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Urban forests are often remnants of former larger forested areas, and traditionally considered as degraded habitats due to negative effects of urbanization. However, recent studies have shown that urban forests managed for recreational purposes can be structurally close to natural forests and may provide habitat features, such as dead wood, that are scarce in intensively managed forest landscapes. In this study, we assessed how urbanization affects polypore species richness and the number of red-listed polypore species in forest stands, and the occurrences of polypore species on individual units of dead wood. Spruce-inhabiting polypore assemblages and their associations to urbanization, local habitat connectivity and dead-wood abundance were investigated in southern Finland. The effects of urbanization on polypore species richness and individual species were largely negligible when other environmental variability was accounted for. Several red-listed polypore species were found in deadwood hotspots of urban forests, though urbanization had a marginally significant negative effect on their richness. The main driver of total species richness was dead-wood abundance while the number of red-listed species was also strongly dependent on local habitat connectivity, implying that a high degree of fragmentation can decrease their occurrence in urban forests. We conclude that the highest potential for providing habitats for threatened species in the urban context lies in large peri-urban recreational forests which have been preserved for recreational purposes around many cities. On the other hand, overall polypore diversity can be increased simply by increasing dead-wood abundance, irrespective of landscape context.

Urban forests are usually not intensively managed and may provide suitable environments for species threatened by production forestry. Thus, urban forests could have the potential of enhancing biodiversity both within cities and at a larger landscape scale. In this study, we investigated stand structures of boreal urban forests to assess them in terms of naturalness and biodiversity conservation potential. We sampled two types of urban spruce-dominated stands: random urban stands as representatives of average urban forests, and valuable urban stands known to host high polypore richness and assumed to represent urban biodiversity hotspots. Urban forests were compared to rural forests with different levels of naturalness. Living and dead trees and cut stumps were measured from all studied stands. Urban forests had generally diverse living tree structures with abundant large-diameter trees. Random urban forests had more dead wood (median 10.1 m(3) ha(-1)) than production forests (2.7 m(3) ha(-1)) but still considerably less than protected, former production forests (53.9 m(3) ha(-1)) or semi-natural forests (115.6 m(3) ha(-1)). On the other hand, valuable urban forests had relatively high median volume of dead wood (88.2 m(3) ha(-1)). We conclude that the combination of diverse stand composition and the presence of old-growth characteristics in boreal urban forests form a strong baseline from which their biodiversity value can be further developed, e.g. by leaving more fallen or cut trees to form dead wood. We propose that urban forests could become significant habitats for biodiversity conservation in the future.

Preservation of small habitat patches termed as “woodland key habitats” or “especially important habitats” in the Finnish Forest Act has become an integral part of biodiversity-oriented forest management. Forest Act habitats belong to particular habitat types defined in the act, and they are supposed to have natural-like stand characteristics. However, very little is known about the actual stand structure in the designated habitats. Our aim was to compare stand characteristics between brook-side key habitats and comparable managed forests as controls. Seven study areas were selected from four regions across southern Finland. Within each study area ten key habitats and ten controls (140 stands) were randomly selected. Living and dead trees and cut stumps were measured in each stand within a 0.2 ha plot. The average degree of previous cutting was significantly lower whereas the volume of dead wood, volume of deciduous trees, and stand diversity were each significantly higher in key habitats than controls. The average volume of dead wood was 11.7 m ha in key habitats and 6.5 m ha in controls. However, there was considerable variation among individual stands, and a large part of key habitats could not be distinguished from randomly selected control stands with respect to stand characteristics. The preservation of natural brook channels with their immediate surroundings is undoubtedly important for maintaining aquatic and semiaquatic biodiversity. Nevertheless, when complementing the forest conservation network in the future, main emphasis in selecting potentially valuable stands should be placed on important structural features such as dead wood and old trees.3–13–1

Two-year-old containerized Scots pine ( L.) seedlings, raised under different fertilization and watering regimes, were subjected to feeding preference tests with pine weevils ( L.) in a bioassay. In the tests carried out with pairs of seedlings, the weevil preferred water-stressed seedlings to well-watered ones. In the case of well-watered seedlings, the weevil caused significantly more damage to NPK-fertilized seedlings than those given pure PK fertilization, or no fertilization at all. It is apparent that PK fertilization reduces, and water stress increases seedling susceptibility to weevil damage. The results support findings from field trials that water stress (planting shock) predisposes seedlings to weevil damage. Weevil resistance is discussed with respect to fertilization and water stress as determinants of seedling quality.Pinus sylvestrisHylobius abietis