INTERPRETATION OF SUGAR MAPLE (ACER-SACCHARUM) RING CHRONOLOGIES FROMCENTRAL AND SOUTHERN ONTARIO USING A MIXED LINEAR-MODEL

This study presents a new method for assessing the impact of environme ntal factors on the radial growth rate of trees. The natural logarithm of the specific volume increments (SVI) were fitted to a mixed linear model, which included fixed effects for tree age when the increment o ccurs, year, precipitation, and temperature both in the year of growth and in the preceding year, and the geographical locale. The model als o incorporates stand and tree as random effects. By fitting trees of d ifferent ages, the model is able to separate year effects from age eff ects. Age and year were treated as categorical variables and hence no specific form of growth curve is assumed. The model was fitted to log SVI from 84 mature sugar maple (Acer saccharum Marsh.) trees from 42 u neven-aged stands in six regions of southern and central Ontario repre senting a known gradient of air pollution. After adjusting for age, pr ecipitation, and temperature effects, the log SVI increased during the first half and declined during the second half of the 20th century in five of the six regions. This suggests that factors other than those included in the model have affected growth. Air pollution remains a li kely causal agent in this observed decline.