Tree-ring analysis of declining aspen stands in west-central Saskatchewan
Recent decline of trembling aspen (Populus Iremuloides Michx.) near St. Walburg, Saskatchewan, prompted a study to document the onset and progress of aspen decline and to examine how past climate variation and insect defoliation might have contributed to the decline. Tree-ring analysis was conducted on a total of 138 aspen in pure and mixed 50--75-year-old stands, including stands showing heavy decline (more than 40% crown dieback). Past survey records and the pres ence of light-colored (white) growth rings indicated that stands in the study area were severely defoliated by forest tent caterpillar (Malacosoma disstria Hbn.) in 1962-1964 and several years during the period 1979-1990. Regression modeling showed that insect defoliation was the most important factor causing reduced growth in stem basal area, but drought also had a Significant influence. During periods with defoliation, stem growth was often reduced to less than 10% of that recorded during the most favorable periods. In the early 1990s, stem growth had recovered in all stands except those in the heavy decline class; however, a late winter thaw followed by severe frost in April 1992 caused a temporary reduction in stem growth and might have contributed to the observed dieback. Long-term productivity of aspen stands in this region will likely depend strongly on the future dynamics of forest tent caterpillar and the incidence of extreme climatic events. Crown dieback is expected to occur when drought occurs in combination with several consecutive years of defoliation.
Hogg, Edward H. and Shwarz, A.G., "Tree-ring analysis of declining aspen stands in west-central Saskatchewan" (1999). Aspen Bibliography. Paper 1056.