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Understanding Mountain Laurel’s Impact on Oak Regeneration

Photo of A mixed-oak forest with a dense understory of mountain laurel in eastern Pennsylvania. Note the 8-foot range pole in the center of the photograph. Recent research shows that when mountain laurel cover exceeds 25 percent, regenerating oaks becomes extremely difficult. Pat Brose, U.S. Department of Agriculture Forest Service.A mixed-oak forest with a dense understory of mountain laurel in eastern Pennsylvania. Note the 8-foot range pole in the center of the photograph. Recent research shows that when mountain laurel cover exceeds 25 percent, regenerating oaks becomes extremely difficult. Pat Brose, U.S. Department of Agriculture Forest Service.Snapshot : When did the dense understories of mountain laurel seen in some mixed-oak forests become established, and why? How dense does mountain laurel have to be to interfere with oak regeneration?

Principal Investigators(s) :
Brose, Patrick 
Research Location : Pennsylvania
Research Station : Northern Research Station (NRS)
Year : 2016
Highlight ID : 1112

Summary

Regenerating a significant proportion of oak over time in today’s mixed-oak forests is a challenge that has engaged scientists and the public for decades. In the Appalachian Mountains of eastern North America, mountain laurel (Kalmia latifolia) may interfere in the regeneration of mixed-oak (Quercus spp.) forests. To verify this, a Forest Service scientist conducted a dendroecology study from 2001 to 2005 in three mixed-oak stands with mountain laurel thickets to elucidate how and when the thickets originated, developed, and were impacting hardwood seedlings. At all three sites, the oldest mountain laurel dated to the 1930s, when the stands emerged from a period of recurring disturbance. Most of the mountain laurel has originated since the 1950s, when the stands were generally undisturbed. More recently, insect defoliations have accelerated the development of the thickets by increasing available sunlight. A strong negative relationship exists between the percent cover of mountain laurel and the density of hardwood seedlings with 20 to 30 percent cover being sufficient to inhibit seedling establishment and survival. Perpetuating mixed-oak forests containing mountain laurel thickets will require reducing shrub cover to less than 20 to 30 percent at the beginning of the regeneration process to ensure adequate densities of hardwood seedlings.

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