Chemical site preparation influences productivity, composition, and structure of boreal mixedwoods in Ontario, Canada.

摘要

We examined the effects of chemical site preparation on jack pine (Pinus banksiana) and black spruce (Picea mariana) plantations 14 years after application on boreal mixed wood sites in Ontario, Canada. The experimental treatments included 4 rates (0, 1, 2, and 4 kg (a.i.) ha-1) of hexazinone formulated as Velpar-LReg. and 2 planting years (immediately and 1 year after herbicide application) in a split-plot design. At the individual tree level, this study supported the findings from previously published short-term results, i.e., increased crop tree diameter and volume growth with increasing hexazinone rates. At the stand level, volume of planted conifers did not increase with hexazinone rate for jack pine, but increased significantly for both container and bareroot black spruce. Planting immediately after hexazinone treatments resulted in greater crop tree and stand volume for both container jack pine and black spruce, but not for bareroot black spruce. Total stand volume did not change with hexazinone rate or planting year, but stand composition shifted from hardwood-dominated to mixed woods for both black spruce stock types while the compositional shift was less apparent in the jack pine plantations. An importance value used to describe height structure did not differ with hexazinone rate or planting year for jack pine. For black spruce plantations, the importance values for non-crop conifer and hardwood decreased with increasing hexazinone rate, indicating a non-stratified, single-storied canopy structure on sites with high hexazinone rates and a stratified, two-storied structure on sites with lower hexazinone rates at the early stages of stand development..