Water and carbon dioxide exchange at a boreal young jack pine forest in the BOREAS northern study area

Climatological measurements, including carbon dioxide flux density, were ma de from May to September 1994 and from May to November 1996 at a young jack pine (Pinus banksiana Lamb.) forest near Thompson, Manitoba, Canada, as pa rt of the Boreal Ecosystem-Atmosphere Study (BOREAS). The study periods wer e warmer and drier than the 24 year climate normals, and in general, 1996 w as warmer but wetter than 1994. Volumetric soil moisture above a depth of 8 cm in 1994 was often less than 5%. Albedos for solar radiation and photosy nthetic photon flux density (PPFD) were 0.13 and 0.05, respectively, in bot h years. The Bowen ratio for days of year 144-262 was 1.7 in 1994 and 1.5 i n 1996, with maximum daily Bowen ratios from 4 to 6. The range in CO2 flux densities was the same in both years, with maximum uptake values of -0.55 m g m(-2) s(-1) in midsummer. Average diurnal patterns of CO2 exchange for 19 94 were similar to those for 1996, characterized by maximum uptake in the m orning and a gradual decrease through the afternoon. Rectangular hyperbolic response curves showing CO2 uptake in relation to incident PPFD show that changes between the,morning and the afternoon, and because of environmental controls, were as great or greater than changes between designated 3 and 4 week measurement periods. Over a period of 119 days the young jack pine fo rest accumulated approximately -200 g C m(-2) in 1994 and -267 g C m(-2) in 1996. Reproduction of CO2 exchange trends will be important for modeling e fforts involving; northern ecosystems.