Aboveground growth rates of seedlings of bunchberry (Cornus canadensis L.), oval-leaf blueberry (Vaccinium ovalifolium Sm.), salmonberry (Rubus spectabilis Pursh), devilsclub (Oplopanax horridus (Sm.) Miq.), and western hemlock (Tsuga heterophylla (Raf.) Sarg.) were compared in a study of their responses to an artificial light gradient in an Oregon greenhouse and in a study of response to overstory and soil type in a field manipulation experiment in southeast Alaska. Seedlings of all five species were grown independently under nine intensities of light for 156 days, and their oven-dry weight of new leaves and twigs was measured and expressed as a percentage of their maximum growth observed under all light treatments. Results indicated strongly differential responses to light, with bunchberry responding most strongly to very low intensities and western hemlock requiring mid to high intensities of light to reach its maximum growth rate. The same five species were planted in plastic grow pots placed in the ground under overstory canopies of red alder (Alnus rubra Bong.) and dense, young-growth western hemlock for one annual growing season (May through August). Soils were artificial and of two contrasting types, one strongly mineral and the other mineral mixed with organic matter. Measures of total aboveground production of new leaves and twigs (oven-dry grams per plant) indicated differential responses among the species and significant differences in canopy and soil treatments for all species except bunchberry. Statistically significant (P < 0.05) interactions of canopy by soil (alder canopy and mixed soil producing greatest growth) were observed in oval-leaf blueberry and salmonberry, both of which also had a significant main effect of soil (mixed > mineral). The canopy main effect (alder canopy > conifer canopy) was significant for all species except bunchberry. Overall, light availability was a strong ecological factor in both studies, but responses to light differed among species. Knowledge of such differential responses is important for designing silviculture treatments for multiple benefits.
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