Nutrient cycling of aboveground poplar and Chinese fir at different maturity stages.

aAnnual nutrient increment + annual nutrient return
b∑ (annual biomass increment of each poplar tissue × nutrient concentration of each tissue)
c∑ (aboveground litterfall biomass of poplar of each month in the stand × nutrient concentration in litterfall of each month)
d(annual nutrient return / annual nutrient uptake) ×100%; e data are from Sheng and Fan (2005).
Nutrient cycling of aboveground poplar and Chinese fir at different maturity stages.