Messier, C., 1992. Effects of neutral shade and growing media on growth, biomass allocation, and competitve ability of Gaultheria shallon. Can J. Bot. 70:2271-2276.

Following canopy disturbance, the understorey shrub salal (Gaultheria shallon) can sprout vigorously and develop a dense cover which reduces the growth of young conifers. The growth, biomass allocation and competitive ability of salal in relatively rich and poor growing media were studied in pots placed in an open field under 100, 30, 10, and 5% of full sunlight on northern Vancouver Island, British Columbia. The salal plants were grown from stem and rhizome cuttings in association with Sitka spruce (Picea sitchensis) and western red cedar (Thuja plicata) seedlings. Salal cuttings were established on one-half of each pot and subjected to one of the shade treatments, while the conifer seedlings were established on the other half and were growing in 100% sunlight. After two growing seasons salal produced, on average, 5 times as much total dry weight in 100% as in 5% sunlight; no statistical differences in salal growth were found between the growing media or between Sitka spruce and western red cedar. The leaf to fine-root ratios of salal were 3.7 and 8.7 times greater under 5% vs. 100% sunlight on the relatively rich and poor growing media, respectively. Proportionally more leaf and less fine-root and rhizome biomass of salal were produced at 5 and 10% compared with 30 and 100% full sunlight. Rhizome production was the component of salal the most affected by shading. Leaf area of salal increased and leaf thickness and specific leaf weight decreased with shading. The growth of both conifer species was improved slightly by a reduction in salal biomass. These results indicate that light intensity alone is a very important factor influencing salal growth, biomass allocation, and competitive ability.