Retrospective Analysis of Growth and Reproduction in Cassiope tetragona and Relations to Climate in the Canadian High Arctic

Abstract

Techniques of retrospective growth analysis, adapted from dendrochronology, were applied to Cassiope tetragona, an evergreen dwarf-shrub, sampled at Alexandra Fiord, Ellesmere Island, Canada. A new method of delimiting annual growth increments through patterns in leaf node placement along a stem was utilized. Chronologies of mean annual stem elongation, leaf production, and flower production were developed, and estimates of these parameters agree with those obtained for other arctic populations of C. tetragona. Stem elongation and leaf production were positively correlated in the same year. Flower production was positively correlated with growth in the previous year, but negatively correlated with growth in the same year. This pattern was interpreted as the effects of resource allocation strategies, namely, the preemption of within-plant resources by flower production once flowering is initiated. All chronologies were significantly correlated with climate records from Alexandra Fiord and Eureka, Ellesmere Island, with the majority of significant correlations occurring with June and July temperatures. Flower production appeared to be most sensitive to variations in summer temperatures, and climate response functions which included previous growth explained up to 84% of the variation in the flowering chronology. Unstandardized leaf and flower number chronologies were used to provide an independent test of the climate transfer function presented in Havström et al. (1995). The results indicate that C. tetragona may be used successfully to generate proxy climate data, although use of standardized chronologies is recommended. Two predictive models for July temperatures at Alexandra Fiord, based on standardized chronologies, are presented to provide future opportunities for verification and application of this technique.