Thomas-Van Gundy et al., 2014
RESEARCH BRIEF 9
Fire treatments reduced understory maple abundance and importance
Browse control may be necessary to promote oaks with fire or canopy removal treatments
Multiple fire treatments may be necessary to increase oak abundance and importance
In this study, the authors evaluate how different disturbance processes (surface fire, canopy gaps, browsing) regeneration at two mixed mesophytic hardwood forest sites in the western Allegheny Mountains of West Virginia: the Fernow Experimental Forest (FEF) and the Monongahela National Forest (MNF). Here, as is the case in many areas of the central hardwood forest region, oak-dominated overstories are being succeeded by tree species that are browse/shade-tolerant and fire intolerant. Compared to historical conditions, these second growth forests contain increased deer densities, reduced fire frequencies, denser forest canopies, and smaller canopy gaps. These legacy effects are all frequently attributed as causes of low levels of advanced oak regeneration.
In this study, the authors evaluate treatment effects (prescribed fire, browsing exclusion fences, and mechanically-created canopy gaps) and their interactions on seedling and sapling demographics.
Four study plots were installed; two at FEF, two at MNF. Half of each main plot was burned once, and within these treatments, subplots were randomly assigned to fenced, gap, fence + canopy gap, or control. Canopy gaps (average size ~250 m2) were created by girdling overstory trees and injecting them with an herbicide, prescribed fires were strip head fires, and browsing exclusion fences were two meters tall.
The researchers found that, independent of the presence of canopy gaps or browsing exclusion fences, fire significantly reduced the important values and relative abundance of red maple seedlings, sugar maple seedlings and striped maple seedlings and saplings. Similarly, independent of canopy gaps or fire, browsing decreased the relative abundance of sugar maple and red maple seedlings. Canopy gaps led to an increase in maple seedling abundance and maple sapling importance. Yellow poplar, considered fire-sensitive though well suited to colonize after a disturbance, increased in abundance and importance after a single prescribed fire.
Oak seedlings showed the greatest increase in importance values in areas with canopy gaps and browse exclusion, independent of fire (see figure on next page). No combination of treatments contributed to increased relative abundance of oaks. Previous studies have shown that one fire is typically not sufficient to reverse decades of effects of fire suppression and that multiple fire treatments may be necessary to increase oak abundance and importance (see Alexander et al. 2008 and Iverson et al. 2008).
The authors emphasize the importance of considering species regeneration strategies when determining management plans. For example, oaks rely on a bud bank (seedling sprouts resulting from dieback and resprouting and stump sprouts), as opposed to yellow poplar which rely on a seed bank that can be viable for up to 4 to 7 years (see Johnson and Shifley 2009, Dey et al. 2010, and Heggenstaller et al. 2012).
Thomas-Van Gundy, M., J. Rentch, M. B. Adams, and W. P. Carson. 2014. Reversing legacy effects in the understory of an oak-dominated forest.Canadian Journal of Forest Research 44: 350-364.
FOR FURTHER READING
The Oak Woodlands and Forests Fire Consortium seeks to provide fire science to resource managers, landowners, and the public about the use, application, and effects of fire in the region. www.oakfirescience.com
This research brief was funded by The Joint Fire Science Program. http://www.firescience.gov/