UBC Theses and Dissertations
Comparison of carbon and energy balances of a Douglas-fir forest from pre- to post-harvest Paul-Limoges, Eugenie
Stand-replacing disturbances, such as harvesting, have a major impact on the exchanges of carbon (C) and energy between forested land and the atmosphere. The former forest CO₂ sinks become net CO₂ sources due to the continued respiratory losses and to the significantly reduced photosynthetic uptake. Chronosequence studies, where current different-aged stands are used to reconstruct the development of an older stand, have been widely used to quantify the influence of harvesting on C and energy exchanges of forested stands. Almost no replicated measurements have been made within the Fluxnet community for same-age stands within an ecozone. Chronosequence studies assume that all sites differ only in age, and have had the same history in their abiotic and biotic components; this main assumption has been shown to be invalid in several ecological studies using chronosequences and replications are needed to explain these differences. This study used data from the well-studied Fluxnet-Canada Douglas-fir chronosequence on Vancouver Island, where the most mature site recently reached harvesting age and was commercially harvested. C and energy balances were measured using the eddy-covariance technique and other micrometeorological instruments at the recently harvested site (HDF11) for two years following the harvest. These measurements were then compared to pre-harvest measurements at the same site (DF49) and to post-harvest measurements from another previously harvested stand (HDF00) 3 km away in the chronosequence. The results from this study showed that the net radiation decreased from pre- to post-harvest due to the increase in albedo and surface temperature. The average annual Bowen ratio increased slightly due to the reduction in evapotranspiration following the harvest. From pre- to post-harvest, the site transitioned from being a moderate sink to being a strong source of CO₂. In comparison, the previously harvested stand (HDF00) was a weaker source of CO₂ due to lower respiratory rates and faster vegetation recovery. The results show the importance of replicated measurements to characterize the C and energy exchanges for an ecosystem-specific stand age following a stand-replacing disturbance.
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