PARENT SESSION
Poster Session 2: Forest Ecology
Monday, August 8, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

When do sub-boreal clearcuts become net sinks for CO₂.

Fredeen, Arthur^{*,1, 2}, Pypker, Thomas³, Waughtal, Jennifer², ¹ Faculty of Natural Resources and Environmental Studies, Prince George, BC, Canada² Ecosystem Science and Management, Prince George, BC, Canada³ College of Oceanic and Atmospheric Sciences, Corvallis, OR, U.S.A.

ABSTRACT- Forest harvesting activities in Canada are resulting in the replacement of old-growth primary forest with younger planted second-growth stands. The way in which this landscape alteration will influence greenhouse gas accumulations is still poorly understood. After primary forest is harvested, a regenerating forest is typically a net source for CO₂, becoming a net CO₂ sink at some point commonly thought to be around 10 years into regeneration. We have been seeking to determine the timing of the source to sink transition for sub-boreal clearcuts in central British Columbia, Canada. An 84 ha forest was clearcut in the UNBC/UBC Aleza Lake Research Forest located approximately 60 km east of Prince George (122°03′40 W, 54°03′11 N) in 1994 and planted back to interior spruce (Picea glauca x engelmannii) in the summer of 1995 at a density of 1200 seedlings ha-1. This region has a 40 year mean annual temperature range of +2 to 5°C and typically has snow accumulation from November to April. Soils are suhb-hygric and classisted as Ortho Luvic Gleysols. In 1999, we established a 1 ha plot within this clearcut with a fetch of at least 300 m in all directions. A Campbell Scientific Bowen-ratio energy balance system (023/CO₂, Li6200), was installed in the center of the 1 ha plot for two consecutive growing seasons (1999 and 2000) and a Campbell Scientific Eddy Covariance system (CSAT3 and Li7500) installed in the same location for the 2002 and 2004 growing seasons. The ecosystem CO₂ exchange data clearly show that clearcuts in central sub-boreal British Columbia are sources for CO₂ in years 5 and 6, but become sinks for CO₂ again by year 8 to 10. Interannual comparisons of fluxes will be made as well as inclusion of non-growing season respiration information for the site.

Key words: sub-boreal, clearcut, CO₂-fluxes, carbon