Is the impact of loggings in the last primeval lowland forest in Europe underestimated?

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Is the impact of loggings in the last primeval lowland forest in Europe underestimated? The conservation issues of Białowieża Forest Article in Biological Conservation · September 2018 DOI: 10.1016/j.biocon.2018.09.001

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Short communication

Is the impact of loggings in the last primeval lowland forest in Europe underestimated? The conservation issues of Białowieża Forest

T

⁎

Grzegorz Mikusińskia,b, , Jakub Witold Bubnickic, Marcin Churskic, Dorota Czeszczewikd, Wiesław Walankiewiczd, Dries P.J. Kuijperc a

Swedish University of Agricultural Sciences SLU, Department of Ecology, Grimsö Wildlife, Research Station, 730 91 Riddarhyttan, Sweden Swedish University of Agricultural Sciences SLU, School for Forest Management, Box 43, 739 21 Skinnskatteberg, Sweden c Mammal Research Institute, Polish Academy of Sciences, ul. Stoczek 1, 17-230 Białowieża, Poland d Siedlce University of Natural Sciences and Humanities, Faculty of Nature Science, Department of Zoology, ul. Prusa 12, 08-110 Siedlce, Poland b

A R T I C LE I N FO

A B S T R A C T

Keywords: Salvage logging Core area Forest biodiversity Landscape effects

Loggings in biodiversity hot-spots are perceived as very serious threat to forest species and habitats of high conservation interest. In this paper we scrutinize the spatial impacts of recent loggings in the Polish part of the renowned Białowieża Forest being the last remaining area of lowland temperate forest with a primeval character in Europe with the status of World Heritage and Natura 2000 site. The loggings have been applied in order to cope with the outbreak of the spruce bark beetle Ips typographus. We used satellite images to perform cover change detection analysis that delineated areas being logged in Białowieża Forest between July 2015 and June 2018. Next, we assessed the extent of forest loss in areas with different management regimes as well as landscape-scale impacts. The total area of detected clear-cuts amounted to at least 675 ha, including 229 ha of oldgrowth stands. Assuming a buffer of 100 m from the edge of cleared forest patches, the cumulative direct and indirect impact of recent logging activities was estimated to amount to at least 4073 ha of affected forest.

Logging activities resulted in a 26% increase in fragmentation in the entire Natura 2000 area. We argue that the ecological impact of logging extends beyond the logged areas by modifying the landscape structure and affecting ecosystem functioning on a landscape scale. As such, the recent salvage loggings in the Białowieża Forest clearly damaged the conservation value of this precious area, not in the least by increasing its fragmentation. To avoid further degradation, we strongly argue for allowing natural tree regeneration on clear cuts and also for the extension of Białowieża National Park to cover the entire forested area.

1. Introduction International reporting concerning an immediate threat to forest biodiversity through logging activities usually relates to primary tropical or subtropical forests in developing countries (Lindenmayer, 2010). The value of primary forests relative to degraded forests is superior in terms of biodiversity, carbon sequestration and storage, water provision and the maintenance of human health (Watson et al., 2018).

In areas that have already lost most primary forests due to long history of human exploitation, the conservation focus is on securing the protection of the last remaining patches and on restoration of diverse oldgrowth forests (Chazdon, 2008). This is crucial since these remaining forests of high conservation value are subjects to increasing impact of various disturbance events related to global climate change (e.g. fire,

pathogens, insect outbreaks) posing a new conservation challenge (Müller et al., 2018). Therefore, disturbing them even further by human activities is highly unfavorable for biodiversity conservation (Lindenmayer et al., 2017).

In Europe, conservation of the remaining valuable old-growth forests has been attempted by national forms of nature protection (e.g. national parks, nature reserves) as well as by supranational activities like the Natura 2000 network (Winkel et al., 2015). Moreover, the efforts to integrate forest biodiversity conservation and its restoration in the European Union by Green Infrastructure approach largely based on forest habitats, is currently under implementation (Snäll et al., 2016).

In spite of all these efforts, the maintenance and restoration of forest biodiversity in this wealthy region of the Global North is often not secured due to conflicts of interest among different stakeholders (Niemelä

⁎ Corresponding author at: Swedish University of Agricultural Sciences SLU, Department of Ecology, Grimsö Wildlife, Research Station, 730 91 Riddarhyttan, Sweden.

E-mail address: grzegorz.mikusinski@slu.se (G. Mikusiński).

https://doi.org/10.1016/j.biocon.2018.09.001 Received 20 December 2017; Received in revised form 23 August 2018; Accepted 3 September 2018 0006-3207/ © 2018 Elsevier Ltd. All rights reserved.

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2.2. Data sources

et al., 2005), ongoing climate change, and especially by the generally low forest cover in comparison to pre-industrial era and the extreme shortage of forests with a primary character (Hannah et al., 1995).

Therefore any form of active management of such forests should be performed with extreme caution.

In this paper we scrutinize the most recent developments in the Polish part of the renowned Białowieża Forest (BF) focusing on the spatial extent of direct and indirect impacts of recent salvage loggings in this last remaining area of lowland temperate forest with a primeval character in Europe. Although the conflict concerning the conservation of this area has been going on for several decennia (Wesołowski, 2005; Niedziałkowski et al., 2014), the present stage of the conflict has an unpreceded amplitude that engage the Polish political scene, European Union, the international scientific community and nature interested public worldwide (e.g. Schiermeier, 2016; Nelsen, 2017). The trigger for the current conservation conflict was the recent outbreak of spruce bark beetle Ips typographus that killed a considerable proportion of Norway spruce Picea abies in the Polish part of BF (Stockland, 2017).

The State Forests Holding that manages the BF outside of the Białowieża National Park (BNP), decided to remove dead and dying trees by means of modern technology (harvesters, forwarders), hence creating sizable clear-cuts. Based on analyses of high-resolution satellite images, our study is the objective estimate of the extent of logging (since 2015) in zones with different UNESCO protective status, and a quantification of the potential landscape-scale impact beyond the spatial extent of the actual loggings. We discuss the possible direct and indirect ecological effects of the recent salvage logging in this unique area, and provide recommendations for future management of Białowieża Forest to mitigate these human-induced impacts.

To perform a three-year (2015.07–2018.06) forest cover change detection analysis we used Sentinel-2 (S2) data which is an innovative wide-swath, high-resolution (10–60 m), multi-spectral satellite with 13 spectral bands launched in June 2015 by the European Space Agency (ESA). Two best, least cloudy S2 scenes (2015.07.25 and 2018.06.09) were selected and downloaded from the Copernicus Open Access Hub (https://scihub.copernicus.eu/). We focused our change detection exercise on forest stands, excluding all open areas and non-forest vegetation. To develop a high resolution forest mask we performed a supervised classification of S2 image from 2015 using the Support Vector Machine (SVM) classifier (see the online Appendix).

2.3. Forest cover change detection For a change detection analysis we used the iteratively re-weighted Multivariate Alteration Detection method (iMAD), followed by the Maximum Autocorrelation Factors (MAF) post-processing (Canty, 2014). The first three MAF variates were used in the supervised classification (SVM) of the observed types of forest cover change. We distinguished two classes of forest cover change; 1) resulting from logging (both clear-cuts and selective logging) or natural gap formation, 2) resulting from forest stand defoliation caused, in the case of BF, primarily by bark beetle attack of spruce trees. The third class consisted of the areas where no significant changes had occurred.

In order to map all logging activities in the study area during the observed period it was necessary to distinguish between real logging (clear-cuts and selective logging) and other forest losses resulting from the natural canopy gaps dynamics. A parameter helpful in separating these two types of events is the size of each forest loss polygon. To find an objective threshold value for this parameter we compiled the histogram of the sizes of all forest loss polygons detected within the protected zones (zones 1 & 2, Fig. A5). This reference area includes the nature reserves and BNP, all by definition excluded from the logging activity. As we were aware of safety logging activity along the road in one nature reserve (“Szafer's Reserve”) we excluded it from our consideration. Finally, we chose a 0.95 quantile of the compiled reference distribution of forest loss areas (Fig. A5).

We have to note that our threshold-based method to identify forest loss areas caused by logging does not account for new, relatively large windthrow areas that emerged during the study period. We identified one extreme storm event during the study period (2017.08.27) that locally affected the south-western part of the study area. However, based on data provided by the State Forest Holding and photo-interpretation of pre- and post-event satellite images we estimated the total area of windthrow areas classified as forest loss and larger than the estimated threshold (i.e. 0.2449 ha) to be 5.48 ha which corresponds to only 0.8% of all forest loss areas included in our landscape analysis. The rest of identified windthrow areas were smaller than the threshold or were classified by our change detection algorithm (1 year after the disturbance) as defoliated forest stands (dead trees), likely because of a large amount of dead wood accumulated on the ground.

2. Material and methods 2.1. Study area The Białowieża Forest is a contiguous forest complex (150,582 ha) bordering Poland and Belarus. It is perceived as the best preserved fragment of lowland temperate forest that once covered the European Plains. The Polish part of BF (41% of surface area) consists of: a national park (17%), nature reserves (20%) and managed stands (63%).

The entire BF is a UNESCO World Heritage Site, whereas the Polish part is also Natura 2000 site (Puszcza Białowieska, PLC200004), a protected landscape area and a Biosphere Reserve. The BF is characterized by many well-preserved tree stands with characteristics of primeval forest: multi-species, uneven-aged, with a high proportion of dead wood and the occurrence of natural gap formation (Jędrzejewska and Jędrzejewski, 1998). It is treated as a forest biodiversity hot-spot with virtually complete sets of ungulate species, predators and old-growth specialists (e.g. woodpeckers or saproxylic insects) representative for temperate lowland forests.

Across this UNESCO World Heritage Site (http://whc.unesco.org/ uploads/nominations/33ter.pdf) different protective regimes occur, from the strict protection (UNESCO zone 1), through the partial protection of part of BNP, the nature reserves (zone 2) and the most valuable forest stands outside the reserves (zone 3), to the active protection of the remaining area managed by the State Forests Holding (zone 4). According to the agreement with UNESCO, cutting is only allowed in zone 4. For our analyses, we quantified the impact of logging in these different protective zones (i.e. in total Natura 2000 area and UNESCO zones 1–4). Additionally, we looked at the logging impact in old-growth stands (defined as stands with at least 10% of trees of one species being 100 years old or more), which overlap with the different protective zones, as they are the most valuable tree stands occurring outside the strictly protected area (zone 1).

2.4. Landscape analysis Based on the results of change detection analysis we estimated the direct area loss of forest due to recent loggings (see an example on Fig. 1) and indirectly affected forests according to different ranges of (cumulative) impact zone, assuming buffers around the logged areas of radius 10, 50, 100 and 500 m. We use those measurements to provide opportunity to discuss the impact of loggings exceeding the actual clear-cuts including the disturbance effects of forestry machines used to perform current felling and removal of trees and future silvicultural measures (e.g. soil scarification, planting, thinning), negative edge effects and the loss of core areas with forest interior conditions. Although 267

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Fig. 1. Spruce bark beetle infestations (left) increase the amount of standing and laying dead wood, change tree stand structure and openness, which is beneficial for dead wood specialists, such as white-backed and three-toed woodpeckers and many threatened saproxylic insects. Logging leads to complete habitat destruction for many species (right). Both pictures are taken in Białowieża Forest stands belonging to State Forests Holding. Photos: D. Kuijper.

0.2449 ha minimum area threshold, and 294,030 m3 and 304,622 m3 using the 0.10 ha and 0.05 ha thresholds, respectively (see Table A4 and the External validation section in the online Appendix for details). For comparison, the total harvested timber volume in the study period according to official statistics provided by the three relevant forest districts was 308,640 m3. Most logging occurred in UNESCO zones 4 and 3 with 361 ha (3.05%) and 299 ha (1.23%) of forest logged, respectively.

In zone 2, 8.1 ha (0.05%) were logged while no loggings occurred in zone 1. The mean size of logged areas was similar for zone 3 (1.07 ha) and 4 (1.27 ha; Fig. A6). Using 100 m buffer around clear-cuts to define indirect impact of loggings, the total area of Natura 2000 directly and indirectly affected by recent loggings (cumulative impact) amounted to 4,073 ha (7%). For impact zone set to 500 m, the corresponding figures were 20,827 ha and 35.7%.

The area of potential indirect impact on core forest areas (i.e. forests with some minimum distance to the edge) depended strongly on the buffer width applied (Fig. 4, Table A1). When core forest area was assumed to be located at least 100 m from the edge of clear-cuts, the calculated loss in Natura 2000 was 3,693 ha (7.43%) of such core areas.

The observed loss of core areas with the same definition applied (i.e. > 100 m from the clear-cut edge) and expressed by percentages were at similar levels in zone 3 (8.9%) and in old-growth stands (7.0%) but higher in zone 4 (17.4%). Use of 500 m from the clear-cuts edge in defining the core areas, resulted in much higher estimations of losses: 66% in zone 4 and 26.4% (4,634 ha) in Natura 2000 area.

The entropy index, calculated to estimate the landscape fragmentation resulting from the loggings, increased by approximately 26% since 2015 in the entire Natura 2000 area (Fig. 5, Table A2). The largest increase (about 89%) in fragmentation of forests occurred in zone 4, and increased to a smaller extent in all types of designated conservation areas but zone 1.

In total, over 7621 ha of forest (the sum of all bark-beetle affected pixels from 2015 (baseline) and all pixels classified as bark-beetle affected between July 2015 and June 2018), comprising 13% of total forest cover and 27.5% of coniferous dominated stands was affected by the spruce bark beetle (Fig. 6, Table A3). Interestingly, the level of barkbeetle infestation in UNESCO zone 1 (corresponding to the strictly protected part of BNP) was much lower in comparison to all other areas (Fig. 6).

our choice of impact ranges was somewhat arbitrary and we are aware of the fact that every species respond to human-disturbance in a species-specific way, we selected ranges to be close those described in scientific literature (Esseen, 1994; Ruete et al., 2016; Pfeifer et al., 2017). The logging was performed using heavy machinery (such as harvesters) and timber had to be extracted from the forest with tractors and big trucks, which all led to much collateral damage of the forest.

Hence the impacted area is logically larger than the logged areas only.

To quantify the landscape fragmentation resulting from logging activities, we estimated and compared between two focal dates (2015.07.25 and 2018.06.09) the entropy index (Vogt and Riitters, 2017) and the forest core area as obtained by the morphological spatial pattern analysis (MSPA; Soille and Vogt, 2009). We repeated MSPA analysis with the five different values of the forest edge width parameter (0, 10, 50, 100 and 500 m). Finally, we summarized the output of this analysis accounting for the different protective zones in the study area: 1) NATURA 2000 site (a whole study area), 2) UNESCO Natural Heritage Site (4 zones). Additionally, within each protection zone, we quantified the total area of defoliated forest stands (dead trees), which are mainly spruce stands affected by bark beetle outbreak. A detailed description of methodology is available in the online Appendix.

3. Results We achieved a very high accuracy of SVM classifications of both land-cover and forest change classes with the overall classification accuracy scores 0.97 (kappa = 0.96) and 0.96 (kappa = 0.93), respectively (see Appendix for more details). Based on the histogram of the size of forest loss areas compiled for the zones 1 and 2 (Fig. A5) we chose the value of 0.2449 ha (0.95 quantile) for the threshold above which we interpreted the forest loss as caused by logging. This threshold was very conservative when compared to reported sizes of natural canopy gaps in the BF (Bobiec, 2007). The selected threshold likely underestimated the actual logging area, excluding small-scale selective logging from our consideration. Still, the fact that new small gaps (i.e. smaller than 0.2449 ha) seem to be concentrated around larger logged areas and are very rare in protected parts of BF (see Fig. 1) indicates that great majority of them is of anthropogenic origin.

The highest concentrations of loggings occurred in the north-western and central parts of the BF (Fig. 2). The total area of clear-cuts in Natura 2000 amounted to 675 ha (1.16% of the total forest cover, Fig. 3, Table A1), including 229 ha of old-growth stands. Based on this value, the estimated (approximate) total volume of logged trees for the entire study area during the study period was 263,270 m3 using the

4. Discussion The salvage logging, defined as removal of trees and other biological material from sites after natural disturbance events, is an extreme 268

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Fig. 2. The spatial distribution of detected forest cover changes in the Polish part of the Białowieża Forest. The forest loss areas larger than 0.2449 ha (in red), were interpreted as caused by logging. However, very few forest loss patches smaller than our threshold (in black) were detected in the protected areas (Białowieża National Park and nature reserves) indicating that the great majority of those patches originated also from loggings.

case of clear-cutting appearing to be particularly damaging to the forest ecosystems. It reduces biological legacies, affect rare post-disturbance habitats, alter community composition, impair natural vegetation

recovery, facilitate the colonization of invasive species, alter soil properties, increase erosion, modify hydrology, and alter patterns of landscape heterogeneity (Lindenmayer and Noss, 2006). Blair et al.

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Fig. 3. The cumulative impact of logging in different protective zones in the BF according to assumed different ranges of their impact. The buffer of 0 m corresponds to a direct loss of forest caused by logging. The numbers above each bar show a proportion of each protective zone affected by logging.

effectively “perforated” the BF, indicated by the significant increase in entropy used here as a measure of landscape fragmentation. The logging activities resulted in a 26% increase in fragmentation in the entire Natura 2000 area, with the most pronounced increase in the UNESCO zone 4 (89%) and 3 (52%). Our analysis confirms the usefulness of publicly available high-resolution remote sensing data (like Sentinel-2 missions) for timely assessments of the degree valuable forest are being degraded (Miettinen et al., 2014). In the case of BF, when other reliable data is not available, our assessment based on objective, scientific methods is of particular value. Moreover, since the future management regime for BF is not yet decided, it may help in making the evidencebased decision.

Forest systems with a long-term temporal continuity, an extensive spatial contiguity and the occurrence of natural processes structuring the forest like BF (Mikusinska et al., 2014; Latałowa et al., 2015) are extremely rare in the European temperate zone (Hannah et al., 1995; Bengtsson et al., 2000) and as such have very high conservation value.

Moreover, across Europe, there is great interest in improving the

(2016) have recently identified salvage logged areas as supporting the lowest diversity of plants in a disturbance gradient; even severely burned sites had a more diverse flora. In the global meta-analysis by Thorn et al. (2017a) revealed that salvage logging is not consistent with the conservation objectives of protected areas.

In our analysis, we quantified the extent of salvage loggings in the best preserved European temperate lowland forest. We showed that at least 675 ha of forest have been logged in this area with an internationally recognized high conservation status as World Heritage site, Biosphere reserve, and Natura 2000. Due to large size of Białowieża Forest, the proportion of forest logged (1.16%) appears relatively small.

However, the area of estimated potential indirect impact on core forest areas was much greater and depended strongly on the edge buffer applied, approaching, using 500 m edge buffer, whole 72% of area impact of the UNESCO zone 4, and 26% of the entire Polish part of BF (i.e.

Natura 2000). Taking into account the proven negative effects of salvage logging on forest ecosystems, we argue that this will have a serious impact on the natural dynamics in this area. Moreover, these loggings

Fig. 4. The loss of forest core areas (i.e. forests with some minimum distance to the edge) in different protective zones in the BF linked to recent loggings according to different parameter levels based on the distance from the forest edge. The numbers above each bar show the percentage of each protective zone affected by logging.

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Fig. 5. The entropy index in year 2015 (before loggings) and in 2018 (A) and its absolute and proportional (the numbers above each bar) change (B) calculated for different protective zones in the Białowieża Forest. Since no logging occurs in UNESCO-zone 1, it was omitted from Fig. 4B.

Fig. 6. The total forest area affected by bark beetle (i.e. area of pixels classified as dead trees; state for 2018.06.09) calculated for different protective zones and two basic forest types within each zone. As we did not include mixed forest types in our land-cover classification we interpreted the coniferous class as dominated by coniferous tree species and the deciduous class as dominated by deciduous tree species. The numbers above each bar show the percentage of each protective zone affected by bark beetle.

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regeneration of for example long-lived foundation species like oak, Quercus robur (Smit et al., 2012). Recent studies from the BF show yet another mechanism of how tree logs can promote natural tree regeneration by creating places with higher perceived predation risk. Red deer, as the main browser in this system, avoid foraging close to tree logs (Kuijper et al., 2015; van Ginkel et al., 2018) resulting in lower browsing pressure on trees and higher regeneration success (Kuijper et al., 2013). Moreover, we predict that changes in landscape structure and openness will also influence predator-prey interactions on the longterm as landscape structure, particularly habitat openness, is a key factor determining predation and hunting success of large carnivores (Creel et al., 2005; Kauffman et al., 2007). Predation pressure on ungulate prey species may thus be altered resulting from changes in habitat structure. This shows the complexity of the trophic interactions that are likely strongly affected via changed landscape structure and which are difficult to predict (Kuijper et al., 2016). But the fact that salvage logging disrupts natural trophic interactions, which are one of the main conservation goals for this unique forest complex, is highly worrying for the natural functioning of this ecosystem.

Even if exact quantification of direct and indirect ecological effects of the salvage loggings performed in BF is difficult, the existing knowledge predicts large-scale and for species with high conservation value clearly negative consequences. The fragmentation and perforation of BF by highly artificial habitat (i.e. salvage logged areas) affect the ecological integrity of this unique and valuable forest is thereby in conflict with Habitat Directive (Art. 6, P. 3) applicable to this Natura 2000 site. Moreover, the status of BF as UNESCO World Heritage Site obliged the managers to protect natural ecological processes; the salvage logging obviously violate this obligation.

conservation status of forests within the Natura 2000 network (Kallimanis et al., 2015). Moreover, the Aichi Biodiversity Target 11 requires from signatory states to increase the area of terrestrial ecosystems that are not negatively affected by human activities to 17% of the total country surface area. Therefore the salvage logging, in response to a natural disturbance such as outbreak of spruce bark beetles in the best preserved and the largest area of lowland temperate forest with primeval character in Europe is alarming.

4.1. Potential direct and long-term impacts of logging on biodiversity and ecosystem functioning The impact of clear-cutting goes beyond the time and space of logged areas by directly affecting the neighboring stands both in the short and long-term. The direct, short-term disturbances are mainly related to the presence and movement of large machinery. Loggings have also long-term spatial-temporal consequences with wide-ranging effects on species groups and encompass e.g. changed microclimate and increased sun exposure (Wicklein et al., 2012), uprooting of trees exposed to wind (Esseen, 1994) or increased predation (Storch et al., 2005). The existing research results originating from BF and some other European forests allow for making some predictions concerning these impacts.

The period of salvage loggings in BF using heavy harvesters partially overlapped with the birds breeding season obviously impacting several rare species with high conservation priority (e.g. white-backed Dendrocopos leucotos and three-toed Picoides tridactylus woodpeckers, Tengmalm's Aegolius funereus and pygmy Glaucidium passerinum owls), and as such were violating Natura 2000 status of the area. Forestry practices during the breeding season are source of direct disturbance reducing reproduction and fitness of bird communities, especially of old-growth forest specialists (Pettersson et al., 1995). Moreover, the large alterations of forest structure will have long-term effect on the quality of breeding habitat for these specialists that especially rely on old and decaying trees. For example, Czeszczewik and Walankiewicz (2006) demonstrated that logging and removal of dead trees was detrimental for white-backed woodpecker population density in managed parts of BF. Other studies from this forest show that bird community structure is largely different between intensively managed stands and natural stands, again illustrating the long-term effects of active management (Czeszczewik et al., 2015). Obviously, the removal of old and decaying trees during salvage logging causes a large reduction of tree cavity resources (Walankiewicz et al., 2014), hence directly affecting the breeding habitat quality for many dependent species. In general, conversion of primary old-growth forests to secondary habitats may cause a parallel loss of multiple bird-mediated ecosystem services (Albrecht et al., 2014). For lynx Lynx lynx, a species with high conservation value, salvage logging will lower habitat suitability since it has been shown that it selects sites in the BF that are characterized by high complexity (linked to fallen logs) and dense undergrowth useful for stalking their prey species (Podgórski et al., 2008). Research from other temperate forests in Europe clearly indicates that salvage logging leads to structural and compositional homogenization of stands and delays regeneration processes (Michalová et al., 2017; Thorn et al., 2017b). We argue that also in the case of BF it will take several decades before tree stands retrieve some of the value that they had before salvage logging and before these habitats become suitable again for oldgrowth specialists.

Besides these potential direct effects of logging on habitat quality for a range of species we expect that large-scale ecosystem processes will be strongly affected by salvage logging. On the long-term, changes in the landscape structure can largely alter herbivore-plant and predator-prey interactions that operate at a landscape scale (Hebblewhite et al., 2005). The presence of tree logs promotes natural regeneration of trees by providing physical protection against ungulate browsing (Smit et al., 2015). Removal of dead trees will thus lead to reduced natural

4.2. Lessons learned and recommendations for future management As mentioned above BF has many different designations and their conservation goals are not necessarily compatible with each other and such situation may be used by opposing sides of the conflict in their argumentation. Taking into account earlier plans to continue salvage logging also in the remaining areas of BF affected by the bark beetle outbreak, its potential damaging effect on biodiversity and ecosystem functioning would greatly exceed our estimates. One can pose the question which particular designation played a main role in preventing the continuation of logging in the forest? Apparently national designations as Białowieża National Park, nature reserves along with status of UNESCO zone 1 and zone 2 functioned relative effectively as obstruction to salvage logging (only some 8 ha in UNESCO zone 2 according to our analysis). One of the designations that encompass the entire Polish part of BF is Natura 2000 based on both Habitats and Birds Directives. The effectiveness of Natura 2000 network in conserving biodiversity is often questioned (e.g. Trochet and Schmeller, 2013; Lisón and Sánchez-Fernández, 2017). In this particular case, the role of its Natura 2000 designation and the existing European mechanisms (through NGO's appeal to European Commission and decision of European Court of Justice) in preventing further damage caused by salvage logging must be fully acknowledged.

The protection of the BF and conservation of ecosystem processes that drive this system requires a science-based management demanding new approaches to assure its maintenance in the face of increasing number of disturbances related to global climate change and generally growing human pressure on valuable forests (Lindenmayer et al., 2017; Müller et al., 2018; Watson et al., 2018). We see therefore two important steps to mitigate the damage that has already been inflicted to this unique area.

Firstly, the logged areas should be left for natural regeneration. The State Forests Holding proposes that the logged areas will be cultivated, prepared for replanting and later thinned, which will continue the process of using machinery and affecting the adjacent forest stands for decades. When this approach is followed, the replanted gaps will form 272

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unnaturally regenerated patches influencing the long-term stand development and all its associated dynamic processes, including changes in trophic chain relationships (Broadbent et al., 2008). Hence, we strongly support allowing natural regeneration as occurs in the neighboring Białowieża National Park (see Kuijper et al., 2010) to create natural tree stands that are better adapted to the current climatic conditions (see also Żmihorski et al., 2018).

Secondly, we strongly recommend extending the national park to the whole BF. Currently, the area is partly managed by three districts of the State Forests Holding, partly by the Regional Directorate for Environmental Protection and partly by the BNP. In addition to securing natural functioning of this valuable ecosystem, enlarging the national park would allow for much better coordination of BF's management including development of ecotourism in the area. This would also be a sensible step towards achieving target 11 of the Aichi Biodiversity Targets in Poland (CBD, 2010). The Białowieża Forest, that represents the last-remaining large complex of lowland temperate forest with a primeval character, would then serve as a source of invaluable knowledge concerning the interplay of natural processes and biodiversity. This knowledge could be in turn applied in other areas where restoration of naturally dynamic forest is necessary.

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Acknowledgements We are grateful to two anonymous reviewers for their very constructive comments. GM acknowledges economic support from the Faculty of Forest Sciences of the Swedish University of Agricultural Sciences SLU. The work of DPJK was supported by funding of the National Science Centre, Poland (grant nr: 2015/17/B/NZ8/02403).

Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.biocon.2018.09.001.

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