Micrometeorological and flux measurements over a permafrost black spruce forest in Interior Alaska

A measurement site of energy, water, and carbon fluxes was established in a black spruce forest at the center of a flat basin of Poker Flat Research Range (PFRR), University of Alaska Fairbanks (UAF), located in Interior Alaska, as a key observation site of JAMSTEC-IARC Collaboration Study (JICS). This forest is characterized by an open canopy structure of a black spruce stand with its floor covered by vegetation such as sphagnum moss, tussock sedges, shrubs, and herbs, which is typical in Interior Alaska associated with the presence of permafrost. To obtain reliable flux data for a long period with minimum data loss, an improved closed-path CO2/H2O gas analyzer LI-7200 (LI-COR) was used. In addition, to consider the effect of the angle of attack dependent errors of ultrasonic anemometer on eddy fluxes, a WindMaster Pro ultrasonic anemometer (Gill) was employed. Measurements started in October 2010. Comparing the fluxes measured on the tower (11m) and forest floor (1.85m), the ratio of the CO2 flux of the overstory black spruce to the total CO2 flux was almost 1 until the understory plants emerged, and gradually decreased as the understory plants grew. On the other hand, most of the evapotranspiration was explained by the forest floor, and the contribution of the overstory black spruce trees was negligibly small. The decoupling coefficient of the whole canopy was almost less than 0.1, and typically less than 0.05, indicating that the leaf and surface of this black spruce forest were strongly coupled to the prevailing weather. In fact, most of evapotranspiration was explained by the adiabatic term with saturation deficit and wind speed, and the contribution of the available energy was less important. This low decoupling coefficient may be due to the high surface roughness with the open canopy structure of the black spruce forest.