidence of a lactone used as a male-produced pheromone in scarab beetles. We propose that the strong signal from males is a sexually selected trait used to compete for females and matings. The signal could work within trees but also act as a guide to tree hollows, which are an essential resource for O. eremita. Males may, thus, attract females dispersing from their natal tree by advertising a suitable habitat. This signal could also be exploited by other males searching for tree hollows or for females, which would explain the catch of several males in our traps.

Attraction of the larval predator Elater ferrugineus to the sex pheromone of its prey, Osmoderma eremita and its implication for conservation biology

Elater ferrugineus is a threatened click beetle inhabiting old hollow trees. Its larvae consume larvae of other saproxylic insects including the threatened scarab beetle Osmoderma eremita. Recently, (R)-(+)-γ-decalactone was identified as a male-produced sex pheromone of O. eremita. Here we present evidence that E. ferrugineus adults use this odor as a kairomone for location of their prey. In field trapping experiments, significantly more trapping events of E. ferrugineus beetles were observed in Lindgren funnel traps baited with (R)-(+)-γ-decalactone than in control traps (20 vs. 1, respectively). Analyses of headspace collections from E. ferrugineus beetles indicate that the predator itself does not produce the substance. Both sexes were attracted to the prey pheromone, suggesting that E. ferrugineus males use the odor as an indirect cue for location of mates or of the tree hollows, which make up their habitat. When compared to pitfall traps, the Lindgren system was significantly more effective in trapping E. ferrugineus, and no difference could be established for O.eremita, showing the high potential to use odor-based systems to catch both species. We suggest that (R)-(+)-γ-decalactone could be used as a master signal in monitoring programs for these vulnerable beetle species, which are both regarded as indicators of the associated insect fauna of the threatened habitat of old hollow trees.

Forest fuel piles as ecological traps for saproxylic beetles in oak

Abstract Biodiversity management in broadleaved forests includes partial cutting to improve conditions for species that benefit from semi-open stand structure. The harvested wood is usually used as fuel and, therefore, it is stockpiled in situ for months before further processing. If such forest fuel piles attract saproxylic insects, they are likely to be ecological traps, because the settling cost for insects is death as the wood is chipped and used for energy. This study investigated beetle species composition in piles of oak wood in southern Sweden. Species density and frequency of occurrence were compared in wood with different diameters and at the top, middle and bottom parts of piles. A total of 39 species (six red-listed) and 3528 individual beetles emerged. The highest density of both individuals and species was in the top layer. No species was significantly more frequent in the middle or bottom layers. Diameter had only a limited effect on species density and individual species reproduced in both coarse and fine wood. In conclusion, forest fuel piles can be ecological traps for several uncommon and red-listed saproxylic beetles. The negative effects can be mitigated by removing the piles before the insects colonize them. If this is not possible, then the top layer should be retained.

Biodiversity and sustainable forestry in changing landscapes – principles and southern Sweden as an example

Abstract We discuss die human impact on the forests of northwestern Europe, especially changes in disturbance regimes and changes in the density of important features for biodiversity preservation. In southern Sweden, human impacts have decreased densities of old (>150 years) living trees and large (DBH > 40 cm) dead trees to less than 1% of their original densities. In the same fashion, forest fires have decreased enormously in extent during the last 300 years, except in southwestern Sweden where the original fire frequency was presumably lower. These changes have had a tremendous impact on forest biodiversity. The number of extinctions in Sweden increases rapidly from the north to the south both for forest living species and other species. The number of threatened species shows a similar pattern and it is probable that many of these species belong to the extinction debt, especially those species that are dependent on sun-exposed old living and dead deciduous trees. Rapid restoration measures, such as increasing the number of old sun exposed oaks and large dead deciduous trees in the vicinity of existing hot-spots, may prevent some impending extinctions. Fire is important to use when managing forests for preserving biodiversity, especially in areas where fires more recently have been suppressed and where a relict fire-adapted fauna is Still present.

Air sampling of its pheromone to monitor the occurrence of Osmoderma eremita, a threatened beetle inhabiting hollow trees

Osmoderma eremita is a threatened scarab beetle living in the hollows of old deciduous trees and is regarded as an umbrella species of the beetle fauna associated with this habitat. Several methods like pitfall trapping and wood mould sampling have been used to monitor the occurrence of O. eremita, but these methods cannot be applied for trees with certain characteristics. Recently, (R)-(+)-γ-decalactone was identified as a male-produced sex pheromone of the species. Here, we show that γ-decalactone can be detected in hollow trees by air sampling and that the presence of the compound is strongly correlated with the occurrence of living male beetles in the same trees. Air was sampled from tree cavities and extracts analysed using gas chromatography–and mass spectrometry. There was a 89% match between the detection of γ-decalactone in extracts and the occurrence of male O. eremita±2 days from the sampling event. In the absence of males, samples never contained γ-decalactone, and the presence of this compound in a tree cavity appears to be a good predictor of O. eremita occupancy. Air sampling can be a useful complement to other methods when trying to detect as many trees housing this beetle as possible, which is crucial when estimating populations sizes and developing conservation strategies for this species.