The dynamics of understory and below-ground communities in lodgepole pine forests after simulated mountain pine beetle red attack in a novel landscape

Background/Question/Methods

As climate changes and disturbance regimes shift, we need to better understand and anticipate potential impacts of both natural and anthropogenic disturbance agents on forested ecosystems. Lodgepole pine forests in western Canada are experiencing an unprecedented mountain pine beetle (MPB) outbreak, and the ecosystem-level effects of ongoing expansion of MPB into novel habitats east of the Canadian Rockies are unknown. To better understand the ecological impacts of disturbance in lodgepole pine ecosystems we asked: i) what are the effects of simulated MPB attack and salvage harvest on above- and below-ground dynamics of these forests?” and ii) what is the potential for pine regeneration among these forest treatments? Our repeated measures study compared twelve mature lodgepole pine stands in the Upper Foothills of western Alberta before, during and after four simulated MPB treatment levels (control, 50% MPB mortality, 100% MPB mortality, salvage harvest) with respect to both understory plant community composition (% cover by species) and below-ground attributes (e.g., decomposition, pH, microbial community structure and function). We also quantified seedbed availability and advance regeneration, and compared lodgepole pine recruitment of sown seed on five different seedbed types (i.e., moss, shallow organic, deep organic, decayed wood, and mineral soil) among the treatments.

Results/Conclusions

Overall, we found short-term resistance to ecosystem change after simulated MPB attack, compared with more immediate ecosystem changes in response to salvage harvest. One year post-disturbance, significant differences in understory (diversity, richness, percent cover) and below-ground (e.g., nutrient availability) attributes were predominantly found in the salvage harvested stands. Recruitment from sown seed 1-3 years after simulated MPB attack was poor across stand treatment types for moss and both organic seedbed types. Decayed wood and mineral soil were the best seedbed types, with higher recruitment rates than the organic and moss seedbeds, although recruitment was still relatively low. Recruitment rates of seedlings on decayed wood and mineral soil seedbed types increased with increasing levels of disturbance; recruitment was lowest in control stands, higher in the simulated MPB-attack treatments, and highest in the salvage logged stands. However, these favorable seedbeds were scarce among all stand treatment types. Pine regeneration appears unlikely to occur in the short term after MPB attack without active silvicultural intervention. This study provides novel insights into the ecology of lodgepole pine forests in the face of changing disturbance regimes and forest management practices, demonstrating the important ecological roles that ecosystem properties and processes play in these forests.