Undergrowth Vegetation Effects on the Nutrient Content of Litterfall and Soils in Red Pine and Birch Stands in Northern Minnesota

The role of hazel shrub and herbaceous undergrowth layers in nutrient cycling was studied in two red pine (Pinus resinosa Ait.) and two paper birch (Betula papyrifera Marsh.) stands on similar soil types in northern Minnesota. The annual litterfall produced by these undergrowths and by the overstory was sampled at 15 points in each stand as was the forest floor; the top 3 cm of mineral soil was sampled at 7 of the points. In the pine stands both undergrowth layers significantly added to the total dry weight of litterfall. Under hazel there was significantly more N, Ca, and Mn, and under herbs there was more than twice the amount of K in the litterfall than were these undergrowth layers were absent. In the birch stands the differences in the nutrient content of the litterfall beneath these undergrowth layers were not great, and undergrowth layers had less effect on the nutrient cycle. Although greater amounts of nutrients occurred in the litterfall under hazel and herbaceous layers, the amounts of total nutirents in the forest floor under each undergrowth type were not significantly different nor were total N, available P, or exchangeable K, Ca, Mg, and Mn in the top 3 cm of mineral soil. Turnover rates were different under each type of undergrowth and in red pine stands the forest floor under hazel and herbs appeared to decompose more rapidly than the forest floor of pure pine, but not as rapidly as the forest floor under either hazel or herbs in the birch stands.