Saproxylic beetles in artificially created high-stumps of spruce and birch within and outside...

Biodivers Conserv (2007) 16:3213–3226 DOI 10.1007/s10531-007-9173-7

ORIGINAL PAPER

Saproxylic beetles in artiWcially created high-stumps of spruce and birch within and outside hotspot areas

Matts Lindbladh · Markus Abrahamsson · Meelis Seedre · Mats Jonsell

Received: 3 May 2006 / Accepted: 7 March 2007 / Published online: 6 June 2007© Springer Science+Business Media B.V. 2007

Abstract ArtiWcially created high-stumps (snags) are created regularly during forestfelling operations in Swedish coniferous production forests. The saproxylic beetle fauna inhigh-stumps of spruce and birch, on 20 clearcuts in Southern Sweden, were sampled bybark sieving. Ten of the clearcuts were located in hotspot areas with documented occur-rence of many red-listed saproxylic beetle species. The other ten clearcuts were located in atypical production forest landscape (i.e. the matrix). Our aim was to investigate whether thebeneWt of creating high-stumps diVers if the clearcuts is located in a hotspot area or in thematrix. In total 4,179 saproxylic beetles were found, belonging to 66 species, 9 of whichwere red-listed. Birch high-stumps hosted more species, on average, than spruce high-stumps. In an ordination analysis, tree species had the strongest explanatory eVect amongthe environmental variables. No diVerence in beetle fauna could be found between the hot-spot and matrix clearcuts, for neither birch nor spruce, according to all parameters: speciesnumbers, species composition and red-listed species. The study does not indicate that con-servation eVorts in coniferous production forests should be concentrated to hotspot areas.

Keywords Betula · Biodiversity · Coleoptera · Colonization · Dead wood · Landscape patterns · Matrix · Picea · Snags

Introduction

Until 200–300 years ago, forests in southern Sweden were dominated by temperate decidu-ous trees (Lindbladh et al. 2000). Today intensively managed production forests of spruce

M. Lindbladh (&) · M. Abrahamsson · M. SeedreSouthern Swedish Forest Research Centre, SLU, Box 49, Alnarp, 230 53, Swedene-mail: [email protected]

Present Address:M. SeedreFaculty of Forestry and the Forest Environment, Lakehead University, 955 Oliver Road, Thunder Bay, ON, Canada, P7B 5E1

M. JonsellDepartment of Entomology, SLU, Box 7044, Uppsala, 750 07, Sweden

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(Picea abies) and pine (Pinus sylvestris), of limited conservational value (Nilsson 1997),make up ca. 80% of both volume and area. This change, however, has not aVected southernSweden uniformly; in some areas the fauna and Xora is retained because of land-use ormanagement history (e.g. Karström 1992; Nilsson et al. 1995; Nilsson and Baranowski1997; Hanski 2000; Jonsell and Nordlander 2002), underlying biogeographical landscapefactors such as climate (Väisänen and Heliövaara 1994) or a combination of both (Nilsson2001; Lindbladh et al. 2003; Økland et al. 2005). Although coniferous production forestsare dominant in these hotspot areas, they hold a higher proportion of temperate deciduoustrees (e.g., oak (Quercus sp.) and beech (Fagus sylvatica)) compared to the surroundingtypical production forests landscape, i.e. the matrix (Andersson and Löfgren 2000; Nilsson2001; Niklasson and Nilsson 2005). These deciduous trees host a large disproportionalshare of red-listed species relative to their abundance (Berg et al. 1994; Jonsell et al. 1998).

In addition to deciduous trees becoming scarce, the amount of dead wood in theforests of southern Sweden is generally very low (Fridman and Walheim 2000). Thishas had a negative eVect on saproxylic (i.e. wood-dependent) beetles, ultimately threat-ening many species in this group (Berg et al. 1994, Jonsell et al. 1998, Gärdenfors2005). To mitigate this, artiWcial dead-wood is regularly created during forest fellingoperations. The most common type is high-stumps (snags), which are mandatoryaccording to the Swedish certiWcation standards of both the Forest Stewardship Council(FSC) and the Programme for the Endorsement of Forest CertiWcation schemes (PEFC)(Anon. 2000a; Anon. 2000b). Several recent studies have shown that high-stumpscan be important for many species, including red-listed species (Jonsell et al. 2004;Lindhe and Lindelöw 2004; Jonsell et al. 2005; Lindhe et al. 2005; Abrahamsson andLindbladh 2006).

Most of the created high-stumps are spruce (83%, Anon. 2005) and while birch (Betulaspp.) is often the only available alternative for creating deciduous high-stumps, its potentialas a host for saproxylic beetles in high-stumps in southern Sweden has received less atten-tion than that of spruce. Birch is considered less important for saproxylic beetle fauna thanmany temperate deciduous trees, but it is being used by several red-listed species (Jonsellet al. 2004; Lindhe and Lindelöw 2004). Furthermore, compared to spruce, birch can sup-port a fauna that is much more similar to that of temperate deciduous trees (Palm 1959;Jonsell et al. 1998; Lindhe and Lindelöw 2004).

Considering the diVerences between the hotspot and matrix areas, the beneWt of cre-ating high-stumps, measured as the number of breeding species and breeding red-listedspecies, can be expected to be larger in a hotspot area compared to the matrix. The ben-eWt can also vary with tree species, i.e. a birch high-stump in a hotspot area should hostmore species than a spruce high-stump. Understanding these relationships is fundamen-tal in making conservation eVorts more cost-eVective (Weitzman 1998; Carlén et al.1999), and it will contribute to landscape ecological issues, e.g. if conservation eVortsare to be concentrated to certain areas or be spread evenly across the landscape (Hanski2000).

We sampled the saproxylic beetle fauna by sieving the bark of high-stumps of spruceand birch, on clearcuts within and outside Wve hotspot areas in southern Sweden. Our spe-ciWc aim was to investigate how the number of species (total number and red-listed num-ber) or species composition in high-stumps varied according to: the location of the clearcut(in hotspot areas or in the matrix); the high-stump tree species (birch or spruce); the biogeo-graphical patterns of the clearcut (temperature, precipitation, latitude, longitude); and thediameter of the high-stump

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Methods

Study sites and sampling procedure

The Swedish Environmental Protection Agency has identiWed forest areas in southern Swe-den that are particularly valuable from a conservation point of view (Andersson and Löf-gren 2000). These hotspot areas are characterized by hilly landscapes, proximity to theocean or a large lake, encompassing a large concentration of ancient cultural landscapesand they have a size of ca.100–300 km2. Within the three counties included in our study(Halland, Kronoberg and Kalmar), nine areas have been identiWed and we chose to studyWve of these, all with documented occurrence of many red-listed saproxylic beetle species(Nilsson 2001). The hotspot areas included are among the top in that aspect (Nilsson 2001),and one area, Hornsö, has the highest number of red-listed species recorded in the country(Nilsson and Huggert 2001). Birch is considered to be among the three most importanttrees for the red-listed beetle species in all of the hotspot areas investigated, and the othertop ranked species are oak and beech (Nilsson 2001).

The Wve regions (each encompassing two hotspot clearcuts and two matrix clearcuts)were named according to their geographical location: ‘West’ (W), ‘Mid-west’ (Mid-W),‘Mid’ (Mid), ‘Mid-east’ (Mid-E) and ‘East’ (E) (Table 1, Fig. 1). We chose clearcuts thatwere of the pre-deWned age class and located as close as possible (0–5 km, average <2 km)to sites previously shown to have a rich fauna (Andersson 2001; Nilsson 2001, Sven G.Nilsson pers. comm.). Although some of these clearcuts are located several kilometersfrom the previously sampled sites in Nilsson’s (2001) compilation, they are all within ahotspot area as deWned by Andersson and Löfgren (2000). We can assume that the saproxy-lic fauna is rich within the whole hotspot area based on the fact that most saproxylic insectshave a rather good colonization capacity at this scale (Jonsson 2003; Komonen 2006), andthat they have been present in the hotspot area for many decades. The ten matrix clearcutswere located at a distance of 10–50 km (average ca. 20 km) from the hotspot areas, in whatwas judged to be a normal production forest landscape. Unfortunately, relevant forestinventory data for areas within and outside the hotspots is diYcult to obtain. We did man-age, however, to obtain some data for the West region. In the 92 ha forest surrounding theTönnersjö clearcut (site C––matrix clearcut) spruce and pine make up 96.2% of the totalvolume, while beech and oak only account for 0.3% (Abrahamsson 2002). In contrast, the90 ha forest surrounding the clearcuts within the Biskopstorp hotspot (sites A and B), con-sists of 27.2% beech and oak and 65.1% spruce and pine.

Before felling, all stands were production forests dominated by spruce 60–100 years old,but some harbored a signiWcant amount of pine, at most ca. 50% of the total volume. Gen-erally, there were only a few mature birch trees present in the stands, but some stands couldinclude up to ca. 5% birch. The size of the clearcut varied from 1 to 12 ha, with an averagesize of ca. 5 ha. All high stumps were created during clear felling in the winter of 2001/2002, except the stumps on clearcuts A and C, which were created one year earlier. Thesampling was carried out in September and October 2004 when the stumps were three orfour years old.

On each clearcut three spruce and three birch high-stumps were sampled, making a totalof 120 high-stumps in the study. For each stump, the tree species (spruce or birch) anddiameter was recorded. To collect the beetles, a 50 £ 50-cm area (0.25 m2) of bark wasstripped from each stump with an axe and then sieved in a sifter with a mesh size of 4 mm.Most of the loose material under the bark square was included in the sample. The majorityof the samples were taken at breast height, but if this area did not contain any bark, the bark

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sample was taken as close to breast height as possible. The sieved bark samples were pre-served in textile bags and transported to the laboratory within 36 h. The samples wereplaced in a Tullgren Funnel for at least 24 h (New 1998), i.e. on a wire mesh over ethanoldilution (50%) under the heat of a 25-W lamp.

Table 1 The study sites

The number of recoded red-listed species from Nilsson (2001). Clearcut letters refer to signs on Fig. 1

Region Hotspot area (no. of recorded red-listed species)

Clearcuts

Within Outside

‘West’ (W) Biskopstorp (41) A––Silverberget C––TönnersjöB––Styrestad D––Illrahultsvägen

‘Mid-west’ (Mid-W) Toftaholm (38) E––Rödjan G––SchedingsnäsF––Kors H––Gylteboda

‘Mid’ (Mid) Möckeln area (83) I––Stenbrohult K––SkatebodaJ––Läng L––Holmsjön

‘Mid-east’ (Mid-E) Åsnen-Bjurkärr (61) M––Munkanäs O––BastaremålaN––Slagestorp P––Vieboda

‘East’ (E) Allgunnen-Hornsö (218) Q––Böta kvarn S––VenningehultR––Hornsö T––Skogsholm

Fig. 1 Map of southern Sweden and the location of the study sites and hotspot areas (circles with shading).See Table 1 for the naming of the sampling sites. The location of the hotspot areas from Andersson andLöfgren (2000)

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Rickard Andersson identiWed the beetles following the nomenclature of Lundberg andGustafsson (1995). We deWned red-listed species according to the lists from both 2000 and2005 (Gärdenfors 2000, 2005). There are diVerences between the two versions as manyspecies were removed in the revision, since the criteria for red-listing species was adjustedand the criteria were more strictly applied. Although these discarded species do not reachthe level required for red-listing, they represent a larger conservational interest than theother species recorded.

Statistics

The diVerence in the number of beetle species, which occurred on spruce and birch, wastested with a paired t-test (the stumps were pooled within each clearcut). The same testwas used to see diVerences in species number between hotspot and matrix clearcuts. Thiswas done for spruce and birch separately and the two sites of each category in each regionwere pooled. DiVerences in species number between regions were tested using one-wayanalysis of variance (ANOVA). All clearcuts within each region were pooled and the testwas done for spruce and birch separately as well as pooled together. Regression analysiswas used to determine whether the number of species was related to stump diameter.

The diVerence in the number of individuals per beetle species between hotspot andmatrix clearcuts was determined using a paired t-test, with the two clearcuts from each cat-egory (hotspot and matrix) pooled. The analyses were made for spruce and birch separatelyand the beetle species included had to be present in at least four of the Wve regions or in atleast six of the ten pooled samples.

The relationship between species composition and substrate/environmental variableswas analyzed with Canonical Correspondence Analysis (CCA). The ordination was carriedout with PC-ORD (McCune and MeVord 1999). The three high-stumps of the same speciesat the same clearcut were pooled, and 40 diVerent clearcuts were tested. To increase theexplanatory strength of the analysis, only species that occurred on at least two clearcutswere included in the ordination run; thus, 23 of 66 species were removed. The variablestested included tree species, hot-spot/matrix clearcut, tree diameter (the mean of the threehigh-stumps of the same species at the same clear-cut), summer temperature (sum of meanmonthly temperature June–August), annual precipitation (mm/year), latitude, and longi-tude. The climatic data were from the closest meteorological station to the clearcut beingtested (Alexandersson and Eggertsson Karlström 2001). In the CCA run, two of the envi-ronmental variables were strongly correlated to each other (precipitation and longitude)making the canonical coeYcients unstable. We therefore used the intraset correlation forthe interpretation which does not suVer from this problem (Ter Braak 1986). A DCA run ofthe species data gave a slightly lower eigenvalue for axis 2 compared to the CCA, butalmost the same values for axis 1 and 3. This means that the measured environmentalvariables account for the main variation in the species data (Ter Braak 1986).

Results

Total material

In total 4,179 individuals of saproxylic beetles were found in the 120 high-stumps,belonging to 66 species, 9 of which were red-listed. For a complete species list consultAppendix A.

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Species numbers and high-stump speciWc variables

In total, 47 species were found in spruce and 49 in birch. There were 17 and 19 speciesunique to spruce and birch, respectively, and 30 beetle species were found in both tree spe-cies. The diVerence in number of beetle species between spruce and birch was signiWcantwith 11.9 species in birch samples compared to 9.6 in spruce samples (t-value: ¡2.6,DF = 19, P = 0.02).

Tree diameter was not correlated with the number of species for either spruce (r = 0.12,P = 0.366) or birch high-stumps (r = 0.03, P = 0.848). The highest number of species in aspruce stump was 12, which was found in two stumps with the diameters of 23 and 34 cm.The spruce high-stump with the largest diameter (58 cm) hosted only 7 species. The twobirch high-stumps with the largest diameters, 40 and 39 cm, hosted 9 and 4 species, respec-tively, while the birch high-stump with the smallest diameter (21 cm) hosted the highestnumber of species (11).

Species numbers and site variables

The number of species found at hotspot (17.6) and matrix clearcuts (17.0), was not signiW-cantly diVerent for birch (paired t-test n = 10, t-value = 0.19, P = 0.43). Of the 49 speciesfound in birch, similar numbers of species were found in hotspot (n = 37) and matrix(n = 40) clearcuts. Consequently, hotspot clearcuts hosted 9 unique species and matrixclearcuts hosted 12. Fifteen species were individually tested and none were found to be sig-niWcantly more abundant on birch high-stumps in hotspot than on matrix clearcuts. Phloeo-charis subtilissima was the only beetle that was signiWcantly more common on birch inmatrix clearcuts than in hotspot clearcuts (paired t-test, n = 5, t-value = ¡2.86, P < 0.05).

The number of species found on spruce in hotspot and matrix clearcuts did not diVer sig-niWcantly, the average being 14.8 and 14.0, respectively (paired t-test, n = 10, t-value = 0.40, P = 0.35). Of the 47 species found on spruce 35 were found in hotspot and 35on matrix clearcuts. Consequently, both hotspot and matrix clearcuts each hosted 12 uniquespecies on spruce high-stumps. None of the nine individually tested species were signiW-cantly more abundant on hotspot than matrix clearcuts. Phloeocharis subtilissima was alsosigniWcantly more common on spruce in matrix than hotspot clearcuts (paired t-test, n = 5,t-value = ¡2.84, P < 0.05).

The average number of species per clearcut in each region (both hotspot and matrixclearcuts pooled) varied between 14.5 and 20.0 for both tree species (West 20.0 species,Mid-west 16.8, Mid 14.5, Mid-east 15.8, East 16.8), but the diVerences were not signiWcant(ANOVA f-value = 1.39, P = 0.28). The average number of species in each region variedfor birch and spruce between 13.0 and 10.0 and 13.0 and 7.3 respectively, neither weresigniWcantly diVerent between the regions (ANOVA birch: f-value = 1.33, P = 0.33; sprucef-value = 1.58, P = 0.24).

Species composition

In the CCA analysis, axis 1, 2 and 3 have eigenvalues of 0.612, 0.188 and 0.111 respec-tively and together they explain 28% of the variation among the environmental variables(Table 2). The Monte Carlo test showed that the eigenvalues for the two Wrst axes arehigher than the range expected by chance if there was no relationship between the speciesdata and the environmental data (P-values < or = 0.01 for both), but it was somewhat lowerfor axis 3 (P = 0.1).

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Tree species had the strongest explanatory eVect among the variables and it was stronglycorrelated to axis 1, which explains 18.9% of the total variation (Table 2). The ordinationalmost perfectly separated spruce and birch (Fig. 2). Precipitation, longitude and diameterwere the variables most strongly correlated to axis 2, but this axis only explains 5.8% oftotal variation. Even so, the West clearcuts were separated from most other clearcuts byhigh scores on axis 2 while the East clearcuts had relatively low scores. The clearcuts cate-gories hotspot/matrix had little contribution to the axes in the CCA.

Red-listed species

In total, 19 red-listed individuals belonging to 9 diVerent species were found on 11 diVerenthigh-stumps in the study (Gärdenfors 2000) (Table 3). Seven species appeared on birch andfour on spruce. Red-listed species appeared in all regions except the ‘Mid’ region. The

Table 2 Parameters for the Wrst three axes in the CCA analysis of species composition

Axis 1 Axis 2 Axis 3

Eigenvalue 0.612 0.188 0.111% of variance explained 18.9% 5.8% 3.4%Cumulative % explained 18.9% 24.6% 28.0%Correlation with various variablesTree species ¡0.970 ¡0.052 ¡0.186Close/distant 0.091 0.206 ¡0.280Diameter 0.273 ¡0.551 ¡0.059Summer temperature 0.369 0.244 ¡0,642Precipitation ¡0.244 0.642 ¡0.103Latitude 0.180 0.239 0.279Longitude 0.331 ¡0.559 0.394

Fig. 2 Ordination plot of the CCA analysis. Each point represents the pooled high-stumps of the same treespecies in each region. The Wve regions are named after their geographical location ‘West’ (W), ‘Mid-west’(M-W), ‘M’ (Mid), ‘Mid-east’ (M-E) and ‘East’ (E). The variables tested and included in the Wgure are treespecies, hotspot/matrix clear-cut, tree diameter, annual precipitation (mm/year) and longitude

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‘East’ and the ‘West’ regions were the richest, with four species each. Three of the high-stumps with red-listed species were located on a hotspot clearcut and eight were located onmatrix clearcuts. Five of the red-listed species were removed from the red-list in 2005(Gärdenfors 2005), and for two of the species the threat level was reduced.

Discussion

Patterns of hotspot and matrix clearcuts

No diVerence was found in beetle fauna between the high-stumps on the hotspot and matrixclearcuts. This was true for both birch and spruce according to all parameters: species num-bers, species composition and occurrence of red-listed species. Below we discuss possibleexplanations for the lack of diVerence

Three-year-old high-stumps may not be a substrate used by species characteristic of thehotspot areas. Other substrates, such as downed coarse wood, or oak and beech with mouldWlled cavities might rather be expected to host such species (Nilsson and Baranowski 1997).Although birch has several beetle species in common with oak and beech (Palm 1959; Jon-sell et al. 1998; Lindhe and Lindelöw 2004), our data suggest that recently dead high-stumpsmight be a ‘too trivial’ dead wood substrate to aVect the hotspot-matrix variable. Other stud-ies however, have been able to demonstrate an inXuence of hotspot area characteristics onspecies assemblages. Such a trivial microhabitat as fruiting bodies of one of the most com-mon polypores, Fomes fomenatrius, was shown to host many species restricted to histori-cally less managed forests (Jonsell and Nordlander 2002). In a seven-year study by Lindheand Lindelöw (2004) in a hotspot area in central Sweden, a large number of saproxylic bee-tles and red-listed species were recorded on high-stumps of spruce (31 species and 1.52 red-listed species per stump) and birch (26, 1.14) compared to aspen and oak, showing thepotential of these tree species in hotspot areas. The data is not comparable with our study,however, as they used a diVerent sampling method where the beetles were trapped within netenclosures, and a very large number of individuals were captured (ca. 47,000).

This leads to a second possible explanation. If sampling does not target the speciWcmicrohabitat of a rare species, many individuals have to be sampled to Wnd the species in

Table 3 Record of red-listed beetle species in the samples

Threat levels from Gärdenfors (2000; 2005): Data deWcient (DD), Least concern (LC), Near threatened (NT),Vulnerable (VU), Endangered (EN), Critically endangered (CR), Regionally extinct (RE)

Species and threat level (2000–2005) Tree species Stump diameter

Region Hotspot/matrix Individuals

Phyllodrepoidea crenata (EN ! DD) Birch 23 W Hotspot 3Euryusa castanoptera (NT ! LC) Birch 23 W Hotspot 5Globicornis marginata (NT ! LC) Birch 35 Mid-W Hotspot 1Ipidia binotata (VU ! NT) Spruce 35 W Matrix 1Dendrophagus crenatus (NT ! LC) Spruce 26 W Matrix 1Cis rugulosus (NT ! NT) Birch 33 E Hotspot 1

Birch 37 Mid-E Matrix 1Cis castaneus (NT ! NT) Spruce 43 E Matrix 2

Birch 30 E Matrix 1Corticeus unicolor (NT ! LC) Birch 27 E Matrix 1Tetratoma fungorum (NT ! LC) Spruce 35 E Matrix 1

Birch 23 E Matrix 1

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question (Martikainen and Kouki 2003). The number of individuals captured in this studymay be too few to Wnd many of the rare or red-listed species, and perhaps our result doesnot reXect the entire species assemblage. Jonsell and Eriksson (2001) used window (Xightintercept) traps attached to high-stumps of spruce and birch inside and outside an old-growth forest reserve in central Sweden. Compared with our study, they caught more indi-viduals as well as more red-listed individuals and species. Since they also failed to Wndmore red-listed species inside the reserve, this indicates that a very large sample is neces-sary to detect the possible diVerence between hotspots and the matrix.

A third possible explanation for the lack of diVerence could be that some of the matrixclearcuts were located in areas with a high diversity of beetles. Although we could not Wndany diVerence in species number between the regions, the CCA analysis disclosed a geo-graphic pattern. Even if the explanatory power was relatively low, did the coastal regions(in particular West) deviate from the other regions on axis 2 (Fig. 2). There is a strong pre-cipitation gradient in southern Sweden from Halland county in the west (>1,200 mm/yr) toKalmar county in the east (<400 mm/yr) which probably inXuences the species composi-tion, a Wnding that has been shown for the insect group mycetophilids (Økland et al. 2005).Moreover, all but 2 of the 19 red-listed individuals were found in East or West. Beetle col-lectors have known for a long time that several sites in the East county (Kalmar) house alarge and diverse fauna of saproxylic beetles (Lundberg 1993), which has been conWrmedin recent compilations (Nilsson and Huggert 2001; Brunet et al. 2005). The relatively warmand dry summer climate in combination with somewhat more open forests (lower share ofspruce forests) may explain such diversity and numbers (Lindbladh et al. 2003). The westcounty, Halland, has been less investigated, but there seems to be a rich saproxylic fauna inthat region also (Andersson 2001; Jansson 2004). This coincides with the fact that thecoastal regions harbor (and have harbored) a greater share of temperate deciduous foreststhan the Mid areas (Björse et al. 1998; Eliasson and Nilsson 2002; Anon. 2005). Conse-quently, even if the number of species between the regions did not diVer in our study, thereis some evidence suggesting the East and West clearcuts are located in regions with ahigher overall diversity than the three mid regions. Thus, the between region variationcould be of more relevance for saproxylic beetles diversity than within region variation(Väisänen and Heliövaara 1994).

Tree species

In agreement with earlier studies (e.g. Palm 1959; Jonsell et al. 1998), we found largediVerences in species assemblages between spruce and birch. These diVerences can beexplained by the diVerent physical properties of the wood and the bark/cambium but also,and maybe more importantly, the fungal Xora in the stumps. Wood from diVerent treespecies is more or less likely to get infected by diVerent decay fungi, e.g. white rotting orbrown rotting fungi, which to some extent determines the beetle fauna (Jonsell andNordlander 2004; Jonsell et al. 2005).

Birch hosted, on average, more species per high-stump and more red-listed species thanspruce. The number of species found on birch in this study (49 on 60 stumps) is lower thanthat found in a study from central Sweden (53 on 40 stumps), using the same high-stumpage and sampling technique (Jonsell et al. 2004). This comparison does not suggest thatbirch high-stumps should be more important in southern Sweden than in other parts of thecountry that hold a lesser share of temperate deciduous trees. Since seven red-listed specieswere found on birch in this study, however, this indicates birch high-stumps are used ashabitat by beetle species important from a conservational point of view.

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The number of species found on spruce high-stumps was much higher in this study (47 on60 stumps) than in another study (18 on 64) in southern Sweden with three-year-old high-stumps, using the same sampling technique (Abrahamsson and Lindbladh 2006). It was alsohigher than in a study (42 on 59) with the same sampling technique from central Sweden (Jon-sell et al. 2005). The relatively large number of species found on spruce indicates that spruce isalso used by many saproxylic beetles despite being this far south, close to its southern distribu-tion range and where deciduous trees used to dominate in the recent past (Lindbladh et al.2000). Moreover, the fact that several of the spruce stumps (four in total) in this study hostedred-listed species suggests that spruce high-stumps are of importance for conservation.

Diameter

Large-diameter dead wood is thought to host a higher number and a greater diversity ofsaproxylic species than thin-diameter dead wood (Grove 2002 and references therein). Nei-ther was the number of species correlated with diameter of the high-stump for either spruceor birch, nor was the diameter variable found to be of particular importance in the CCAanalysis. This is in accordance with other studies of high-stumps, which generally haveshown that diameter has little eVect on species number and composition (Sverdrup-Thyge-son 2002; Jonsell et al. 2004; Jonsell et al. 2005; Lindhe et al. 2005). The relatively youngage of the high-stumps as well as the small range of diameters included in many studies,could explain the lack of eVect. A more evident eVect has been shown for aspen snags inthe less managed forests of Canada (Hammond et al. 2004). Our study however, was donein managed forests where most trees were between 20 and 40 cm and only a few sprucehigh-stumps were up to 58 cm. Although we found no eVect of diameter on species compo-sition our study shows that small-diameter stumps can be used by many species, includingred-listed species. The spruce high-stumps with the highest number of species (12 and 10)were in the lower end of the range (23, 26 and 34 cm) and for birch the thinnest stump(21 cm) hosted the largest number of species (11). Furthermore, many of the red-listed spe-cies individuals were found on small-diameter high-stumps; this is particularly true for thespecies found on birch. Two 23-cm birch stumps hosted red-listed species, one categorizedas endangered (EN). Thus, high-stumps of a wide diameter range can host a large numberof species as well as rare species. A coarse high-stump, however, will probably host morespecies than a thin high-stump during its ‘life time’ because of its longer time for decay.

Conclusions and practical implications

The lack of diVerence in beetle fauna between the high-stumps on the hotspot compared tomatrix clearcuts does not indicate that conservation eVorts in production forests should beconcentrated to hotspot areas, at least at the ‘within region scale’. That the red-listed spe-cies caught in this study occurred on both hotspot and matrix clearcuts is a further indica-tion speaking against concentrating conservation eVorts to certain areas. Our study showsthat spruce and birch high-stumps host a partly complementary fauna, and hence the crea-tion of high-stumps of more than one tree species during Wnal felling is preferable from aconservational point of view. Even in southernmost Sweden where spruce dominance israther recent, high-stumps of spruce seems to be an important substrate for many beetlespecies. No signiWcant eVect of high-stump diameter could be detected on species numberor on the occurrence of red-listed species, therefore suggesting that high-stumps of all sizeclasses are preferred from a conservational point of view.

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It should be noted that this study represents a snapshot in time. The results andconclusions may be diVerent when the total succession of species colonizing dead woodduring the decay process is completed. This is something future studies could bringinsight in.

Acknowledgements We are grateful to Richard Andersson for beetle identiWcation. We are grateful to thepersonnel at Sveaskog, Södra, Skogsstyrelsen, Asa and Tönnersjöhedens experimental forests for assistanceduring the site selection. Thanks to all the landowners who let us use their high-stumps. Mats Niklasson, SvenG. Nilsson and Jonas Hedin contributed signiWcantly during the project’s planning phase, thanks. We are alsograteful to Michelle Slaney for a linguistic improvement of the paper. Financial support for this study wasprovided by the ‘Norway Spruce Programme’ at the Southern Swedish Forest Research Centre at the SwedishUniversity of Agricultural Sciences.

Appendix A

List of all species encountered in high-stumps in southern Sweden, sorted in systematicorder according to Lundberg and Gustafsson (1995)

Species Red list category(2000 and 2005)

Number of individuals on spruce

Number of individuals on birch

Number of stumpswith species

Plegaderus vulneratus 13 4Stenichnus godarti 1 1Stenichnus bicolor 5 1Gabrius splendidulus 12 2Nudobius lentus 19 19 23Bibloporus bicolor 19 10 12Bibloporus minutus 6 3Euplectus nanus 1 1Euplectus punctatus 47 15 21Euplectus karsteni 5 2Euplectus fauveli 2 2Tyrus mucronatus 2 1Hapalaraea gracilicornis 2 1Phloeonomus pusillus 1 1Phyllodrepoidea crenata EN-DD 3 1Phloeocharis subtilissima 261 164 64Phloeopara testacea 2 8 9Phloeopara corticalis 2 22 11Dadobia immersa 3 3Dinaraea aequata 1 1 2Leptusa pulchella 1 1 2Leptusa fumida 29 46 33Leptusa ruWcollis 5 16 17Euryusa castanoptera NT-LC 5 1Anomagnathus cuspidatus 43 202 55Globicornis emarginata NT-LC 1 1Ptinus subpilosus 1 1Ipidia binotata VU-NT 1 1Glischrochilus quadripunctatus 1 1Rhizophagus dispar 15 99 28Rhizophagus bipustulatus 2 72 27Rhizophagus nitidulus 1 10 5

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Threat levels from Gärdenfors (2000, 2005): Data deWcient (DD), Least concern (LC), Near threatened (NT),Vulnerable (VU), Endangered (EN), Critically endangered (CR), Regionally extinct (RE)

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