Carbon dioxide emission from soils plays a critical role in biogeochemical cycling of carbon in terrestrial ecosystems. Although most temperate forests are actively managed for timber production, few data exist regarding the long-term effects of forest management on soil carbon dynamics. In order to evaluate the influence of forest management practices on soil respiration for the understanding of carbon sequestration, we examined the effects of thinning, lime addition and litter removal treatments on soil respiration in 27-year old red pine (Pinus resinosa Ait.) plantations in Ontario, Canada. We measured soil respiration rate (FCO₂), soil temperature (T_soil), soil moisture (W_g), soil depth to C horizon, soil organic matter contents and soil pH, in the growing seasons of 2004 and 2005.

Results/Conclusions

All treatments had immediate effects on FCO₂. In the first year after thinning, mean FCO₂ was higher in thinned sites than controls under lime addition. Soil FCO₂ significantly decreased in litter removal plots in both thinned and control sites while soil FCO₂ increased in limed plots only in conjunction with thinning. T_soil and W_g were higher in thinned sites than in control sites, and litter removal also had significant effects on T_soil and W_g. In contrast to the large effects in the first year, there were no significant treatment effects on FCO₂, soil temperature and moisture in the second year post-treatment. Our results indicate that the short-term pulse in FCO₂ following forest thinning was driven by an increase in microbial respiration related to fine root decay; however, the magnitude of this heterotrophic respiration pulse depended strongly on soil conditions, being most pronounced in plots with both liming and litter removal. Our results suggest that losses of soil carbon following thinning may be mitigated by maintaining soil conditions less favourable for microbial decomposers, such as avoiding liming immediately following thinning in managed forest stands.