Development of the Red Maple Understory in Northeastern Oak Forests

Permanent plot records ranging from 13 to 42 years in duration were used to study understory development in four upland oak forests in Massachusetts and New York. All tracts have a dense understory of shade-tolerant species dominated by red maple ( Acer rubrum L.) but sparse representation of oak saplings. Mortality rates for red maple have been low compared to other species, and maples have increased in size and numbers on all tracts. For example, on one tract, 57 percent of the red maples in the 10-cm diameter class advanced two or more 2-cm classes over a 19-year period, and the number > 11 cm dbh increased from 30 to 80/ha. Diameter growth of red maple is highest among trees receiving substantial direct sunlight, and red maple may comprise a large proportion of the overstory on well-drained sites with a relatively low density of oak stems. There are currently no indications of decline of red maple canopy trees 80 years old, and growth rate shows a positive linear correlation with size. A severe drought of 1962-66 appeared to cause substantially higher mortality in the New York stands but had little impact on the Massachusetts stands. Drought did not cause a long-term setback in the red maple diameter distribution on any of the sites. Forest Sci. 30:3-22.