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Detailed stem analysis was used to measure historical growth of three coniferous tree species assumed to represent a wide range of susceptibility to potential acidic deposition effects on cation leaching. Sample trees were growing on an outwash plain in even‐aged monoculture plantations with similar stand histories and soils. Stepwise multiple regression was used to assess relationships between observed variations in growth and climatic variables. The ring‐number sequence, a relative measure of historical tree growth that did not require standardization, was particularly useful in analyses of growth‐environment relationships for young trees that exhibit consistent apical growth. Species/site groups assumed to be more susceptible to acidic deposition effects exhibited significant decreases in growth after 1960, but these decreases were correlated with climatic variables. Growth‐climate relationships derived for the pre‐1960s period did not predict decreases in tree growth observed during the mid‐1960s and late‐1970s, indicating a lack of time stability in growth‐climate relationships. This may be due to many factors, including maturation, climatic anamolies, and/or acidic deposition effects. This correlational study can not establish cause‐and‐effect relationships between tree growth and climate or acidic deposition. Independent confirmation and studies of the physiological mechanisms involved are needed to substantiate these results.

Radial growth of three coniferous tree species, representing an assumed spectrum of susceptibility to acidic deposition effects on cation leaching, was analyzed by detailed stem analysis to determine if a decline in growth, unrelated to natural determinants of growth, has occurred since the 1950s. Various measures of tree growth derived from detailed stem analysis are shown to be very useful in assessing tree growth responses to environmental factors. Correlations between breast height and whole‐stem analysis data were highly variable and generally poor for two of three species studied. Species/site groups identified as potentially more susceptible to acidic deposition effects exhibited synchronous decreases in growth after 1960, but the initiation of decreased growth was coincident with documented climatic anomalies (drought and winter temperatures) and cannot be directly attributed to acidic deposition effects. Quantitative dendroclimatological analyses are necessary to assess the relationship between these episodes of decreased growth and climatic variables before the role of potential acidic deposition‐mediated effects can be evaluated. The role of acidic deposition in the observed growth declines cannot be discounted based on our analyses. However, tenable alternative hypotheses involving the action of natural determinants of growth (climate and maturation) are presented.

AbstractOptimum size of a sample unit and within-branch distribution of overwintering spruce budworm were determined for black spruce in northern Maine. No significant differences in sample reliability were found between whole-branch and 45-cm branch-tip samples. Larval distribution on branches varied with total branch length and a model was developed to estimate the whole-branch population from a 45-cm branch tip. Use of a 45-cm branch-tip sample unit is recommended because it is biologically and statistically valid and reduces sampling costs.