Boreal forest carbon (C) budgets are of great interest because of their possible role as a C sink and their future potential to become a C source if predicted warming trends occur (Goulden et al. 1998). Black spruce forests (Picea mariana [Mill.] BSP) are a major boreal ecosystem in North America (Van Cleve et al. 1983, Aber and Melillo 1991) and are one of the ecosystems studied in the BOREAS (BOReal Ecosystem Atmosphere Study). At least two contrasting black spruce forest communities exist: closed-canopy black spruce overstory with a continuous feathermoss (Pleuroziumschreberi and Hylocomium splendens) ground cover on moderately well-drained sites, and open-canopy black spruce overstory with a Sphagnumspp. ground cover on poorly drained sites (Harden et al. 1997, Goulden et al. 1998). These communities differ in carbon content and hydrology (Harden et al. 1997, Trumbore and Harden 1997), species composition, and most likely in nutrient availability, net ecosystem exchange (NEE), and net primary production (NPP). NEE is defined as the balance between NPP and heterotrophic respiration and determines whether an ecosystem is a sink (+ NEE) or source (- NEE) of carbon.

I am focusing my research on the two dominant black spruce communities - black spruce/feathermoss and black spruce/ Sphagnum spp. - to better understand 1). C distribution within black spruce forests, 2). C allocation within dominant species in black spruce communities, 3). NEE, and 4). factors controlling these processes. I am also conducting a study along transects crossing the two major black spruce communities and a third, drier, less extensive community comprised of open-canopy black spruce and jack pine overstory with a feathermoss - reindeer lichen (Cladinaspp.) ground cover. Normalized difference vegetation index (NDVI) will be related to NPP along the transects to better understand the implications of these within stand differences for estimating NPP at large scales using remote sensing techniques.

Publications
Bisbee, K., S.T. Gower, J.M. Norman, and E.V. Nordheim. Environmental factors controls on the distribution and NPP of bryophytes in a southern boreal black spruce forest. Oecologia (submitted).