Abstract
The current unprecedented outbreak of mountain pine beetle (Dendroctonus ponderosae) in lodgepole pine (Pinus contorta) forests of western Canada has resulted in a landscape consisting of a mosaic of forest stands at different stages of mortality. Within forest stands, understory communities are the reservoir of the majority of plant species diversity and influence the composition of future forests in response to disturbance. Although changes to stand composition following beetle outbreaks are well documented, information on immediate responses of forest understory plant communities is limited. The objective of this study was to examine the effects of D. ponderosae-induced tree mortality on initial changes in diversity and productivity of understory plant communities. We established a total of 110 1-m2 plots across eleven mature lodgepole pine forests to measure changes in understory diversity and productivity as a function of tree mortality and below ground resource availability across multiple years. Overall, understory community diversity and productivity increased across the gradient of increased tree mortality. Richness of herbaceous perennials increased with tree mortality as well as soil moisture and nutrient levels. In contrast, the diversity of woody perennials did not change across the gradient of tree mortality. Understory vegetation, namely herbaceous perennials, showed an immediate response to improved growing conditions caused by increases in tree mortality. How this increased pulse in understory richness and productivity affects future forest trajectories in a novel system is unknown.
Highlights
Over the past century, forests in North America have experienced increased disturbances from insect outbreaks, wildfire, and harvesting [1]
All model assumptions were checked by visual inspection of residual patterns [33]. Using these linear mixed effects models, we developed candidate models that included all combinations of the explanatory variables and their interactions (i.e., D. ponderosae-induced tree mortality, soil moisture, light, and nutrients) and used information-criteria to rank the relative importance of those variables in the models
We found that understory diversity of herbaceous perennials increased and understory biomass nearly doubled across the gradient of D. ponderosae-induced tree mortality driven by initial increases in soil nutrients followed by increased soil moisture in the following year
Summary
Forests in North America have experienced increased disturbances from insect outbreaks, wildfire, and harvesting [1]. Disturbances, such as wildfire and harvesting, PLOS ONE | DOI:10.1371/journal.pone.0124691. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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