Canadian Forest Service Publications
Stand dynamics and the mountain pine beetle — 30 years of forest change in Waterton Lakes National Park, Alberta, Canada. 2018. Axelson, J.N., Hawkes, B.C., van Akker, L., Alfaro, R.I. Can. J. For. Res. 48: 1159–1170.
Issued by: Pacific Forestry Centre
Catalog ID: 39364
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The mountain pine beetle (MPB; Dendroctonus ponderosae Hopkins) is a native bark beetle and a major disturbance agent in western North American forests. In the 1970s and 1980s, a MPB outbreak occurred in Waterton Lakes National Park (WLNP) in southwestern Alberta. The MPB outbreak resulted in variable levels of mortality of mature lodgepole pine (Pinus contorta var. latifolia Engelm. ex S. Watson), reducing density, volume, and basal area of overstory trees. By 2010, lodgepole pine was proportionally no longer the dominant overstory species, with increases in non-pine conifer and broadleaf species. The MPB susceptibility index decreased in most stands over time, especially in stands with the highest MPB-caused mortality. Downed woody material was characterized by fine and coarse fuel mass and volume, which both increased from 2002 to 2010, and the abundance of coarse fuels was highest in 2010, nearly 30 years after peak MPB activity. Density of understory saplings and small regeneration increased from 2002 to 2010 and was dominated by non-pine conifer and broadleaf species; lodgepole pine was nearly absent. Hierarchical clustering using 2010 MPB susceptibility and composition data characterized biological legacies remaining after the MPB outbreak. These legacies suggest multiple successional trajectories in WLNP dominated by species other than lodgepole pine. The MPB outbreak resulted in greater heterogeneity in composition and structure and suggests that stands have been resilient to this disturbance.
Plain Language Summary
Mountain pine beetle (Dendroctonus ponderosae; MPB) is a major natural disturbance agent in pine ecosystems. In the 1970s a MPB outbreak occurred in Waterton Lakes National Park (WLNP) in southwestern Alberta. This study evaluates forest dynamics over 30 years in low elevation stands in WLNP. The 1970s MPB outbreak resulted in variable mortality of mature lodgepole pine, reducing density, basal area and volume. By 2010, lodgepole pine was no longer the dominant overstory species, and there were increases in conifer and broadleaf species. MPB susceptibility index decreased in most stands over time, especially in stands with high MPB mortality. Surface fuel loads increased between 2002 and 2010, and coarse fuels took nearly 30 years to peak. Understory, saplings and seedlings, tree density increased in 2002 and 2010. Understory species were dominated by non-pine conifer and deciduous species, and there was little to no lodgepole pine. Different types of forests resulting from 1970s outbreak are described and results indicate that future forests may be dominated by shade tolerant species, Douglas-fir or balsam poplar. The 1970s MPB outbreak in WLNP stands resulted in greater variation in species composition and tree size within stands.