Effects of bigleaf maple on the growth and morphology of mature conifers in the southern coastal forests of British Columbia.

The influence of bigleaf maple (Acer macrophyllum) on the growth of mature conifers in the coastal forests of British Columbia has not been previously assessed. I used a paired plot design to evaluate the influence of mature bigleaf maple on the growth and morphology of Douglas-fir (Pseudotsuga menziesii) and western hemlock (Tsuga heterophylla). Twelve conifer plots including bigleaf maple trees in the center (BLM) were paired with twelve plots that had only conifers present (DF). For the Douglas-fir and western hemlock growing in these plots, the diameter at breast height (DBH), height, age, volume, canopy morphology, site index, stand basal area, tree density and competition index were compared using paired-t tests between BLM and DF plots. Cores taken from Douglas-fir and western hemlock trees were used to assess growth chronologies; and radial growth rates and basal area increment (BAI) were compared between BLM and DF plots. There were no significant differences in tree height, tree age, site index or competition index for both Douglas-fir and western hemlock, and DBH for Douglas-fir, when compared between BLM and DF plots. DBH was greater for western hemlock in BLM as compared to DF plots. Both Douglas-fir and western hemlock that were growing next to bigleaf maple had significantly higher radial growth rates and BAI than Douglas-fir and western hemlock surrounded by conifers only. BLM plots did not have a different standing wood volume (total or conifer-only) than DF plots. My findings suggest that the inclusion of bigleaf maple in conifer stands could enhance biodiversity without negatively affecting timber production.