View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Helsingin yliopiston digitaalinen arkisto Carabid beetles (Coleoptera, Carabidae) in boreal managed forests – meso-scale ecological patterns in relation to modern forestry Matti Koivula This thesis is based on the following articles: 0) Summary I) Koivula, M.: Alternative harvesting methods and boreal carabid beetles (Coleoptera, Carabidae). — Submitted manuscript. II) Heliölä, J., Koivula, M. & Niemelä, J.: Distribution of carabid beetles (Coleoptera, Carabidae) across a boreal forest–clearcut ecotone. — Conservation Biology (in press). III) Koivula, M.: Boreal carabid-beetle (Coleoptera, Carabidae) assemblages in fresh clear-cuts and uneven-age structured stands. — Submitted manuscript. IV) Koivula, M., Punttila, P., Haila, Y. & Niemelä, J. 1999: Leaf litter and the small-scale distribution of carabid beetles (Coleoptera, Carabidae) in the boreal forest. — Ecography 22: 424–435. V) Koivula, M., Kukkonen, J. & Niemelä, J.: Boreal carabid-beetle (Coleoptera, Carabidae) assemblages along the clear-cut originated succession gradient. — Submitted manuscript. 4 Contributions Contributions The following table shows the major contributions of authors to the original articles (referred to as I–V) I II III IV V Initiative MK, JN JH, MK, JN MK, JN YH, JN, PP MK Experimental design MK, JN JH, MK, JN MK, JN YH, MK, JN, PP MK, JK Data gathering MK JH MK MK JK, MK Analyses MK MK, JN, JH MK MK, PP MK Manuscript preparation MK JN, MK, JH MK MK, PP, JN MK, JN, JK Supervised by Prof. Jari Niemelä University of Helsinki Finland Reviewed by Dr. Konjev Desender Royal Belgian Institute of Natural Sciences Belgium Prof. Pekka Niemelä University of Joensuu Finland Examined by Prof. John R. Spence University of Edmonton Canada Carabid beetles in boreal managed forests 9 Introduction time, the structures of the plant and animal as- semblages of boreal forests have been strongly This thesis consists of five research papers altered (Heliövaara & Väisänen 1984, Esseen et (hereafter referred to as I–V) and a summary. al. 1992, Niemelä 1997). Forestry is responsible The summary begins with a general background for 30.7% of the Finnish red-listed species be- of the studies (forest fragmentation, manage- ing threatened (Rassi et al. 2000). Perhaps the ment and their consequences) and reviews cur- most important reason for this is the fragmenta- rent knowledge concerning fauna of boreal tion of old-growth forests. In southern Finland, managed forests. Further, the designs and main roughly 1% of forest cover is protected and only results of the studies I–V are presented, and 0.5% of these are old-growth forests (Virkkala these results are discussed in the context of for- et al. 2000). Obviously, protecting all the re- est management. maining old-growth forests in these regions is an inadequate measure for the protection of old- Forest fragmentation growth forest specialists (e.g. Heikkinen et al. Habitat fragmentation is one of the most impor- 2000). Thus, in addition to protection, the resto- tant causes of species declines and extinctions ration of mature, managed forests and the im- across the world (Saunders et al. 1991, Haila et provement of the quality of the surrounding al. 1994, Didham et al. 1996, Didham 1997a, managed landscape matrix through the devel- Davies et al. 2000). Forest fragmentation leads opment of appropriate management methods to isolation and reduction in size of mature-for- are needed (Niemelä 1997, 1999, Nilsson 1997, est fragments and an increase in the proportion Mönkkönen 1999). of edge habitat at the expense of interior habitat (Ranney et al. 1981, Harris 1984, Murcia 1995). Selecting the study subjects Edge is a habitat on which an adjacent habitat The long-term persistence of many forest spe- has an effect e.g. through climatic alteration, cies is dependent on populations living in man- whereas within interior habitat such an effect is aged forests (Lindenmeyer & Franklin 1997). not discernible. Deforestation and consequent Since maintaining viable populations of all spe- loss of forest species in tropical forest ecosys- cies is of central importance in conservation, tems have received considerable attention (Lau- species that are most sensitive to fragmentation rance & Bierregaard 1997). Erwin (1982) esti- should determine conservation actions. How- mated that tropical forests may host as many as ever, managed forests host fewer threatened 30 million arthropod species, while the number forest-specialist species than do old-growth for- of all known species was estimated to be ca. 1.4 ests and also many common species occur at million at that time (Wilson 1988). Since recent low abundance in managed forests. Examples extinction rates are more than 100 times greater of this difference are e.g. bryophytes and epi- than background geological ones (Pimm 1998), phytic lichens (Söderström 1988, Andersson & much of the tropical diversity is lost before it Hytteborn 1991, Kuusinen 1994, 1996, Dettki has been even discovered. However, boreal re- & Esseen 1998), beetles living in dead wood gions also host a rich fauna. For example, (Väisänen et al. 1993, Siitonen & Martikainen Hanski & Hammond (1995) suggested that bo- 1994, Jonsell et al. 1998) and Mycetophilidae real forests may house only seven times less insects (Økland 1994). However, Martikainen beetle species than tropical ones. (2000) showed that many saproxylic species Over 90% of the forests in Sweden and Fin- can live in managed forests if they contain a suf- land are managed (Angelstam 1997, Sevola ficient amount of dead or dying wood. 1999) and form a mosaic of different suc- Most forest species require specific ele- cessional stages (Hansson 1992). This is a con- ments of forests rather than “average forest” sequence of forestry-caused fragmentation over (Niemelä et al. 1996). Consequently, individu- several centuries but the most drastic effects of als of such species are more common in their fa- forestry on forest biota have taken place for only voured habitat and thus are distributed non-ran- 50 years (Niemelä 1999). Over this period of domly among forest patches and within stands 10 Koivula, M. (Niemelä et al. 1992a). Environmental diversity nes&Tømmerås 2000) and the microclimates creates a richer within-stand habitat mosaic in of clear-cut and closed-canopy sites differ naturally-developing forests compared to man- (Matlack 1993). Open sites are windier and the aged ones (Haila et al. 1994, Esseen et al. 1992, diurnal light, temperature and humidity vary Dettki & Esseen 1998). Decaying wood, tree- more; the sun dries and heats the ground, caus- species admixture and large trees, for example, ing the decrease of dwarf shrubs (Vaccinium are usually lacking from managed forests spp.) and forest mosses, and the drying of (Esseen et al. 1997, Niemelä 1997, 1999). Site Sphagnum moss mires (Niemelä 1997, 1999). characteristics may also appear different for dif- These factors affect carabid-beetle distribution ferent species. Consequently, some species with directly and indirectly (Thiele 1977). Carabids strict microhabitat demands occur in metapopu- are often more numerous and more speciose in lations (Hanski 1999), whereas for some other open habitats than in forests (Niemelä & Halme species with wider tolerances the environment 1992, Kinnunen 1999) but clear-cutting also has may be divided into source and sink habitats negative effects on the abundance of forest-spe- (Pulliam 1988) with some species using several cialist species (Niemelä et al. 1993a, b, Langor microhabitat and forest types. In a given habitat, et al. 1994, Spence et al. 1996). colonisations and extinctions may occur, with The effects of modified cutting methods are the most successful species persisting for a lon- much less studied. For example, studies con- ger time (Lockwood et al. 1997). The species in cerning thinning have mostly focused on its ef- the forests thus form gradually changing assem- fects on tree growth. In this thesis, three modi- blages rather than strict communities of species fied cutting methods are examined (I, III). Cre- (e.g. Niemelä et al. 1990). ating openings of a few acres into stands may Intermediately common species, with strict mimic natural gap formation (Sousa 1984, microhabitat demands, can potentially be used Attiwill 1994, Kuuluvainen 1994). Another as indicators of environmental quality in order method with small, retained tree groups has no to study whether or not new, modified manage- obvious natural analogue but retained trees may ment methods have an effect on forest-species act as stepping stones or “lifeboats” for forest assemblages (Haila & Kouki 1994). Such spe- specialists (Franklin et al. 1997). Finally, un- cies can be found among carabid beetles even age structure of trees is an important fea- (Coleoptera, Carabidae). They are easy to col- ture of naturally developing forests (Lähde et al. lect in sufficient quantities using pitfall traps 1991, Esseen et al. 1997) but invertebrate stud- and form an ecologically and taxonomically ies concerning its importance are lacking. In well-known group (Niemelä et al. 2000), being this thesis, beetle catches of stands where thin- often classified into forest, open-habitat and ning (aiming at uneven age structure of trees) generalist species groups (e.g. Niemelä et al. are studied (III). 1988, 1993a, Niemelä & Halme 1992). Cara- Changes in abiotic and biotic conditions in bids also reflect changes in their environments the forest – clear-cut edge as compared to the and many intermediately common species with forest interior are collectively called “edge ef- relatively strict microhabitat requirements oc- fects” and are studied in paper II. Clear-cutting cur (Thiele 1977, Lindroth 1985, 1986, Nie- creates relatively sharp habitat boundaries melä et al. 1992a, Langor et al. 1994). Clear- (ecotones) to which species may respond as cutting, for example, is shown to alter carabid conduits, filters or barriers, sources or sinks, assemblages (Haila et al. 1994, Didham et al. habitat and feedback (i.e. edges amplify or re- 1998).