RELATIONSHIPS AMONG CROWN CONDITION, GROWTH, AND STAND NUTRITION IN 7NORTHERN VERMONT SUGARBUSHES

We compared growth with soil and foliar elemental composition in seven stands of sugar maple (Acer saccharum Marsh.) in northern Vermont cha racterized by high or low incidence of crown dieback over the period 1 989-1992. In stands with low-quality crown conditions, such as elevate d crown dieback, long-term basal area growth rates were approximately half of those in stands with higher crown quality. Average annual basa l area growth was 17.5 cm(2) for dominant trees in these stands during the period 1953-1992 compared with 32.3 cm(2) for trees in higher qua lity stands. The occurrence of elevated crown dieback was apparently u nrelated to stand characteristics such as stand age, basal area, stem density, elevation, or aspect among the stands sampled. Stands with el evated crown dieback were found on soils characterized by low pH (<4.0 ), low base cation pools (particularly Ca and Mg), and higher Al in so il surface horizons than higher quality stands. Over 4 years, sugar ma ple stands with elevated crown dieback exhibited significantly lower ( P < 0.01) foliar Ca concentrations and somewhat lower foliar N and Mg than higher quality stands, while soil and foliar K were similar in bo th dieback classes. Among survey plots sampled in 1989, soil pH and Ca were strongly correlated with foliar Ca and K (P < 0.001). Soil pH, s oil Ca, and foliar Ca were also strongly correlated with the level of crown dieback among plots and stands (P < 0.0001). Our results indicat e that podzolic soils in northern Vermont may present marginal conditi ons for sugar maple growth in terms of soil pH and soil Ca availabilit y, but that P and K pools appear to be sufficient for growth. While a lack of historical data prevents identification of long-term trends in nutrient availability in these soils, factors promoting losses of bas e cations from acidic, base-cation-poor Podzols may also exacerbate fo liar nutrient deficiencies and thus affect the crown condition of suga rbushes in northern Vermont.