When do replanted sub-boreal clearcuts become net sinks for CO sub(2)?

• Published in: Forest ecology and management 2007-02, Vol.239 (1-3), p.210-216
• Main Authors: Fredeen, AL, Waughtal, J D, Pypker, T G
• Format: Article
• Language: English
• ISSN: 0378-1127
• DOI: 10.1016/j.foreco.2006.12.011

After forest harvesting, sites are initially sources of CO sub(2), but eventually become sinks for CO sub(2) after some period of years following reforestation. This period for boreal forests has been assumed to be 10 years, but this has not been validated empirically for most forest types including sub-boreal spruce-dominated forests of central British Columbia, Canada. Therefore, we sought to determine the timing of the source to sink transition for a sub-boreal clearcut. Clearcuts such as the one documented in this study occurring on glaciolacustrine deposits with relatively poor drainage represent about 20% of the 1.5millionha in the Prince George area. Net ecosystem CO sub(2) exchange (NEE) for a clearcut was measured over four growing seasons in years 5, 6, 8 and 10 after harvest. A Bowen ratio approach in combination with a bottom-up modeled NEE based on ecosystem component CO sub(2)-flux measurements was used for years 5 and 6. In years 8 and 10, growing season NEE was measured using an open-path eddy covariance system. A cross comparison of Bowen ratio and eddy covariance systems was performed and measurements agreed relatively well (r super(2)=0.58). The results demonstrated that while this clearcut was still a source for C (NEE of +336 to +487gCm super(-) super(2)) after 6 years, it was most likely a sink for C between 8 (NEE of -189 to -52gCm super(-) super(2)) and 10 (NEE of -185 to -48gCm super(-) super(2)) years following harvest.