Stand dynamics and the mountain pine beetle — 30 years of forest change in Waterton Lakes National Park, Alberta, Canada

Abstract

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.

What Are Intermediate-Severity Forest Disturbances and Why Are They Important?

“…Intermediate-severity disturbances typically increase stand-level structural complexity through coarse woody debris inputs, creation of canopy voids, alteration of the seedbed, and changes in the light regime [14,15,73,80,121,122]. Importantly, intermediate-severity disturbances often result in multi-aged stands [123].…”

Addressing Gender Inequities in Forest Science and Research

“…Dr. Axelson uses a variety of quantitative tools, such as forest biometrics, dendrochronology and wood anatomy, to study these dynamics across spatial and temporal scales. Notable works include her research on stand dynamics following mountain pine beetle outbreaks [43,44], tree growth response [45] and wood anatomical characteristics due to western spruce budworm defoliation [46]. Her recent efforts have focused on interdisciplinary collaboration, communicating the drivers of massive tree mortality events to the public, land managers and policy makers [47,48], and on Twitter (@DisturbedDendro) and co-leading the California Tree Mortality Data Collection Network.…”

Soil inoculation of lodgepole pine seedlings alters root‐associated fungal communities but does not improve seedling performance in beetle‐killed pine stands

“…Lodgepole pine ( Pinus contorta ) is a preferred host of the beetle, and this tree species depends on EcM fungi for establishment (Mikola 1970). The recovery of lodgepole pine forests after beetle outbreaks varies (Kayes & Tinker 2012; Axelson et al 2018); however, most research indicates that unmanaged stands have low pine establishment and/or a shift in dominance to other canopy species such as spruce ( Picea spp.) (Astrup et al 2008; McIntosh & Macdonald 2013; Axelson et al 2018).…”

“…The recovery of lodgepole pine forests after beetle outbreaks varies (Kayes & Tinker 2012; Axelson et al 2018); however, most research indicates that unmanaged stands have low pine establishment and/or a shift in dominance to other canopy species such as spruce ( Picea spp.) (Astrup et al 2008; McIntosh & Macdonald 2013; Axelson et al 2018). Such changes in stand composition can impact long‐term forest management (Parkins & MacKendrick 2007) and influence ecosystem functions, such as nutrient cycling (Griffin et al 2011; Cigan et al 2015; Pec et al 2015).…”