The effect of precipitation on radial increment in Norway spruce (Picea abies Karst.) and on the dynamics of a lepidopteran pest insect.
Increment core samples at b.h. were taken from 15 trees in each of 7 stands (aged 22-68 yr) in North Zealand, Denmark, in Oct.-Nov. 1984. Radial increment could be described as a function of precipitation in May-Sep., incl. a delay effect of the previous 4 yr precipitation. The delay explains a general decrease in increment over the past 20 yr. Based on data for the population dynamics of Epinotia tedella in 1970-85 in the area, a sequence of causal relations between precipitation, tree vigour and pest insect population is proposed together with a simple predictive model for changes in numbers of insects one yr ahead.