445 The preferences of saproxylic beetle species for different dead wood types created in forest restoration treatments Tero Toivanen and Janne S. Kotiaho Abstract: Restoration by imitating natural disturbances is widely practised in boreal forests to increase the availability of habitats for specialized species. We studied the abundance and species richness of saproxylic beetles on different types of created dead wood during 2 years after restoration. The study was conducted on areas of a large-scale experiment in which Norway spruce (Picea abies (L.) Karst.) forests were restored by controlled burning and partial harvesting with down wood retention in southern Finland. More beetle species were attracted to spruces than to birches and more species were attracted to burnt trees than to unburnt trees killed by girdling. Birch-living species consistently benefited from fire, but on spruce, the abundance of cambium consumers and their associates was negatively affected by fire. Trees at harvested sites attracted more beetles in the first year, but the volume of down wood retention had only minor effects. Beetle assemblages were strongly altered by burning and harvesting. We conclude that burning and harvesting are efficient tools to promote species richness within a short time period, but there is a risk that the dead wood resource may be rapidly exhausted. Moreover, many saproxylic species of spruce forests may not be adapted to open habitats formed by stand-replacing distur- bances. Re´sume´ : La restauration qui imite les perturbations naturelles est largement utilise´e dans les foreˆts bore´ales afin d’ac- croıˆtre la disponibilite´ des habitats pour les espe`ces spe´cialise´es. Nous avons e´tudie´ l’abondance et la richesse en espe`ces des cole´opte`res saproxyliques pendant 2 ans sur les diffe´rents types de bois mort apparu a` la suite d’une restauration. L’e´tude a e´te´ re´alise´e sur le territoire d’une expe´rience a` grande e´chelle ou` des foreˆts d’e´pice´a commun (Picea abies (L.) Karst.) ont e´te´ restaure´es par un bruˆlage dirige´ et une coupe partielle avec re´tention du bois au sol dans le sud de la Fin- lande. Plus d’espe`ces de cole´opte`res ont e´te´ attire´es par les e´pice´as que par les bouleaux et plus d’espe`ces ont e´te´ attire´es par les arbres bruˆle´s que par les arbres non bruˆle´s tue´s par anne´lation. Les espe`ces vivant sur le bouleau ont invariable- ment be´ne´ficie´ du feu. Par contre sur l’e´pice´a, l’abondance des cole´opte`res qui attaquent le cambium et leurs associe´s e´taient ne´gativement affecte´s par le feu. Les arbres sur les stations coupe´es ont attire´ plus de cole´opte`res durant la pre- mie`re anne´e mais le volume de re´tention de bois au sol a eu seulement des effets mineurs. Les assemblages de cole´opte`res ont e´te´ fortement modifie´s par le bruˆlage et la coupe. Nous concluons que le bruˆlage et la coupe sont des outils efficaces pour favoriser la richesse en espe`ces sur une courte pe´riode de temps mais qu’il y a un risque que les ressources en bois mort soient rapidement e´puise´es. De plus, plusieurs espe`ces saproxyliques associe´es aux foreˆts d’e´pice´a ne sont peut-eˆtre pas adapte´es aux habitats ouverts cre´e´s par les perturbations qui provoquent le remplacement des peuplements. [Traduit par la Re´daction] Introduction dynamics of natural forests, such as reintroducing fire as a disturbance factor, to create structural elements and resour- To protect biodiversity in boreal forests, the need for ac- ces important for biodiversity (Kuuluvainen et al. 2002). tive management in terms of restoration is widely recog- Disturbance dynamics are also used as a guideline in devel- nized (Angelstam 1998; Kouki et al. 2001; Kuuluvainen et oping new forest management practices (Fries et al. 1997; al. 2002). Restoration, aiming to the rehabilitation of natural Bergeron et al. 2002; Franklin et al. 2002) that include, for structures, processes, and species composition in ecosystems example, the retention of living or dead trees and promoting altered by human actions (Bradshaw 1997), can be seen as a multilayered forest structure. tool to complement the traditional approach of conserving Saproxylic species, defined as being dependent on dead biodiversity by means of networks of reserves (Kouki et al. wood or on another dead wood dependent organism (Speight 2001; Kuuluvainen et al. 2002). Current restoration activity 1989), are a classic example of an ecological group that has in boreal forests is often based on imitating the disturbance been adversely affected by the extensive utilization of boreal Received 18 September 2009. Accepted 19 December 2009. Published on the NRC Research Press Web site at cjfr.nrc.ca on 26 February 2010. T. Toivanen.1 Department of Biological and Environmental Science, University of Jyva¨skyla¨, P.O. Box 35, Jyva¨skyla¨ 40014, Finland. J.S. Kotiaho. Department of Biological and Environmental Science, University of Jyva¨skyla¨, P.O. Box 35, Jyva¨skyla¨ 40014, Finland; Natural History Museum, University of Jyva¨skyla¨, P.O. Box 35, Jyva¨skyla¨ 40014, Finland. 1Corresponding author (e-mail: [email protected]). Can. J. For. Res. 40: 445–464 (2010) doi:10.1139/X09-205 Published by NRC Research Press 446 Can. J. For. Res. Vol. 40, 2010 forests (Grove 2002; Jonsson et al. 2005). The reasons that fecting the colonization and reproduction success of beetles: have led to the decline of these species include the reduction heavily charred wood hosts low arthropod densities (Saint- in the area of habitats (Axelsson and O¨ stlund 2001), the loss Germain et al. 2004) but even burnt logs (logs typically be- of connectivity between habitats (Komonen et al. 2000; Sii- come more charred than standing trees) may host high spe- tonen and Saaristo 2000), and the decline in the quality cies diversity and distinct species assemblages (Wikars (e.g., Fridman and Walheim 2000) and quantity (e.g., Siito- 2002; Gibb et al. 2006). An interesting aspect of burning is nen 2001) of dead wood. In particular, the absence of large- that it may reduce the resource specificity of saproxylic spe- diameter dead wood in managed forests and the changes in cies by enabling normally specialist species to utilize several disturbance dynamics (such as the prevention of forest fires tree species and thus making species assemblages of differ- and the removal of trees from storm damaged areas) can be ent tree species more similar (Wikars 2002). seen as major factors that have driven many saproxylic spe- Current restoration practices in boreal forests (Kuulu- cies to the edge of extinction. For example, in Finland, there vainen et al. 2002), of which controlled burning and creating are 183 threatened or extinct beetle species associated to dead wood by felling and damaging trees are most com- forests, of which 112 have been primarily affected by the monly used, are expected to improve habitat quality and in- loss of dead wood (Rassi et al. 2001). crease the availability of resources for saproxylic species. Several saproxylic species show resource specificity to a However, the effects of ongoing restoration actions are still particular tree genus, to a particular stage of wood decay, or inadequately understood. Here, we report results from a to a particular species of wood-decaying fungi (Jonsell et al. study in which we explored the relative importance of dif- 1998; Jonsson et al. 2005). For example, decaying deciduous ferent types of dead wood that had been created in restora- trees host assemblages that are distinct from those of coni- tion treatments for saproxylic beetles. Our main aims were fers. Within the boreal coniferous zone, the tree species to determine whether the abundance, species richness, and hosting most diverse assemblages is Norway spruce species assemblages of beetles differ between burnt and un- (Jonsson et al. 2005), but the role of aspen in hosting many burnt dead trees, how the increase in sun exposition due to rare or threatened saproxylic species is highlighted in sev- partial harvesting affects the beetle assemblages of the trees, eral studies (Jonsell et al.1998; Martikainen 2001; and how the responses of beetle assemblages to burning and Sverdrup-Thygeson and Ims 2002). The occurrence of the harvesting differ between two tree species. In addition, we majority of saproxylic invertebrates, and beetles in particu- studied whether down wood retention (DWR) had indirect lar, is often restricted to the first years following tree death effects on the beetle assemblages of the study trees via, for (Esseen et al. 1997; Jonsell et al. 1998). At the early decay example, fire intensity or affecting the attraction of beetles stages, the specialization of saproxylic invertebrates to a to the study sites. particular tree species is relatively high, but as the wood de- cay progresses, the tree species becomes less important. In Material and methods contrast, the role of wood-decaying fungi in determining the invertebrate community becomes more evident during the Study area later decay stages (Jonsell et al. 1998). The study was conducted on areas of a large-scale restora- Sun exposure is regarded as an important factor affecting tion experiment (Vanha-Majamaa et al. 2007) that were lo- species richness and species assemblages of saproxylic spe- cated in the vicinity of Evo, southern Finland (61811’N, cies. In natural conditions, sun-exposed habitats are formed 25805’E), within the south boreal vegetation zone. In total, by major disturbances such as forest fires and heavy storms. there were twenty-four 2 ha study plots located within a The majority of saproxylic beetles have been found to fa- 25 km  15 km area.