The BOREAS Information System

Summary of Results From BOREAS

The 1993-1994 BOREAS field year has been completed. In terms of data acquisition, the effort must be considered a great success with the collection of comprehensive surface, airborne and satellite data sets accomplished almost exactly as planned; the few blank spots being due to smoke contamination of some of the optical remote sensing work in IFC-2 and similar problems with daytime clouds in IFC-1. Surface flux data were collected throughout the growing season from the towers using eddy correlation and other techniques and over 350 research flights (remote sensing and airborne eddy correlation) were flown in support of the operation.
A surprising picture of the energy, water and carbon dynamics of the boreal ecosystem is emerging, even at this early stage in the experiment. In simple terms, the lowland forests of the boreal ecosystem in Saskatchewan and Manitoba grow on flat terrain, with a mineral soil base overlain by a very thin layer of live and decomposed moss. Observations show that the root zone of the conifers, which comprise the bulk of these forested lowlands, is very thin (less than 40 cm deep) and is contained entirely within the live/decomposed moss (moss/humus) layer. In short, the boreal lowland soils behave hydrologically much like a gently rolling semi-impermeable floor, with a thin layer of cotton on top.
In terms of the water and energy balance, we have seen that the boreal ecosystem often behaves like an arid landscape, particularly early in the growing season. This is because even though the moss layer is wet for most of the summer, the poor soils and harsh climatic conditions lead to low photosynthetic rates, which in turn lead to low evapotranspiration rates. Much of the precipitation simply penetrates through the moss and sand to the underlying semi-impermeable layer and runs off. Most of the incoming solar radiation is intercepted by the vegetation canopies, which exert strong control over transpiration water losses, rather than by the moist underlying moss/soil surface. As a result, much of the available surface energy is dissipated as sensible heat which often leads to the development of a deep (3000m) and turbulent atmospheric boundary layer. These insights into the partitioning of the surface energy should have a significant impact on the development of climate and weather models, most of which currently characterize the boreal landscape as a freely evaporating surface.
Importantly, it has been reported that the moisture level in the moss/humus layer never gets low enough to induce moisture stress in the overlying vegetation (Margolis and colleagues; TE-9). If this finding holds up under further analysis, it would imply that root zone moisture, a difficult variable to quantify over large spatial scales, does not exert significant control on the surface energy balance. Rather, the important variables controlling photosynthesis and evaporation appear to be soil temperature in the spring, and atmospheric relative humidity and air temperature in the summer and fall.
This new understanding of controls on regional evaporation rates is relevant to the issue of whether the boreal ecosystem is a sink or source of carbon, but until the analysis is further along this question will remain unresolved. We have learned that sequestration of carbon by conifers, the largest component of the boreal ecosystem, is limited in the spring by frozen or cold soils, and in the summer by hot temperatures and dry air. In the fall, the conifers were observed to have the largest carbon uptake of the season; presumably as soils are warm, the air temperatures are not so hot, and the air is not so dry. Leaf-level measurements suggest that the end of the growing season may be induced by frost. Measurements show that at temperatures below about -5 to -10 degrees C, black spruce needles do not recover, and photosynthesis stops.

In Summary:

1. The photosynthetic machinery of the boreal forest has considerably less capacity than the temperate forests to the south. This is reflected in low photosynthetic and carbon drawdown rates which are associated with low transpiration rates.
2. The coniferous vegetation in particular follows a very conservative water use strategy. The vegetation transpiration stream is drastically reduced by stomatal closure when the foliage is exposed to dry air, even if soil moisture is freely available. This feedback mechanism acts to keep the surface evapotranspiration rate at a steady and surprisingly low level (less than 2 mm/day over the season).
3. The low evapotranspiration rates coupled with a high available energy during the growing season (the albedos are among the lowest observed over vegetated regions) can lead to high sensible heat fluxes and the development of deep planetary boundary layers, particularly during the spring and early summer. These planetary boundary layers are often characterized by intense mechanical and sensible heat-driven turbulence.
4. As far as we know, all current climate and numerical weather prediction models grossly overestimate evap-otran-spiration from the region.

The next few years will see analyses and publication of the results from this field year. Some limited visits back to the field are anticipated.

Acknowledgments/Contributions

All the BOREAS Scientists and Staff contributed to this paper in one way or another. Scientists who contributed preliminary data sets are identified in the text and figure captions. The BOREAS Operations Group responsible for the design and oversight of the field experiment consists of Piers Sellers, Forrest Hall, Dennis Baldocchi, Josef Cihlar, Barry Goodison, Hank Margolis, Michael Apps, Bob Kelly, Jerry den Hartog, Mike Ryan, Patrick Crill, Dennis Lettenmeier and Jon Ranson.
The BOREAS Principal Investigators are listed on the BOREAS Personel Web page. Almost all investigators took on project-related duties in addition to their own research tasks during the field year. The BOREAS and BORIS staff members are Laura Blasingame, Carla Evans, Scott Goetz, Dan Hodkinson, Fred Huemmrich, Fred Irani, David Knapp, David Landis, Elissa Levine, Beth McCowan, Valerie McElroy, Blanche Meeson, John Metcalfe, Karen Mitchell, Theresa Mulhern, Ross Nelson, Jeffrey Newcomer, Jaime Nickeson, Carey Noll, Adam Rosenbaum, Amy Ruck, Al Schmidt, Tracy Twine, Anthony Young, Barrie Atkinson, Mary Dahlman, Michael Fitzsimmons, Tom Gower, John Martin, Joe Niederleitner, John Norman, Paul Rich, Sandra Schussel, D'Arcy Snell, Sarah Steele, John Stewart, Karl Spence, David Terroux, Gillian Traynor, Jason Vogel. All are warmly thanked. Darrel Williams, branch head of 923, NASA/GSFC is also thanked for his tolerance and humor throughout the entire project.
The research aircraft crews and management performed their tasks with unflagging professionalism and patience. Special thanks go to George Alger, Chris Jenison and Richard Rose (C-130); Gary Shelton (ER-2); Willie Dykes, Charlie Walthall, Charles Smith, Jeff Sigrist, Ed Melson and Pete Bradfield (Helicopter); Larry Hill, Lawrence Gray, Ted Sedes (Chieftain); Chris Scofield and Michele Vogt (DC-8); Charles Livingstone and Brian Spicer (CV-580); Tom Carrol and Rob Posten (Aerocommander); Paul Spyers-Duran, Henry Boynton and Jerry Tejcek (Electra); John Aitken, Brian Bertrand, Murray Morgan, John Croll and Charles Taylor (Twin Otter); George Bershinsky and Ernest Gasaway (Kingair); and Ed Dumas and Robert McMillen (for Long EZ). While these (generally unsung) heroes are specifically mentioned, we are fully aware that a tremendous job was done by many other people under frequently trying conditions.
BOREAS contributes to both the U.S. and the Canadian Global Change Research Programs. For the United States, the effort is being led by the National Aeronautics and Space Administration's Mission to Planet Earth, with participation from the National Oceanic and Atmospheric Administration, the National Science Foundation, the United States Geological Survey and the Environmental Protection Agency. Participating Canadian agencies include the Canada Centre for Remote Sensing, Environment Canada, Natural Sciences and Engineering Council, Agriculture Canada, National Research Council, and Canadian Forest Service. The BOREAS Project was overseen by program managers from the participating agencies who made up the BOREAS Coordinating Committee (BCC). The membership of the BCC is Richard Asselin, Barbara Conway, Michael Coughlan, James Edwards, Peter Hall, Jean-Claude Henein, Bruce Hicks, Gerry Marsters, Jeffrey McQueen, Jarvis Moyers, Leo Sayn-Wittgenstein, Tim Schowalter, Mac Sinclair, Lowell Smith, Pam Stephens, Robert Stewart, John Stone and Diane Wickland.
BOREAS is an element of the International Satellite Land Surface Climatology Project (ISLSCP) which is part of the World Climate Research Program - Global Energy and Water Cycle Experiment (WCRP-GEWEX). BOREAS is also contributing to three International Geosphere Biosphere Program (IGBP) core projects; Biospheric Aspects of the Hydrological Cycle (BAHC), Global Change and Terrestrial Ecosystem (GCTE), and International Global Atmospheric Chemistry (IGAC).

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