Distribution and Cycling of Nutrients in a Natural Pinus Banksiana Ecosystem

Data on dry matter and N, P, K, Ca, and Mg contents and movements in soil and ground vegetation in a 30-yr-old natural Pinus banksiana Lamb. stand in northern Ontario are presented, together with previously published aboveground data. Dry matter and N, P, K, Ca, and Mg contents of trees were 90,700; 165; 14; 82; 112; and 18 kg/ha, respectively--less than in many Pinus spp. of comparable age in other parts of the world. A comparison with nutrient contents in younger (20 yr) and older (65 yr) stands on the same site indicated that most nutrient accumulation in vegetation takes place in the first decades of stand development. Annual nutrient uptake by all vegetation was 32 kg N, 2 kg P, 18 kg K, 21 kg Ca, and 3 kg Mg per hectare. Between 71% and 89% of the elements taken up annually by trees were returned to the soil by litterfall and leaf wash. There was a buildup of forest floor organic matter with stand age and N, P, and Mg accumulated in this material faster than the other elements. Soil reserves of plant-available or mineralizable nutrients were maintained by nutrient replenishment from precipitation and vegetation-soil nutrient cycling. Thus, we conclude that removal of elements from the ecosystem by logging or burning should not result in significant impoverishment of this site.