Daj. Ryan et al., INTERPRETATION OF SUGAR MAPLE (ACER-SACCHARUM) RING CHRONOLOGIES FROMCENTRAL AND SOUTHERN ONTARIO USING A MIXED LINEAR-MODEL, Canadian journal of forest research, 24(3), 1994, pp. 568-575
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.