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There is an increasing interest in mixed conifer-broadleaf stands as a way to increase the diversity and productivity of managed forests. This study examined the impacts of varying densities of planted broadleaf trees on conifer performance, total stand productivity, and understory plant cover 20 years after stand establishment. The study took place in the Malcolm Knapp Research Forest in Maple Ridge, British Columbia. It used a randomized complete block design to compare treatments containing low, moderate, or high broadleaf densities added to a constant conifer density. Each block contained a conifer-only plot as a control. Conifers were composed of equal amounts of western hemlock, western redcedar, and Douglas-fir. Broadleaves were composed of either red alder or paper birch. We found that conifer volume was significantly lower in most broadleaf treatments relative to the control, due to lower hemlock and redcedar volumes. Douglas-fir, on the other hand, had a higher volume—albeit not significant—in the broadleaf treatments. There were no significant differences in total stand volume between any of the treatments and the control. Shrub cover was significantly higher in the low and high alder treatments relative to the control, but there were no differences in shrub cover between birch treatments and the control. The results suggest that low alder density provides a good balance of conifer yield and understory development. [ABSTRACT FROM AUTHOR]

Abstract: Sustained growth responses and large reductions in rotation length can be achieved by repeatedly fertilizing young boreal forests. This paper reports the effects of different regimes and frequencies of fertilization on the foliar nutrition and growth of 10-year-old sub-boreal white spruce {Picea glauca (Moench) Voss) in central British Columbia. Mean stand volume in treatment plots fertilized twice (at 6-year intervals) with N and B (totaling 400 kg N/ha and 3 kg B/ha) was 20 m3/ha (75%) greater than in the unfertilized control at year 12. Significantly larger stand volume gains (34 m3/ha, 128%) were obtained when S (totaling 100 kg S/ha) was added to this treatment. The inclusion of other nutrients (P, K, and Mg) with N, S, and B did not result in further incremental growth gains. When combined with other nutrients, yearly applications of 100-200 kg N/ha (totaling 1600 kg N/ha) produced 74 m3/ha (277%) more volume compared with the unfertilized stand at year 12. The large effects of fertilization on stand growth were accompanied by large increases in leaf area. Results indicate that repeated fertilization of young sub-boreal spruce forests may offer an excellent opportunity to increase fibre yield and reduce rotation length. [ABSTRACT FROM AUTHOR]

Broadleaf trees are routinely removed from conifer plantations during vegetation management treatments, but whether the removal increases tree productivity or affects root disease and plant diversity is unknown. The effects of manual and chemical reduction of paper birch (Betula papyrifera Marsh.) and trembling aspen (Populus tremuloides Michx.) on conifer survival, growth, root disease incidence, and plant community diversity were investigated for 5 years in Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) and lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) plantations in southern interior British Columbia. Broadleaves were reduced by manual, girdling, and cut-stump glyphosate treatments for 5 years but most severely following cut-stump glyphosate and with a delay due to slow death following girdling. Conifer survival was reduced for 3–5 years following manual cutting or girdling of birch because of a 1.5- to 4-fold increase in mortality due to Armillaria ostoyae (Romagn.) Herink, but this did not occur following cut-stump glyphosate treatment of birch or manual cutting of aspen. Conifer diameter increased with treatment intensity and productivity of the vegetation complex. Competition thresholds were identified for diameter but not survival, although Armillaria-caused mortality tended to increase near the minimum growth threshold. Structural diversity increased following manual cutting and cut-stump glyphosate because birch dominants were removed and understory layers increased, but species richness and diversity were unaffected. Forest managers can expect increased conifer growth with birch removal but also small increases in mortality due to Armillaria ostoyae root disease following manual treatments and loss of large birch trees in all treatments. [ABSTRACT FROM AUTHOR]