The conundrum of creating understory light conditions conducive to promoting oak reproduction: midstory herbicide and prescribed fire treatments
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Challenges remain to regenerating oak (Quercus spp.) in eastern upland hardwood forests. It is well established that to be competitive, advance oak reproduction must be of sufficient size to respond favorably upon release. We also know altering the understory light regime, through reductions in stand stocking, basal area, or canopy cover, promotes the growth and competitiveness of small oak advance reproduction. Reductions in stand density can be accomplished by herbicide treatment of the existing midstory, prescribed fire, or harvesting. We found midstory herbicide treatment resulted in an ephemeral increase in light, from < 1 percent of full sunlight pretreatment to 15 to 20 percent post-treatment. This increase in light levels dissipated after three growing seasons. Oak seedlings responded to increased light levels but so did both sugar maple (Acer saccharum L.) and yellow-poplar (Liridendron tulipifera L.). One and two prescribed fires, implemented on a 3-year-return interval, resulted in 12 percent of full sunlight, compared to 8 percent pre-burn. Conversely, a one-time thin to 50 BA (basal area in square feet per acre) resulted in 50 percent full sun following the initial thin and burn and 37 percent after the second burn. Because these fires were repeated on a 3-year interval, the increase in light was sustained over time compared to the thin only. However, much of the growing space was occupied by aggressive red maple (Acer rubrum L.) sprouts after the prescribed burning.