Evidence of Climatic Control from Population Age Structure of Artemisia tridentata Nutt.in Southern British Columbia

Abstract

Age structure data from eight stands of Artemisia tridentata Nutt. in southern British Columbia are compared to local climatic records by stepwise multiple regression. Climatic variables appear to account for between 40% and 50% of the age structure variance, after correction for adult mortality. Recruit- ment failure in this species may result from drought or heavy rain in autumn, leading to low seed crops, or from high seedling mortality which may be related to low spring temperatures, summer drought, or high autumn and low winter temperatures. Estimates of the spatial pattern of average establishment success are derived using the predictive equations from the regression analyses, and mean climatic data from regional stations. Estimated establishment indices tend to discriminate between stations within and beyond the present species range boundaries, and decline with increasing elevation, as do regional plant densities. The method would appear to have some potential for the analysis of climatic or other environmental controls on species population dynamics; particularly for long-lived species growing in unstable environments. The results indicate that both the range and temporal dynamics of Artemisia tridentata in this area are subject to a complex variety of climatic controls.