Boreal Carabid Beetles (Coleoptera, Carabidae) in Managed Spruce Forests – a Summary of Finnish Case Studies
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Silva Fennica 36(1) discussion papers Boreal Carabid Beetles (Coleoptera, Carabidae) in Managed Spruce Forests – a Summary of Finnish Case Studies Matti Koivula and Jari Niemelä 1 Introduction forest specialists (e.g. Heikkinen et al. 2000). Thus, in addition to protection, the restoration of Over 90% of the forests in Sweden and Finland mature, managed forests and the improvement of are managed (Angelstam 1997, Sevola 1999) and the quality of the surrounding managed landscape form a mosaic of different successional stages matrix through the development of appropriate (Hansson 1992). This is a consequence of forestry management methods are needed (Niemelä 1997, practices over several centuries, but the most 1999, Nilsson 1997, Mönkkönen 1999). drastic effects of forestry on forest biota have Managed forests host fewer threatened forest- taken place during the past 50 years (Niemelä specialist species than do old-growth forests, 1999). Over this period of time, the structures and also many common species occur at low of the plant and animal assemblages of boreal abundance in managed forests. Examples of forests have been strongly altered (Heliövaara this difference are e.g. bryophytes and epiphytic and Väisänen 1984, Esseen et al. 1992, Niemelä lichens (Söderström 1988, Andersson and Hytte- 1997). Forestry is responsible for approximately born 1991, Kuusinen 1994, 1996, Dettki and 30% of the Finnish red-listed species being Esseen 1998), beetles living in dead wood threatened (Rassi et al. 2000). Perhaps the most (Väisänen et al. 1993, Siitonen and Martikainen important reason for this is the fragmentation of 1994, Jonsell et al. 1998) and Mycetophilidae old-growth forests. Habitat fragmentation is one insects (Økland 1994). However, the long-term of the most important causes of species declines persistence of many forest species is dependent and extinctions across the world (Saunders et on populations living in managed forests (Linden- al. 1991, Haila et al. 1994, Didham et al. 1996, meyer and Franklin 1997). The maintenance of Didham 1997a, Davies et al. 2000). In southern these populations can possibly be achieved by Finland, roughly 1% of forest cover is protected ecological planning of forestry. Moreover, the and only 5% of these are old-growth forests importance of ecological forestry planning is not (Virkkala et al. 2000). Protecting all the remain- just to maintain old-growth forests but also to ing old-growth forests in these regions is an inad- prevent the decrease of overall forest biodiversity equate measure for the protection of old-growth at the within-stand, regional and national scales. Keywords boreal, Carabidae, clear-cutting, edge, forestry, landscape, logging, management, retention felling, succession, selective felling Authors´ address Department of Ecology and Systematics, Division of Population Biology, P.O. Box 65, FIN-00014 University of Helsinki, Finland E-mail matti.koivula@helsinki.fi ; jari.niemela@helsinki.fi Received 31 October 2000 Accepted 20 March 2002 423 Silva Fennica 36(1) discussion papers Since maintaining viable populations of all (Vanha-Majamaa and Jalonen 2001). Retained species is of central importance in conservation, trees may also act as stepping-stones or “life- species that are most sensitive to fragmentation boats” for forest specialists (Franklin et al. 1997). should determine conservation actions. Scarcity Thirdly, carabid assemblages of stands where itself, however, makes studying these species selective felling, aiming at an uneven age struc- diffi cult and costly. Therefore, intermediately ture of trees, was applied were studied. Uneven common species, with strict microhabitat age structure of trees is an important feature of demands, can potentially be used as indicators naturally developing forests (Lähde et al. 1991, of environmental quality in order to study e.g. Esseen et al. 1997), but invertebrate studies con- whether or not new, modifi ed management meth- cerning its importance are lacking. Studies con- ods have an effect on forest-species assemblages cerning different thinning methods have mostly (Haila and Kouki 1994). Such species can be focused on their effects on tree growth. found among carabid beetles (Coleoptera, Cara- We also present results of studies where carabid bidae), although none of Finnish forest-carabid assemblages at forest/clear-cut edges (Heliölä et species are classifi ed as threatened (Rassi et al. al. 2001) and in a 60-year time scale of secondary 2000). They are easy to collect in suffi cient quan- succession, caused by clear-cutting (Koivula et tities using pitfall traps and form an ecologically al. 2002), were studied. Changes in abiotic and and taxonomically well-known group (Niemelä biotic conditions in the forest/clear-cut edge as et al. 2000), being often classifi ed into forest, compared to the forest interior are collectively open-habitat and generalist species groups (e.g. called “edge effects” (Murcia 1995, Risser 1995). Niemelä et al. 1988, 1993a, Niemelä and Halme Clear-cutting creates relatively sharp habitat 1992). Carabids also refl ect changes in their boundaries (ecotones) to which species may environments and many intermediately common respond as conduits, fi lters or barriers, sources species with relatively strict microhabitat require- or sinks, habitat and feedback (i.e. edges amplify ments occur (Thiele 1977, Lindroth 1985, 1986, or reduce the intensity of ecological processes) Niemelä et al. 1992, Langor et al. 1994). (Kolasa and Zalewski 1995). To counteract the effects associated with edge, it is important to understand how species respond to the conditions at habitat edges (Haila et al. 1994). Forest edges 2 Aims of the Study harbour a rich invertebrate fauna (e.g. Helle and Muona 1985, Jokimäki et al. 1998), but very few We summarise the main results of our four recent of these species appear to be edge specialists studies, focused on the effects of various logging (Didham 1997a, b). regimes on boreal-forest carabid assemblages, Species’ responses to habitat variability and and partly reanalyse the datasets. The biotic and natural and anthropogenic processes may be abiotic effects of clear-cutting are well docu- determined by different factors acting at different mented (e.g. Huhta 1976, Haila et al. 1994, Pet- time (Niemelä 1999), and spatial levels (Addi- tersson 1996, Davies and Margules 1998, Didham cott et al. 1987, Wiens 1989). It is, therefore, et al. 1998, Abildsnes and Tømmerås 2000), but important to examine the ecological effects of the effects of modifi ed logging methods are much logging at several scales (Haila and Kouki 1994). less studied. A temporal scale from days to hundreds of years, In this paper, three different modifi ed logging and a spatial scale from metres to hundreds of methods are compared (for details of the treat- kilometres, form a relevant framework for stud- ments, see section 3). Firstly, gap felling may ies concerning forest management and forest- mimic natural gap formation (Sousa 1984, Atti- species conservation; the “meso-scale” (Niemelä will 1994, Kuuluvainen 1994). Secondly, retain- 1999). A 120-year time-scale, reaching from ing small tree groups (e.g. 10–30 mature trees; recently-logged to mature stands, covers the 3–4 such groups per hectare) in the clear-cuts normal logging rotation (80–120 years) in south- mimics small-scale disturbance events: such tree ern and central Finnish spruce forests (Kuusela groups are often left in moist sites after fi re 1990). 424 Koivula and Niemelä Boreal Carabid Beetles in Managed Spruce Forests – a Summary of Finnish Case Studies 3 Sampling Designs and were cut, and accordingly, 433–1050 trees per ha were retained. Each treatment (represented by Material 1–2-ha stands) was replicated eight times. The adjacent surroundings of the selectively felled The summarised studies were performed in south- and uncut stands were mapped in order to study central Finland, at the border between the south- whether the landscape mosaic (distance to the ern and middle boreal zones (Ahti et al. 1968). nearest mature stand and to open habitat) infl u- The study forests were spruce (Picea abies) domi- enced carabid abundance patterns. The number nated, Myrtillus-type forests (Cajander 1949). and the placement of the traps were as in Koivula The natural succession of spruce forests begins (2002a). The carabid dataset consisted of 13 689 with a deciduous phase and continues towards individuals representing 45 species. spruce dominance (Esseen et al. 1997). Mature In this paper we also included previously stands had the age of the dominant trees being unpublished carabid data of three stands where 90–120 years. Spruce was the dominant tree gap felling with mechanical soil preparation species, with pines (Pinus sylvestris), birches was applied. These stands were sampled in (Betula spp.) and aspens (Populus tremula) as 1997–1998 in three of the eight study areas of an admixture. The herb layer was usually domi- Koivula (2002a, b). The stands, being 1–2 ha in nated by Vaccinium vitis-idaea and V. myrtillus size, had three 1600-m2 openings. During the fol- dwarf shrubs, and Dicranum, Pleurozium and lowing summer after logging (1996), mechanical Hylocomium mosses covered most of the bottom soil preparation was applied: the humus layer layer. The sampling designs of the four studies was partly removed in narrow (approximately 50 are given below. cm wide) strips. This is a common practice in The beetles were collected using pitfall traps Fennoscandia to help the saplings to establish. (Greenslade 1964, Southwood 1978). The nomen- The number and the placement of the traps were clature follows Lindroth (1985, 1986). as in Koivula (2002a). This dataset, together with The short-term (two years after logging) those of Koivula (2002a, b) are used to analyse responses of carabids to clear-cutting and two the possible differences among carabid catches of modifi ed logging methods were studied in the studied logging and soil preparation regimes. 1995–1998 (Koivula 2002a). The study was car- These additional data consisted of 2307 carabids ried out at eight separate areas, each including representing 23 species.