A common lack of demographic equilibrium among tree species in Białowieża National Park (NE Poland): evidence from long‐term plots

Abstract

Questions: Does the size structure characterizing particular tree species in natural forest stands converge towards a steady state? What is the main reason for departures of observed tree size distributions from equilibrium models? What is the consequence of long-term strict protection for the demography of tree species and the conservation of associated biota?Location: Stands of natural forest in Białowie_ za National Park (NE Poland) that have been under strict protection for about 90 yr.Methods: Data on recruitment, growth and mortality of approximately 10 000 trees representing 11 species (aspen, birch, alder, pine, oak, maple, ash, elm, spruce, lime and hornbeam), from seven replicated surveys of five permanent monitoring plots (total size = 15.44 ha), established in 1936, were used to derive theoretical, species-specific equilibrium distributions as a basis for evaluating the demographic changes of the species involved.Results: Over a monitoring period of 76 yr, there were strong downward trends in the population densities of several tree species of different successional status and light requirements. A vast majority of the conspecific equilibrium curves, modelled on the basis of growth and mortality data, revealed a 'rotated sigmoid' shape when plotted in semi-log plots. In contrast to these equilibrium curves, the observed tree size distributions of most species were unimodal, at both the beginning and the end of the study period. Departures between theoretical and observed distributions increased over time, particularly for shadeintolerant and intermediate species.Conclusions: The populations of several tree species occurring in the Białowie_ za National Park are demographically unstable -a fact reflected in large and steadily increasing differences between theoretical and actual tree size distributions. The main reason for this are the insufficient recruitment rates typical of most species. Some tree species may very soon disappear almost entirely, and this will certainly lead to far-reaching changes in the functioning of local forest communities. Among other consequences, the current demographic trends, as observed for Białowie_ za tree species, are very likely to have a strong effect on the long-term survival of numerous forest organisms (such as insects, fungi, lichens, etc.), which depend, directly or indirectly, on the presence and balanced demography of particular tree species.

Structural diversity of selected oak stands (Quercus roburL.) on the Krotoszyn Plateau in Poland

“…Whilst analysing the growth and development of stands at permanent experimental plots, they found that some of the so-called primeval species, such as oak, pine, ash and aspen, are now ageing populations, threatened by an at least temporary disappearance from the stand layer. The most expansive species in areas under strict protection proved to be hornbeam and lime (Brzeziecki et al 2012;Brzeziecki et al 2016). The authors also pointed out that the likely loss of some forest tree species in the stand will result in a decrease of the overall diversity of the forest ecosystems in Białowieża Forest.…”

“…As a heliophilous species, it is not finding favourable regeneration sites under the dense canopy of hornbeam. Interesting research spanning several decades on the variability of species composition in the protected forests of Białowieża National Park (BNP) is presented by Bernadzki et al (1998), Brzeziecki et al (2012) and Brzeziecki et al (2016). Whilst analysing the growth and development of stands at permanent experimental plots, they found that some of the so-called primeval species, such as oak, pine, ash and aspen, are now ageing populations, threatened by an at least temporary disappearance from the stand layer.…”

“…In protected forests using passive protection, natural processes shape the structure and composition of the forests. as shown by many years of research on the dynamics of these forests, their structural diversity can be surprisingly low (Brzeziecki et al 2016). …”

“…Frequently, forests located in nature reserves or national parks, whose structure is largely the result of natural forces, are provided as examples of highly structured forests. However, long-term studies focused on natural forests indicate that the natural processes occurring in them can lead to the development of a simple system in terms of their species composition and structure (Brzeziecki et al 2012;Brzeziecki et al 2016). However, achieving the postulates of having managed forests be as close as possible to natural ones, that is, by using complex forms of fellings, regeneration methods mimicking the natural regeneration of various species and silvicultural practices carried out in forest ecosystems, may even encourage the development of more diverse stands (Paluch, Bielak 2009;Jaworki 2011).…”

Should the whole Białowieża Forest be a national park?

“…Many forest studies, especially long-term ones, describing the dynamics of forest ecosystems found outside of direct human influence, may contain valuable guidelines that can be used to protect forests with unique characteristics (e.g. Andrzejczyk, Brzeziecki 1995, Bernadzki et al Bielak 2009Drozdowski et al 2010;Brzeziecki et al 2016;Brzeziecki et al 2017). Some of the foresters' antagonists are clearly fearful that foresters will start looking at the trees of the Forest through the prism of the raw wood that can be obtained and sold, which would undoubtedly threaten the Forest's sustainability.…”