Effectsof biomass harvest intensity and soil disturbance on jack pine stand productivity: 15-year results

Rising demands for forest biomass have raised concerns that the increased removal of organic residues and harvest impacts may reduce longer term site productivity. Replicated field experiments examining the effects of stem-only harvest with disc trenching (SO T ), whole-tree harvest with (WT T ) and without (WT) disc trenching, whole-tree harvest with forest-floor removal by blading (WT B ), and blading followed by compaction (WT BC ) were installed on nine sandy jack pine (Pinus banksiana Lamb.) sites in northern Ontario. At year 5, planted-tree diameters, dominant tree heights (H D ), and stand aboveground biomass (jP P Bio) were smaller without soil disturbance (the WT), but were otherwise similar among treatments. At year 15, planted-tree size and stand yield rankings were WT T = SO T = WT > WT B = WT BC . Biomass production by natural regeneration and total stand aboveground biomass (TotBio) treatment rankings were SO T ≥ WT T ≥ WT > WT B = WT BC . H D , jP P Bio, and TotBio showed increasing divergence over time in WT B vs. WT T – SO T response, whereas statistical equivalence of the WT T and SO T treatments was shown for most tree and stand growth responses. There was some evidence of increasingly negative impacts of WT B as site index declined. Overall, negative WT B effects on tree and stand productivity have become increasingly apparent.