MODELING POTENTIALLY SUSTAINABLE BIOMASS PRODUCTIVITY IN JACK PINE FOREST STANDS

A steady-state mass balance model (ForSust), developed to simulate pot entially sustainable levels of tree biomass growth and related nutrien t uptake dynamics, was applied to 17 jack pine sites across Canada. Th e model simulates potential tree biomass growth based on nutrient inpu ts from estimated atmospheric deposition (N, Ca, Mg, K) and soil weath ering (Ca, Mg, K), and matches the resulting nutrient supply rates wit h calculated nutrient demand. Nutrient demand calculations are based o n nutrient concentrations in wood, bark, branches, and foliage. Specif ically, the model simulates sustainable annual increment (SAI) of biom ass growth for stem-only and whole-tree (aboveground biomass) harvesti ng, and for recurring forest fire conditions. Calculated SAI levels we re compared with field-estimated mean annual increments for abovegroun d forest biomass (MAI). For recurring forest fires, it was found that SAI values, as simulated, corresponded with the MAI field estimates in general. For whole-tree harvesting, SAI was lower than MAI for most b ut not all sites. For stem-only harvesting, SAI corresponded with MAI, but there was a greater scatter between SAI and MAI values than what appeared to be the case for the recurring forest fire scenario.