Forest harvesting effects on soil temperature, moisture, and respiration in a bottomland hardwood forest

The effect of forest disturbance on C cycling has become an issue, given concerns about escalating atmospheric C content. We examined the effects of harvest intensity on in situ and laboratory mineral soil respiration in an East Texas bottomland hardwood forest between 6 and 22 mo after harvesting. Treatments included a clearcut, a partial cut wherein approximately 58% of the basal area was removed, and an unharvested control. The soda-lime absorption technique was used for in situ respiration (CO₂ efflux) and the wet alkali method (NaOH) was used for laboratory mineral soil respiration. Soil temperature and moisture content were also measured. Harvesting significantly (P = 0.05) increased in situ respiration during most sampling periods. This effect was attributed to an increase in live root and microflora activity associated with postharvesting revegetation. In situ respiration increased exponentially (Q₁₀ relationship) as treatment soil temperatures increased (mean range 8.3-29.1°C), but followed a parabolic-type pattern through the range of soil moisture measured (mean range 10.4-31.5%). Mean rates of laboratory mineral soil respiration measured during the study were unaffected by cutting treatment for most sampling sessions. Overall, the mean rate of CO₂ efflux in the clearcuts (7.15 g CO₂ m^-2 d^-1) was significantly higher than that in the partial cuts (5.95 g CO₂ m^-2 d^-1), which in turn was significantly higher than that in the controls (4.95 g CO₂ m^-2 d^-1). Mass balance estimates indicate that these treatment differences will have little or no long-term effect on C sequestration of these managed forests.