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Monday, April 9 • 1:30pm - 1:45pm
INSECT & DISEASE OUTBREAKS: Relationships Between Ground Cover and Post-Fire Conifer Regeneration Depend on Pre-Fire Disturbance History

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AUTHORS: Nathan Gill*, Clark University; Dan Jarvis, Vermont Technical College; Tom Veblen, University of Colorado; John Rogan, Clark University; Dominik Kulakowski, Clark University

ABSTRACT: Understory vegetation and ground cover drive many important ecosystem processes, including tree seedling regeneration. The exact effect of ground cover on tree seedling establishment, survival, and growth is dependent on biophysical context. In subalpine forests, this context is largely determined by disturbances such as beetle outbreak, blow down, and fire. Compounded disturbances that overlap in short succession can alter stand properties and trajectories in ways that are not predictable from the additive impact of individual disturbances. The aim of this study is to examine how compounded Dendroctonus rufipennis (Spruce Beetle) outbreak followed by fire and compounded wind blowdown followed by fire each influence the relationship between post-fire ground cover and conifer regeneration. We measured categorical ground cover percentages and conifer regeneration densities in permanent plots from 2003-2014 after stand-replacing fires of 2002 burned stands that had been blown down in 1997, affected by SB outbreak in the 1940s, or neither. We created mixed-effect models to measure the relationships between stand attributes and post-fire ground cover as well as between post-fire ground cover and conifer regeneration densities. Ground cover patterns were sensitive to compounded disturbances, and the relationships between conifer regeneration and ground cover were fundamentally different when fire was preceded by another disturbance. Conifer regeneration densities increased with increased litter coverage in stands that only burned, but decreased with increased litter coverage in stands that were blown down and then burned. Similarly, herbaceous cover changed from facilitative to competitive when fire was preceded by SB outbreak. These compound effects via ground cover are at play across stands of varying composition and structural stage and potentially across broad spatiotemporal scales.

Monday April 9, 2018 1:30pm - 1:45pm CDT
LaSalle 2 (7th Floor)