PRODUCTIVITY AND GROWTH EFFICIENCY IN SUGAR MAPLE FORESTS

Sugar maple (Acer saccharum Marsh.)-dominated northern hardwood forest s were examined at four locations along an acid deposition and climati c gradient in the Great Lakes region of the USA. The study sites were matched in terms of physiography soils, stand history, and vegetative characteristics. Measurements of basal area and biomass growth were ma de for the 1988-1991 growing seasons. There were no significant differ ences in either basal area or biomass increment among the four sites o ver the 4 year period. There was a great deal of year-to-year variabil ity with relative basal area growth rates ranging from as low as 0.2% to as high as 2.4% on a single site in successive years. Growth effici ency measures reflected this variability with as much as an 800% diffe rence between successive years on a single site. When coupled with yea r-to-year variability of up to 34% in leaf area related to heavy seed years and defoliation, this indicates that growth efficiency and leaf area measures are not consistent indicators of aboveground productivit y for tolerant deciduous species, especially if derived from short-ter m measurements or temporary plots.