Using fertilizer to promote diverse seedling development in Allegheny hardwood forests
Many believe that ensuring diverse species composition is one way to increase forest resilience. Forest Service scientists are working to understand and support the factors that lead to diversity. In the Allegheny High Plateau ecoregion, sweet birch dominates recently regenerated forest stands. Prior to 2000, black cherry, an important species for timber and wildlife in northern hardwood forests, was plentiful and developed well in regenerating forests. In fact, black cherry monocultures were a concern because overabundant white-tailed deer limited regeneration of other species. Recently, black cherry seedling numbers have declined with most outcompeted by sweet birch. One hypothesis for declining black cherry is that reduced atmospheric nitrogen deposition has altered soil conditions to favor birch. Forest Service scientists annually applied fertilizer to five shelterwood stands at levels equal to losses in nitrogen deposition. Three adjacent shelterwood stands and three overstory removals were treated with 400 pounds of nitrogen per acre. Researchers found that fertilizer reduced the dominance of birch, favoring red maple in shelterwood stands and black cherry in stands with complete overstory removals. In shelterwood stands, even the small amount of annual fertilization has resulted in fewer tall sweet birch seedlings per acre. Fertilizer may be an important tool to keep black cherry in the next forest and increase species diversity and resilience.
Forest Service Partners