Effects of exploitation and protection on forest structure, ungulate density and wolf predation in Białowieża Primeval Forest, Poland.
The pristine part of Białowieża Primeval Forest (protected as Białowieża National Park, 47.5 km2) is dominated by stands of deciduous trees (mainly oak Quercus robur, hornbeam Carpinus betulus, lime Tilia cordata, and maple Acer platanoides) (72.5% of forested area). Average age of tree stands is 130 yr. The managed part of Białowieża Primeval Forest (530 km2) has been heavily exploited for timber since 1915. Forestry practices have reduced the area of deciduous mature stands (currently 46% of area) and have greatly increased young-age coniferous stands. Pine Pinus silvestris and spruce Picea abies are the most widely replanted species. Average age of these tree stands is 72 yr. Five species of ungulates inhabit Białowieża Primeval Forest: red deer Cervus elaphus, roe deer Capreolus capreolus, moose Alces alces, European bison Bison bonasus, and wild boar Sus scrofa. Their total density in winter was 13-41 (mean 28) individuals km-2 (total biomass 1104-3338 kg, mean 2286 kg) in pristine forests, and 11-24 (mean 15) individuals km-2 (total biomass 1000-1654 kg, mean 1238 kg) in exploited forests. In pristine forests, red deer and wild boar were dominant (on average 43% and 51% of total number of ungulates, respectively), while in exploited forests, red deer and roe deer were the dominant species (39% and 27%). Two factors, percentage of deciduous tree stands and percentage of mature stands (>80 yr), in 11 censused sections of Białowieża Forest explained 71% of variation in ungulate biomass per unit area. Both factors positively correlated with ungulate abundance. Wolves (Canis lupus) preyed selectively on red deer and took fewer wild boar than expected on a random basis. Roe deer fell prey to wolves relatively more often in exploited forests, where it was the second most numerous ungulate in the community, than in pristine forests. Comparison of ungulate densities in pristine and exploited forests of Białowieża with data for six other woodlands in Poland showed that total biomass of ungulates per unit area was positively correlated with percentage area of deciduous forest sites. High food availability in deciduous forests (browse supply, acorn crop, soil invertebrates) is the main factor in determining abundance of ungulates in Polish lowland forests. 'Borealization' of deciduous forests due to forestry practices (favouring pine and spruce in silviculture) is diminishing their carrying capacity, especially for red deer and wild boar.