Erlend Rolstad

Habitat selection as a hierarchical spatial process: the green woodpecker at the northern edge of its distribution range

Abstract Habitat selection can be envisaged as a hierarchical spatial process, from choice of home range to choice of dietary item. The green woodpecker (Picus viridis) is described as being closely bound to cultivated land and deciduous forests, mainly due to its summer diet composed of ants (Hymenoptera: Formicidae) found on meadows and pastures. To explore possible responses of this woodpecker to recent changes in land use practice, we studied home ranges, feeding habitats and food selection of a marginal population (four radio-marked males and five females) in a 30,000-ha conifer-dominated landscape at the northern edge of its distribution range in south-central Scandinavia. We asked: (1) Is the green woodpecker confined to areas with cultivated land and deciduous forest? (2) If so, are important food items (ants) particularly abundant or exclusively found there? (3) Can clearcuts and young plantations substitute for cultivated land as feeding habitat? Home ranges (mean=100 ha) were invariably confined to the parts of the landscape that contained cultivated land (<1% of the total area). In summer, birds preferred to feed in cultivated land, presumably due to a higher overall biomass of ants compared to forest habitats. They avoided clearcuts, but preyed extensively upon soil-dwelling ants in young conifer stands (16–30 years old). We failed to find preferences for particular ant groups (Lasius niger and L. flavus) associated with cultivated land. The principal summer food was Serviformica, an ant group that was equally abundant in cultivated land and forest habitat. A positive correlation between ant body mass and a preference index suggests that the birds selected the larger ant species independent of habitat type. In winter, birds fed exclusively on mound-building Formica rufa-ants in closed-canopy, older forest stands. Our results indicate that the green woodpecker successfully utilizes young conifer plantations as feeding habitat. At a larger scale, we hypothesize that green woodpecker populations fail to establish in managed forest tracts, not because of food shortage, but because the landscapes lack cultivated land serving as a key stimulus encouraging individuals to settle.

EPIPHYTIC LICHENS IN NORWEGIAN COASTAL SPRUCE FOREST: HISTORIC LOGGING AND PRESENT FOREST STRUCTURE

Current forestry policies worldwide aim at conserving and restoring biodiversity in managed forests. In this respect, epiphytic lichens have become a focal group in studies of how logging and silvicultural methods can be adjusted to mimic and restore old-growth conditions. We addressed this issue in a retrospective study in the coastal spruce (Picea abies) forest region of central Norway, surveying 31 old forest sites in order to relate a selected group of epiphytic macrolichens (Fuscopannaria ahlneri, Lobaria pulmonaria, L. scrobiculata, Nephroma spp., Platismatia norvegica, Pseudocyphellaria crocata, Ramalina thrausta, and Sphaerophorus globosus) to forest stand characteristics and previous logging history. The lichens were associated with brook ravines, F. ahlneri and P. crocata mostly so, being 10 times more abundant in ravine valley bottoms than on adjacent slopes and plateaus. All species used spruce trees as their main substrate, but L. pulmonaria, L. scrobiculata, and Nephroma spp. preferred scatt...

Using forest stand reconstructions to assess the role of structural continuity for late-successional species

Abstract Historical reconstructions of past forest dynamics and stand structures have been used to establish reference conditions for managing present forest ecosystems. In this study we (1) developed and combined a suite of stand reconstruction techniques to describe past stand characteristics, and (2) applied these stand histories to evaluate the relationship between wood-decay fungi and forest continuity. Ten previous selectively logged stands of Norway spruce (Picea abies L. Karst.), in the middle boreal zone of southeastern Norway, were studied. We reconstructed stand structures during the 20th century using tree-ring series, growth patterns, age structures, and decay classification and datings of stumps and logs. All stands were selectively logged between 1890 and 1965, with a mean logging interval of 25 years. Harvested volumes (1900–1965) constituted 25–99% of present standing volumes and present volumes were 2.6–21 (median 4) times higher than the lowest estimated historic volumes. Dead wood was categorized into eight decay classes, where one is recently fallen, and eight is almost completely decayed. Six fungus species, assumed to indicate dead-wood continuity, were found on logs in decay classes 2–4, all of which were estimated to be

Black woodpecker nest sites: characteristics, selection, and reproductive success.

To assess whether modern forestry practices pose a threat to the black woodpecker (Dryocopus martius), we studied nest-site selection and reproductive success in an intensively managed, boreal forest landscape of southcentral Scandinavia during 1990-95, We recorded 501 nesting events in 457 excavated holes in 367 trees, of which 180 events were monitored for reproductive success. Radiotelemetry was used to monitor 219 birds. All naturally occurring tree species were used as nest sites, but most nest holes were in live aspen (Populus tremula; 50%) and Scots pine (Pinus sylvestris; 25%). Dead trees were rare (8% of available nest-trees, 0.7 dead trees/100 ha) but constituted the most strongly selected tree type, being used 2.5 times more often than expected from random use of nest trees. The birds selected trees retained on recent clearcuts (used 2 times more often than expected), and they avoided trees in old forest. Selection of nest habitat was consistent with nesting success; the predation rate was lower and fledging rate was higher in clearcuts than in old forest. Selection of nest trees was not consistent with nesting success; the predation rate did not differ, but fledging rate was lower in dead trees compared to live aspen and pine. Habitat characteristics of cavities used for roosting (n = 124) did not differ from cavities used for nesting. Aspen and pine reached minimum critical dimensions (36 and 40 cm dbh) at the age of 55 and 110 years, respectively. In boreal Scandinavia black woodpecker nest sites do not seem to be threatened by modern forestry, provided that dead and green trees are retained on clearcuts and that scattered aspen trees are allowed in young conifer plantations.

Black woodpecker use of habitats and feeding substrates in a managed Scandinavian forest

To investigate whether the black woodpecker (Dryocopus martius) is threatened by modern forestry practices, we studied the use of habitats and feeding substrates in a managed boreal forest landscape of southcentral Scandinavia. Clearcutting practices have affected 80% of the 10,000-ha study area. In total, we located 219 radiotagged birds 5,638 times during 1990-94, of which habitat was described at 722 locations of 103 birds. For feeding habitat, birds preferred young plantations (15-30 yr) dominated by Norway spruce (Picea abies) and with high canopy closure. For feeding substrates, woodpeckers preferred stumps in young plantations and snags in old forest. Forest >50 years old was preferred for resting and display. The preference for young plantations as feeding habitat corresponded with habitats where the staple food source, wood-living ants (mostly carpenter ants; Camponotus spp.), was most abundant. Year-round home ranges decreased in size with an increasing proportion of young plantations in the landscape. We conclude that in continental Scandinavian forests, where snow depths are moderate (<0.7 m), food resources for the black woodpecker are well secured with present-day forestry practices.