GENETIC VARIATION IN RED ALDER (ALNUS RUBRA BONG.) IN RELATION TO CLIMATE AND GEOGRAPHY OF THE PACIFIC NORTHWEST

Genetic variation in red alder was examined in relation to the climate and geography of the Pacific Northwest. Two common garden tests were established with 120 open-pollinated families derived from seed collected in western Washington and Oregon. Seed samples were obtained from stands spanning 1180 m in elevation and 4 degrees in latitude, encompassing a wide array of climatic conditions. Variation was assessed for a number of quantitative traits, including 3-year growth, vegetative phenology, and rates of symbiotic nitrogen fixation.; Genetic variation in all measured traits was strongly related to seed-source climate, suggesting that observed variation reflected adaptations to spatial variation in climate within the region. Multiple regression models with climatic parameters explained 66% of the family variation, with frost-free growing season and annual temperature amplitude being the most important predictor variables. Sources from coastal and low elevation areas with long growing seasons and low temperature amplitudes generally exhibited faster growth rate. Spring phenology showed an accelerated (one week) budburst for coastal sources where spring temperatures are relatively warm and late frosts infrequent. Budburst was closely related to seed-source spring thermal sums calculated for a subsample of seed sources. Fall leaf abscission was accelerated (two weeks) for high elevation seed sources, and was closely correlated with fall frost dates at the seed source.; In comparison with other tree species red alder showed less variation within populations, especially in phenological traits. This finding agrees with genetic theory which predicts less variation within populations of colonizing species as a result of reduced effective population sizes and higher levels of inbreeding.; Genetic variation in symbiotic N{dollar}sb2{dollar} fixation was investigated by examining fixation rates among open-pollinated seedling materials derived high (1180 m) and low (sea level) elevation populations. Repeated in vivo measurements of N{dollar}sb2{dollar} fixation were obtained under uniform greenhouse conditions, along with dry weights of seedling components. High elevation materials exhibited increased growth allocation to roots and nodules, along with a larger N{dollar}sb2{dollar} fixation per unit stem growth. The observed shift in growth allocation among the high elevation materials probably reflects adaptation to the nutrient stresses in the skeletal soils typical of high elevation sites. The practical manipulation of variation in root/shoot growth allocation to enhance N{dollar}sb2{dollar} fixation in alders was discussed, along with the general merits of genetic improvement of symbiotic N{dollar}sb2{dollar} fixation in species of alders.