The Avifauna of Białowie·Za Forest
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The avifauna of Białowieza· Forest: a window into the past Ludwik Tomiałojć and Tomasz Wesołowski 94. Pygmy Owls Glaucidium passerinum may number 30-50 pairs in the Polish part of Białowieza˙ Forest in a good year. Günter Bachmeier ABSTRACT As a result of some 500 years of protection, parts of the Białowieza˙ Forest, in Poland, remain in a near-primeval condition. Studies of the breeding birds in the core part of the forest (Białowieza˙ National Park) over 29 years show that the bird community is species-rich but that densities of individual species are usually low, resulting in only moderate overall densities. In some species, low densities are a consequence of large territories and social exclusion, but more often they reflect the undersaturation of habitats by birds, despite superabundant food supply and nest-sites. Low productivity, resulting from high nest predation, may contribute to undersaturation. Species composition and numbers of birds fluctuate within relatively narrow limits, with the populations of closely related species fluctuating either independently of one another or in parallel; interspecific competition for resources plays a minor role. Some attributes of the Białowieza˙ ecosystems resemble conditions in undisturbed tropical forests but contrast sharply with those in fragmented, temperate secondary forests.The present Białowieza˙ avifauna provides a glimpse of that existing in central European forests before their historical transformation by humans. Its present exceptional character arises from 174 © British Birds 98 • April 2005 • 174-193 The avifauna of Białowie˙za Forest preservation of most of its pristine features.The forest constitutes a critical reference point for studies of woodland ecology, and its preservation should be a high priority. Unfortunately, commercial logging continues, gradually changing the forest’s structure and affecting the birds, especially those dependent on dead wood and old-growth.The relatively small national park (47.5 km2) is increasingly becoming an ‘island’, in which the long-term preservation of primeval forest features will be impossible. ur knowledge of the bird biology of so it is still possible to study birds living in near- pristine forest is full of gaps or misin- pristine conditions. Oterpretation, for the simple reason that The importance of studying European most temperate forests had been transformed woodland birds in pristine habitats became extensively by humans before modern research clear when one of us (LT) visited Britain in started. Consequently, any studies conducted in 1974 at the invitation of the BTO, and realised remnants of ancient temperate woodland are that the habits of birds in fragmented British important, providing crucial baseline data woods were strikingly different from those of against which to measure research from sec- birds occupying larger forests in central Europe. ondary or ‘man-made’ woodlands (Tomiałojć et These findings led to the launch (in 1975) of a al. 1984; Blondel 1995; Angelstam et al. 1997). comprehensive programme of ornithological In Europe, apart from some still extensive studies in the remaining tracts of primeval boreal (taiga) woodland, only two areas in the forest in BiałowieŻa National Park, which has transitional boreal-nemoral zone have retained developed into a long-term (almost 30 years) a substantial proportion of their near-primeval project. In this paper, we summarise the major mixed deciduous-coniferous forest. These are findings of this project, distilled from more the Berezinskiy Zapovednik, in northeast technical papers and reviews. Given that British Belarus (Byshnev 1991), and the BiałowieŻa forests and their birds may once have shared (pronounced ‘Byawovyezha’) Forest on the many of the characteristics of present-day Belarus/Polish border. For millennia, these BiałowieŻa (Tomiałojć 2000), this provides forests were probably quite ordinary parts of readers with an insight into the past, to see how the central European woodland; their present forests and their birds functioned without outstanding position stems from preservation serious human interference. We also hope that of their ancient features (Tomiałojć & this paper will encourage readers to visit Wesołowski 2004). BiałowieŻa owes its survival BiałowieŻa, and to support the struggle to pre- to around 500 years of consistent protection, serve the entire BiałowieŻa Forest for future initially as a prestigious hunting ground for generations. Polish kings and, later, Russian tsars. In the twentieth century, the care by rulers has been Study area and methods replaced by formal nature protection. A small Białowieza˙ Forest part of the forest, some 47.5 km2, has been Situated on the Poland/Belarus border, strictly protected as a nature reserve since 1921, BiałowieŻa Forest (BF), which occupies about and this core part of the forest is termed 1,500 km2 (fig. 1), lies at approximately the BiałowieŻa National Park. Apart from some same latitude as Birmingham (the co-ordinates limited intrusion by humans (a few small clear- of BiałowieŻa village are 52° 41’N 23° 52’E), cut or burnt patches), this area has remained within the transition zone between boreal and continuously under forest cover for approxi- nemoral forests, where Norway Spruce Picea mately seven millennia, so its forest ecosystems abies contributes to most types of local tree- have been shaped by natural ecological stands. The area is low (mostly 165-170 m processes without direct human intervention. above sea level) and flat, the climate subconti- Despite quite extensive, and worrying, recent nental, with warm summers and fairly cold changes in the neighbourhood, which we winters, sometimes quite severe (snow up to discuss below, these processes still operate there, 1 m deep, temperatures dropping to -25°C), Footnote: ‘nemoral’: the temperate broadleaf forest zone and with a growing season of c. 208 days. For British Birds 98 • April 2005 • 174-193 175 The avifauna of Białowie˙za Forest © Fluke Art © Fluke Fig. 1. Map of the whole Białowieza˙ Forest and its surroundings, showing three zones of its protection and the contraction of the former high-forest area. BNP denotes the Polish Białowieza˙ National Park (composed of two protection zones). Key: 1 strictly protected parts of the neighbouring two national parks; 2 remaining parts of both national parks; 3 the Polish managed part shown jointly with its partly managed nature reserves; 4 main human settlements; 5 dam reservoir; 6 forest boundary in the seventeenth century; 7 present forest boundary; 8 state border. details, see Faliński (1986, 2002), Tomiałojć & uprooted trees There is a great deal of dead Wesołowski (1990, 1994) and Jędrzejewska & wood – standing trees, stumps, freshly Jędrzejewski (1998). uprooted trees and old fallen logs – on The BF primeval stands are distinctive average 130 m3/ha in oak-lime-hornbeam among European temperate forests owing to stands (Bobiec 2002). There are many root- certain features which are characteristic of rich pads (discs of flat root-systems of uprooted pristine forests in various climatic zones. These trees), some rising vertically up to 7.5 m, are as follows: forming ‘walls’ up to 10-20 m long, and con- stituting a structure intermediate between • Multi-storey profile of stands In particular, the ground and the tree-layers (plate 95). those of the oak Quercus-lime Tilia-horn- • Impressive tree height The maximum height beam Carpinus type can be subdivided into for Norway Spruces in BF is 55-57 m, and 5-6 layers. Huge spruces, which rise 10-15 m for some deciduous tree species 42-45 m above the main canopy, are the equivalent of (Faliński 1968, 1986). the emergents of tropical forests. • Diverse tree community BF stands harbour • Large amounts of dead timber, with many 26 species of trees and 55 shrub species. The 176 British Birds 98 • April 2005 • 174-193 The avifauna of Białowie˙za Forest oak-lime-hornbeam stands alone may be dead wood and covering some 22% of BNP; composed of a dozen or so tree species. They and (iii) mixed coniferous forests (plate 98, are also strongly diversified according to the p 184), dominated by spruces and Scots Pine age (up to 400-500 years old) and size of the Pinus sylvestris (covering 28% of BNP). The trees. More details and photographs are remaining parts are composed of old meadows given in Tomiałojć et al. (1984), Faliński partially overgrown by secondary woodland. (1986), Tomiałojć & Wesołowski (1990, Beginning in the late nineteenth century, the 1994, 2004). hunting records of BF birds were collected with varying intensity in different periods. Those Long-term ornithological research phases of extensive, qualitative surveys are sum- Most of our detailed studies were carried out in marised in Borowski & Okołów (1988) and the strictly protected fragment of the Tomiałojć (1995, 2001). Our own intensive, BiałowieŻa National Park (BNP; fig. 1). quantitative studies began in 1975, focusing on Although the park was enlarged to 105 km2 in the ecology and behaviour of birds breeding in 1996, in this paper we define BNP as the strictly the primeval old-growth stands. We have exam- protected older part, comprising 47.5 km2, ined the structure and dynamics of whole which has remained free of human intervention breeding communities, as well as the long-term since 1921 and has at no time been affected by dynamics of individual species. We have also forest exploitation other than localised charcoal investigated how variation in environmental production or cattle grazing (Faliński 1968). conditions (e.g. weather, food, predators) influ- Most of the BNP area is covered by three types ences bird numbers. Long-term data on popula- of old-growth stands: (i) oak-lime-hornbeam tion sizes originate from territory-mapping on forest (plate 96, p 181), the richest in terms of seven permanent census plots, each 24-33 ha in tree species and structurally the most diverse, size (see Wesołowski et al. 2002 for a description and also the most extensive (covering some of methods). In addition, we have carried out 44% of the BNP area); (ii) swampy deciduous intensive population studies on the breeding forests (riverine stands and alder Alnus carrs, ecology and behaviour of 12 species.