Journal of Environmental Management 92 (2011) 2539e2546 Contents lists available at ScienceDirect Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman The role of power line rights-of-way as an alternative habitat for declined mire butterflies Terhi Lensu a, Atte Komonen a,*, Outi Hiltula a, Jussi Päivinen b, Veli Saari a, Janne S. Kotiaho a,c a Department of Biological and Environmental Science, P.O. Box 35, University of Jyväskylä, 40014 Jyväskylä, Finland b Metsähallitus, Etelä-Suomen luontopalvelut, PL 36, 40101 Jyväskylä, Finland c Natural History Museum, P.O. Box 35, University of Jyväskylä, 40014 Jyväskylä, Finland article info abstract Article history: Habitat loss is one of the greatest threats for biodiversity. In Finland, two thirds of natural mires have Received 28 May 2008 been drained for silviculture, which transforms open wetlands into dense forests. However, vegetation Received in revised form management of power line rights-of-way (ROW) maintain the drained mires as open areas. The aim of 29 April 2011 this study was to determine the effect of the power line ROW vegetation management on butterfly Accepted 18 May 2011 abundance, species richness and community structure by comparing the managed power line ROWs to Available online 12 June 2011 unmanaged drained control sites and to natural mires. The species richness or abundance of mire butterflies did not differ between the power line ROWs and natural mires. In contrast, both species Keywords: fl Lepidoptera richness and abundance of butter ies was low on the unmanaged control sites. Tree canopy cover had fl Mires a negative effect on mire butter ies and this is most likely related to changes in microclimate. The results Vegetation management indicate that the active vegetation removal in the power line ROWs maintain alternative habitats for mire ROW butterflies; yet, the power line ROWs cannot substitute the natural mires. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction and Reinikainen, 2001). Growing tree stock increases evaporation, and consequently the water level subsides even further and the There is increasing evidence that the immediate cause of the microclimate of mires changes (Päivänen and Paavilainen, 1998; worldwide biodiversity loss, the so called ‘sixth extinction crisis’,is Heikkilä et al., 2002). In addition, the gradually increasing over- a combination of anthropogenic disturbance, climate change and shadowing cause further changes to indigenous vegetation of mires habitat loss (Wilson, 1985; Pimm et al., 1995; Chapin III et al., 2000, still decades after drainage (Heikkilä et al., 2002). Thomas C. et al., 2004, Thomas J.A. et al., 2004). Of these, the most The 2010 Red List of Finnish Species identifies 420 species that important and immediate threat is likely to be the habitat loss: are primarily or secondarily dependent on mires (Rassi et al., 2010). human landuse has already transformed nearly 50% of natural Of the red-listed species that are primarily dependent on mires, biotopes worldwide (Fischer et al., 2007). One biotope that has Lepidoptera is the largest group. Of the c. 100 butterfly species that been heavily affected by landuse is the peatlands. In Europe c. 60% are regularly found in Finland many occur in wetlands, but only 9 of of the area of all peatlands has been transformed: 50% of these for these are specialised to live on mires (Marttila, 2005)(Table 1). the agriculture, 30% for silviculture and 10% for peat industry Throughout southern Finland, mire butterflies have declined (Vasander et al., 2003). In Finland, the percentage is even greater during the past two decades, and in places they have been driven to totalling c. two thirds of the original peatland area (Aapala and local extinction (Kontiokari, 1999; Marttila, 2005; Rassi et al., 2010). Lappalainen, 1998; Vasander, 1998; Virkkala et al., 2000; Heikkilä Mire butterflies are highly specialised on mire habitats and they are et al., 2002). seldom found from other kinds of biotopes. It has been argued that Peatlands are drained for silvicultural purposes. As a conse- mire butterflies have suffered especially from the changes of quence of drainage, subsidence of water level leads to changes in microclimate that result from drainage (Pöyry, 2001), and from the vegetation: characteristic mire vegetation declines, tree growth decline of the larval food plants due to increasing overshadowing of increases, and eventually open land area expires (Vanha-Majamaa the tree canopy (de Becker et al., 1991; Aapala and Lappalainen, 1998; Pöyry, 2001). A few studies have examined the effects of drainage on mire fl * Corresponding author. Tel.: þ358 (0) 14 260 2471. butter ies in more detail. Pöyry (2001) suggested that some E-mail address: atte.komonen@jyu.fi (A. Komonen). species, such as Pyrgus centaureae, Boloria freija, Boloria frigga and 0301-4797/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvman.2011.05.019 2540 T. Lensu et al. / Journal of Environmental Management 92 (2011) 2539e2546 Table 1 Mire butterflies of this study. Mire species ¼ species dependent on mire; other species ¼ may occur on mire, but is not dependent on mire (based on Marttila, 2005). Butterfly/Scientific name Butterfly/Common name Host plant/Scientific name Host plant/Common name Pyrgus centaureae Northern grizzled skipper Rubus chamaemorus Cloudberry Colias palaeno Arctic sulphur Vaccinium myrtillus, Vaccinium uliginosum Bilberry, Bog bilberry Boloria eunomia Bog fritillary Andromera polifolia, Vaccinium uliginosum Bog rosemary, Bog bilberry Boloria freija Zig-zag fritillary Rubus chamaemorus, Vaccinium uliginosum Cloudberry, Bog bilberry Boloria frigga Willow-bog fritillary Rubus chamaemorus Cloudberry Boloria aquilonaris Cranberry fritillary Vaccinium oxycoccos, Andromeda polifolia Small cranberry, Bog rosemary Coenonympha tullia Large heath Carex sp. Sedges Erebia embla Lapland ringlet Carex sp., Poaceae sp. Sedges, grasses Oeneis jutta Baltic grayling Carex sp., Poaceae sp. Sedges, grasses Erebia embla, will disappear soon after drainage, whereas Boloria from that of traditional grasslands. Studies carried out by Kyläkorpi eunomia survives until the drained mire turns into peat heath. and Grusell (2001) show that also in Sweden several grassland Kontiokari (1999) determined the changes in butterfly communi- butterfly species have been observed to utilise power line ROWs. In ties of two drained mires in South-Ostrobothnia over twenty years fact, in some areas power line ROWs are vitally important alterna- and concluded that the populations of most mire species decreased tive habitat for populations of Euphydryas aurinia (Kyläkorpi and strongly or disappeared completely. Similar conclusions about the Grusell, 2001), a species enshrined by EU habitat directive. decline of mire butterflies following drainage were also reached Our aim in this study is to determine whether declining mire by Pöyry (2001) and Uusitalo et al. (2006). The conclusion from butterflies use power line ROWs as an alternative habitat. This was these studies is that drainage is a serious threat to specialist mire achieved by comparing the abundance, species richness and butterflies. community structure of butterflies on power line ROWs to the ones Over 20 m wide power line rights-of-ways (ROW) cover almost at unmanaged drained mire control sites and at natural mires. 500 km2 in Finland (A. Levula, personal communication). In general, the construction and maintenance of power line ROWs 2. Materials and methods have negative ecological effects such as fragmentation of contin- uous forest habitats (Rich et al., 1994; Nellemann et al., 2001, 2003; 2.1. Study sites Vistnes et al., 2004) and related edge effects, which favour habitat generalist species at the expense of forest interior species (Rich This comparative study was carried out during 2004 and 2006. et al., 1994). Power line ROWs may also filter animal movement Study sites were located in Central Finland (62 C, 26 E) in middle (Willey and Marion, 1980; Doucet and Brown, 1997; Vistnes et al., boreal vegetation zone. The 220 kV power line ROW is 65 m wide and 2004), cause bird mortality due to collisions with overhead wires runs about 70 km from south to north from Uurainen to Karstula. (e.g. Henderson et al., 1996; Bevanger, 1998; Bevanger and Brøseth, We established butterfly monitoring transects on habitats that 2004), and expose species to electromagnetic fields (e.g. Fernie and had experienced three different management regimes: drained Bird, 1999; Fernie et al., 2000). However, vegetation management mires with vegetation management (on power line ROWs) (n ¼ 15), on power line ROWs is essential to ensure secure and uninterrupted drained mires without the management (adjacent to power line transfer of electricity. Corridors are maintained by mechanical ROWs) (n ¼ 15), and natural mires without drainage or manage- cutting on an average of six year rotation. Clearing of vegetation ment (adjacent to or near power line ROWs) (n ¼ 5) (Fig.1). Number maintains open, mainly treeless areas in various successional stages of natural mires we could find from the area adjacent to or near the (Vuorinen, 2001). Evaporation and shading decrease, while mois- power line ROWs was only 5 and this reflects the fact that nearly all ture, light intensity and openness increase, which may to some mires are effectively drained in the study area. extent counterbalance the effect of drainage on mire microclimate. On each of the drained mires we established two transects: one Thus, the creation of open habitat on power line ROWs may be on the power line ROW and another on c. 70 m outside the power beneficial to species that thrive in early successional habitats (e.g. Confer and Pascoe, 2003; Askins, 1994; Lanham and Nichols, 2002; Yahner et al., 2001; Smallidge et al., 1996). Some studies indicate that ROWs can serve as an alternative habitat for threatened plant, grassland butterfly and bee species (de Becker et al., 1991; Smallidge et al., 1996; Piirainen, 1997; Sheridan et al., 1997; Kyläkorpi and Grusell, 2001; Kuussaari et al., 2003; Forrester et al., 2005; Russel et al., 2005).