Study reveals how to minimize overstory mortality when using shelterwood-burn techniques to restore oak forests
On the Fernow Experimental Forest in West Virginia, Forest Service scientists conducted an experiment comparing two stand manipulation treatments and a control treatment in a hardwood forest. Both manipulation treatments were site-prepared with prescribed fire and thinned selectrively to promote new seedlings, a regeneration method known as shelterwoods. To reduce competition to oak seedlings, an additional prescribed fire post-establishment was applied in the shelterwood-burn treatment. Forest Service researchers measured species and tree size (measured as diameter at breast height, or DBH), and tree crown classification on the treatments and control to determine their impacts on overstory tree survival. Research results showed increasing tree size decreased the risk of mortality from natural causes and prescribed-fire by 3 to 16 percent per inch increase in DBH, with an even greater mortality reduction of 16 to 31 percent per inch when solely examining prescribed-fire mortality. Crown class, species, and treatment were factors only in mortality from natural causes. Considering fire mortality alone, there were no differences in survival rates between the shelterwood and the shelterwood-burn. Overall, trees with large diameters in the dominant and codominant crown classes were key factors for overstory tree survival on hardwood sites that need prescribed fires to reduce competition to oak seedlings. Forest managers can use these findings to apply site treatments that will achieve desired outcomes while minimizing negative impacts in hardwood forest regeneration efforts.