COMPOSITION, BIOMASS AND NUTRIENT DISTRIBUTION IN MATURE NORTHERN HARDWOOD AND BOREAL FOREST STANDS, MICHIGAN

There are few studies of biomass and nutrient content in mature boreal forests outside Alaska. The quantification of ecosystem nutrient and energy reservoirs are essential baseline data in studies of ecosystem structure and function. The objective of the study reported here was to compare the aboveground vegetation stand structure and composition in two watershed ecosystems located in Michigan's Upper Peninsula and on Isle Royale National Park, one dominated by mature boreal forest and the other by mature northern hardwoods, and quantify biomass and nutrient content of ecosystem components. The boreal forest stand contained 10 canopy species and had an aboveground biomass of 108 t ha-1 while the northern hardwood stand had 15 canopy species and a biomass of 267 t ha-1. The boreal understory had a larger number of saplings (10,440 stems ha-1) and much greater biomass (2275 kg ha-1) than did the northern hardwood stand (2938 stems ha-1, 85 kg ha-1). Its vascular ground cover also contained more biomass (1180 to 34 kg ha-1 for northern hardwoods). The forest floor contained 21% of the aboveground organic matter in the boreal forest and 4% in the northern hardwood stand. Calcium was the most abundant nutrient in the biomass of both stands, followed by N > K > Mg > S > P (P > S in northern hardwoods). The largest reservoirs were: Ca (92 kg ha-1), northern hardwood bark; K(85 kg ha-1), P(39 kg ha-1), northern hardwood bole; Mg(77 kg ha-1), N (113 kg ha-1), S (58 kg ha-1), boreal forest Oa horizon. Overall, the biomass in northern hardwoods had the larger nutrient content. In the boreal ecosystem, the Oi, Oe and Oa horizons had the largest nutrient content with most of it in the Oa horizon.