Initial results from the boreal ecosystem-atmosphere experiment, BOREAS

Abstract

BOREAS is a four-year, regional-scale experiment to study the forested continental interior of Canada. The objective of BOREAS is to improve our understanding of the interaction between the earth's climate system and the boreal forest at short and intermediate time scales, in order to clarify their role in global change. During the winter, spring and summer of 1994, five field campaigns were conducted. About 85 investigation teams including nearly 300 scientists participated, including forest ecologists and ecophysiologists, atmospheric physicists, boundary-layer meteorologists, hydrologists, biochemists, atmospheric chemists and remote sensing specialists. Data from the field campaigns is being placed into a central archive at the Goddard Space Flight Center for immediate access by all participating scientists, and eventually by the outside scientific community. Analysis of the data began in mid-summer as the data were being collected and continues at a rapid pace. The findings so far have been significant in terms of their implications for global change. The boreal ecosystem, occupying roughly 17 percent of the vegetated land surface and thus an important driver of global weather and climate, absorbs much more solar energy than is assumed by operational numerical weather prediction models. Albedo measurements in BOREAS shows that this forest absorbs nearly 91 percent of the sun's incident energy. Additionally, while it is known that much of the boreal ecosystem consists of forested wetlands, numerous lakes, bogs and fens, tower and aircraft measurements during 1994 show that the atmosphere above was extremely dry; humidity and deep boundary layer convection (3000 m) mimicked conditions found only over deserts. Physiological measurements of the trees during BOREAS show that this atmospheric desiccation was a result of the forest's strong biological control limiting surface evaporation. The data further show this tight control was linked to the low soil temperatures and subsequently reduced rates of photosynthesis. BOREAS measurements also focused on net ecosystem carbon exchange. Data acquired during the late spring and summer, showed the boreal forest to be a net carbon sink. However, no measurements were taken in the early spring following thaw, and in the late fall, where the balance between photosynthesis and respiration is poorly understood. During 1996 additional data will be acquired to resolve the annual carbon budget and how it might depend on interannual climate differences.