Expected decrease in diameter growth of even-aged red spruce

Weibull functions provide close least square fits to tables for stand basal area and density versus age in even-aged, second-growth red spruce as reported by W. H. Meyer (USDA Tech. Bull. No. 142. 1929). The annual mean radial and basal area increments of the trees can be calculated from the two Weibull functions. For a stand following Meyer's tables and reaching breast height in 1915, mean tree basal area increment increases steadily to a maximum in the early 1960's and then declines; mean radial increment is constant from 1925 to 1955 and then declines rapidly. This behavior matches very closely the results from 3001 red spruce increment cores in New England and New York, which suggests that forest aging is an important cause of decreasing red spruce diameter growth.