Conservation of beetles in boreal pine forests: the effects of forest age and naturalness on species assemblages

Biological Conservation 106 (2002) 19–27 www.elsevier.com/locate/biocon

Conservation of beetles in boreal pine forests: the effects of forest age and naturalness on species assemblages M. Simila¨*, J. Kouki, P. Martikainen, A. Uotila Faculty of Forest Sciences, University of Joensuu, PO Box 111, FIN-80101 Joensuu, Finland Received 11 April 2001; received in revised form 25 September 2001; accepted 9 October 2001

Abstract The effort of boreal forest conservation has emphasised the preservation of old-growth forests while the role of young successional stages in maintaining biodiversity has remained largely unstudied. We compared the richness of beetle species and composition of species assemblages between managed and seminatural forests in five stages of forest succession. The sites were in boreal sub-xeric pine-dominated forests in eastern Finland. Seminatural study sites, especially the recently burned sites, were important habitats for threatened and near-threatened species. We propose that young stages of natural succession should be included in the network of protected forest areas. On the other hand, the composition of saproxylic species assemblages in seminatural forests differed from the assemblages in managed forests, indicating also the need to improve the forest management guidelines so that they better address the requirements of species protection. Regeneration methods applied should resemble or mimic the natural disturbances more closely. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Species richness; Coleoptera; Conservation; Forest succession; Forest management

1. Introduction Human caused alterations can be seen almost overall in the forests of Fennoscandian countries (Bryant et al., 1997; O¨stlund et al., 1997; Lo¨fman and Kouki, 2001). The most intense and visible utilisation of forests took place in the middle of twentieth century when modern forestry practises—such as clear cutting—were adopted in use. The modern forestry has an important role in controlling the structure and processes of boreal forest ecosystem and the populations of species living in it (Kouki, 1994; Esseen et al., 1997; Martikainen et al., 2000b). The forest utilisation has led to the multitude of changes in the local forest conditions, e.g. in the volume of dead wood and in the stand age structure (Esseen et al., 1997; Anon., 2000). Management practices have also caused landscape-scale changes, by fragmenting and otherwise modifying the spatial landscape configuration (Lo¨fman and Kouki, 2001). One of the most fundamental changes, affecting both local and * Corresponding author. Tel.: +358-13-251-4059; fax: +358-13251-4444. E-mail address: maarit.simila@joensuu.fi (M. Simila¨).

landscape structures, has been the alteration of the disturbance dynamics. For example, forest fires have been efficiently suppressed from the end of nineteenth century (Zackrisson, 1977; Lehtonen and Huttunen, 1997) and nowadays the young stages of forests are almost solely managed in origin. Almost half of the 43 000 species recorded from Finland live in forests. The timber production oriented forest management has led to clear difficulties for many species to persist in the managed forests. For example, roughly 37% of threatened species in Finland are forestdwelling (Anon., 2000). Species protection could be based on nature reserves that ideally protect the elements of biodiversity from the processes that threaten their existence in the wild (Margules and Pressey, 2000). Although this is often an effective solution, its implementation may be difficult in areas where majority of habitats have already lost their natural characteristics. This applies especially to forests in Fennoscandia, but also in several areas in Russia and North America. For example, only about 3.6% of Finnish forests are tightly protected (Anon., 1999) and increasing this amount seems very difficult as practically all the remaining forest areas are more or less intensively managed and have

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lost their natural characteristics (Uotila et al., 2001a). Alternative and complementary protection activities can be sought from developing management guidelines so that they address also the needs of species protection (Kouki et al., 2001). However, this requires better documentation of the habitat associations of threatened species. Of forest-dwelling species at least 20% are saproxylic species in Finland (Siitonen, 2001). The great majority (73%) of threatened forest beetle species are saproxylic (Anon., 2000). They are, during some part of their life cycle, dependent on dead wood, wood rotting fungi or on other saproxylic species (Speight, 1989). Living conditions of these species are reduced when the total volume of dead wood decreases and when the continuity of different stages of decaying wood, large dead wood in particular, disappears or becomes scattered in managed landscape. Until recently, the preservation of natural structures has concentrated almost exclusively on the conservation of the remaining old-growth forest patches. However, young stages of succession also have been an important part of the boreal forest landscape (Syrja¨nen et al., 1994; Johnson et al., 1998). Several recent studies (Kaila et al., 1997; Jonsell et al., 1998; Martikainen et al., 2000a; Martikainen, 2001) have emphasised their role as a habitat for many threatened species which earlier were assumed to require old-growth forests. The role of young successional stages in maintaining biodiversity has, however, remained largely unstudied (Kouki et al., 2001). One reason to that has been the paucity of naturally regenerated young stands in Fennoscandian boreal forests. We studied the beetle species richness and species assemblages along the successional gradient in sub-xeric pine dominated forests. Our main aims were: 1. to investigate the difference in species richness and in the composition of species assemblages between managed and seminatural forests; and 2. to assess the value of young stages of forest succession for maintaining and conserving species diversity in boreal forests.

2. Material and methods 2.1. Study sites We studied beetles in sub-xeric Scots pine (Pinus sylvestris) dominated forests both in managed and seminatural stands in North-Karelia, in eastern Finland (ca. 63
170 N, 30
420 E), near the Russian border (Fig. 1). For the purposes of this study, we classified forests to five successional stages: I was the sapling stage, clear-cut or burnt 7 years ago; II young forest: about 40 years

Fig. 1. Location of the study area. Vegetation zones are after Kalliola (1973).

old; III middle aged forest: about 70 years old; IV mature forest: about 110 years old and; V old-growth or over-mature forest: more than 150 years old. Number of replicates was three both in managed and seminatural forests except for the stage II in seminatural forests where only two replicates were available. The seminatural study sites represent the most naturallike sub-xeric stands in North-Karelian forest reserves (Uotila et al., 2001a, 2001b). Nevertheless, most of these sites have been slightly utilised in the past but they have been untouched at least for 50 years. The managed sites were in ordinary cultivated forests managed by Finnish Forest and Park Service. Young stages (I–II) were in clear-cut stands and older stages (III–V) in selectively cut stands. Seminatural sites of stage I were located in an area (143 ha) that was completely burned in 1992 and had been in commercial use before the forest fire (mean age of trees about 130 years). The distance between study sites was at least 50 m in two rarest succession stages (seminatural stages I and II), otherwise it was at least 1 km. Stand characteristics were measured during the years 1994–1998 (Uotila et al., 2001b) from the circles of 900, 1600 or 2500 m2, on each study site, depending on the density of stand measured (in a dense stand a small circle; Isoma¨ki, 1995). Living trees (Fig. 2a) as well as dead wood (Fig. 2b) consisted of small amounts of spruce and birch in addition to the dominant Scots pine.

M. Simila¨ et al. / Biological Conservation 106 (2002) 19–27

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Fig. 2. Volume (means and standard deviations) of (a) living and (b) dead wood in five successional stages (I–V) of managed and seminatural forests.

2.2. Beetles We sampled beetles with window traps. Each trap consisted of two transparent plastic panes (4060 cm) placed crosswise, with a funnel and a container below the panes. We used salt water with detergent in the containers for preservation of the insects. We located five traps as five points in a dice on each study site and the distance between traps was about 40 m. Total number of traps was 145. Trapping period was 25 May–8 September 1998. We emptied the traps four times during the period. Beetles were identified to species level and the nomenclature follows Silfverberg (1992). Species were separated into six ecological groups: (1) saproxylic species that were further separated into two subgroups: (1a) bark beetles, and (1b) other saproxylic species; (2) non-saproxylic species that were separated into four subgroups: (2a) myrmecophilous species, (2b) herbivores, (2c) species on ephemeral resources, e.g. carrion, dung and mushrooms, and (2d) other non-saproxylic species that inhabit different kinds of microhabitats on the forest floor. The grouping followed the classification used in Martikainen et al. (2000b). We classified species as common or rare according to the frequency score list of the Finnish Coleoptera (Rassi, 1993). This list gives the actual or estimated number of records (in 1010 km squares) for each species found in Finland during 1 January 1960–1 January 1990. We classified species with more than 50 records as common and species with less than 50 records as rare. Threatened species are after Rassi et al. (2000). 2.3. Data analysis As an indicator of species richness we used the pooled number of species caught with five window traps on each study site. According to the Mann–Whitney U-test the total number of individuals per site within successional

stages did not differ between managed and seminatural study sites (P50.05). Thus, we used Mann–Whitney Utest to compare the absolute numbers of all, saproxylic and non-saproxylic species and individuals as well as the number of rare and common species within successional stages. Because the number of individuals varied a lot between successional stages it was not appropriate to compare species richness in ecological groups directly among stages. To show the changes in proportions of ecological groups along the succession gradient we calculated percentage shares of groups on each sampling site. We used the analysis of variance (ANOVA) to analyse the effects of forest naturalness (managed vs. seminatural), stage of succession and their interaction with the species richness in six ecological groups. Dunnett T3 was used as a post hoc test to compare differences among successional stages. We used the detrended correspondence analysis (DCA ordination) to explore the structure of species assemblages on study sites. Ordination was performed with PC-ORD (McCune and Mefford, 1999). We used log (x+1) transformation and all species were equally weighed. Species occurring once only were excluded. Axes were rescaled with 26 segments.

3. Results 3.1. Species richness and species assemblages A total of 13 082 beetle individuals (6899 in managed and 6183 in seminatural forests) and 514 species were caught. Total number of species was almost equal in managed (394) and in seminatural forests (395). More than a half of the species (54%) were caught both in managed and seminatural forests. These species made up 97% of the total catch. A total of 119 species were caught on managed sites only and 120 species on seminatural

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sites only. One hundred and seventy-six species were caught on one sampling site only. Within the successional stages the number of all beetle species tended to be higher and number of all beetle individuals lower on seminatural than on managed sites (Table 1) although the differences were not statistically significant (Mann–Whitney U, P > 0.05 in both cases). Richness of saproxylic species was usually higher in seminatural forests and richness of nonsaproxylic species in managed forests (Table 1) but the only statistically significant difference was in saproxylic species in stage I. The proportions of bark beetles and other saproxylic species were higher in seminatural than in managed forests (ANOVA, F1,19=23.574, P < 0.001 for bark beetles and F1,19=9.733, P < 0.01 for other saproxylic species). The proportion of other non-saproxylic species was higher in managed than in seminatural forests (ANOVA, F1,19=19,142, P < 0.001). The proportion of bark beetles increased from young to old stages of succession (ANOVA, F4,19=8.726, P < 0.001): there were statistically significant differences between stages I/IV and I/V (P < 0.05 in both cases). The proportion of herbivores first increased and then decreased along the successional gradient (ANOVA, F4,19=7.411, P < 0.01): statistically significant differences existed between stages I/II (P < 0.01), I/III and II/V (P < 0.05 in both cases). Proportion of other non-saproxylic species (ANOVA, F4,19=9.460, P < 0.001) decreased from young to old stages of succession: between stages I/IV (P < 0.01) and I/V (P < 0.05) the difference was statistically significant. The only group where the naturalness and successional stages interacted was the proportion of ephemeral species (ANOVA, F4,19=3.059, P < 0.05). The DCA ordination of saproxylic species (Fig. 3) showed that species assemblages in stage I were clearly different from the rest of the stages. Similar patterns were observed in the ordinations of all and nonsaproxylic species. Ordination of saproxylic species separated species assemblages between managed and seminatural sampling sites but not among successional stages II-IV (Fig. 3). Considering all species, the species composition tended to change from younger (stage II)

to older stages. The assemblages between managed and seminatural sampling sites overlapped in ordination of all and non-saproxylic beetle species. There were 13 species (Table 2) in the pooled data that were at least ten times more abundant in the pooled sample of stage I than in the pooled sample of stages IIV (number of individuals was roughly the same in these two groups). On the other hand, 35 species (Table 3) were at least 10 times as abundant in stages II–V as in stage I and thus seemed to avoid the first successional stage. There were no species so clearly confined to successional stages II–V only. 3.2. Rare and threatened species Altogether 74 rare species were observed, 47 in managed forests (53% of them saproxylic) and 56 in seminatural forests (68% saproxylic). Number of rare saproxylic species (Fig. 4a) tended to be higher on seminatural than on managed study sites although the difference was not statistically significant in any stage (Mann–Whitney U-test, stage I: P=0.05, stages II–V: P > 0.05). Number of rare non-saproxylic species

Fig. 3. DCA-ordination of saproxylic species. Open shapes are seminatural and filled shapes are managed study sites. Eigenvalues are in parenthesis and total inertia of ordination is 1.9997.

Table 1 The number of all, saproxylic and non-saproxylic beetle species and all beetle individuals in five successional stages (I–V) in both managed (M) and seminatural (SN) forests (means and standard deviations) I M

II SN

M

III SN

M

IV SN

M

V SN

M

SN

Number of species Saproxylic Non-saproxylic

125.010.6 133.32.1 63.712.1 82.08.5 66.717.6 72.0 12.2 84.7 6.1 76.310.4 81.731.7 90.09.5 52.7 4.9* 61.06.9* 24.37.0 45.05.7 28.38.6 39.3 12.9 45.7 2.3 45.36.5 40.021.7 56.311.7 70.0 6.2 70.75.1 39.35.0 36.52.1 37.310.4 32.3 2.1 39.0 8.0 31.07.0 41.310.4 33.73.5

Number of individuals

1084270

1029230

25083

35858

25363

217 97

413 39

249 90

303191

* Statistically significant difference (P<0.05) between managed and seminatural classes according to Mann–Whitney U-test.

330117

23

M. Simila¨ et al. / Biological Conservation 106 (2002) 19–27 Table 2 Species more than 10 times as abundant in stage I as in stages II–V, in managed (M) and seminatural (SN) forests Species

Acmaeops pratensis (Laicharting) Altica chamaenerii Ha˚kan Lindberg Anaspis frontalis (L.) Bromius obscurus (L.) Cyphon coarctatus Paykull Dasytes niger (L.) Dasytes obscurus Gyllenhal Euglenes pygmaeus (Degeer) Judolia sexmaculata (L.) Leiodes picea (Panzer) Leptura quadrifasciata L. Mordella holomelaena Apfelbeck Orithales serraticornis (Paykull)

Ecologya

s – s – – s s s s – s – –

Total number of species Total number of individuals a

Stage I

Stages II-V

M

SN

M

SN

9 10 18 26 0 16 101 4 53 9 10 6 531

466 23 3 44 32 4 38 7 8 5 3 6 175

0 0 1 0 2 0 3 0 4 0 0 0 26

0 1 1 1 0 2 0 1 2 0 0 0 6

12 793

13 814

5 36

7 14

s, Saproxylic species; –, other non-saproxylic species.

(Fig. 4b) was almost equal between managed and seminatural forests in different stages. Five threatened species were caught (Table 4). All of them were saproxylic species and were caught from the seminatural forests. In addition, seven near threatened species—also saproxylic ones—were found (Table 4). For threatened and near threatened species especially the first stage of succession in natural forests (sites in burned forest) seemed to be important.

4. Discussion Clear-cutting, as a regenerating force of forest, has been argued to resemble the natural stand-replacing disturbances because it releases the growing space for new tree generation. However, there are decisive differences between clear-cut and fire-disturbed stands, and they were visible also on our study sites. The microclimate of completely burned forest, where almost all trees have died, may partly resemble the climate in clear-cut (e.g. in the diurnal changes of temperature) but the volume of dead wood is remarkably larger after intensive forest fire than after the clear-cut harvesting. Although the beetle species assemblages were superficially similar in clear cut and on burned sites, there were clear differences in saproxylic species assemblages. Furthermore, threatened species were almost exclusively, and near-threatened specimens mainly, found on the burned sites showing the importance of dead wood in sunny locations for such species. In general, the structure of the forest strongly changes when succession proceeds. There are many characters related to living plants which change in parallel way both in managed and natural stands along the succession,

although the conditions in the beginning are dissimilar (Vanha-Majamaa, 1988). Volume of living trees increases (Fig. 2), vegetation on the ground layer changes (e.g. Tonteri, 1994) and so do the microhabitats on the forest floor. Against this background it is not surprising that the species richness was of the same magnitude in managed and seminatural forests, and assemblages of all species changed along the succession gradient rather than in managed-seminatural axis. For example, the proportion of other non-saproxylic species living in the different microhabitats on the forest floor decreased and proportion of bark beetle species increased both in managed and seminatural forests along the succession gradient. 4.1. Species assemblages Assemblages of beetles in the first stage of succession were very distinct and clearly separated from the other stages, both on managed and seminatural sites. In general, species which seemed to avoid the first stage of succession did not make a difference between clear-cuts and burned sites but avoided them both. Interestingly, the number of threatened and near threatened species found was higher in this particular stage than in the other four stages together, due to species caught on the burned study sites. This observation is in agreement with Kaila et al. (1997), Jonsell et al. (1998), Martikainen (2001) and Sverdrup-Thygeson and Ims (2000), who have emphasised the role of sunny, early successional habitats for threatened beetles. The detrended correspondence analysis showed that there were also important differences between managed and seminatural forests, but only in saproxylic species. Although the richness of saproxylic species was not

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Table 3 Species more than 10 times as abundant in stages II–V as in the stage I on managed (M) and seminatural (SN) study sites Species

Anaspis arctica Zetterstedt Anthonomus phyllocola (Herbst) Aphodius depressus (Kugelann) Aphodius rufipes (L.) Apion simile Kirby Atomaria peltata Kraatz Brachyderes incanus (L.) Brachonyx pineti (Paykull) Calomicrus pinicola (Duftschmid) Cerylon ferrugineum Stephens Cryptophagus dorsalis Sahlberg Dalopius marginatus (L.) Dromius agilis (Fabricius) Enicmus fungicola Thomson Enicmus planipennis Strand Epurea aestiva (L.) Epurea pygmaea (Gyllenhal) Haploglossa villosula (Stephens) Hylobius abietis (L.) Hylastes brunneus Erichson Hylastes cunicularius Erichson Hylecoetus dermestoides (L.) Hylurgops glabratus (Zetterstedt) Otiorhynchus scaber (L.) Pityophagus ferrugineus (L.) Pityophthorus lichtensteini (Ratzeburg) Polydrusus fulvicornis (Bonsdorff) Prosternon tessellatum (L.) Rhizophagus ferrugineus Gyllenhal Selatosomus aeneus (L.) Strophosoma capitatum (Degeer) Tetratoma ancora Fabricius Trypodendron lineatum (Olivier) Trypodendron proximum (Niijima) Xylita laevigata (Hellenius)

Ecologya

Stage I

s h e e h e – h – s – – s s s – s – s s s s s h s s – – s – h s s s s

Total number of species Total number of individuals a

Stages II–V

M

SN

M

SN

0 1 0 0 0 1 0 0 2 0 0 3 0 0 0 0 0 0 6 3 15 0 1 0 1 0 1 0 0 0 0 0 0 0 4

0 1 1 3 0 0 0 0 0 0 0 1 0 1 2 2 1 0 2 13 14 1 0 0 0 0 0 0 2 0 0 0 1 0 10

7 19 7 23 8 6 6 7 25 3 39 25 12 11 18 14 8 6 74 151 141 5 4 24 7 30 7 26 20 7 157 6 6 2 114

16 18 4 15 2 13 51 6 2 9 34 36 19 19 11 13 16 10 91 241 167 19 14 12 5 40 5 59 50 6 130 6 52 9 79

11 38

15 55

35 1025

35 1279

s, Saproxylic; h, herbivore; e, ephemeral; –, other non-saproxylic species.

much higher on seminatural than on managed sites, the species assemblages were clearly different. Similar observations were made by Martikainen et al. (2000b) in a comparison between old managed stands and oldgrowth stands in spruce-dominated forests. There seems to be a general pattern: forest management has a strong effect on species dependent on dead wood (Martikainen et al., 2000b; Siitonen, 2001), while many other species dependent on other resources may remain almost unaffected (Martikainen et al., 2000b). On our study sites the volume of dead wood was relatively high in managed forests compared to the published reports from some regions in Finland (e.g. in northern Savo: on average 2.9 m3 ha1; Tomppo et al., 1999). This suggests that differences in the beetle fauna

between managed and unmanaged stands should be more pronounced in many other parts of Finland. On the other hand, our results also show that even if the amount of decaying wood in managed forests could be increased to correspond to the level observed on our managed study sites, the saproxylic fauna would still be clearly different from natural forests. 4.2. Implications for forest conservation and management Our results highlight the conservation value of the first stage of natural succession, because this stage maintains very different species composition compared to closed forest, and seems to contain more rare and

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Fig. 4. Number of rare (see definition in Section 2) (a) saproxylic and (b) non-saproxylic species (means and standard deviations) in five successional stages (I–V) of managed and seminatural forests.

Table 4 Threatened (endangered and vulnerable) and near-threatened species and number of individuals in five successional stages (I–V) in managed and seminatural forests Species

Managed forests

Seminatural forests

I

II

III

IV

V

Total

Endangered Ampedus lepidus (Ma¨klin)

–

–

–

–

–

0

Vulnerable Acmaeops marginata (Fabricius) Acmaeops septentrionis (Thomson) Boros schneideri (Panzer) Ceruchus chrysomelinus (Hochenwarth)

– – – –

– – – –

– – – –

– – – –

– – – –

Near threatened Ampedus suecicus Palm Lacon conspersus (Gyllenhal) L. fasciatus (L.) Melandrya dubia (Schaller) Peltis grossa (L.) Sphaeriestes stockmanni (Bistro¨m) Tomoxia bucephala Costa

3 – 2 – – – –

– – – – – – –

– – – – – – –

– – – – – – –

Total number of species Total number of individuals

2 5

0 0

0 0

0 0

threatened species than the first stage of managed forest succession, clearcuts. Preserving only the oldest stage of succession may leave out many threatened species which prefer sunny, open habitats and require large amounts of dead wood. In our material only 5% of species were absent from the combination of managed sites and the youngest and oldest stages of seminatural forests. Of threatened and near-threatened species found, only one species was missing from this combination. The important role of young, disturbed sites for threatened species is not restricted to pine-dominated forests. Observations from other forest site types (Kaila

I

II

III

IV

V

Total

1

–

–

–

–

1

0 0 0 0

1 1 1 –

– – – –

– – – –

– – – 1

– – – –

1 1 1 1

– 2 – – – – –

3 2 2 0 0 0 0

– – 3 – 1 1 2

1 – 1 – – – –

– – – – – – –

– – – – – – –

– – – 1 1 – –

1 0 4 1 2 1 2

1 2

3 7

8 11

2 2

0 0

1 1

2 2

11 16

et al., 1997; Sverdrup-Thygeson and Ims, 2000; Martikainen, 2001) and organism groups (Martikainen et al., 2000a) demonstrate that this is a common pattern. That is a challenge for the conservation of boreal fauna. The successful conservation of all forest-dwelling species seems to require that different successional stages— of different forest types—are included in the network of protected areas. Unfortunately the naturally regenerating young forests are very rare in the current forest protection network (Anon., 2000). However, inclusion of the naturally originated young stands with plenty of dead wood is urgently needed to cover the ecologically important succession gradient of boreal forests.

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Restoration of natural forest characteristics is an emerging and potentially effective way to alleviate the negative consequences that past forest management has had on natural biota (see also Kouki et al., 2001). However, before these activities will be implemented, their ecological consequences should be adequately understood. The results of the current study are among the first ones to empirically show that there are clear benefits to be expected (see also other studies in Jonsell et al., 1998; Linder, 1998; Kouki et al., 2001). The proportion of young natural successional stages in protected areas can be increased by maintaining the structural variation in boreal forests by mimicking the natural dynamics e.g. with forest fires (Haila and Kouki, 1994; Linder et al., 1997; Linder, 1998). Fire is effective in making dead wood (Linder et al., 1998). In burned areas the volume of standing and fallen dead trees is high, and many times there are also living trees left (Eberhart and Woodard, 1987; Linder et al., 1998). It can be expected that the continuity of decaying wood is secured for decades even in completely burned forests when standing dead trees fall down at their own rates, although the succession of coarse woody debris after fire is poorly explored. Fire gives more variation into the quality of dead wood compared to the clear-cut harvesting that increases the amount of small diameter coarse woody debris in short time (see also Sippola et al., 1998). Only few threatened saproxylic species are pyrophilous (Jonsell et al., 1998; Anon., 2000) but most of the saproxylic species benefit from large amounts of dead wood after forest fire. However, as the total amount of protected forest areas in Finland is low, the restoration operations should not be done at the expense of old-growth forests, but rather applied in less natural parts of the larger national parks. The opportunities of species conservation in boreal forests lie in the implications which our results have on the management recommendations of forests in commercial use. To substantially increase the suitable habitat available for the threatened fauna requires that also the managed areas can be used for species protection (Kouki et al., 2001; Martikainen, 2001). Our results show that there exists a large and underexploited potential especially in younger successional stages (see also Kouki et al., 2001). However, to take advantage of this potential requires that the regeneration methods applied must resemble or mimic more closely the natural disturbances. In practice this means that living and dead trees should be left in the clear-cut areas to improve the continuity and quality of dead wood and that the use of fire also in the managed forests should be promoted. These would most likely increase the suitability of the managed forests also for many currently threatened species (see also Hanski, 2000; Kouki et al., 2001; Martikainen, 2001).

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