Disturbance interactions modulate how microhabitat influences conifer regeneration

Authors: Nathan Gill*, University of Wisconsin-Madison, Dan Jarvis, Vermont Technical College, Dominik Kulakowski, Clark University, John Rogan, Clark University
Topics: Biogeography, Mountain Environments
Keywords: beetle outbreak, blowdown, compounded disturbance, conifer regeneration, facilitation, fire, post-fire regeneration, subalpine forest, vegetation dynamics
Session Type: Paper
Day: 4/4/2019
Start / End Time: 9:55 AM / 11:35 AM
Room: 8228, Park Tower Suites, Marriott, Lobby Level
Presentation File: No File Uploaded

Climatically-driven increases in disturbance frequency and extent are causing increased disturbance interactions with potential for compound effects. We examine how interacting disturbances influence microhabitat and, in turn, conifer regeneration. Drawing upon well-studied subalpine forests that experienced compounded wind blowdown and fire or beetle outbreak and fire, we asked: 1) How does microhabitat (logs, litter, herbaceous cover, and bare ground) respond to interacting disturbances? And 2) How are post-disturbance relationships between ground cover and regeneration of the dominant lifeform, conifer trees, different under different contexts? We measured ground cover and conifer regeneration from 2003-2014 in stands that burned in stand-replacing fires in 2002. Burned stands varied in age and composition and had either been blown down in 1997, affected by Dendroctonus rufipennis (spruce beetle; SB) outbreak in the 1940s, or neither. We used mixed-effects models to measure the relationships between stand attributes and post-fire ground cover and between post-fire ground cover and conifer densities. Ground cover was sensitive to disturbance interactions, and the relationships between conifer regeneration and ground cover were fundamentally different when fire was preceded by another disturbance. Regeneration densities increased with plant litter in stands that only burned, but decreased with litter cover in stands that were blown down and burned. Herbaceous cover was competitive rather than facilitative when fire was preceded by SB outbreak. Disturbance interactions influenced ground cover and fundamentally altered relationships of regenerating trees with microhabitat heterogeneity, demonstrating that compound effects on dominant life forms can arise via biophysical context, which is dynamic.

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