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

Abstract

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 (SOT), whole-tree harvest with (WTT) and without (WT) disc trenching, whole-tree harvest with forest-floor removal by blading (WTB), and blading followed by compaction (WTBC) were installed on nine sandy jack pine (Pinus banksiana Lamb.) sites in northern Ontario. At year 5, planted-tree diameters, dominant tree heights (HD), and stand aboveground biomass (jPPBio) were smaller without soil disturbance (the WT), but were otherwise similar among treatments. At year 15, planted-tree size and stand yield rankings were WTT = SOT = WT > WTB = WTBC. Biomass production by natural regeneration and total stand aboveground biomass (TotBio) treatment rankings were SOT ≥ WTT ≥ WT > WTB = WTBC. HD, jPPBio, and TotBio showed increasing divergence over time in WTB vs. WTT – SOT response, whereas statistical equivalence of the WTT and SOT treatments was shown for most tree and stand growth responses. There was some evidence of increasingly negative impacts of WTB as site index declined. Overall, negative WTB effects on tree and stand productivity have become increasingly apparent.