Alternative Silvicultural Practices in Irregular Boreal Forests: Response of Beetle Assemblages
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Silva Fennica 45(5) research articles SILVA FENNICA www.metla.fi/silvafennica · ISSN 0037-5330 The Finnish Society of Forest Science · The Finnish Forest Research Institute Alternative Silvicultural Practices in Irregular Boreal Forests: Response of Beetle Assemblages Jean-Philippe Légaré, Christian Hébert and Jean-Claude Ruel Légaré, J.-P., Hébert, C. & Ruel, J.-C. 2011. Alternative silvicultural practices in irregular boreal forests: response of beetle assemblages. Silva Fennica 45(5): 937–956. In the process of implementing sustainable management in the eastern Canadian boreal forest, we tested two selection cutting methods and compared them with two widely used practices in the boreal forest: clearcutting with protection of the advanced growth and soils and irregular shelterwood cutting leaving small merchantable stems. We used old-growth irregular stands as references in comparing the impact of these silvicultural treatments on the diversity and abundance of beetles. Three groups were targeted: saproxylic flying beetles, epigaeic saproxylic beetles and epigaeic non-saproxylic beetles. A sampling design including 320 pitfall traps and 80 multidirectional flight-interception traps was deployed in 2007. A total of 26 906 beetles was captured including 407 taxa distributed among 52 families. We found that clearcutting with protection of the advanced growth and soils and irregular shelterwood cutting leaving small merchantable stems had a greater impact on beetle communities than both selection cuttings. Canopy opening as well as the presence of snags and downed woody debris appear as important attributes for several saproxylic and non-saproxylic species. Beetle communities in selection cuttings remained more similar to those found in controls; these silvicultural treatments are new tools to implement ecosystemic and sustainable management in irregular boreal forests. Keywords biodiversity, old-growth forest, irregular stands, selection cutting, coarse woody debris, sustainable management Addresses Légaré and Ruel, Université Laval, Faculté de foresterie, de géographie et de géoma- tique, Pavillon Abitibi-Price, Québec, Canada; Hébert, Natural Resources Canada, Canadian Forest Service, Laurentian Forestry Centre, 1055 du P.E.P.S., P.O. Box 10380, Stn. Sainte-Foy, Québec (Québec), G1V 4C7, Canada E-mail [email protected] Received 29 October 2010 Revised 28 July 2011 Accepted 13 October 2011 Available at http://www.metla.fi/silvafennica/full/sf45/sf455937.pdf 937 Silva Fennica 45(5), 2011 research articles 1 Introduction ral disturbance regimes such as snags and coarse woody debris (Niemelä 1997, Harvey et al. 2002, Until 1990’s, Canadian forestry was mostly Bauhus et al. 2009). At the landscape scale, the focused on timber production (CCFM 2003). size and distribution of forest harvesting patches However, the concept of sustainable management, should reproduce the spatial arrangement gener- which aims to meet the needs of the present with- ated by natural disturbances in order to preserve out compromising the ability of future generations enough suitable habitats for maintaining species to meet their own needs (Brundtland 1987), has with low dispersal ability that would be otherwise required changes. Sustainable management of at risk (Jonsson et al. 2005). forest ecosystems has been defined to preserve The dynamics of natural disturbances are strongly ecological functions as well as the ecological influenced by climatic conditions, which vary widely processes supporting these functions. Biodiversity among regions. In the province of Québec, Canada, conservation has been recognized as a central the eastern boreal forest is dominated by old-growth criterion in all international initiatives to evaluate stands, which are characterized by irregular struc- progress toward forest sustainable management tures and a strong component of balsam fir (Abies (Simberloff 1999, 2001, CCFM 2003). In boreal balsamea (L.)) (Boucher et al. 2003, Bouchard et forests, impacts of harvesting on faunal and floral al. 2008). This results from an increasing gradient diversity are known to be mainly due to the loss of precipitation from western to eastern Québec and fragmentation of old-growth forests com- that lengthens the fire cycle up to 200–300 years bined with alteration of structural components (Bergeron et al. 2004) and even over 500 years in and natural processes of this ecosystem (Bonan the most easterly part of the region (Foster 1983), and Shugart 1989). Some species associated with compared with the 100–200 year cycle in western old-growth forests may not persist under inten- Québec (Bouchard et al. 2008). Such long periods sive harvesting regimes (Niemelä 1997, Pohl et without fire allow stands to reach the senescent al. 2007), particularly rare species (Spence et al. stage, where trees die and develop in an irregular 1996). Thus, adapting forestry practices in order and more diversified structure (McCarthy 2001, to maintain species associated with old-growth Pham et al. 2004, McCarthy and Weetman 2006). forests appears to be a major challenge of modern Disturbances like wind, insects and diseases play forestry (Niemelä 1997). To develop sustainable an important role in the dynamics of this forest forest management, new silvicultural treatments (Boucher et al. 2003). In the North Shore region are thus needed (Haila 1994, Groot et al. 2005). of eastern Québec, 70% of the unharvested forest Over the last 20 years, the concept of ecosystem is composed of old-growth stands of irregular or management has also attracted much attention uneven-aged structure (Boucher et al. 2003). across the scientific community (Attiwill 1994, This structural complexity, at both the stand and Angelstam 1998, Bergeron et al. 1999). It has landscape levels, plays a key role in maintaining been presented as the best approach to maintain biodiversity because complex structures generate a the natural processes that regulate forest eco- greater variety of habitats, compared with regular system dynamics (Attiwill 1994, Niemelä 1999, even-aged stands, and should therefore host more Simberloff 1999, Gauthier et al. 2009). Forest species of plants and animals (Hansen et al. 1991). ecosystem management is based on natural distur- A recent study indicates that a combination of both bance regimes and it aims to maintain ecosystems structural and compositional habitat heterogeneity within their natural range of variability, based on maximizes beetle richness in old-growth stands of the pre-industrial period. Thus, species should the North Shore region (Janssen et al. 2009). not be exposed to conditions that they have never Most species found in forest ecosystems are faced before (Hunter 1990). Such an approach arthropods, mainly insects (Kim 1993). Nearly takes into account the forest at both the stand and 30 000 insect species were recorded in Canada landscape scales (Bergeron et al. 1999, Harvey 20 yrs ago (Danks and Foottit 1989) and they et al. 2002, Ruel et al. 2007). At the stand scale, account for 65 to 70% of overall forest species forestry practices should attempt to maintain key richness (Langor and Spence 2006). Several stud- structural attributes that are generated under natu- ies have focused on beetles, which are known as 938 Légaré, Hébert and Ruel Alternative Silvicultural Practices in Irregular Boreal Forests: Response of Beetle Assemblages effi cient indicators of habitat changes (Niemelä assemblages of beetles at a level similar to that 1997, Martikainen et al. 1999, 2000, Langor and of the old-growth irregular forest of this region. Spence 2006, Pohl et al. 2007). These studies Specifi cally, our objectives were to determine if were generally conducted to identify the links these alternative silvicultural practices maintain between different forest attributes and commu- attributes and biodiversity of the natural old- nities of particular groups, such as carabid bee- growth irregular forest. We addressed this issue tles (Niemelä et al. 1996, Halaj et al. 2008) or by studying three groups of beetles: 1) fl ying saproxylic beetles (Jonsell et al. 2004, Gibb et saproxylic beetles, 2) epigaeic saproxylic beetles al. 2006, Halaj et al. 2009). and 3) epigaeic non-saproxylic beetles. In our study, we examined the infl uence of four silvicultural treatments in irregular stands of the eastern boreal forest: two types of selec- tion cutting, clearcutting with protection of the 2 Materials and Methods advanced growth and soils (in French, “Coupe avec Protection de la Régénération et des Sols; 2.1 Study Area hereinafter CPRS) and irregular shelterwood cut- ting leaving small merchantable stems (in French, The study was conducted in the North Shore “Coupe avec Protection des Petites Tiges March- region of Québec, Canada, which belongs to the andes; hereinafter CPPTM). Old-growth stands eastern spruce-moss subdomain of the boreal were conserved as controls. We hypothesized forest. More specifi cally, the area was located that silvicultural treatments that maintain the in the Manicouagan reservoir sector, between structural heterogeneity at the stand level should the 49th and 52nd parallels (Fig. 1). The domi- make it possible to maintain species richness and nant tree species found in the area are black Fig. 1. Study area and distribution of experimental blocks in a forest matrix dominated by old-growth boreal forests in the North Shore region of Québec, Canada. 939 Silva Fennica 45(5), 2011 research articles spruce (Picea mariana (Mill.) B.S.P.), balsam