Black spruce and vegetation response to chemical and mechanical site preparation on a boreal mixedwood site

Abstract

The growth and development of outplanted black spruce (Picea mariana (Mill.) BSP) and competing vegetation five growing seasons after mechanical and chemical site preparation treatments are presented. The largest stem volume increase for black spruce coupled with the lowest vegetation indices for competing trees and shrubs were recorded on the treatment consisting of chemical site preparation with liquid hexazinone applied at 3.1 kg active ingredient (a.i.)·ha-1 followed by chemical tending in the second and fourth growing season with glyphosate applied at 1.78 kg a.i.·ha-1. Black spruce stem volume growth was second highest and the vegetation indices for competing trees and shrubs the highest, on plots treated with hexazinone site preparation. Among mechanical treatments, black spruce stem volume was highest on plots treated with mixed-mound site preparation. No other mechanical site-preparation treatment improved the growth of black spruce over boot-screef site preparation alone. The vegetation index of trembling aspen (Populus tremuloides Michx.) was reduced on mixed-mound and area-mixed site preparation treatments. The vegetation index of red raspberry (Rubus idaeus L.) was reduced on area-mix and area- and strip-screef treatments. By the fifth growing season, site-preparation treatment had little effect on the comparative growth of grasses and forbs. High-speed strip-mixing with 80 cm wide strips spaced at 2-m centres, on deep, fertile, silty loams of Site Region 3W-Lake Nipigon, does not appear feasible as an alternative to chemical site preparation or conventional manual and mechanical site preparation.