Biodivers Conserv (2014) 23:449–466 DOI 10.1007/s10531-013-0612-3

ORIGINAL PAPER

Importance of high quality early-successional habitats in managed forest landscapes to rare

Diana Rubene • Lars-Ove Wikars • Thomas Ranius

Received: 11 June 2013 / Accepted: 20 December 2013 / Published online: 3 January 2014 Ó Springer Science+Business Media Dordrecht 2014

Abstract Species adapted to early-successional forest habitats are in managed landscapes largely confined to clearcuts. To improve habitat quality on clearcuts, green tree and dead retention is widely applied in forestry; however, its effects on rare early-successional species have rarely been shown. We repeatedly surveyed two red-listed beetle species ( ceramboides and Platysoma minus) on clearcuts in a managed boreal forest land- scape. We found that U. ceramboides decreased its occupancy over time while P. minus increased, indicating that red-listed species vary in their ability to successfully utilise managed habitats. We found no effect of connectivity on probability of occurrence, col- onisation or per clearcut. Trees retained alive improved habitat quality of clearcuts, since both species were more frequent in dead wood of such trees, in comparison to logging residues. We suggest that retention can be improved by protecting and creating dead wood as intact trees during harvesting. Rare specialist species require habitat of high quality, and consequently it is impossible to meet the requirements of these species on every clearcut. To preserve all early-successional species at a regional scale, we recom- mend focusing retention of green trees and dead wood to one or a few trees species on each clearcut and in each landscape.

Keywords Boreal forest Connectivity Colonisation Dead wood Retention forestry SaproxylicÁ Á Á Á Á

D. Rubene (&) L.-O. Wikars T. Ranius Department of Ecology,Á SwedishÁ University of Agricultural Sciences, Box 7044, 75007 Uppsala, e-mail: [email protected] L.-O. Wikars e-mail: [email protected] T. Ranius e-mail: [email protected]

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Introduction

Early-successional habitats in natural forests are often characterized by high species richness, as legacies from previous forest stage combine and interact with new conditions created by disturbance (Lindenmayer and Franklin 2002; Swanson et al. 2010). In natural forest landscapes, early-successional habitats are created by various disturbances, from small scale gap dynamics and individual wind-felled trees, to large stand-replacing events such as storms and intense forest fires (Esseen et al. 1997; Franklin et al. 2002). The large- scale disturbances provide resources that are rare in mature forests, e.g. sun-exposed injured and dead trees and exposed patches of mineral soil (Swanson et al. 2010), and host distinct species assemblages (Simila¨ et al. 2002; Boucher et al. 2012). In Europe and parts of North America, many forests lack natural disturbance dynamics, because they are managed for wood production. Salvage logging is widely practiced after windstorms and fires, which removes dead trees left by disturbance and thereby impairs key ecosystem processes (Lindenmayer et al. 2004; DellaSala et al. 2006; Cobb et al. 2011; Boucher et al. 2012). Natural early-successional habitats have consequently become rare with negative consequences for many species (Kaila et al. 1997; Swanson et al. 2010). Managed forests are denser (to maximize production per area) and conditions thereby more shaded than in naturally shaped forests, further disfavouring organisms dependent on open forest conditions (Linder and O¨ stlund 1998). Today, early-successional forest stages in many managed landscapes are predominantly created by clearcutting. As a consequence, species that are naturally adapted to utilize habitats created by windstorms, fires and gap dynamics may be restricted to clearcuts (Kaila et al.1997; Jonsson and Siitonen 2012). Species specialized in disturbed forest habitats can only persist in a certain habitat patch for a limited amount of time, until it becomes unsuitable through succession. Long-term species persistence is thus only possible on landscape level and requires a continuous creation of new patches that can be colonised by species to compensate for deterministic local (Jonsson 2012). Many species that depend on early post-fire forest hab- itats may be able to survive in harvested forest patches, if habitat quality and patch network density in the landscape is high enough (Hanski 2008). In attempt to emulate natural disturbance in managed forests, retention of living trees, in particular trees, and dead wood on clearcuts is today a common silvicultural practice (Franklin et al. 1997; Gustafsson et al. 2010). However, dead wood volume retained at harvesting is insufficient to fully mimic the natural post-disturbance habitat (Gustafsson et al. 2010). Insufficient dead wood amount and diversity sets strong limitations on managed forests’ capacity to host species-rich communities (Siitonen 2001; Simila¨ et al. 2003). Furthermore, soil preparation and planting is used to speed up , significantly shortening the time span during which clearcut habitat can be used by early-successional species (Swanson et al. 2010). In addition, deciduous trees, which are characteristic components of natural disturbance-shaped boreal forests, have decreased in many regions of Northern Europe as a consequence of management (Fransson 2011). Therefore, species associated with decid- uous trees or dead wood, with high demands for habitat quality or connectivity might be unable to persist in managed forest landscapes. Studies on early-successional species have mostly considered diversity patterns at forest stand level a year or two after clearcutting (e.g. Hyva¨rinen et al. 2009), but there is a lack of understanding of species temporal dynamics on landscape level. In this study, we have analysed the importance of habitat quality on clearcuts and spatiotemporal dynamics on landscape scale of two rare early-successional , Upis ceramboides and Platysoma minus. We chose these as model species as they are considered to be negatively affected by

123 Biodivers Conserv (2014) 23:449–466 451 intensified forest management, since in natural landscapes they occur in recently burned forests (Palm 1951; Pettersson and Ehnstro¨m 2010). Threatened dead wood dependent species appear to particularly depend on high amount and diversity of dead wood, and to have lower occurrence in managed compared to semi-natural forests (Simila¨ et al. 2002). We have repeatedly surveyed U. ceramboides and P. minus in early-successional habitats created by clearcutting in a forest landscape in central Sweden in order to (i) analyse which factors affect colonisation and extinction probability by observing changes in species occurrences over time, (ii) determine the importance of amount and spatial distribution of dead wood within clearcuts for species occurrence and (iii) study the successional patterns in habitat use of the main study species vs. more common dead wood inhabiting beetle species over time. We expect that species occupancy per clearcut will change over time according to the amount of suitable habitat. We predict that habitat amount and suitability will affect species occurrence on several scales: by the properties of the dead wood objects, properties of the habitat patches (clearcuts) themselves and by connectivity to dispersal sources in the landscape.

Methods

Study species

The studied species, U. ceramboides (Tenebrionidae) and P. minus (), are saproxylic (=dependent on dead wood) beetles that inhabit boreal forests of Europe, Asia and North America. These species are thought to benefit from forest fires which create open, sun-exposed habitats rich in dead wood (Palm 1951). In managed forests of North America, U. cerambiodes appears to be strongly associated with open areas on clearcuts (Webb et al. 2008). Also in Sweden, the species does not appear to use closed canopy forest as habitat, which makes it particularly dependent on quality of clearcuts (L. Wikars, pers. obs., from previous surveys of *1,000 substrates in forests, most of them close to clearcuts with the species present). Larvae of both species develop under bark of sun- exposed dead deciduous wood, usually , which is white-rotted by fungi like Fomes fomentarius (Palm 1951; Ehnstro¨m and Axelsson 2002). Upis ceramboides larvae feed and develop in the phloem and superficial wood of dead birch over 2–3 years (Pettersson and Ehnstro¨m 2010). Larvae and adults of P. minus are predators (Baranowski 1994). In Sweden, both species are included in the red list (U. ceramboides VU, P. minus NT), because their distribution area is limited, highly fragmented and currently shrinking (Ga¨rdenfors 2010). Upis ceramboides has in Sweden a clearly documented regional extinction pattern from the South to the North. It has been recorded from most Swedish provinces, but gone regionally extinct from southern Sweden during late 1800s and early 1900s (Ga¨rdenfors 2010). The southernmost is today found in our study area, separated from a larger distribution area in the North by about 200 km. The species seems to still be abundant on clearcuts in northernmost Sweden (Naalisvara 2013). Platysoma minus is widely distributed across Sweden, but very little is known about its ecology, and it is thought to be declining on national level (Ga¨rdenfors 2010).

Study area

We studied a 225 km2 landscape in central Sweden, situated at an elevation of 250–500 m and covered by managed boreal forest, with Scots pine (Pinus sylvestris) and

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Table 1 Descriptive characteristics of the inventoried clearcut sites (mean values) Year No. of cleracuts No. of Clearcut Clearcut Dead wood Substrate Prop. of analysed substrates area (ha) age (years) aggregation decay substrates (nr of searched analysed density class with substrates) (m3 ha-1) white-rot

2004 65 (927) 231a 17.05 8.21 35.57b 2.87 0.52 2010 110 (898) 898 18.37 9.61 47.04b 3.45 0.50 a Substrate properties were measured on three clearcuts in 2004 b Highest dead wood density was measured on different scales (59 smaller scale in 2010) spruce (Picea abies) as the dominant tree species. The forest has been managed by clearcutting for about 50 years and is owned by a private company, Holmen Skog AB, which has been certified by FSC since 1998 and by PEFC since 2003. The area has historically (until 1900) been strongly affected by fires and has therefore had a consider- able component of deciduous trees. Currently, on regional level, only about 10 % of the forest stands have[35 % deciduous trees. The average amount of dead deciduous wood is 2.3 m3 ha-1 (Fransson 2011). During the last decade, at least two large forest wildfires (followed by salvage logging) have occurred and prescribed burning has been employed on some clearcuts, resulting in approximately 340 ha burned and harvested area.

Site selection

We conducted landscape surveys in 2004 and 2010. Clearcut forest stands for the surveys were selected using aerial photographs in 2004 (Wikars and Orrmalm 2005) and using GIS data from the forest company on forestry operations in 2010. Stands of age 3–14 years (harvested 1990–2001) were included in the first survey, and the age limit was based on previous knowledge about U. ceramboides habitat use. We set the minimum age to three years due to that the species does not use fresh dead wood (L. Wikars, pers. obs.) and most of the dead wood is created during harvesting. Further, the species have only been found on sun exposed substrates (see Study species) and almost all substrates become too shaded when planted forests are more than 14 years old (Jonsson et al. 2006). In the second survey, we revisited all the previously surveyed clearcuts and additionally all newly established ones, which were at least three years old (harvested 2001–2007). Totally 73 clearcut stands were surveyed in 2004 and 213 in 2010. All stands in the landscape harvested in 2001–2007 were surveyed and 40 % of the stands harvested in 1990–2000. When calculating connectivity, we took into account all clearcuts, also those not surveyed (see section on connectivity). Prior to analyses, clearcuts bordered to each other and within 5 years of age difference were pooled to one single data point, as species likely perceive them as one single habitat patch. Data were then combined as a weighted average for the whole area. Clearcuts where no birch wood was present were excluded from analyses as they do not constitute habitat. In the final analysis there were 65 clearcuts for 2004 and 110 for 2010. Summary of descriptive habitat properties of the surveyed clearcuts can be found in Table 1.

Species survey

The aim of the first survey was to analyse U. ceramboides occupancy in relation to habitat properties on clearcut level and substrate (dead wood object) level. In addition, we

123 Biodivers Conserv (2014) 23:449–466 453 recorded presence/absence of P. minus adults and larvae of another two common beetle species inhabiting dead birch: the mordax (found in birch wood in our study region) and the lamellicorn beetle Trichius fasciatus (deciduous wood) (Ehnstro¨m and Axelsson 2002). The common species were recorded in order to obtain a basis of comparison for habitat associations and changes in occupancy of the more poorly known . Population sizes may vary over time, both due to long-term trends and annual variation in weather, thus validity of any observed changes in occupancy of the threatened species would benefit from a comparison to a larger number of species. We recorded only larval stage of U. ceramboides because the adult beetles do not live under bark and can only rarely be observed. Both larvae and adults of P. minus live in dead wood, however, only adults can be recorded reliably, since the larvae are very small and could not be identified in the field. In 2010, P. minus was also included as a main study species, as it is red-listed and seemed to depend on similar habitats as U. ceramboides. The aim of the second survey was, in addition to habitat analyses as in 2004, to also study events of colonisation and extinction in relation to habitat characteristics. The surveys were carried out from middle of May to beginning of July. Dead wood of birch (cut logs and fallen trees) was searched for larvae of U. ceramboides and adults of P. minus by peeling off 0.25 m2 of bark per substrate and noting species presence/absence (see Table 1 for total number of substrates). In 2004, number of searched substrates per clearcut depended on dead wood availability and reached a maximum of 47 objects. In 2010, up to twenty substrates per harvested stand (one clearcut could contain several stands) were searched for beetles. If fewer suitable objects were available, all were sur- veyed. Only objects with diameter[5 cm and length[1 m with intact bark were included in the survey, as smaller objects were unlikely to be suitable for larval development. Also, objects of decay class 1 or 6 were considered to be unsuitable for the species, based on previous ecological knowledge. Such objects were only searched in occasions when no other substrates were available. The search was stopped on the particular clearcut when both main species were encountered, because the search method is destructive for species habitat.

Habitat characteristics

Species presence/absence was related to habitat characteristics on two spatial scales, clearcut level and substrate level. For each clearcut, data on habitat characteristics were obtained from the forest company (age and area) or estimated in the field (amount of dead birch wood). Connectivity was calculated for each clearcut by accounting for distance to occupied clearcuts in the surroundings and their habitat amount. Geographic coordinates of each clearcut were included in analyses to account for spatial North–South and East–West patterns. Colonisation and extinction events were observed by comparing the occurrence data from 2004 and 2010. As P. minus was not the main focus of the first survey, we could only be confident about colonisations of new clearcuts (created after the first survey). Clearcuts present in 2004 were therefore excluded from analyses.

Clearcut level

Clearcut age (time since clearcutting) was divided into categories prior to analysis, in order to better assess non-linear species response to age. We chose an assignment that gave the most similar number of clearcuts per category, resulting in a slightly different grouping for 2004 and 2010 (Table 2).

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Table 2 Habitat characteristics, measured for each clearcut; variables measured in two or more classes were analysed as categories Variable Units and description

Area ha (sum for contiguous clearcuts) Age Years since clearcutting (average for contiguous clearcuts) Divided in classes for analyses; 2004: 1 = 3–6 years, 2 = 7 years, 3 = 8–9 years, 4 = 10–14 years; 2010: 1 = 3–4 years, 2 = 5–8 years, 3 = 9–11 years, 4 = 12–14 years, 5 = 14–20 years Burned Clearcut burned (1) or not (0) South-North Geographic coordinates (m) for location of each clearcut West-East Geographic coordinates (m) for location of each clearcut Connectivity Calculated according to Eq. 1 Nr birch Number of dead birch substrates ha-1 (measured 2004) Area birch Area on clearcut with dead birch wood present (ha) (2010) Density birch Maximum aggregation density of dead birch wood (m3 ha-1) (2010)

The amount of dead birch wood per clearcut in 2004 was estimated as number of substrates ha-1 in 10 9 50 m transects in the most substrate-rich parts of the clearcut (Fig. 1). Two or three transects per clearcut (depending on area) were placed in parts of the clearcut with the highest density of birch dead wood (Fig. 1a). Number of substrates ha-1 was calculated from the transect data and the highest value used in analysis. The amount of dead birch wood on clearcut level was estimated with two different proxies in 2010. First, we estimated the clearcut area where dead birch wood was present, i.e. habitat area for the species. Second, we estimated the maximum aggregation density of substrate for each clearcut. Area with dead wood was estimated by walking all over the clearcut and counting 25 9 25 m squares where dead birch substrate with a diameter C5 cm of totally C3 m in length was present, i.e. a minimum density of 0.4 m3 ha-1 (Fig. 1b). The counting was done in a way that minimises the number of squares, e.g. two objects 20 m apart made up one, not two squares. The number of habitat squares was summed for each clearcut and recalculated into hectares of habitat area. Aggregation density was estimated in 10 9 10 m squares (1–3 per clearcut) in areas with the highest dead wood density (Fig. 1c). Diameter and length of all objects was measured within the squares and the total volume calculated. If a part of an object lay outside the square, only the part within the square was included. The volume of the square with highest density was used to calculate volume ha-1.

Substrate level

Effect of substrate properties and dead wood aggregation on U. ceramboides was studied in detail on three clearcuts which had the highest amounts of dead wood and highest species frequency in 2004. To test if U. ceramboides benefit from aggregation of dead wood (as spatial distribution of dead wood may be important for saproxylic beetles: Schiegg 2000), total volume of all birch substrates within four transects (10 9 50 m) on each clearcut was calculated. Between 10 and 24 substrates per transect were searched for beetles. Substrate properties, such as decay class, size, presence of fungi, etc. were measured and related to species presence/absence for each investigated object (Table 3).

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Fig. 1 Dead wood survey methods: a Nr Birch 2004, b Area Birch 2010 and c Density Birch 2010. The larger rectangles represent clearcuts, the smaller squares or rectangles are sample plots and the black dots are dead wood objects

In 2010, in order to gain a better understanding of species habitat use across the landscape, species-substrate associations were studied on all clearcuts for both U. ce- ramboides and P. minus. Decay stage was recorded at several positions for large dead wood objects and the average calculated, resulting in a continuous variable used in anal- yses. We also recorded if a substrate was in direct contact with another dead wood object (a measure of small-scale aggregation), whether it was burned and whether it was an intact fallen tree, i.e. trees likely retained for conservation purpose, not logging residues (Table 3). Burning was included as a factor in the analyses on both clearcut and substrate levels, as many saproxylic beetles are more frequent in burned wood (e.g., Hyva¨rinen et al. 2009). 95 burned substrates were surveyed in 2010 on five burned clearcuts.

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Table 3 Substrate characteristics, measured for each investigated dead wood object Variable Units and description

Length m Diameter cm Decay class (1–6) 1: fresh wood to 6: highly decomposed wood (scale according to Siitonen and Saaristo 2000); treated as continuous variable in 2010 Bark cover (%) Proportion of object with bark (used to calculate bark area) Sun exposure (1–3) 1: completely open, 2: predominantly open, 3: partially shaded Ground contact (1–4) Proportion of object in direct contact with the ground: 1 = \25 %, 2 = 25–50 %, 3 = 50–75 %, 4 = [75 % White-rot fungi 2004: presence (1)/absence (0) of fruiting bodies (F. fomentarius, Trametes zonatella, T. hirsuta); 2010: mycelium in wood, living (1) or dead (0) Burned Object burned (1) or not (0); there were no burned objects in 2004 Additional variables 2010 Contact Object in contact with other object (1) or not (0) Intact tree Downed intact tree (1) or cut fragment (0) Variables measured as two or more classes were analysed as categories

Connectivity

We estimated connectivity (S) for each clearcut i in 2004 and 2010 using the following equation: n Si exp a dij pjHj; for all j i 1 ¼ j 1 ðÀ Þ 6¼ ð Þ X¼ where dij = distance between clearcut i and j; n = total number of clear-cuts (including those not surveyed); p = species presence, with p = 1 at species presence, p = 0 at species absence and p = average probability of occurrence in the landscape, when species had not been surveyed; Hj = habitat amount in clearcut j; and a is a parameter controlling the rate with which the frequency of dispersal events, or correlation between probability of occurrence, decrease with distance. We used the negative exponential function, because it has been found to fit rather well with dispersal patterns of species (Moilanen and Nieminen 2002). We identified the scale that generated the minimum residual deviance for the total statistical model by graphically comparing spatial scales (i.e. 1/a, in whole meters) within an interval from 10–10,000 m. As an estimate of habitat amount, we used the measure of dead birch wood which best explained species presence (‘‘Nr birch’’ in 2004, ‘‘Area birch’’ for U. ceramboides and ‘‘Density birch’’ for P. minus in 2010). We obtained two different measures of connectivity for 2010 occurrence models, by using data on habitat (dead wood) amount of occupied sites (Hj and p in Eq. 1) either from 2004 or 2010. Data that resulted in a better model fit were used in final analysis (Table 5). The past habitat amount may better relate to occupancy if the species respond slowly to changes in the landscape. To make the connectivity measures from the periphery of the study area comparable with the centre, we took into account presumable occurrences of P. minus outside the study area by creating a 2 km buffer zone around the study area and including clearcuts in the buffer in the connectivity calculation. We assumed the same frequency of species occurrence and dead wood amounts as within the landscape, so all added clearcuts were given the average value for probability of occurrence and for dead

123 Biodivers Conserv (2014) 23:449–466 457 wood amount. This was also done for the clearcuts within the landscape not surveyed in 2004 (both species). Due to the size of buffer, we used a 2 km distance limit (i.e. if dij [ 2 km the clearcut j did not add to the connectivity in Eq. 1) for when calculating connectivity for every clearcut. Connectivity for U. ceramboides was calculated to all clearcuts within the landscape, irrespective of distance. We assumed that U. ceramboides was absent from the buffer area. The species has been searched for and has not been found outside the study area in thorough surveys of the landscape by L. Wikars in 2003 and Olof Hedgren in 2009 (unpubl. data). It is therefore likely that the species was absent from the nearest sur- rounding landscape. In 2010, the species frequency in the landscape was so low that the connectivity estimates would not be significantly affected by adding additional buffer area, while in 2004 it might have some effect.

Analyses

All analyses were conducted in R version 2.14.0 (R Core Team 2012), using package lme4 (Bates et al. 2011). Continuous explanatory variables (clearcut level analyses) were log- transformed prior to analyses to improve skew distributions and minimise impact of extreme values. To avoid multicollinearity, we calculated variation inflation factors (VIF) for all models. Variables with VIF [3 were excluded from the models (Zuur et al. 2010); this was ‘‘bark area’’ (correlated with length and diameter) on substrate level 2010. Species presence/absence per clearcut was analysed with multiple logistic regression (glm in R), with habitat characteristics and connectivity as explanatory variables (Table 2). The model with the lowest AIC (Akaike information criterion) value was considered to provide the best explanation of the data. We used backward elimination—all variables and biologically relevant interactions were included in the initial model, then variables that gave the largest decrease in AIC were dropped one at a time, until a model with the lowest AIC was reached. Events of colonisation and extinction between the surveys were also analyzed in relation to habitat characteristics in 2010. To test whether occupancy had changed between 2004 and 2010, we used a generalised linear mixed effects model (glmer in R), with survey year as a fixed categorical factor and clearcut identity as a random factor. Species presence/absence per substrate in 2004 (3 clearcuts, 231 substrates) was ana- lyzed in relation to substrate properties (Table 3) and dead wood amount per transect with a generalised linear mixed effects model (glmer). Clearcut identity and transect identity were included as nested random factors. Due to many possible interactions, the models were built by forward selection, i.e. adding one variable at a time, starting with the variable that gave lowest AIC, until adding more variables no longer decreased AIC. Species presence/absence on substrate level 2010 (110 clearcuts, 898 substrates) was analysed similarly, with clearcut identity as random factor. The quadratic term of the decay class in 2010 was tested to account for non-linear response.

Results

Landscape level

We observed different trends in occupancy per clearcut for the two study species. Upis ceramboides showed a decrease from 29 % in 2004 to 7 % in 2010 (glmer:

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Upis ceramboides Platysoma minus Absence

Presence 2004

Presence 2004+2010

Presence 2010

Fig. 2 Presence/absence of U. ceramboides (a) and P. minus (b) in the studied landscape, size 20 9 20 km

Table 4 Species occupancy per clearcut (%), colonisation (Col) and extinction (Ext) rates as % of all clearcuts where colonisation/extinction was possible; colonisations if only new clearcuts are considered in parentheses Species Occupancy Col Ext

2004 2010

U. ceramboides 31 7 3 70 P. minus 32 60 62 (60) 57 R. mordax 54 38 36 (39) 63 T. fasciatus 48 55 48 (45) 37

The two other species, R. mordax and T. fasciatus, are shown for comparison

coefficientyear =-9.82; p = 0.057; Fig. 2; Table 4), while P. minus increased its occu- pancy from 30 to 60 % (glmer: coefficientyear = 1.17, p \ 0.001; Fig. 2; Table 4). In comparison to the common species R. mordax and T. fasciatus, we observed very few colonisations and many extinctions of U. ceramboides. Clearcuts with required habitat amount for this species appears to be rare, as more than 90 % of all surveyed clearcuts had low amounts of dead birch wood (‘‘Area birch’’) and consequently low species occupancy (Fig. 3).

Clearcut level

On clearcut level, occurrence of both species depended mainly on the habitat amount (dead wood) and clearcut age (Table 5; Fig 4). The frequency of U. ceramboides increased with the number of substrates (2004) and area with dead wood (2010), while dead wood aggregation density had strongest effect on the probability of occurrence of P. minus. Upis ceramboides was most frequent 8–9 years after clearcutting, while P. minus occurred most frequently on older clearcuts (12–14 years). Connectivity did not predict presence/absence for any of the species. However, the geographical gradients were important for P. minus, with higher probability of occurrence and colonisation towards the northern part of the landscape (Table 5). Also, we found no effect of burning on species occurrence. Exinctions

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Fig. 3 Relationship between 0.7 area with birch dead wood per clearcut and (i) occupancy of 0.6 clearcuts U. ceramboides (grey columns), 0.5 U. ceramboides and (ii) proportion of all clearcuts in the landscape in 2010 (black 0.4 columns). Of all existing 0.3 clearcuts, 10 % have the \ Frequency amount of habitat needed to 0.2 achieve a high occupancy of U. ceramboides 0.1 0 <1 1-2 2-3 >3 Area with dead wood/clearcut (ha)

Table 5 Final logistic regression models explaining species presence/absence on clearcut level Independent U. ceramboides P. minus P. minus P. minus variable 2004 2010 2010 Cola Ext

Area – – – – -4.02 Age cat 2 3.46* – -0.97 -0.81 – Age cat 3 4.69* – 1.42 1.95# – Age cat 4 4.52* – 1.83# na – Age cat 5 na – 0.49 na – Nr Birch 7.92** na na na na Area Birch na 6.5* 4.04* 3.57# -18.1# Density Birch na – 2.15** 1.82# – South-North – – 1.8 9 10-4** 1.9 9 10-4*– West-East -1.5 9 10-4# –– – – Presence 2004 na 3.04** -1.75* na na Connectivity 29.8 – -0.95# -3.15# na a (Eq. 1) 20 – 480 20 na

Hj (Eq. 1) Nr Birch – Nr Birch Density Birch na Explained variation 60 % 33 % 29 % 25 % 47 % ‘‘na’’ indicates that the factor was not measured/tested and ‘‘–’’ that the factor was tested but not a part of the final model. Age category 1 was reference category. Coefficients and significance codes (#0.1 \ p \0.05, *0.05 \ p\0.01, **0.01 \ p \0.001, *** p \ 0.001) are shown. Connectivity was excluded from the model for U. ceramboides in 2010 due to too few species occurrences a colonisations of sites inventoried 2004 were not included in the analyses of U. ceramboides could not be explained by any habitat property (adding habitat variables gave no improvement in AIC compared to intercept-only model). Due to only three observed colonisations by U. ceramboides, no meaningful analysis could be done.

Substrate level

An important factor determining species presence/absence on substrate level was wood decay class. Platysoma minus was frequent in far decayed wood, while U. ceramboides

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R. mordax R. mordax 60 10 50 8 40 6 30

20 4 Occupancy (%)

10 Occupancy (%) 2

0 0 3-6 7-10 11-14 15-20 2345 Clearcut age (years) Substrate decay class U. ceramboides U. ceramboides 16 40

12 30

20 8

10 4 Occupancy (%) Occupancy (%)

0 0 3-6 7-10 11-14 2345 Clearcut age (years) Substrate decay class

P. minus P. minus 100 30

80 20 60

40 10 Occupancy (%)

20 Occupancy (%)

0 0 3-6 7-10 11-14 15-20 2345 Clearcut age (years) Substrate decay class T. fasciatus T. fasciatus 80 30

60 20 40

10

Occupancy (%) 20 Occupancy (%)

0 0 3-6 7-10 11-14 15-20 2345 Clearcut age (years) Substrate decay class

Fig. 4 Occupancy per clearcut and per dead wood object (%) of four beetle species on clearcuts of different age and in substrates of different decay stage in 2010 (except U. ceramboides, for which 2004 data were used), illustrating patterns of succession

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Table 6 Final models explaining species presence/absence on substrate level

Variable U. ceramboides P. minus

2004 2010 2010

Diameter – – 0.06*** Bark area 0.47 na na Birch vol/transect 5.63** na na Decay class* na – 0.82*** Decay class 3 1.47* na na Decay class 4 0.16 na na Decay class 5 -0.71 na na Decay class 6 -14.9 na na White rot 1.77** na na Contact na 2.25# – Intact tree na 2.1# 1.04***

‘‘na’’ indicates that the factor was not measured/tested and ‘‘–’’ that the factor was tested but not part of the final model. Decay class 2 was reference category; *continuous variable for decay class used in 2010. Coefficients and significance codes (#0.1 \ p \0.05, *0.05 \ p \0.01, **0.01 \ p \0.001, ***p \ 0.001) are shown was associated with intermediate decay stages (Fig. 4; Table 6). Platysoma minus was strongly associated with large-diameter dead wood objects. Both species were more fre- quent in intact trees compared to cut wood like tops, branches and stem fragments. Occupancy of U. ceramboides per substrate increased if substrates were aggregated within clearcuts (Volume/transect, 2004; Table 6) and in direct contact with other substrates (Contact 2010; Table 6).

Discussion

We show that clearcuts in managed forest landscapes constitute important habitat for early- successional forest species. We have observed that species track the dynamics of their habitat—they colonise clearcuts, remain during the time when conditions are suitable and go locally extinct as forest and dead wood succession proceeds. During the open-habitat stage of clearcuts, there is a species succession driven by the decay of dead wood (Fig. 4). For the species of this study, amount and quality of dead wood is important, and that is strongly affected by forestry operations. The observed occurrence patterns and changes in occupancy of P. minus were clearly associated with habitat dynamics on landscape scale, as we predicted. The species effectively colonised newly established habitats with suitable properties (age, dead wood amount). The observed decline of U. ceramboides, however, cannot be attributed to habitat succession on landscape scale.

Occupancy changes in the landscape

We observed different occupancy patterns over time for the main study species; U. ce- ramboides decreased in occupancy while P. minus showed a strong increase between 2004 and 2010. It is difficult to determine whether the observed changes are long-term trends or caused by annual fluctuations of population sizes. However, the long development time of U. ceramboides (Pettersson and Ehnstro¨m 2010) should reduce large fluctuations in the

123 462 Biodivers Conserv (2014) 23:449–466 larval population. This suggests that the population of U. ceramboides is indeed decreasing, which is consistent with the long-term decrease of the distribution area for this species in Sweden (Ga¨rdenfors 2010). The low number of occurrences and colonisations by U. ceramboides (Table 4) is a strong indication that the species is at risk of extinction in the studied landscape. Many apparently suitable clearcuts were not occupied, e.g. 49 % of the clearcuts were of the most suitable age (8–9 years) and 43 % of the substrates were of the most suitable decay stage (suitability according to Fig. 4). Even among clearcuts with the highest amounts of dead wood, less than 40 % were occupied (Fig. 3). Intensified forest management during the last century has resulted in, among other, decreased abundance of old and large deciduous trees, and it is likely that this has caused a decline of U. ceramboides. Species usually track changes in habitat amount with a time lag, resulting in an in recently fragmented or degraded landscapes (Hanski and Ovaskainen 2002). It has been estimated that in , which has rather similar conditions to central and northern Sweden, about 1000 species constitute an extinction debt, which in the long run will go regionally extinct unless habitat is restored (Hanski 2000). Species that are specialised on a very particular type of habitat, like U. ceramboides, can be expected to suffer earlier than more generalistic species (e.g. Henle et al. 2004). In this study we used R. mordax and T. fasciatus as more generalistic species for comparison, since they occur in forest of various successional stages and can use dead wood of other tree species. Occupancy of these species appears quite stable (Table 4), suggesting that habitat amount in the landscape is sufficient for successful reproduction and colonisation by common generalist species. Rather surprisingly, P. minus increased its occupancy in the landscape, despite that it is a red-listed species and generally thought to be negatively affected by forest management. On the one hand, this may be because it is a predator species and is therefore not directly dependent on dead wood quality, but indirectly through prey abundance. On the other hand, predatory species belong to a higher trophic level than consumers and might thereby be more sensitive to habitat loss or degradation (Davies et al. 2000). Platysoma minus appears to be colonising newly established clearcuts throughout the landscape. The high frequency of colonisation for P. minus, which was independent on connectivity, indicates that the species is not dispersal limited and highly mobile on landscape level. We could not explain extinction rates with clearcut age for any of the species, likely because clearcuts that were old enough ([20 years) were by intention not surveyed. However, extinction of early-successional species could be expected to occur in old clearcuts with high shading and most of the dead wood decayed. Unexpectedly, we did not find a significant effect of connectivity on species occurrence. However, Hodgson et al. (2009) have shown that although connectivity affects colonisation and is consequently important for persistence of a species, effect of connectivity on occupancy might not be apparent in short-lived habitats. Other studies have found that connectivity is indeed important for colonisation of saproxylic beetles in short-lived dead wood objects (e.g. Ranius et al. 2011), including a species inhabiting high-stumps on clearcuts (Schroeder et al. 2006). In accordance with our study, Sahlin and Schroeder (2010) found that habitat patch size, but not connectivity, increased saproxylic beetle occupancy per dead wood object. Generally, the amount and quality of breeding habitats are relatively more important for species persistence than the habitat spatial arrangement (Hodgson et al. 2011). Nevertheless, we found higher occurrence and colonisation of P. minus towards the north of the landscape (Table 5). This geographical pattern may be due to variation in forest history, i.e. that modern forestry started later in the north of the study landscape.

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Clearcut quality

We have shown that different species that share the same post-disturbance habitat are associated with somewhat different stages of clearcut age and dead wood decay (Fig 4). The main part of the dead wood is created during harvesting, and more dead wood is supplied by death of retained living trees during the following years. Thereby, dead wood of various decay stages can be found on young as well as old clearcuts (in our data, clearcut age and average substrate decay stage are moderately correlated, Pearson correlation coefficient = 0.55). This makes it possible for early-successional species to use the hab- itats over longer period of time, provided that the dead wood stays sun-exposed. However, planting of conifers shortens the time of sun-exposed conditions on clearcuts. This affects less species which use dead wood of early decay stages, e.g. the Rhagium species, but for many species adapted to sun-exposed dead wood of intermediate or late decay stages, conditions within the dense young stands are probably poor. Upis ceramboides and P. minus represent a species community that has historically been favoured by forest fires. In this study, the species were not more frequent in burned wood and on burned clearcuts compared to unburned clearcuts. Our results are in accordance with earlier findings that most early-successional species do not need fire or burned wood itself, but a habitat with sufficient amounts and diversity of sun-exposed dead wood (Kaila et al.1997; Johansson et al. 2007). Positive effect of burning on saproxylic beetles has been found by Toivanen and Kotiaho (2007) and Hyva¨rinen et al. (2009). The effect was, however, only studied early in succession (1–2 years after burning). Both U. ceramboides and P. minus colonise clearcuts several years after the disturbance, and such species might not respond strongly to burning.

Dead wood quality and aggregation

Our results show that whole dead trees were more frequently occupied by P. minus and U. ceramboides than cut logs and fragments. This may be because the time-window for possible use by beetles is longer in an intact tree, because it contains parts of a variety of dimensions, with a faster decay in small-diameter parts compared to the stem. Also, the dead wood created during harvesting might be of lower quality compared to naturally down trees, e.g. because of size difference and bark damage (mean bark area 6.4 m2 per whole tree, compared to 1.6 m2 for other substrates). Importance of large diameter trees that supply high-quality substrate for rare beetles has been shown by Simila¨ et al. (2003). Large-diameter dead wood present before harvesting is often damaged and fragmented by machinery (Hautala et al. 2004). Bark-free dead wood is useless to the studied species. Therefore, the best habitat for P. minus and U. ceramboides is provided when retained green trees of birch die soon after clearcutting. Occupancy of both species increased when substrate was aggregated within clearcuts, but on different scales. Upis ceramboides appeared to benefit from high densities of birch wood on substrate level in 2004. Also in 2010, the species was more frequent in substrates in direct contact with other dead wood objects. Occurrence probability of P. minus increased with a higher wood aggregation density on clearcut level. Also in an earlier study, a positive effect of small-scaled aggregation of dead wood on diversity of saproxylic insects has been suggested (Schiegg 2000). We can merely speculate about the underlying mechanisms behind these observations; possibilities include species movement behaviour (e.g. walking rather than flying between substrates) and search behaviour during dispersal.

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The observed patterns nevertheless suggest that substrates close to each other are more valuable for than evenly dispersed substrates.

Conservation and management implications

Current reserve networks are dominated by old-growth forests and have limited benefit for early-successional species, if natural disturbances are not reintroduced. Protection in reserves should, therefore, be complemented with improved habitats in surrounding managed landscapes (Kouki et al. 2001; Franklin and Lindenmayer 2009; Kuuluvainen 2009). Clearcuts and young forests with retention in landscapes dominated by dense managed forest have high potential for conservation of disturbance-favoured species (Kouki et al. 2001; Lundstro¨m et al. 2011), since high quality early-successional stages can be created with relatively low cost and little effort compared to, e.g., burning protected mature forest to create early-successional habitats. However, there is a need to a larger extent restore natural forest characteristics, e.g. number of large living trees and volume and diversity of dead wood (Simila¨ et al. 2002, Simila¨ et al. 2003). By applying appropriate management, the population size of threatened species can indeed increase even in man- aged forests (Djupstro¨m et al. 2012). Importance of green-tree and dead wood retention at clearcutting is highlighted by our finding that species are more frequent in naturally created dead wood than in wood from the clearcutting (Table 6). Creation of dead wood should be done by cutting or injuring whole trees after soil preparation to avoid damage from machinery. Already existing and newly created dead wood could be aggregated in some parts of each clearcut and avoided during soil preparation, e.g. along edges of retention groups of living trees. Trees that are retained alive will provide substrate in the future. Living trees may also to some extent locally set back regeneration of the new stand (Jacobsson and Elfving 2004), whereby dead wood close to living trees stays sun-exposed for a longer period. In combination with allowing natural regeneration instead of planting in these aggregations, the time when natural-like early-successional conditions prevail on parts of clearcuts could be prolonged. Any other measures that delay densification of young stands, such as pre-commercial thinning, would also be beneficial. To ensure a continuous supply of habitat for our study species, which depend on deciduous wood in conifer-dominated landscapes, landscape scale planning of living tree and dead wood retention in forest management is essential. The specialised species U. ceramboides occupies only clearcuts with the highest amounts of dead wood, and the current amount of such habitat is low on landscape level (Fig 3). Therefore, instead of retaining dead wood of different tree species on each clearcut, it is better to focus on one tree species per clearcut, given the volume of wood to be retained is constant. This applies even to retention on landscape scale, as concentrating efforts to improve habitat quality to some areas is more useful for threatened species compared to spreading them out evenly but thinly over an entire forest landscape (Hanski 2000). Many dead-wood associated forest species can successfully use natural early-successional habitats (Kouki et al. 2001). Thus, creating networks of natural-like early-successional habitats of high quality in managed forest landscapes may substantially counteract the loss of biodiversity from such landscapes.

Acknowledgments We thank Martin Schroeder for advice during project planning and together with the Smart Tree Retention research group for useful discussion and comments on the manuscript, and Mikael Andersson for statistical support. Also, thanks to Carola Orrmalm for sharing data from her project and Lisa Karlsson for assistance with field work. This research was funded by the Swedish Research Council Program FORMAS (grant no. 215-2009-569 and 215-2008-539).

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References

Baranowski R (1994) Faktablad: Platysoma minus: sexstrimmig plattstumpbagge. Swedish Species Infor- mation Centre, Uppsala In Swedish Bates D, Maechler M, Bolker B (2011) lme4: Linear mixed-effects models using S4 classes. R package version 0999375-42. http://CRAN.R-project.org/package=lme4. Accessed 5 Dec 2012 Boucher J, Azeria ET, Ibarzabal J, He´bert C (2012) Saproxylic beetles in disturbed boreal forests: temporal dynamics habitat associations and community structure. E´coscience 19(4):328–343 Cobb TP, Morissette JL, Jacobs JM, Koivula MJ, Spence JR, Langor DW (2011) Effects of postfire salvage logging on deadwood-associated beetles. Conserv Biol 25:94–104 Core Team R (2012) R: ZA language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Davies KF, Margules CR, Lawrence JF (2000) Which traits of species predict population declines in experimental forest fragments? Ecology 81:1450–1461 DellaSala DA, Karr JR, Schoennagel T, Perry D, Noss RF, Lindenmayer D, Beschta R, Hutto RL, Swanson ME, Evans J (2006) Post-Fire logging debate ignores many issues. Science 314:51–52 Djupstro¨m LB, Weslien J, Hoopen J, Schroeder LM (2012) Restoration of habitats for a threatened sapr- oxylic beetle species in a boreal landscape by retaining dead wood on clear-cuts. Biol Conserv 155:44–49 Ehnstro¨m B, Axelsson R (2002) Insektsgnag i bark och ved. ArtDatabanken SLU, Uppsala In Swedish Esseen P-A, Ehnstro¨m B, Ericson L, Sjo¨berg K (1997) Boreal forests. Ecol Bull 46:16–47 Franklin JF, Lindenmayer DB (2009) Importance of matrix habitats in maintaining biological diversity. PNAS 106:349–350 Franklin JF, Berg DR, Thornburgh DA, Tappeiner JC (1997) Alternative silvicultural approaches to timber harvesting: variable retention systems. In: Kohm KA, Franklin JF (eds) Creating a Forestry for the 21st Century. Island Press Washington DC, The Science of Forest Management, pp 111–139 Franklin JF, Spies TA, Pelt RV, Carey AB, Thornburgh DA, Berg DR, Lindenmayer DB, Harmon ME, Keeton WS, Shaw DC, Bible K, Chen J (2002) Disturbances and structural development of natural forest ecosystems with silvicultural implications using Douglas-fir forests as an example. For Ecol Manage 155:399–423 Fransson J (ed) (2011) Forestry statistics 2011: official statistics of Sweden. Swedish University of Agri- cultural Sciences, Umea˚ Ga¨rdenfors U (ed) (2010) Ro¨dlistade Arter i Sverige 2010: The 2010 Red List of Swedish Species. Art- Databanken, SLU Uppsala Gustafsson L, Kouki J, Sverdrup-Thygeson A (2010) Tree retention as a conservation measure in clearcut forests of northern Europe: a review of ecological consequences. Scand J For Res 25:295–308 Hanski I (2000) Extinction debt and species credit in boreal forests: modelling the consequences of different approaches to biodiversity conservation. Ann Zool Fenn 37:271–280 Hanski I (2008) conservation in boreal forests. J Insect Conserv 12:451–454 Hanski I, Ovaskainen O (2002) Extinction debt and extinction threshold. Conserv Biol 16:666–673 Hautala H, Jalonen J, Laaka-Lindberg S, Vanha-Majamaa I (2004) Impacts of retention felling on coarse woody debris CWD in mature boreal spruce forests in Finland. Biodivers Conserv 13:1541–1554 Henle K, Davies KF, Kleyer M, Margules C, Settele J (2004) Predictors of species sensitivity to frag- mentation. Biodivers Conserv 13:207–251 Hodgson JA, Moilanen A, Thomas CD (2009) responses to patch connectivity and quality are masked by successional habitat dynamics. Ecology 90:1608–1619 Hodgson JA, Moilanen A, Wintle BA, Thomas CD (2011) Habitat area quality and connectivity: striking the balance for efficient conservation. J Appl Ecol 48:148–152 Hyva¨rinen E, Kouki J, Martikainen P (2009) Prescribed fires and retention trees help to conserve beetle diversity in managed boreal forests despite their transient negative effects on some beetle groups. Insect Conserv Diver 2:93–105 Jacobsson R, Elfving B (2004) Development of an 80-year-old mixed stand with retained Pinus sylvestris in Northern Sweden. For Ecol Manage 194:249–258 Johansson T, Hja¨lte´n J, Gibb H, Hilszczanski J, Stenlid J, Ball JP, Alinvi O, Danell K (2007) Variable response of different functional groups of saproxylic beetles to substrate manipulation and forest management: implications for conservation strategies. For Ecol Manage 242:496–510 Jonsson BG (2012) Population dynamics and evolutionary strategies. In: Stokland JN, Siitonen J, Jonsson BG (eds) Biodiversity in dead-wood. Cambridge University Press, New York, pp 338–355 Jonsson BG, Siitonen J (2012) Dead wood and sustainable forest management. In: Stokland JN, Siitonen J, Jonsson BG (eds) Biodiversity in dead-wood. Cambridge University Press, New York, pp 302–337

123 466 Biodivers Conserv (2014) 23:449–466

Jonsson M, Ranius T, Ekvall H, Bostedt J, Dahlberg A, Ehnstro¨m A, Norde´n B, Stokland JN (2006) Cost- effectiveness of silvicultural measures to increase substrate availability for red-listed wood-livin organisms in Norway spruce forests. Biol Conserv 127:443–462 Kaila L, Martikainen P, Punttila P (1997) Dead trees left in clearcuts benefit saproxylic Coleoptera adapted to natural disturbances in boreal forest. Biodivers Conserv 6:1–18 Kouki J, Lo¨fman S, Martikainen P, Rouvinen S, Uotila A (2001) Forest fragmentation in Fennoscandia: linking habitat requirements of wood-associated threatened species to landscape and habitat changes. Scand J For Res Supplement 3:27–37 Kuuluvainen T (2009) Forest management and biodiversity conservation based on natural ecosystem dynamics in northern Europe: the complexity challenge. Ambio 38:309–315 Lindenmayer D, Franklin JF (2002) Conserving forest biodiversity: a comprehensive multiscaled approach. Island Press, Washington Lindenmayer DB, Foster DR, Franklin JF, Hunter ML, Noss RF, Schmiegelow FA, Perry D (2004) Salvage harvesting policies after natural disturbance. Science 303:1303 Linder P, O¨ stlund L (1998) Structural changes in three mid-boreal Swedish forest landscapes 1885–1996. Biol Conserv 85:9–19 Lundstro¨m J, O¨ hman K, Perhans K, Ro¨nnqvist K, Gustafsson L (2011) Cost-effective age structure and geographical distribution of boreal forest reserves. J Appl Ecol 48:133–142 Moilanen A, Nieminen M (2002) Simple connectivity measures in spatial ecology. Ecology 83:1131–1145 Naalisvara R (2013) Clear-cut and substrate characteristics important for the occurrence of the beetle Upis ceramboides. MSc Thesis. SLU, Department of Ecology, Uppsala Palm T (1951) Die Holz- und Rinden-Ka¨fer der nordschwedischen Laubba¨ume. Meddelanden fran Statens Skogsforskningsinstitut 40 In German Pettersson R, Ehnstro¨m B (2010) Faktablad: Upis ceramboides: sto¨rre svartbagge. Swedish Species Infor- mation Centre, Uppsala In Swedish Ranius T, Martikainen P, Kouki J (2011) Colonisation of ephemeral forest habitats by specialised species: beetles and bugs associated with recently dead aspen wood. Biodivers Conserv 20:2903–2915 Sahlin E, Schroeder L (2010) Importance of habitat patch size for occupancy and density of aspen-asso- ciated saproxylic beetles. Biodivers Conserv 19:1325–1339 Schiegg K (2000) Effects of dead wood volume and connectivity on saproxylic insect species diversity. E´ coscience 7:290–298 Schroeder LM, Ranius T, Ekbom B, Larsson S (2006) Recruitment of saproxylic beetles in high stumps created for maintaining biodiversity in a boreal forest landscape. Can J For Res 36:2168–2178 Siitonen J (2001) Forest management coarse woody debris and saproxylic organisms: fennoscandian boreal forests as an example. Ecol Bull 49:11–41 Siitonen J, Saaristo L (2000) Habitat requirements and conservation of Pytho kolwensis a beetle species of old-growth boreal forest. Biol Conserv 94:211–220 Simila¨ M, Kouki J, Martikainen P, Uotila A (2002) Conservation of beetles in boreal pine forests: the effects of forest age and naturalness on species assemblages. Biol Conserv 106:19–27 Simila¨ M, Kouki J, Martikainen P (2003) Saproxylic beetles in managed and seminatural Scots pine forests: quality of dead wood matters. For Ecol Manage 174:365–381 Swanson ME, Franklin JF, Beschta RL, Crisafulli CM, DellaSala DA, Hutto RL, Lindenmayer DB, Swanson FJ (2010) The forgotten stage of forest succession: early-successional ecosystems on forest sites. Front Ecol Environ 9:117–125 Toivanen T, Kotiaho JS (2007) Burning of logged sites to protect beetles in managed boreal forests. Conserv Biol 21:1562–1572 Webb A, Buddle CM, Drapeau P, Saint-Germain M (2008) Use of remnant boreal forest habitats by saproxylic beetle assemblages in even-aged managed landscapes. Biol Conserv 141:815–826 Wikars L-O, Orrmalm C (2005) The occurrence of the threatened wood-living beetle Upis ceramboides: a species dependent on high densities of aggregated dead-wood. Ent Tidskr 126:161–170 In Swedish Zuur AF, Ieno EN, Elphick CS (2010) A protocol for data exploration to avoid common statistical problems. Methods Ecol Evol 1:3–14

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