Structural Estimation onAnnual Net Productivity of Tree Layer by Data fromPermanent Sample Plots in Tiantai

Mean annual growth rate of biomass of reserved tree, mean annual retention rate of biomass, mean annual growth rate ofingrowth-treeand mean annual number of ingrowth-tree per unit area was structurally estimated by using the permanent sample plot dataduring 2009-2014, 2014-2016 and 2016-2017 of Tiantaicounty, Zhejiang province, with different forest types, tree species groups and age groups.The result showed that mean annual growth rate of biomass of each reserved tree species group decreased with the increase of age group.The average annual growth rate of reserved tree biomass in commercial forest was higher than that in ecological forest.The mean annual retention rate of biomassof all tree species groups in ecological forest was lower than that in commercial forest.The mean annual growth rate ofingrowth-tree biomass of tree species in ecological forest was higher than that in commercial forest except hard broad I.With the increase of age group, the number of ingrowth-tree per unit area decreased.Under any age group, the annual number of ingrowth-tree per unit area inecological forest was higher than that in commercial forest.