SEASONAL PATTERNS OF SOIL RESPIRATION IN INTACT AND CLEAR-CUT NORTHERN HARDWOOD FORESTS

The flux of CO2 from forest soils is controlled by the respiration of plant roots and soil microorganisms, the rates of which are likely to change following forest harvesting. Root respiration should decrease, whereas microbial respiration should increase, in response to warmer s oil temperatures and greater soil C availability following removal of the overstory. We investigated the influence of forest harvesting on s easonal patterns of soil respiration in two different northern hardwoo d ecosystems. One ecosystem was dominated in the overstory by Acer sac charum Marsh. and Quercus rubra L., and the other by A. saccharum and Tilia americana L.; two stands were studied in each ecosystem type. We measured daily rates of soil respiration using the soda-lime techniqu e. Averaged across ecosystems, daily rates of soil respiration did not significantly differ between intact and clear-cut plots, nor did they differ between ecosystems or sites nested within ecosystems. Peak dai ly rates ranged from 2.75 to 3.00 g CO2-C.m(-2).day(-1) during mid to late summer in both intact and clear-cut plots. Soil temperature accou nted for 43 and 58% of the variation in daily rates for intact and cle ar-cut plots, respectively. Annual soil respiration rates in intact (4 78 g CO2-C.m(-2).year(-1)) and clear-cut (470 g CO2-C.m(-2).year(-1)) plots did not differ significantly. Our results suggest that greater r ates of microbial respiration in clear-cut plots proportionally offset a decrease in root respiration following clear-cut harvest.