Soil respiration rates of five successional forest stands dominated by bigtooth aspen (Populus grandidentata Michx.) in northern lower Michigan were measured during the growing seasons of 1981-1983. Forest age ranged from 11-70 yr, and aboveground biomass varied fivefold among sites. There were no significant differences among sites in soil respiration rate in any one year. Mean rates over all sites from June through September were 9.1, 8.6 and 6.1 g/m2/day in 1981-1983, respectively. Rates in 1983, which had a dry, warm summer, were significantly lower than rates in 1981 and 1982, which did not differ. Estimated yearly CO2 released ranged from 1700-2250 g/m2. Litterfall on the sites (3-yr mean) ranged from 187-408 g/m2/year, with leaves contributing 90.1% of the litter. Litter inputs accounted for only 15-30% of the yearly CO2 released from the soil. Similarity of soil respiration rates among sites resulted in no correlation with forest age, aboveground woody biomass, or site fertility.