Given their importance as a resource for many forest organisms, tree cavities were inventoried in the managed pine forests of north-east Poland, in relation to the: 70–100, 101–130 and >130 year age-classes within the clear-cutting system. The densities at which cavities were present was found to depend on forest age, given that stands 70–100 years old were characterised by an average density of 0.62 trees ha, while forests older than 130 years reported 3.28 trees ha. Stands aged 70–100 years differed from those aged 130+ in having just 0.27 trees ha of cavity trees, as compared with 2.91 trees ha. The total volume of cavity trees in stands up to 100 years old was 0.37 mhaon average, as compared with 5.42 mha in stands over 130 years old. The cavities created by woodpeckers constituted 76% of all of those found, and included 53% excavated by great spotted woodpeckers ( L.) and 23% by black woodpeckers (L.) The proportion of cavities excavated by was highest in the youngest age class of stands. There, cavities made by constituted only 8% of the total, as compared with 31% in the oldest stands. The abundance of cavity trees thus differed along an age gradient, though in any event the availability of cavity trees appears to be too limited to provide for the needs of hole-nesting birds. Forest managers must thus take more account than hitherto of the need to protect cavity trees.–1 –1 –1 –1 3 –1 3 –1 Dendrocopos major Dryocopus martius D. major D. martius

In 1989–1991, the feeding ecology of Tawny Owl (Strix aluco) was studied in Wigry National Park (NE Poland). Diet composition was investigated by analysis of pellets gathered in stands under roost trees or nest boxes from April to August in 3-5 home ranges each year. In order to assess potential prey, small animals were caught in 28 traps. Small mammals composed 66.5% of prey items and 78.9% of food biomass of Tawny Owl, birds - 8.1% and 13.9%, and frogs - 17.4% and 6.8% of prey and biomass, respectively. The diet was dominated by rodents, mainly bank vole (Clethrionomys glareolus) and common vole (Microtus arvalis), which together composed 37.0% of prey items and 37.2% of the biomass consumed. Among birds, the most common prey was Song Thrush (Turdus philomelos). Slightly preferred prey were field mouse (Apodemus agrarius), short-tailed vole (Microtus agrestis) and bank vole. One pellet contained 1-11 (mean 2.34 ± 0.09) prey items. Amphibians were the most numerous during May and June.

We assessed the assemblages of birds inhabiting pine-dominated managed forest, aged between 1–5 years and above 140 years. Birds were counted on study plots representing eight different phases to the forest's development, with nesting, foraging and migratory guild categories recognised. Numbers of bird species and population densities, both increased markedly with stand age (respectively r = 0.988 and r = 0.936, P < 0.001). While numbers of ground-nesting bird species failed to correlate with stand age, successively older stands did support ever-greater proportions of species in the assemblage that nested in tree crowns (r = 0.976, P < 0.005) or tree holes (r = 0.833, P < 0.005). Raptors were most abundant in forest at the oldest stages of growth, and there was an age-gradient-related increase in the shares of both plant-eating species (r = 0.952, P < 0.005) and raptors (r = 0.764, P < 0.005). Resident birds were most numerous in the oldest forest. PCA for ten selected variables (relating to guil...

The twinflower Linnaea borealis L. is a rare, boreal plant species that grows in coniferous forests and is partly protected in Poland. We studied its distribution and the condition in the Augustów Forest (NE Poland) describing 22 twinflower patches in total. The following features were assessed: (1) patch area, (2) distance between individual twinflowers, (3) patch density, (4) intensity of flowering, (5) fruiting, (6) main accompanying plant species, (7) plant community structure, (8) species composition and age of the forest stands, (9) canopy cover of the forest stands, (10) existing and potential threats. In the northern part of the forest where suitable pine sites dominated, twinflowers were distributed irregularly and unevenly. Twinflowers in the Augustów Forest occur in relatively big areas with individual patches covering from 100 m ² to 3000 m ² , but most commonly 500–1000 m ² . The mean distance to the nearest neighbouring twinflower was 1600 m (range from 250 m to 6035 m). This pattern of distribution and separating distance does allow for sexual reproduction within the studied forest stand and blooming was confirmed in 21 out of 22 patches. In four locations, intensive blooming with >50 flowers shoot/m ² was observed. We did not observe a dependency of the flowering intensity on patch size. Despite the intensive and frequent flowering, as well as the presence of fruits, which were found in 15 patches, the twinflower reproduces mainly vegetatively. Twinflowers grew in 34–166 years-old pine-spruce stands with moderate canopy cover, but there was no relationship between the age of forest stands and the size of a flower patch. Plant species, which commonly occurred with twinflowers were: Vaccinium myrtillus , Calamagrostis arundinacea , Goodyera repens , Rubus saxatilis, Fragaria vesca, Pleurosium schreberi. Twinflower communities are threatened by invasive species in the forest understory in two locations only, while in the other locations no active protection is needed and the plants should rather be protected and monitored through multifunctional forest management. We emphasise the importance of the Augustów Forest for the twinflower in Poland, because about 10% of the Polish population grows in this forest complex.