CARBON DISTRIBUTION AND ABOVEGROUND NET PRIMARY PRODUCTION IN ASPEN, JACK PINE, AND BLACK SPRUCE STANDS IN SASKATCHEWAN AND MANITOBA, CANADA

The objectives of this study are to (1) characterize the carbon (C) co ntent, leaf area index, and aboveground net primary production (ANPP) for mature aspen, black spruce, and young and mature jack pine stands at the southern and northern Boreal Ecosystem-Atmosphere Study (BOREAS ) areas and (2) compare net primary production and carbon allocation c oefficients for the major boreal forest types of the world. Direct est imates of leaf area index, defined as one half of the total leaf surfa ce area, range from a minimum of 1.8 for jack pine forests to a maximu m of 5.6 for black spruce forests; stems comprise 5 to 15% of the tota l overstory plant area. In the BOREAS study, total ecosystem (vegetati on plus detritus plus soil) carbon content is greatest in the black sp ruce forests (445,760-479,380 kg C ha(-1)), with 87 to 88% of the C in the soil, and is lowest in the jack pine stands (68,370-68,980 kg C h a(-1)) with a similar distribution of carbon in the vegetation and soi l. Forest floor carbon content and mean residence time (MRT) also vary more among forest types in a study area than between study areas for a forest type; forest floor MRT range from 16 to 19 years for aspen st ands to 28 to 39 years for jack pine stands. ANPP differs significantl y among the mature forests at each of the BOREAS study areas, ranging from a maximum of 3490 to 3520 kg C ha(-1) yr(-1) for aspen stands to 1170 to 1220 kg C ha(-1) yr(-1) for jack pine stands. Both net primary production (NPP) and carbon allocation differ between boreal evergree n and deciduous forests in the world, suggesting global primary produc tion models should distinguish between these two forest types. On aver age, 56% of NPP for boreal forests occurs as detritus and illustrates the need to better understand factors controlling aboveground and belo w-ground detritus production in boreal forests.