Effects of neutral shade and growing media on growth, biomass allocation, and competitive ability of Gaultheria shallon

Abstract

The growth, biomass allocation, and competitive ability of salal (Gaultheria shallon) were studied in pots grown in an open field under 100, 30, 10, and 5% full sunlight in relatively rich and poor growing media. 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 four neutral shade treatments, whereas the conifer seedlings were established on the other half and were growing in 100% full sunlight. After two growing seasons salal produced, on average, 5 times as much total dry weight in 100% as in 5% full sunlight; no statistical differences were found between the relatively rich and poor growing media and between the Sitka spruce and western red cedar species. The leaf to fineroot ratios of salal were 3.7 and 8.7 times greater under 5% compared with 100% full 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. Key words: Gaultheria shallon, shade, biomass allocation, root competition, rhizome growth.