Bottom-up versus top-down control of tree regeneration in the Białowieża Primeval Forest, Poland

• Published in: The Journal of ecology Vol. 98; no. 4; pp. 888 - 899
• Main Authors: Kuijper, Dries P.J, Cromsigt, Joris P.G.M, Jędrzejewska, Bogumiła, Miścicki, Stanisław, Churski, Marcin, Jędrzejewski, Włodzimierz, Kweczlich, Iwona
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01-07-2010; Blackwell Publishing; Blackwell Publishing Ltd
• Subjects: Abiotic factors; Alces alces; Animal behavior; Biodiversity; Bison; Capreolus capreolus; Cattle; Cervus elaphus; Deer; deer cervus-elaphus; Ecosystems; exclosure; Forest canopy; Forest ecology; Forest regeneration; Forests; herbaceous vegetation; Herbivores; herbivory; hornbeam; moose; natural regeneration; plant-communities; Plant-herbivore interactions; predation risk; primary productivity; red deer; roe deer; Saplings; Seedlings; Soil fertility; species diversity; tolerance to browsing; Trees; Ungulates; Vegetation; Vegetation cover; white-tailed deer; wild boar; wild boars; yellowstone-national-park; Poland; Europe
• ISSN: 0022-0477; 1365-2745
• DOI: 10.1111/j.1365-2745.2010.01656.x

1. We tested the interactions between biotic and abiotic factors in structuring temperate forest communities by comparing tree recruitment after 7 years inside 30 pairs of exclosure (excluding ungulates: red deer, roe deer, bison, moose, wild boar) and control plots (7 x 7 m each) in one of the most natural forest systems in Europe, the Białowieża Primeval Forest (eastern Poland). The strictly protected part of that forest hosts the complete native variety in trees, ungulates and their carnivores and excludes human intervention. 2. We analysed whether the exclosure effect interacted with abiotic factors, relevant for tree recruitment (canopy cover, ground vegetation cover, soil fertility and soil wetness) at different stages of tree regeneration (seedlings, saplings [less-than or equal to] 50 and > 50 cm). 3. Contrary to our expectations, a single factor dominated at each stage of tree regeneration. Herbaceous vegetation cover was the main factor determining the number of seedlings with an optimum at 38% of cover. Soil fertility determined the density of saplings [less-than or equal to] 50 cm, with on average three times higher density on eutrophic than on oligotrophic soils. Herbivory was the main factor determining recruitment rate of trees into > 50 cm size classes only. 4. The density of saplings that grew into the > 50 cm size class was more than three times higher in the exclosures than in the control plots during 7 years. In the absence of ungulates, on average 3.1 species recruited into the > 50 cm size class compared to 1.7 in control plots. Tree species occurred in more equal proportions inside exclosures, whereas species composition was pushed towards strong dominance of a preferred forage species, Carpinus betulus, in the presence of ungulates. This suggests that preference of species by ungulates can coincide with tolerance to browsing. 5. Synthesis. The study showed that abiotic conditions dominated the early stages and ungulate impact the later stages of tree regeneration, indicating the context-dependence of herbivore top-down effects. Heterogeneity in abiotic and biotic conditions may, therefore, have an important influence on the strength of top-down effects and the role that herbivores play in natural ecosystems.