Adaptive variation in growth, phenology, cold tolerance and nitrogen fixation of red alder (Alnus rubra): Evidence from common garden experiments in two contrasting climates

Background/Question/Methods

Red alder (Alnus rubra Bong.) is the most abundant deciduous tree on the north Pacific coast of North America and its use as a timber species is increasing. To explore adaptive variation and genotype × environment interactions in this species, we examine the pattern and degree of variation in growth, phenological and physiological traits among 59 families of red alder, and then relate this variation to the climates of family origin i.e., the climate at each family’s seed source. Red alder families from six regions along the coast of British Columbia were grown in common garden experiments at two test sites with contrasting climate regimes: a warm, relatively dry southern site and a cool, more continental northern site. We determined the degree of local adaptation among red alder families and the major climatic variables driving adaptive variation in this species.

Results/Conclusions

Significant genetic variation among regions was detected in height, diameter, canopy cover, cold hardiness and nitrogen concentration of red alder families. Families from cool and moist northern regions had earlier bud burst at the warm southern test site, and less autumn canopy cover, lower nitrogen concentrations but higher nitrogen fixation at both test sites, compared to families from other regions. Height and cold hardiness were negatively correlated at the southern test site but positively correlated at the northern test site. Differences in continentality and available moisture of the seed source location explained most of the among-family variation in autumn canopy cover and bud burst, whereas temperature and growing season length were associated with differences in cold hardiness and growth. Red alder families vary in the degree of phenotypic plasticity; however, most red alder families tested are relatively tightly adapted to their climate of origin and may perform sub-optimally if planted in a contrasting climate. Survival, phenology, height and cold hardiness of tightly adapted families will be most affected by long-term climate change or assisted migration. Families with higher plasticity and/or weaker adaptation to their climate of origin may be more able to acclimate to climate change and increased climate variability.