Identifying suitable woodpecker nest trees using decay selection profiles in trembling aspen (Populus tremuloides) Lori A Blanc a,b,⇑ , Kathy Martin a,c a Centre for Applied Conservation Research, Department of Forest Sciences, University of British Columbia, 2424 Main Mall, Vancouver, British Columbia, Canada V6T 1Z4 b Department of Biological Sciences, Virginia Tech, Blacksburg, VA 24061, United States c Environment Canada, Pacific Wildlife Research Centre, 5421 Robertson Rd., RR1, Delta, British Columbia, Canada V4K 3N2 article info Article history: Received 6 January 2012 Received in revised form 11 August 2012 Accepted 17 August 2012 Available online 25 October 2012 Keywords: Cavity nest web Suitable woodpecker nest tree Woodpecker decay selection profile Aspen decay transition dynamics Trembling aspen Woodpecker habitat management abstract Woodpeckers are the primary tree-cavity producers in North America and, through their process of cavity excavation, they create nesting and roosting habitat for a complex web of cavity-using species. Managing for potential woodpecker nest trees requires an understanding of factors that influence decisions by which woodpecker select trees for nest cavity excavation, including tree decay availability associated with softened heartwood and sapwood in trees. We evaluated woodpecker nest cavity excavation in rela- tion to the nature and availability of decay in trembling aspen (Populus tremuloides) using 12 years of nest and tree decay class data from British Columbia. We used a cavity-nest web to visually depict decay selection profiles for six woodpecker species and compared these woodpecker decay selection profiles to the availability of decay in aspen (96.7% of all cavity nests found), identifying the most suitable nest tree stages used by woodpeckers. The suitable woodpecker nest tree stage consists primarily of live unhealthy trees and recently dead trees (93.9% of active nests found in aspen). Compared to non-nest trees (trees within which no cavity nests were found during the study period), live trees that were used for nest cavity excavation had higher annual probabilities of entering the suitable woodpecker nest tree stage than non-nest trees, and they also had a lower probability of progressing outside of this stage. This suggests excavation decisions involve a balance of competing tradeoffs between ease of excavation and tree security. Nest trees remained within the suitable woodpecker nest tree stage for an average of 11.8 years, and almost half of this time involved live trees in an unhealthy state. We suggest that forest management guidelines that focus on retaining only dead trees to provide cavities for wildlife are missing a significant component of available and future tree cavity resources. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction As the primary excavators of tree cavities, woodpeckers play an important ecological role by providing nesting and roosting habitat for a broad range of fauna, including birds, mammals, reptiles, amphibians and insects (Dennis, 1971; Martin et al., 2004; Mikusin ´ ski, 2006). Tree cavities are particularly important to the maintenance of avian diversity, as cavity-nesting birds can com- prise 30–45% of the avifauna within forested systems (Scott et al., 1980). Indeed, there is a strong general relationship between woodpecker species richness and richness of forest birds at both the stand and landscape levels (Mikusin ´ ski et al., 2001; Drever et al., 2008) and woodpeckers may be reliable indicators of overall forest health (Lindenmayer et al., 2000; Virkkala, 2006). Thus, managing for woodpecker habitat in general may benefit forest biodiversity (Drever and Martin, 2010), and managing for potential woodpecker nest trees in particular may contribute to forest biodi- versity by facilitating the process of cavity excavation. Managing for potential woodpecker nest trees requires an understanding of factors that influence woodpecker nest-site selection, and thus, the ecological processes involved in creating trees that are suitable for cavity excavation. One such process is fungal decay, which causes the progressive softening of heartwood and sapwood in trees (Thomas et al., 1979; Bull et al., 1997; Jackson and Jackson, 2004). As trees become unhealthy, decay and die, they change in form and function to wildlife. Classification schemes that characterize trees from live healthy trees into a gra- dation of decay classes, ranging from recently dead trees to a fully decayed and downed log, are used to inform management guide- lines for wildlife habitat (Thomas et al., 1979; Cline et al., 1980; Backhouse and Louiser, 1991; reviewed in Table 1). Previous studies have used the decay classes of woodpecker nest trees to inform woodpecker habitat management, with a 0378-1127/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.foreco.2012.08.021 ⇑ Corresponding author at: Department of Biological Sciences, Virginia Tech, Blacksburg, VA 24061-0406, United States. Tel.: +1 540 231 5256; fax: +1 540 231 9307. E-mail address: lblanc@vt.edu (L.A. Blanc). Forest Ecology and Management 286 (2012) 192–202 Contents lists available at SciVerse ScienceDirect Forest Ecology and Management journal homepage: www.elsevier.com/locate/foreco