Prasad A FEMC2007

Mid-term Timber Supply in the Wake of the Mountain Pine Beetle

Atmo Prasad, Ministry of Forests and Range, P.O. Box 9512, Stn. Prov. Govt , Victoria, V8W 9C3, BC, Canada, Atmo.Prasad@gov.bc.ca
Andrew Fall, Gowlland Technologies Ltd, 220 Old Mossy Road, Victoria, BC, V9E 2A3, Canada, andrew@gowlland.ca
Barry Snowdon, Ministry of Forests and Range, P.O. Box 9512, Stn. Prov. Govt , Victoria, V8W 9C3, BC, Canada, Barry.Snowdon@gov.bc.ca

Our aim was to design an approach to incorporate the dynamics and impact of large-scale natural disturbances, which may span management unit boundaries, into a timber supply model. The example disturbance presented is the current mountain pine beetle (Dendroctonus ponderosae Hopk.) epidemic. The scale of this outbreak is unprecedented in terms of extent, duration and severity. British Columbia Ministry of Forest and Range aerial survey data show the beetle had affected about 8.5 million hectares of British Columbia’s Interior in 2005.
A provincial scale empirical outbreak projection model (BCMPB Eng et al. 2005, <http://www.for.gov.bc.ca/hre/bcmpb>) forecasts the possible impact of this outbreak for the next 20 years. The BCMPB model projected that by 2013 the infestation will have largely run its course and 80% of the merchantable pine volume will be killed. One key result of the BCMPB project is that due to the magnitude of the outbreak management actions can have little effect on its progression. This means that we can incorporate MPB effects into a timber supply model without the need for feedback.

We combined annual severity maps produced by BCMPB (proportion of a stand killed) with a “shelf life” function (proportion of original pine that remains merchantable over time) to produce another time series of potential salvage. These two time series are used to drive disturbance and salvage dynamics in a spatial timber supply model implemented in SELES (Spatially Explicit Landscape Event Simulator). Within the main timber supply model, salvaged stands are regenerated as managed plantations. Stands not salvaged before shelf life expires are regenerated on post-MPB site conditions to allow exploration of assumptions regarding regeneration age and yields (e.g. regeneration delay to account for changed light conditions or advanced regeneration to account for residual understory and canopy trees).
Our approach can capture the complex spatial and temporal pattern of the outbreak (e.g. partial mortality in mixed stands) and subsequent dynamics of the dead wood. We have applied our approach in the Morice timber supply area to support an expedited timber supply review process. The flexibility enabled us to explore a variety of assumptions regarding management policy, shelf life, and post-MPB regeneration to help provide an adequate analysis context for decisions regarding appropriate harvest levels.

Provided harvesting would not significantly impact the progression of a disturbance at a broad scale, we believe the approach could apply to any large scale insect outbreak or fire.