Partitioning net carbon dioxide fluxes between the overstorey and understorey of a northern boreal forest

Northern boreal forests represent a substantial storage component of the global carbon balance. Large amounts of carbon are locked up in their soils due to low decomposition, which results from cold, wet conditions and short growing seasons. Northern ecosystems may be particularly susceptible to climate warming. Whether or not warming will enhance the net uptake or net release of CO2 from these ecosystems is not known. Uncertain photosynthetic and respiratory responses by the diverse understorey and overstorey to climate change confound the future role of these forests. Generally, abundant soil moisture, open canopies and the productivity of bryophytes and lichens result in productive forest floors. The primary goal of this investigation was to determine the controls on net ecosystem photosynthesis (NEP) and ecosystem respiration (ER) at the understorey or floor of an open-canopy spruce/tamarack forest near Churchill, Manitoba, Canada.; Daytime community-scale CO2 fluxes were measured via a closed 20-litre chamber system at the four dominant ground cover vegetation types during the 2000 growing season. Photosynthetically active radiation (PAR), temperature and various water relations were found to control the exchange of CO2 at the forest floor. ER exceeded NEP (positive net ecosystem exchange (NEE)) for Lichen, Hummock and Feather-Moss community types, indicating mean net releases of CO2 during the sampling period. Daytime NEP and ER were found to be in balance at Sphagnum communities. (Abstract shortened by UMI.)...