PARENT SESSION
Contributed Oral Session 4: Forest Management
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 514 A, Level 5, Palais des congrès de Montréal
Soil CO2 efflux in uneven-aged managed forests: temporal patterns following harvest and effects of edaphic heterogeneity.
Peng, Yuan Ying1, Thomas, Sean C.1, 1 University of Toronto, Toronto, Ontario, Canada
ABSTRACT- Forest management is expected to influence soil CO2 efflux (FCO2) as a result of changes in microclimatic conditions, soil properties, and root dynamics. We measured FCO2 during the growing seasons of 2003 and 2004 in both gap and non-gap locations within stands ranging from 0 to 10 years after the most recent harvest in a selection-managed northern hardwood forest in central Ontario, Canada. Soil temperature, moisture, pH, depth to bedrock, and organic matter content were also measured to examine relationships between the soil FCO2 and soil properties. Results showed that timber harvesting resulted in large changes in FCO2 that varied with time since harvest. Immediately following harvest (year 0) CO2 in gaps has increased by 25-50%, then declined to 25-50% below the pre-harvest levels 1-3 years after harvest. FCO2 recovered to the pre-harvest levels about 5 years after harvest. A similar temporal pattern, but with smaller changes, was found in non-gap locations within harvested stands. We suggest that the initial increase in CO2 is attributed to a combination of root decay, soil disturbance, and increased soil temperature in gaps, while the subsequent decrease and recovery are caused by the gradual regrowth of active roots. We also found strong effects of soil temperature, depth to bedrock, and soil water content on soil FCO2; However, soil pH and soil organic matter content had no detectable effect on FCO2. Our results suggest that selection harvests mainly influence FCO2 through changes in tree root respiration, and that the net result is a decrease in FCO2 through the entire felling cycle. This result, combined with the maintenance of high levels of living biomass in selection harvests managed forests (and the production of long-lived forest products), suggests that uneven-aged management systems may maintain a sustained C sink.
Key words: forest carbon dynamics, selection silviculture, soil respiratio, soil temperature