Multiresource Effects Of A Stand Replacement Prescribed Fire In The Pinus Contorta Abies Lasiocarpa Vegetation Zone Of Central Washington

In 1988, three studies were established as part of Experimental Project 995 to study lodgepole pine (Pinus contorta var. latifolia) survival and growth responses to site preparation in the Sub-Boreal Spruce zone of north-central British Columbia. The project examines the effectiveness of several mechanical treatments and localized high-intensity burning, with a focus on disc trenching, which is the most commonly used mechanical site preparation technique in this region. The importance of disc trench orientation, planting aspect, and planting position were investigated, as well as potential interactions between broadcast burning and disc trenching. This report presents 25-year results for the Bednesti North and Bednesti South experiments, and 19-year results for the Tanli experiment. Treatment effects are discussed in relation to: lodgepole pine establishment (survival and early growth to age 5); performance at approximately free-growing age (9 years); and early mid-term growth, stand volume, and site index (as measured at age 25). Of the mechanical treatments tested, coarse mixing was the most effective, resulting in approximately 1-m gains in lodgepole pine height over the control at age 25. This treatment is not practical from an operational perspective, however, and the more common technique of disc trenching with trees planted at the hinge produced the second greatest gains. In contrast, pine planted in trench furrows showed a trend of reduced growth relative to the control. Trench orientation was relatively unimportant, but there was a slight advantage to avoiding north-aspect planting positions. Although broadcast burning alone did not have a significant effect on pine growth, it consistently interacted with disc trenching to produce a mild magnification of responses to that treatment. Pine planted in long, narrow, intensely burned windrow strips were consistently larger than control pine throughout the 25-year assessment period, but they had poor form due to being essentially open-grown.