Forest Investment Account (FIA) - Forest Science Program
FIA Project M075044

    Stand dynamics following mountain pine beetle outbreaks in central British Columbia: a synthesis for decision-support
Project lead: Alfaro, Rene
Author: Alfaro, René I.
Imprint: [BC] :, 2007
Subject: Forest Investment Account (FIA), Dendroctonus Ponderosae, British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
Rationale: As a natural agent of disturbance, beetle outbreaks play an important functional role in directing ecological processes and maintaining biological diversity of forest ecosystems. However, having infested about 8.5 million (BC Ministry of Forests, 2005 aerial surveys) hectares of lodgepole pine forests to date, the current beetle outbreak is unprecedented in scale. Mortality is severe in about 25 % of the infested forests. As lodgepole pine comprises about one quarter of the provincial timber supply, socioeconomic impacts of this outbreak are enormous. A variety of silvicultural tools and management strategies can be used to reduce the effects of timber losses, the most important tool being salvage logging. In the short-term, adjusting harvest scheduling to remove standing beetle-killed trees can compensate some of the timber losses. However, due to numerous market, operational, legal, and ecological constraints the proportion of the beetle-killed forests that can be salvage-logged is limited. As the outbreak continues, and especially after its eventual collapse, forest managers will need to develop strategies to manage the large areas left unsalvaged. For this they will need to quantify the basic stand dynamics processes associated with mountain pine beetle outbreaks, such as host mortality, post-outbreak stand growth, recruitment rates and species composition following mountain pine beetle outbreaks. Currently, this information is scant and our ability to estimate the long-term impacts of beetle outbreaks on BC forests is, therefore, limited. Throughout much of British Columbia, lodgepole pine occurs as a seral species forming even-aged stands initiated by stand-replacing fires. Although such dynamics are considered typical for the species, uneven-aged lodgepole pine stands that have historically been maintained by frequent low-intensity surface fires, are frequent in central BC. Forest landscapes of central BC are dominated by lodgepole pine and can generally be described as a mosaic of even-aged and uneven-aged stands (Agee 1993). However, the disturbance ecology of these forests is changing. The frequency of fires has decreased over the last century mostly due to effective fire suppression programs. When fire is infrequent, outbreaks of mountain pine beetle are likely to have a greater impact on forest structure, composition and dynamics. However, we know surprisingly little about the changes in forest characteristics following beetle outbreaks. Roe and Aman (1970) studied the dynamics of lodgepole pine stands in areas of western USA infested by mountain pine beetle and, more recently, Hawkes et al. (2004) studied stand composition following the 1980s outbreak in central BC. Outbreaks of mountain pine beetle have long occurred British Columbia (Alfaro et al. 2004, Campbell and Alfaro 2005). Massive mortality caused by beetle outbreaks releases resources that are potentially available to outbreak survivors (either lodgepole pine or other species that occur on the site), and to recruitment individuals that subsequently become established (Heath and Alfaro 1990). Therefore, in addition to mortality, outbreaks also affect tree growth rates and establishment patterns, which in turn, alter stand productivity, structure, and composition. Conceptual models of succession in pine ecosystems suggest that beetle outbreaks may, in the absence of fire, accelerate the successional process in favour of non-susceptible trees (Veblen et al. 1991). We suspect that this proposition is correct for even-aged lodgepole pine stands, but will be less appropriate in uneven-aged stands. We propose that in at least some uneven-aged stands the response to canopy mortality may be increased growth of surviving, small lodgepole pine, in a self-perpetuating lodgpeolpe pine climax. Fundamental to achieving the goal of sustainable forest management in areas infested by mountain pine beetle are reliable decision support tools (e.g., stand dynamics models) that incorporate the impacts of beetle outbreaks into forecasts of future stand conditions and projections of future timber supplies. However, we still lack information necessary to reliably implement these tools in some forests, particularly uneven-aged lodgepole pine forests. This project aims a filling these information gaps and addresses the following questions: 1. What is the composition of residual forests left after beetle epidemics? 2. What is the future composition and growth of the residual forests? 3. How future management interventions may alter future path of affected stands, thereby leading to long-term future compensation for beetle-related losses, and Research approach - The study will combine existing knowledge from previous studies in BC, with data from specific intensive field studies, and with model simulations, to study beetle impacts on future stand dynamics. Existing data: we will use results obtained from Hawkes et al (2004) on stand structure after the 1980’s outbreak collected in a wide range of lodgepole pine stands surveyed in 2001-2003. New data: Dendrochronological techniques will be used in a selected number of even-aged and uneven aged stands to reconstruct stand dynamics, from stand initiation following beetle or fire disturbance, to present day conditions (2006) in beetle impacted stands in central BC. This study will provide important data on recruitment rates after beetle currently lacking. Modelling future stand composition: In collaboration with the B.C. Ministry of Forests, we will incorporate these data into model simulations of stand dynamics following beetle outbreaks in central British Columbia. The Tree and Stand Simulator (TASS) (Mitchell 1975, Mitchell and Cameron 1985, Mitchell and Bloomberg 1987, Goudie et al. 2005) will be used for even-aged stands. For uneven-aged stands we will evaluate the applicability of the new version of TASS III (FSP project number Y061088) as well as other stand dynamics models like PrognosisBC (Snowdon 1997).
Contact: Alfaro, René, (250) 363-0660,


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Updated August 16, 2010 

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