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 depends on biophysical context. In subalpine forests, this context is largely determined by disturbances such as beetle outbreak, blowdown, 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; SB) 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 used 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. Forest regeneration following compound disturbances is at least partly modulated by disturbance-induced changes in ground cover.
Did the research upon which this submission is based involve human subjects/participants?
Gill, Nathan; Jarvis, Dan; Veblen, Tom; Rogan, John; and Kulakowski, Dominik, "Data: Pre-fire disturbance history modulates relationships between ground cover and post-fire conifer regeneration" (2018). Student Works. 14.