GENETIC-VARIATION IN RED ALDER (ALNUS-RUBRA) IN RELATION TO NATIVE CLIMATE AND GEOGRAPHY

Genetic variation was examined within and among populations of red ald er (Alnus rubra Bong.) from elevational gradients in four river draina ges of the Pacific Northwest. Wind-pollinated progenies of 120 trees w ere grown for 3 years in a common garden environment and measured for growth and shoot phenology. Variation in top weight, bud flush, and le af abscission was analyzed in relation to native climate and elevation and compared with sympatric species. Strong geographic patterns of va riation were observed for all measured traits, apparently reflecting a daptations to highly variable climates within the region studied. Grow th traits were correlated with temperature amplitude and length of gro wing season. Growth rhythm in bud flushing and growth cessation was re lated to two important environmental cues, spring thermal sums and fal l frost dates. Overall levels of variation in red alder appeared to be similar to several sympatric conifers, although variation within popu lations of red alder was lower. The latter finding may be due to the d emography of the riparian populations sampled, or perhaps a characteri stic of the species and its colonizing life history.