The impact of natural disturbances on bird communities in Białowieża Primeval Forest disappears within 35-45 years

The impact of natural disturbances on bird communities in Białowieża Primeval Forest disappears within 35-45 years | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed. Data may be preliminary. 5 September 2025 V1 Latest version Share on The impact of natural disturbances on bird communities in Białowieża Primeval Forest disappears within 35-45 years Authors : Rosanne José Michielsen 0000-0002-3136-4048 [email protected] , Michał Walesiak , Paweł Białomyzy , Robert Fuller , Grzegorz Mikusiński , Tomasz Samojlik , and Michał Żmihorski Authors Info & Affiliations https://doi.org/10.22541/au.175708647.75170387/v1 622 views 151 downloads Contents Abstract Statement of authorship in CRediT-format Key words Abstract Introduction Methods Results Discussion Supplementary Material References Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract Forest disturbances play a crucial role in temperate forest dynamics and are often thought to affect species communities for decades or even centuries. We assessed bird communities in 50 wind-created treefall gaps (median = 0.8 ha, max = 14 ha) and 50 control (unaffected) sites in Białowieża Primeval Forest, Poland. The same locations were surveyed in 1988 (0-10 years since gap formation) and again in 2023 (35-45 years since gap formation). In 1988, treefall gaps hosted bird communities distinct from controls, with gap size strongly shaping these differences. By 2023, however, communities in gaps and controls no longer differed, and gap size had no detectable effect. Our results show that the impact of natural disturbance events in primeval forest ecosystems may be shorter-lasting than expected. This study highlights the resilience of the Białowieża Primeval Forest and suggests the resilience of forests shaped by natural disturbances. Rosanne J. Michielsen* 1+ : [email protected] ; +48 725 367 726 Michał Walesiak* 1 : [email protected] Paweł Białomyzy 2 : [email protected] Robert J. Fuller 3 : [email protected] Grzegorz Mikusiński 4,1 : [email protected] Tomasz Samojlik 1 : [email protected] Michał Żmihorski 1 : [email protected] * Contributed equally + Corresponding author 1: Mammal Research Institute Polish Academy of Sciences; ul. Stoczek 1; 17-230; Białowieża, Poland 2: Nature Association Dubelt, Juszkowy Gród 17, 16-050 Michałowo, Poland 3: British Trust for Ornithology, Thetford, Norfolk IP22 4DS, UK & School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK 4: School for Forest Management, Swedish University of Agricultural Sciences SLU, Box 43, SE-739 21, Skinnskatteberg, Sweden Statement of authorship in CRediT-format RJM: Conceptualization, Methodology, Validation, Formal analysis, Data Curation, Writing - Original Draft, Visualization, Project administration, Funding acquisition; MW: Conceptualization, Methodology, Validation, Formal analysis, Writing - Original Draft, Visualization; PB: Investigation; RJF : Conceptualization, Methodology, Writing - Review & Editing; GM: Conceptualization, Writing - Review & Editing, Supervision; TS: Writing - Review & Editing, Visualization; MŻ: Conceptualization, Methodology, Resources, Writing - Review & Editing, Supervision, Funding acquisition Short running title : Vanishing forest disturbance effects on birds Type of article : Letter Number of words in the abstract : 145 Number of words in the main text : 3940 Number of words in text boxes : 0 Number of references : 70 Number of figures : 3 Number of tables : 0 Number of text boxes : 0 Corresponding author : Rosanne J. Michielsen; [email protected] ; +48 725 367 726 Key words biodiversity; blowdown; high-forest hypothesis; long-term dynamics; natural forest; primary forest; secondary succession; treefall gaps; windthrow; wood-pasture hypothesis Abstract Forest disturbances play a crucial role in temperate forest dynamics and are often thought to affect species communities for decades or even centuries. We assessed bird communities in 50 wind-created treefall gaps (median = 0.8 ha, max = 14 ha) and 50 control (unaffected) sites in Białowieża Primeval Forest, Poland. The same locations were surveyed in 1988 (0-10 years since gap formation) and again in 2023 (35-45 years since gap formation). In 1988, treefall gaps hosted bird communities distinct from controls, with gap size strongly shaping these differences. By 2023, however, communities in gaps and controls no longer differed, and gap size had no detectable effect. Our results show that the impact of natural disturbance events in primeval forest ecosystems may be shorter-lasting than expected. This study highlights the resilience of the Białowieża Primeval Forest and suggests the resilience of forests shaped by natural disturbances. Introduction Forest disturbance agents, such as wind, fire or tree-killing invertebrates, play a key role in maintaining habitat heterogeneity of natural forest ecosystems (Franklin et al. 2002; Schaetzl et al. 1988). By creating canopy gaps, they alter the forest structure, forming early-successional forest habitats of high structural diversity (Swanson et al. 2011). Those changes often enhance biodiversity, as many species are specifically associated with the microclimate and resources found within young regrowth (Thom & Seidl 2016). Birds, due to their high mobility, quickly respond to disturbances in forests and may immediately colonise affected habitats (Graser et al. 2025b). On the one hand, natural disturbances are suppressed in modern forests, making disturbed habitats and associated species threatened, endangered or even extinct (Brawn et al. 2001; Viljur et al. 2022). On the other hand, climate change is intensifying forest disturbances, making them more frequent, widespread, and severe (Seidl et al. 2011, 2020). Hence, assessing the effects of natural disturbances on biodiversity in forest ecosystems becomes increasingly important. The disturbance effects on animal diversity (e.g., bird diversity) depends on time. In the first decade following the disturbance event, animal diversity often increases, driven by abundant resources such as dead wood and flowering plants (Cours et al. 2023; Viljur et al. 2022). This is mainly driven by the early forest succession (Hilmers et al. 2018) and the effects of the disturbance – in particular ecological legacies (i.e., structures inherited from the pre-disturbance ecosystem such as tree damages and uprooting; Franklin et al. 2000; Swanson et al. 2011). At later successional stages, gap specialists gradually disappear and are replaced by shrub and closed canopy preferring species, as observed in birds (Begehold et al. 2015; Graser et al. 2025a; Wesołowski et al. 2018). These later stages of forest succession are generally characterized by a decrease (Hilmers et al. 2018) or stabilization (Viljur et al. 2022) of species richness. However, animal communities continue to differ over time; in a Mediterranean oak woodland bird community differences persisted for over 28 years (Jacquet & Prodon 2009) and in the North American boreal forests, for over 22 years (Duguid et al. 2016). In addition, old-growth forest bird species may appear only after 76 years (Schieck & Song 2006). Moreover, saproxylic beetle and bird communities in temperate European primary montane forests remained distinct for up to 250 years (Kameniar et al. 2021; Kozák et al. 2021). These effects may be especially strong and long-lasting in large gaps, as altered abiotic conditions (e.g., light and moisture) may promote the establishment of light-demanding trees, leading to permanent shifts in tree species composition and forest structure (Bernadzki et al. 1998; Dobrowolska et al. 2022; García-Palacios et al. 2016). Large gaps also attract ungulates, potentially suppressing vegetation regrowth as well as promoting browsing-resilient trees (Churski et al. 2017; Kuijper et al. 2010). As a result, disturbed areas may remain ecologically distinct in terms of species richness and community composition for decades or even centuries, with these effects particularly pronounced in larger gaps (Haney et al. 2008; Hilmers et al. 2018; Walesiak et al. 2024). While the effect of disturbances in natural forests may leave long-lasting impacts, the evidence for that remains limited. Most disturbance studies focus on the first few years following an event and rarely extend beyond two decades (Thorn et al. 2018; but see; Kameniar et al. 2021; Koivula, Kukkonen, and Niemelä 2002; Schieck and Song 2006). As a result, our understanding of long-term succession is largely based on space-for-time substitution studies (Kreyling 2024). However, this approach cannot fully replace true time series data and may lead to biased conclusions about post-disturbance succession patterns (Damgaard 2019; Kreyling 2024). Moreover, Since primary—and especially primeval—forests are rare in densely populated regions like Europe (Sabatini et al. 2018), most European disturbance ecology studies focus on managed and secondary forests (Viljur et al. 2022). These forests are usually heavily affected by anthropogenic ecosystem alterations and hence their ecosystem dynamics are disrupted. In contrary, evaluations done in primeval forests, usually acting as forest biodiversity hotspots, are generally lacking (but see Gutowski et al. 2020; Kameniar et al. 2021; Kozák et al. 2021). We studied changes in breeding bird community composition between 1988 and 2023 in windthrow gaps and adjacent closed-canopy forest in the core area of Białowieża Primeval Forest (i.e., the forest shaped primarily by natural disturbances since the last ice age; (Jaroszewicz et al. 2019). We expected that differences in bird communities detected in recently formed gaps in 1988 (Fuller 2000) will be detectable 35 years later, due to disturbance-induced alteration of tree species composition and forest structure. In addition, we expected that some early-successional species will continue to increasingly inhabit gaps due to effective reduction of canopy regeneration by the complete assemblage of native large herbivores present in the forest. In addition, we expected that gap size plays an important role in shaping bird communities in gaps during both study periods. Methods Study area The study was performed in the core area of Białowieża Primeval Forest, encompassing the last European lowland forest with primeval characteristics (Samojlik et al. 2020). Large-scale loggings never occurred in this part of the forest, and since the last glaciation period natural processes have been the major source of disturbance, with limited periods of small-scale human activity spread across hundreds of years (Jaroszewicz et al. 2019; Mikusińska et al. 2013; Samojlik et al. 2013). The forest is shaped by ongoing natural dynamics, and resembles a fine scale mosaic resulting from small disturbance events. It features ample standing and lying dead wood, abundant tree-related microhabitats, a wide variety of tree species, diverse sizes and ages, and dynamic, long-term changes in tree stand composition (Bernadzki et al. 1998; Drozdowski et al. 2017; Jaroszewicz et al. 2019; Przepióra & Ciach 2023). The study area is a highly productive mixed forest dominated by small-leaved lime (Tilia cordata) and common hornbeam (Carpinus betulus), along with abundant Norway spruce (Picea abies), pedunculate oak (Quercus robur), black alder (Alnus glutinosa), birches (Betula pendula and B. pubescens), and Scots pine (Pinus sylvestris) (Drozdowski et al. 2017). Białowieża Primeval Forest is listed as an Important Bird Area (BirdLife International 2025) with around 111 breeding bird species recorded, including multiple old-growth forest specialists such as white-backed- (Dendrocopos leucotos) and three-toed woodpeckers (Picoides tridactylus) (Tomiałojć & Wesołowski 2004). Study sites Between 1978 and 1988 several hurricanes struck Białowieża Primeval Forest, creating a mosaic of windthrow gaps of diverse size. In 1988, 50 of such gaps were selected based on prior knowledge and visual identification. We ensured all gaps contained at least three fallen trees and were at least 40 m across their longest dimension (Fuller 2000). Additionally, we included the largest treefall gaps present in the forest at the time (Fuller 2000). The gap length and width were estimated on site (median = 0.8 ha, maximum = 14 ha, minimum 0.06 ha; Figure S1; Fuller, 2000). Gap area was approximately estimated by multiplying gap width and length (i.e., assuming a rectangular shape of the gap). Within the gaps, the majority of fallen trees were Norway spruces (Fuller 2000). In addition, 50 control sites (i.e., closed-canopy sites without traces of recent disturbance events) were selected to provide a control for the gap effect (Fuller, 2000; Figure 1). Control sites were selected so they resembled the tree species composition and soil type of the treefall gaps. At each site a point was chosen at which the birds were counted (see below); in case of the gaps, this point was as close to the center of the gap as possible (Fuller 2000). While originally a paired-design was implemented (each gap site was paired with nearby control site), we decided to drop this design in our analyses (see the section Statistical Analyses below), as it was rather imperfect (e.g., many paired sites were actually closer to other sites and several sites were paired with sites more than 500m and up to a few kilometers away; Fuller, 2000). Moreover, in a non-paired design, we were able to test for interaction between site type and time period (see the section Statistical Analyses below). Obviously, no GPS coordinates from 1988 were available. However, it was possible to trace back all 100 sites in 2023 (i.e., 35 years later) based on a map of the National Park on which locations of sites were marked manually in the field, with reference to a permanent grid with marker posts, coupled with detailed descriptions. We verified the location of the treefall gaps and control sites in the field, based on cues indicating four decades old forest disturbances (e.g., the presence of pioneer tree species, degraded root plates and tree deformations caused by past treefalls; Figure 1B). We assigned a confidence class to each point (i.e., in a scale 1-4; N = 17, 60, 11 and 12, respectively, see Table S1 for a detailed description). All sites were at least 150 m from each other, except for three pairs of sites (127, 133 and 142 m, respectively). Bird surveys The same methodology for bird surveys was followed in 1988 and 2023: we conducted 5-minute point-counts between sunrise and 11:15 in three surveys: mid-May (11–17 May 1988 and 10-18 May 2023), late-May (20–25 May 1988 and 22-28 May 2023) and early-June (3– 7 June 1988 and 3-6 June 2023) (Fuller 2000). These three survey periods were used to encompass the peak of the vocal activity of the majority of the breeding birds (including residents, short-distance migrants and tropical migrants). During each point-count, only the birds observed within 50 meters of the site were counted to minimize the detection bias created by the habitat and to relate the birds as closely as possible to the target habitat (i.e., treefall gap or control site). Birds leaving upon arrival of the observer were included, but birds flying over - excluded. The sequence of the sites visited was altered between each survey, to make sure all sites received at least one count in the very early morning. Treefall gaps and controls were alternated during the counts to minimize the bias due to the survey time. In each study year, one expert ornithologist conducted all surveys in gaps and control areas, to minimize the observer bias. For each species, the highest abundance from the three visits to each site in a given year was utilized for all the subsequent analyses. Statistical analysis To determine if bird communities differed between the two treatments (treefall gaps vs controls) and years (1988 vs 2023), we calculated the Bray-Curtis dissimilarity matrix and compared the bird communities between treatments in both years, using Permutational Analysis of Variance (PERMANOVA, 10000 iterations; vegan package; Oksanen et al., 2022). Non-metric multidimensional scaling (NMDS) was used to visualize the PERMANOVA results (vegan package; Oksanen et al., 2022). To confirm the robustness of our results, we repeated the PERMANOVA analyses only on the group of points we were able to identify with high confidence (i.e., confidence classes 1 and 2; n = 37 and n = 40 for treefall gaps and controls, respectively. See Table S1 for a more detailed description). To test whether gap size influenced the bird community dissimilarity in both study years, we calculated the Bray-Curtis distances for all combinations of site-pairs within each year (i.e., the Bray-Curtis distance between one site of a certain treatment and all the sites of the other treatment; in total 4950 distances per year; 9900 in total. We extracted the Bray-Curtis distances for control–treefall pairs, assigning the gap size based on the treefall site in each pair. We also extracted control–control pairs, assigning them a gap size of 0 to serve as a baseline for the dissimilarity when the gap size approaches zero. We fitted a Generalized Additive Mixed Model (GAMM; mgcv package; Wood, 2017) with the Bray-Curtis distance as the response variable, using the natural logarithm of the gap area plus one (to handle zero values), the study year, and their interaction as explanatory variables. The two site IDs were included as random effects with ridge penalty splines. We examined the differences between gaps and control sites regarding the total bird species richness, the total abundance and the species-specific abundances (i.e., species with a cumulative abundance of over 30 to avoid problems with model convergence), using separate Generalized Additive Mixed Models. Each model included bird species richness, abundance, or species abundance as the response variable and treatment, study year, and their interaction as explanatory variables. The site ID was included as a random effect with ridge penalty splines. Subsequently, to assess significant differences, we calculated marginal means for each treatment within each year and conducted pairwise comparisons with a Tukey p-value adjustment (using the emmeans package; Lenth, 2023). All GAMMs were fitted with the Restricted Maximum Likelihood method, using a Poisson distribution for species abundance and a Gaussian distribution for total abundance and richness, both with a log-link function. All visualizations were created using the packages ggplot2 and ggeffects (Lüdecke 2018; Wickham 2016). All analyses were conducted in R (R Core Team 2024). Model estimates are reported as means ± SE. Results In 1988 and 2023, 42 and 41 bird species were counted, respectively (Table S2). The four most common species in 1988 were the Eurasian chaffinch ( Fringilla coelebs , n = 246; i.e., the sum of the highest species abundances from the three visits to each site, treefall gaps and controls combined), wood warbler ( Phylloscopus sibilatrix , n = 165), European robin ( Erithacus rubecula , n = 129) and collared flycatcher ( Ficedula albicollis, n = 90), and in 2023 were the Eurasian chaffinch (n = 167), collared flycatcher (n = 110), hawfinch ( Coccothraustes Coccothraustes , n = 96) and European robin (n = 96). In 1988, the bird species composition of treefall gaps differed from the controls (PERMANOVA; F = 11.3, p < 0.001; see also Fuller 2000), but 35 years later this difference was no longer detectable (F = 1.64, p = 0.091; Figure 2A). These results were confirmed on a subset of most certain sites (F = 9.03, p < 0.001 in 1988 and F = 1.20, p = 0.30 in 2023). Furthermore, in 1988, the gap size affected the community dissimilarity, with larger gaps hosting more distinct communities compared to the control sites than smaller gaps (GAMM, estimate = 0.07 ± 0.008, p < 0.001; Figure 2B). In contrast, the gap size, as estimated in 1988, no longer affected the community dissimilarity in 2023 (GAMM, estimate = 0.008 ± 0.007, p = 0.27). The total bird richness was significantly higher in treefall gaps compared to the control sites in 1988 (pairwise comparison: estimate = -0.2 ± 0.06, p = 0.002; Figure 3A; see also Fuller 2000). Total bird abundance followed a similar pattern, with higher values observed in gaps (pairwise comparison: estimate = -0.16 ± 0.05, p = 0.002). However, by 2023, these differences were no longer detectable, with no significant variation in species richness (pairwise comparison: estimate = 0 ± 0.06, p = 1) or abundance (pairwise comparison: estimate = 0.02 ± 0.06, p = 0.75). Five species differed in abundance between treefall gaps and controls in 1988 (Figure 3B; see also Fuller, 2000). Two of them were more numerous in closed-canopy control sites: wood warbler Phylloscopus sibilatrix (pairwise comparison, estimate = 0.72 ± 0.17, p < 0.001) and red-breasted flycatcher Ficedula parva (pairwise comparison, estimate = 2.44 ± 0.74, p = 0.001), while three in treefall gaps: common chiffchaff Phylloscopus collybita (pairwise comparison, estimate = -2.64 ± 0.46, p < 0.001), dunnock Prunella modularis (pairwise comparison, estimate = -0.89 ± 0.38, p = 0.022) and Eurasian blackcap Sylvia atricapilla (pairwise comparison, estimate = -1.5 ± 0.3, p < 0.001). In 2023, only great tit Parus major was more abundant in the control sites as compared to treefall gaps (pairwise comparison, estimate = 0.5 ± 0.25, p = 0.043). For graphs of all species and detailed results on model results and pairwise comparisons, see Figure S2, Table S3 and S4. Discussion In this study we showed that in the old growth stands of Białowieża Primeval Forest, former differences between bird communities of treefall gaps and closed canopy stands (Fuller 2000) virtually disappeared within 35-45 years. In 1988, the impact of treefall gaps on birds was evident both on community and species level (changes in species composition, richness and abundance of closed-canopy species and gap preferring species) and the dissimilarity with control sites was greatest in larger gaps. In 2023, in contrary to our expectations, all former community differences were no longer present, regardless of the gap size. Our results show that the impact of natural disturbance events in a highly productive primeval forest ecosystems excluded from any post-disturbance management may be shorter-lasting than expected, at least from the bird community perspective. Our findings have important ecological implications which we discuss below. In contrast to studies reporting lasting community differences after disturbances on much longer timescales (Hilmers et al. 2018; Kameniar et al. 2021; Schieck & Song 2006), in our study bird communities in control and treefall gaps were no longer distinguishable 35 to 45 years after gap formation. One of the main explanations for the relatively quick restoration on closed-canopy bird communities after the creation of gaps could lie in the relatively small sizes of our disturbed areas (i.e., 0.06 - 14 ha) as compared to timber production forests (i.e., which may reach several hundreds or even thousands of hectares; Reyer et al., 2017; Walesiak et al., 2024). Animal – and particularly bird communities of small gaps tend to host more closed-canopy species than large gaps, possibly resulting in their higher initial similarity to control areas (Kebrle et al. 2022). In 1988, surviving trees in most treefall gaps, albeit damaged, could provide resources for species typical for closed canopy forest (Fuller 2000). Indeed, while two of these species (i.e., wood warbler and red-breasted flycatcher) were less abundant at our disturbed sites, they were still observed there as well. Additionally, at our disturbed sites we did not observe any bird species typical of large-scale stand-replacing disturbances, like yellowhammer (Emberiza citrinella), northern wheatear (Oenanthe oenanthe), white wagtail (Motacilla alba), red-backed shrike (Lanius collurio) and others, commonly reported for post-disturbance landscape (Graser et al. 2025b; Walesiak et al. 2024). A possible explanation is that the studied gaps may be too small to support breeding territories for these species (Żmihorski et al. 2016). With a smaller initial species composition shift, it may take shorter time for the bird communities to converge with control areas. In addition, in small gaps tree species composition may regenerate with lower influx of pioneer species (Dobrowolska et al. 2022), resulting in persistent higher habitat similarity between control and former gaps. As the sizes of our gaps were representative for natural forests in Europe (Maroschek et al. 2024), we believe that the rapid disappearance of natural disturbance effects due to the small gap sizes could be considered a characteristic of natural European lowland forest dynamics. Next to the size of the gaps, also the dynamics of the highly productive and natural forest could explain the rapid fading of the differences between gap and control bird communities. The disturbed areas in our study are situated within a continuous old-growth high forest, which is predominantly shaped by natural dynamics. In natural forests, forest gaps ranging from single treefall gaps up to several hectares are repeatedly created (Maroschek et al. 2024; Nagel et al. 2016; Runkle 1982), boosting forest heterogeneity and biodiversity (Bobiec et al. 2000; Jaroszewicz et al. 2019; Przepióra & Ciach 2023). Indeed, Białowieża Primeval Forest has experienced at least two large bark beetle outbreaks and many wind storms since 1988, resulting in new canopy openings of varying sizes (e.g., at eight of our control sites, new gaps were formed after 1988 within 80 m of the exact point count site; Stereńczak et al. 2020). Moreover, the relatively high soil nutrient concentration and wetness of Białowieża Primeval Forest likely speeds up the canopy gap regeneration (Davis et al. 1999; Sokołowski et al. 2024). Indeed, studies reporting longer lasting disturbance effects are often from montane areas, with probably much poorer soil conditions (Kameniar et al. 2021; Kozák et al. 2021). In addition, ecological legacies such as the pit-and-mound topography typical for windthrow disturbances, likely provide regeneration possibilities for trees (Ulanova 2000). Furthermore, Białowieża Primeval Forest is highly dynamic regarding developmental stages (Bobiec et al. 2000) and the tree species composition (Brzeziecki et al. 2020) and there have been changes in the composition of the bird community related to climate change and other factors (Wesołowski et al. 2022). In such a dynamic system, the effects of certain disturbances may be relatively quickly obscured by the effects of newly created disturbances and other dynamics in the direct surrounding areas. Moreover, even though we reported that single gaps appeared to have closed within four decades, new gaps created in the meantime enable the continuity of early-successional forest habitats. Currently, there are several hypotheses on the natural structure and dynamics of Europe’s primeval forests, that have implications for predicting the gap regeneration in European natural forests. The debate is mainly centered around two hypotheses: the high-forest hypothesis and the wood-pasture hypothesis (Kirby & Watkins 2015). The general conclusion within the high-forest hypothesis, is that since the beginning of the Holocene much of the European continent was covered by closed-canopy mixed-deciduous forest with natural disturbances creating canopy gaps and leading to spatial diversity in successional stand development (Mitchell 2005). The wood-pasture hypothesis challenges the high forest hypothesis by arguing that primeval forests were open, park-like landscapes, kept in their open state by wild large herbivores (Vera 2000). This hypothesis emphasizes the role of grazing, browsing, and trampling in maintaining an open mosaic of woodland, grassland, and scrub. According to this point of view, gaps in the forest would be prevented from regenerating into closed-canopy by large herbivores (Hodder et al. 2005). As the treefall gaps in this study closed rather quickly after their formation and their bird communities resembled closed-canopy forest, we believe that Białowieża Primeval Forest functions as a high forest, despite the high browsing pressure exerted by a full assemblage of extant native large herbivores (i.e., wild boar, Sus scrofa; red deer, Cervus elaphus; roe deer, Capreolus capreolus; moose, Alces alces and European bison, Bison bonasus). This may be due to the absence of true grazers (e.g., the extinct aurochs Bos primigenius and tarpans, Equus ferus) (Lundgren et al. 2024). Moreover, coarse dead wood possibly created areas that were less accessible to herbivores (de Chantal & Granström 2007). Hence, in Białowieża Primeval Forest, the browsing and grazing pressure exerted by the full assemblage of native large herbivores was not sufficient to prevent the forest gaps from regenerating into closed-canopy high-forest. Our findings document the relatively fast forest ecosystem restoration without any management intervention, like planting or fencing. The natural gaps in the Białowieża Primeval Forest, with maintained ecological legacies, apparently regenerated within four decades. Even heavily-disturbed sites (i.e., the largest treefall gaps in our study were around 14 ha), became ecologically similar to undisturbed sites in terms of bird community composition. As birds are usually good indicators of overall ecosystem biodiversity (Fraixedas et al. 2020; Roberge & Angelstam 2006), we conclude that allowing natural ecosystem dynamics to act might be an effective and inexpensive forest restoration strategy. Moreover, as the sizes of our gaps are representative for natural forests in Europe (Maroschek et al. 2024), we expect that biodiversity changes caused by natural disturbances in highly productive and natural lowland forests may disappear within several decades. In conclusion, this study demonstrates the high resilience of the Białowieża Primeval Forest ecosystem and likely reflects the inherent resilience of primeval forests. Acknowledgements We are grateful to Andrzej Keczyński and Ewa Zin, who taught us how to “read” the forest and its disturbance history. We thank Julia Barczyk for guiding us to her research plots, Rik Nienhuis, Flora van Eupen, Ewa Komar, Dominika Koprowska, Nika Knez and Alicja Walesiak for their assistance in identifying the research points from the past and Alexandra Elbakyan for supporting this study. We are grateful to Dries Kuijper, for helping us improving the manuscript by doing a friendly review. Finally, we acknowledge Białowieża National Park for granting us access to conduct research in this precious forest. Open Research Statement All data and R-scripts will be made available upon acceptance of the manuscript. Conflict of Interest Statement The authors declare that they have no known conflict of interest Figure captions Figure 1 : Description of the study sites. Example of a control site (A) and a treefall gap from 1988 in 2024 (B), showing recent uprootings (a), remains from historical uprootings (b) and damaged (malformed) trees (c). Overview of the study area with locations of the studied treefall gaps and controls (C), and the general location of Białowieża Primeval Forest (D). Photographs by Rosanne J. Michielsen. Figure 2 : A: Non-metric multidimensional scaling summarizing the bird community in 1988 and 2023 (stress = 0.29 and 0.31, respectively). Each point represents the NMDS outcome of one site, with the circles representing control sites and the triangles representing treefall gaps. The size of the triangles reflects the estimated gap size in 1988 (ha). Ellipses show the SE of the points. In 1988, the bird community in the controls was significantly different from the treefall gaps (PERMANOVA, p < 0.001), but not in 2023 (PERMANOVA, p = 0.09). B: Predicted Bray-Curtis dissimilarities between control and treefall gaps in relation to gap area based on GAMM models, with the associated 95% confidence intervals. Figure 3 : The average abundance and richness of all bird species pooled (A) and the abundance of several selected species (B) per point-count site presented with the associated 95% confidence intervals. In (B) only species which significantly differed between the two treatments in any of the two study periods are shown. Significant differences (p < 0.05) are indicated with an asterisk, based on the pairwise comparisons of the Estimated Marginal Means with a Tukey p-value correction (see Figure S2 for the results of all species and Table S3 and S4 for the model details). Bird icons by Tomasz Samojlik. Supplementary Material File (figure 1.pdf) Download 17.83 MB References 1. Begehold, H., Rzanny, M. & Flade, M. (2015). Forest development phases as an integrating tool to describe habitat preferences of breeding birds in lowland beech forests. Journal of Ornithology, 156, 19–29. Bernadzki, E., Bolibok, L., Brzeziecki, B., Ząjaczkowski, J. & Żybura, H. (1998). Compositional dynamics of natural forests in the Bialowieza National Park, northeastern Poland. Journal of Vegetation Science, 9, 229–238. BirdLife International. (2025). Site factsheet: Puszcza Bialowieska. Available at: https://datazone.birdlife.org/site/factsheet/bialowieza-forest. Last accessed 21 July 2025. 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Keywords biodiversity blowdown high-forest hypothesis long-term dynamics natural forest primary forest secondary succession treefall gaps windthrow wood-pasture hypothesis Authors Affiliations Rosanne José Michielsen 0000-0002-3136-4048 [email protected] Mammal Research Institute Polish Academy of Sciences View all articles by this author Michał Walesiak Mammal Research Institute Polish Academy of Sciences View all articles by this author Paweł Białomyzy Nature Association Dubelt View all articles by this author Robert Fuller British Trust for Ornithology View all articles by this author Grzegorz Mikusiński Swedish University of Agricultural Sciences School for Forest Management View all articles by this author Tomasz Samojlik Mammal Research Institute Polish Academy of Sciences View all articles by this author Michał Żmihorski Mammal Research Institute Polish Academy of Sciences View all articles by this author Metrics & Citations Metrics Article Usage 622 views 151 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Rosanne José Michielsen, Michał Walesiak, Paweł Białomyzy, et al. The impact of natural disturbances on bird communities in Białowieża Primeval Forest disappears within 35-45 years. Authorea . 05 September 2025. DOI: https://doi.org/10.22541/au.175708647.75170387/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. For more information or tips please see 'Downloading to a citation manager' in the Help menu . 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