Growth and flowering in Eriophorum vaginatum: annual and latitudinal variation

Growth, flowering, and nutrient content of Eriophorum vaginatum were observed annually over 4 yr at 34 sites spanning 5.5@? latitude and 1050 m elevation in northern and central Alaska. We found a strong correlation between the average number of thawing degree-days during the growing season and the peak-season leaf mass per tiller. However, the results from reciprocal transplant gardens established at five sites suggested the correlation was due more to genetic differences among populations than to direct climatic effects. Other variables showed little correlation with long-term degree-day averages, and leaf N and P concentrations were site specific. A year of high inflorescence density at any site along the latitudinal transect was likely to be a high flowering year at all other sites. However, a year of above-average growth north of the Brooks Range did not always coincide with above-average growth to the south, and vice versa. The greatest year-to-year variation was in inflorescence density; least variation was in leaf mass per tiller an N and P concentrations. We conclude that yearly variation in weather affects plants on a broad regional scale, but specific controls over flowering versus growth differ in their geographic extent.