Ecosystem Management in the Boreal Forest

Chapter 7 : Spruce Budworm Outbreak Regimes in Eastern North America

Chapter 7Spruce Budworm Outbreak Regimes in Eastern North America Hubert Morin, Danielle Laprise, Andrée-Anne Simard, and Saida Amouch  The authors thank the Sustainable Forest Management Network, NSERC, the Consortium de recherche sur la forêt boréale commerciale, and the Ministère des Ressources naturelles et de la Faune du Québec for their financial support of this research. Many thanks to Dan Kneeshaw and Marie-Andrée Vaillancourt for the revision and suggestions on an earlier version of the manuscript and to Pierre-Yves Plourde for the drawing of the figures. We are also grateful to Gerardo Reyes for the English translation. The photos on this page were graciously provided by Hubert Morin. 1. Introduction..................................................................................... 157 2. Temporal Patterns of Spruce Budworm Outbreaks over the Past 8,600 Years................................................................ 158 2.1. Dendrochronology.................................................................... 158 2.2. Paleoecology............................................................................. 161 3. Spatial Patterns of SBW Outbreaks................................................. 163 4. Impact of Outbreaks on the Forest................................................. 166 4.1. An Example from Balsam Fir Stands of Boreal Forests . North of Saguenay–Lac-Saint-Jean............................................. 166 4.2. Impact in the Black Spruce–Feather Moss . Bioclimatic Domain................................................................... 171 5. Management Implications in the Context of Climate Change...... 175 5.1. Impact of Outbreak Cycles........................................................ 175 5.2. Impact of Stand Structure and Composition............................. 176 5.3. In the Context of Climate Change. ............................................ 178 References............................................................................................. 179 1. Introduction The spruce budworm (SBW) (Choristoneura fumiferana Clem.) is the principal defoliating insect of fir and spruce in the boreal forests of eastern North America. Outbreaks have occurred every 25 to 40 years at the supra-regional scale during the 20th century (Royama 1984; Candau et al. 1998; Jardon et al. 2003; Royama et al. 2005; Campbell 2007). Although SBW is present in all provinces throughout Canada and can sometimes cause severe defoliation to more than half a million hectares, the provinces of eastern Canada are the most affected, especially Québec, Ontario and New Brunswick. The last outbreak (1974–1988) affected more than 55 million hectares of forest, causing the loss of 139 to 238 million cubic metres of fir and spruce in Québec only (Boulet et al. 1996). The area affected reached 32 million hectares in 1975 in Québec, 19 million hectares in 1980 in Ontario, and 3.5 million hectares in 1975 in New Brunswick (Natural Resources Canada 2001). In eastern Canada, SBW outbreaks are often more important than fire in terms of tree mortality. It used to be believed that the impact of outbreaks was lower in boreal forests dominated by black spruce (Picea mariana [Mill.] B.S.P.). However, recent studies have shown that the last four outbreaks were well recorded in the forest structure of the black spruce–feather moss bioclimatic domain. Indeed, almost all natural balsam fir (Abies balsamea [L.] Mill.) stands found within the spruce–feather moss zone originated from one of these outbreaks , following a cyclical mechanism of regeneration to which balsam fir is well adapted (MacLean 1984, 1988; Morin 1994; Morin and Laprise 1997; Johnson et al. 2003; Parent et al. 2003; Morin et al. 2007). This cyclical regeneration mechanism is, however, not universal. In areas where the balsam fir seedling bank is less abundant, as well as in more southerly locations, different scenarios have been observed, such as a rapid colonization by non-host species (Kneeshaw and Bergeron 1998, 1999; Bouchard et al. 2006a). Regarding black spruce forests, substantial reductions in black spruce growth have been linked to the last­ outbreaks (Lussier et al. 2002). A tri-trophic interaction would exist between the host plant, the insect, and its natural enemies (Royama et al. 2005; Cooke et al. 2007). Balsam fir and white spruce (Picea glauca [Moench] Voss.) are the principal host tree species of the SBW, while black and red spruce (P. rubens Sarg.) are less affected. In eastern Canada, mature stands of balsam fir are most vulnerable to SBW defoliation (MacLean 1980; MacLean and Ostaff 1989; Bergeron et al. 1995; MacLean and MacKinnon 1997). The proportion of hardwoods within a stand and across the landscape can also affect defoliation levels, with areas having greater hardwood densities being less affected (Bergeron et al. 1995; Su et al. 1996; Cappuccino et al. 1998; MacKinnon and MacLean 2003, 2004; Campbell 2007). A forest mosaic dominated by host trees would favor greater SBW population growth compared with its natural enemies, resulting in a more severe impact across the landscape (Bouchard 2005; Cooke et...