RELATIVE GROWTH-RATE AND BIOMASS ALLOCATION OF PAPER BIRCH (BETULA-PAPYRIFERA) POPULATIONS UNDER DIFFERENT SOIL-MOISTURE AND NUTRIENT REGIMES

Seedlings of four geographically diverse paper birch (Betula papyrifer a Marsh.) populations native to British Columbia were grown under low and high levels of water and nitrogen in a greenhouse for 3 months to examine the relative sensitivity of each population to water and nutri ent availability. Nine sequential measurements on height and basal dia meter growth were made, and then the seedlings were harvested for fina l biomass measurements. Under optimal conditions the highest elevation population ceased height growth, while the low-elevation coastal popu lation continued to increase in height under all treatment conditions. Plants of all populations grown under high N conditions grew faster a nd had larger total biomass and lower root/shoot ratios than plants gr own under low N conditions. Relative growth rate was significantly cor related with shoot and foliage biomass, leaf area, and root weight rat io. All populations generally responded more to low N level than to lo w moisture level in terms of height growth, relative growth rate, tota l biomass, and root/shoot ratio. This suggests that the populations ob served in this study are better adapted to drought than poor soil nutr ient availability. Therefore, consideration of site quality, which inc ludes soil moisture regime and soil nutrient regime, should be a prima ry concern when allocating birch seed lots in a planting program.