Sitka alder (Alnus sinuata RYDB.) genetic diversity in germination, frost hardiness and growth attributes

Patterns of genetic variation in adaptive and quantitative attributes of Sitka alder (Alnus sinuata RYDB.) were examined at the population level to provide baseline information on genetic diversity of this species. The studied traits were related to germination, growth and frost hardiness. A total of 28 populations were studied coveting the species range in British Columbia. An additional population from California was included to provide an outlier source. There were large genetic differences among the populations in all measured traits except for spring frost hardiness. Inter-population variations accounted for 78% to 97%, 37% to 65% and 26% to 61% of the total variance for variables related to germination, fall and winter frost hardiness, and biomass, respectively. For frost hardiness, the differences among populations were less pronounced in winter (maximum frost hardiness) than were found in fall indicating that the onset of frost hardiness is different among populations. Variations related to geography were particularly strong in fall frost hardiness, shoot dry weight, growth rate in July and ratio of root dry weight to total dry weight. Most of the geographic variation was due to latitude and distance from the coast. Plants generated from northern seed sources were in general more frost hardy, smaller and allocated more carbon to roots compared to shoots. Plants from the interior wet belt were grouped together with coastal plants in cluster analysis based on frost hardiness measurements suggesting that snow cover plays a role in Sitka alder adaptation to low temperatures. Speed of germination did not affect the plant size after one growing season and was independent from germination completeness. Strong positive correlation was found between timing of frost hardiness development and spring bud break. The observed patterns of large genetic variation among Sitka alder populations have significant implications for the management of the species.