Articles by Rauno Väisänen

Distribution and occurrence of bark beetles and other forest insects in relation to environmental variation were analysed by multivariate methods. Eight different forest edges were studied using 10 x 10 m sample plots that formed 200 m linear transects perpendicular to the forest edge. Forest edge affected the distribution of insect species only in the edges between mature, non-managed spruce stands and clear cuts or young seedling stands, but not in the pine stands. The occurrence of the selected forest insects mainly depended on variables associated with the amount and quality of suitable woody material. The most significant environmental variables were forest site type, crown canopy coverage, tree species, number of stumps, number of dead spruce trunks and amount of logging waste at site. Quantitative classification of species and sample plots showed that some specialized species (Xylechinus pilosus, Cryphalus saltuarius, Polygraphus poligraphus and P. subopacus) adapted to mature spruce forests, tended to withdraw from the forest edge to interior stand sites. By contrast many generalized species (Pityogenes chalcographus, P. quadridens, Pissodes spp., Hylurgops palliatus, Tomicus piniperda, Dryocoetes spp. and Trypodendron lineatum) benefitted from cuttings and spread over stand borders into mature forest.

• Peltonen, E-mail: mp@mm.unknown
• Heliövaara, E-mail: kh@mm.unknown
• Väisänen, E-mail: rv@mm.unknown

Invertebrates of young Scots pine (Pinus sylvestris L.) stands were preliminarily studied along a gradient of industrial air pollutants in Harjavalta, south-western Finland. Bark samples and net samples on pine branches and needles were taken in May–June, 1987. The number of aphids on needles was highest near the industrial plants. The number of mites in bark was positively correlated with the increasing distance from the pollutant source. Detrended correspondence analysis ordination calculated according to the bark invertebrates showed that the sampling sites of the zones far from the emission source formed a distinct group while those of the zones near the source were relatively widely dispersed indicating disturbances in faunal structure.

The PDF includes an abstract in Finnish.

• Heliövaara, E-mail: kh@mm.unknown
• Väisänen, E-mail: rv@mm.unknown

Quantitative variation in the elemental composition of living Scots pine needles was studied along an atmospheric pollutant gradient in the surroundings of the industrial town Harjavalta, south-western Finland. Two 9-km-long transects, each with nine sample plots, running to the S and SW from factory complex were delimited in a homogenous Scots pine (Pinus sylvestris L.) forest. Needle samples were taken from 10 trees at each site, and from two separate sites in Tuusula near Helsinki. There was considerable spatial variation in the elemental composition of the needles. Heavy metals (Cu, Fe, Zn) showed a clear pattern of exponentially decreasing concentration with increasing distance from the emission source. Sodium and potassium concentrations, as well as the ash weight and air-dry weight, also decreased. Magnesium, manganese and calcium concentrations increased with increasing distance.

The PDF includes an abstract in Finnish.

• Heliövaara, E-mail: kh@mm.unknown
• Väisänen, E-mail: rv@mm.unknown

Succession of insect attacks on young Scots pine (Pinus sylvestris L.) was studied in heavily, moderately and slightly polluted pine stands within a three-kilometre distance from a prominent emission source in Western Finland. The total number of pest species was highest in the moderately polluted stand, but unlike other herbivores, aphids were also abundant in the heavily polluted stands. A few positive but no negative interactions were detected between herbivores, which suggests that insect species may benefit from a previous occurrence of other species in the same tree.

The PDF includes an abstract in Finnish.

• Heliövaara, E-mail: kh@mm.unknown
• Väisänen, E-mail: rv@mm.unknown

Paratization of Petrova resinella L. in the gall stage was studied in the surrounding of Harjavalta, south-western Finland, in relation to industrial air pollution. Of the studied 283 galls, 28% produced a moth, 52% of the larvae/pupae were paratisized, and 20% were empty or contained a dead larva. The proportion of paratisized galls did not depend on the distance from emission sources of industrial air pollutants.

The PDF includes an abstract in Finnish.

• Heliövaara, E-mail: kh@mm.unknown
• Väisänen, E-mail: rv@mm.unknown

The presence/absence data of 27 forest insect taxa (Retinia resinella, Formica spp., Pissodes spp., several scolytids) and recorded environmental variation were used to investigate the applicability of modelling insect occurrence based on satellite imagery. The sampling was based on 1,800 sample plots (25 m by 25 m) placed along the sides of 30 equilateral triangles (side 1 km) in a fragmented forest area (approximately 100 km²) in Evo, Southern Finland. The triangles were overlaid on land use maps interpreted from satellite images (Landsat TM 30 m multispectral scanner imagery 1991) and digitized geological maps. Insect occurrence was explained using either environmental variables measured in the field or those interpreted from the land use and geological maps. The fit of logistic regression models carried between species, possibly because some species may be associated with characteristics of single trees while other species with stand characteristics. The occurrence of certain insect species at least, especially those associated with Scots pine, could be relatively accurately assessed indirectly on the basis of satellite imagery and geological maps. Models based on both remotely sensed and geological data better predicted the distribution of forest insects except in the case of Xylechinus pilosus, Dryocetes sp. and Trypodendron lineatum, where the differences were relatively small in favour of the models based on field measurements. The number of species was related to habitat compartment size and distance from the habitat edge calculated from the land use maps, but logistic regressions suggested that other environmental variables in general masked the effect of these variables in species occurrence at the present scale.

• Väisänen, E-mail: rv@mm.unknown
• Heliövaara, E-mail: kh@mm.unknown

Biogeographical patterns of the Scolytidae in Fennoscandia and Denmark, based on species incidence data from the approximately 70 km x 70 km quadrats (n = 221) used by Lekander et al. (1977), were classified to environmental variables using multivariate methods (two-way indicator species analysis, detrended correspondence analysis, canonical correspondence analysis).

The distributional patterns of scolytid species composition showed similar features to earlier presented zonations based on vegetation composition. One major difference, however, was that the region was more clearly divided in an east-west direction. Temperature variables associated with the location of the quadrat had the highest canonical coefficient values on the first axis of the CCA. Although these variables were the most important determinants of the biogeographical variation in the beetle species assemblages, annual precipitation and the distribution of Picea abies also improved the fit of the species data.

Samples with the most deviant rarity and typicality indices for the scolytid species assempblages in each quadrat were concentrated in several southern Scandinavian quadrats, in some quadrats in northern Sweden, and especially on the Swedish islands (Öland, Gotland, Gotska Sandön) in the Baltic Sea. The use of rarity indices which do not take the number of species per quadrat, also resulted high values for areas near Stockholm and Helsinki with well-known faunas. Methodological tests in which the real changes in the distribution of Ips acuminatus and I. amitinus were used as indicators showed that the currently available multivariate methods are sensitive to small faunal shifts even, and thus permit analysis of the fauna in relation to environmental changes. However, this requires more detailed monitoring of the species’ distributions over longer time spans.

Distribution of seven species (Scolytus intricatus, S. laevis, Hylurgops glabratus, Crypturgus cinereus, Pityogenes salasi, Ips typographus, and Cyleborus dispar) were predicted by logistic regression models using climatic variables. In spite of the deficiencies in the data and the environmental variables selected, the models were relatively good for several but not for all species. The potential effects of climate change on bark beetles are discussed.

The PDF includes a summary in Finnish.

• Heliövaara, E-mail: kh@mm.unknown
• Väisänen, E-mail: rv@mm.unknown
• Immonen, E-mail: ai@mm.unknown

The effects of modern forestry on northwest European forest invertebrates are summarized and analysed mainly on the basis of published literature. The direct influence of different practices including clear-cutting, thinning, burning-over, ploughing, changes in tree species composition of stands, fertilization, insecticides, pheromones and biological control are discussed from a forest zoological point of view. Also, the indirect effects of general changes in boreal forest dynamics, loss of primeval forests, cessation of natural fires and the dominance of young stands are described. The direct effects of different silvicultural practices on the species composition and diversity of forest invertebrates are usually considered to be striking but transient. However, when large areas are treated, the species associated with primeval forests, especially with the wood composition system in them, as well as the species associated with fires, seem to have drastically declined. In northwest Europe, efficient forestry has not caused such serious pest problems as is known from tropical countries or North America.

The PDF includes a summary in Finnish.

• Heliövaara, E-mail: kh@mm.unknown
• Väisänen, E-mail: rv@mm.unknown