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Sustaining Forests

Herbicide and Prescribed Fire Treatments in Shelterwood Stands

Research Issue

[photo:] Oak forest after herbicide treatment and prescribed burn.Oak forests have great ecological and economic importance and currently oak remains abundant in the eastern US. However, after nearly a century of effective fire suppression and/or lack of proper silviculture techniques, many historically oak-dominated landscapes are gradually shifting to dominance by other species. Mature second-growth oak forests, many of which established prior to suppression, remain oak-dominated today, but the maples and other tolerant species are usually abundant in the midstory and understory, threatening the long-term sustainability of oak dominance. Shelterwood treatments using herbicides show potential to improve oak regeneration. The shelterwood treatment maintains dominant oaks for reproduction, removes mid-story competitors, and increases light to the forest floor, thus promoting oak seedling growth. However mechanical shelterwood treatments do not consistently improve oak regeneration. A shelterwood harvest followed in several years by a late-spring (growing-season) fire shows promise but may not be possible because of potential off-target effects on wildlife. In some areas, the use of any fire, any time of the year may not be possible. Alternate methods such as herbicide treatments to control competing vegetation need to be investigated in conjunction with thinning.

Our Research

Due to the inconsistent short-term response of oak regeneration to prescribed fire and overstory thinning in our previous studies, we initiated a project in 2005 to examine the effectiveness of a heavy shelterwood harvest, in combination with an herbicide application followed by prescribed fire on oak regeneration, at four study sites in southern Ohio. It was the first study to test the effectiveness of the combined use of herbicide and fire.

Expected Outcomes

This study will help answers management questions such as: (1) Can properly timed, early-growing-season fires be as effective in controlling oak-regeneration competitors as the use of herbicide in shelterwood regeneration harvests? (2) Is the combination of herbicide use and late-season fire in shelterwood regeneration harvests more effective in producing advance oak regeneration than either treatment used separately? (3) Are the used of herbicides and/or late-season fires more effective at producing advance oak regeneration than the dormant season fires used in previous studies?

The information generated by this study will be useful to forest land managers who wish to restore and maintain mixed-oak dominated ecosystems for wildlife habitat, rare plant species assemblages, and/or quality timber production.

Research Results

We found that after 4-6 years after a shelterwood harvest, the proportion of oak-hickory in the advance reproduction layer did not change on either control or herbicide units, although oak-hickory was dominant on a greater proportion of subplots in the herbicide units after the harvest (25%) than before the treatments.  Herbicide effects were limited due to the large number of smaller non-oak stems (<5 cm DBH) that were not treated and also the ineffectiveness of glyphosate to limit red maple stump sprouting.  The impacts of the prescribed fire treatments are currently underway.

Research Participants

Principal Investigators

  • Joanne Rebbeck, US Forest Service- Northern Research Station Plant Physiologist
  • Todd Hutchinson, US Forest Service- Northern Research Station Ecologist

 

Last Modified: March 11, 2016