Aboveground biomass and nutrient accumulation in an age sequence of paper birch ( Betula papyrifera) in the Interior Cedar Hemlock zone, British Columbia

The aboveground biomass and nutrient content (N, P, K, Ca, Mg) of stands of Betula papyrifera Marsh, aged 2, 8, 15, 45, 60, 75 years were measured in the Thompson Moist Warm Interior Cedar Hemlock variant (ICHmw3) of the southern interior of British Columbia. For four of these ages (2, 8, 60 and 75 years) measurements were made on good, medium and poor sites. For the other two ages, only stands on good sites coulde be located. Allometric equations relating dry weights of stemwood, stembark, branches and leaves to tree diameter at breast height (DBH) were developed to estimate aboveground tree biomass. Equations were not significantly different among the three site qualities. Average total aboveground tree biomass for all sites increased with stand age from 1.4 t ha −1 in 2-year-old stands (varying from 0.45 to 2.1 t ha −1 on poor and good sites, respectively) to 202 t ha −1 in the 75-year-old stand (156 and 234 t ha −1 on poor and good sites, respectively). As stand age increased, an increasing proportion of annual biomass increment was allocated to stems, but nutrients were preferentially accumulated in the leaves. Nutrient content of aboveground tree biomass increased with stand age and was generally in the order of N > Ca > K > Mg > P. Average rates of nutrients accumulation in biomass were greatest in the early stages of stand development, and less marked as stands aged. The concentrations of nutrients in tissues decreased in the following order: leaf > branch > stembark > stemwood. Understory minor vegetation contributed little to the nutrient pool of these paper birch ecosystems. Mineral soil contained the largest amount of nutrients among the various ecosystem components.