Comparison of net primary production and light-use dynamics of two boreal black spruce forest communities

Black spruce (Picea mariana [Mill.] BSP) is the most dominant forest ecosystem in the North American boreal region. There are at least two contrasting boreal black spruce forest communities: open-canopy black spruce overstory with Sphagnum ground cover (BSSP) and closed-canopy black spruce overstory with feathermoss ground cover (BSFM). The objectives of this study were (a) to compare net primary production (NPP) and light-use efficiency (LUE) for the two contrasting black spruce communities, and (b) to quantify the contribution of different vegetation strata (bryophytes, understory, overstory, and belowground) to total NPP and LUE in a mature black spruce forest stand in central Saskatchewan, Canada.Total NPP for the BSFM community (446 g biomass m(-2) y(-1)) was significantly greater (P = 0.04) than the BSSP community (276 g biomass m(-2) y(-1)). Bryophyte and understory NPP together comprised the greatest fraction of total (overstory, understory, bryopbytes, and belowground) NPP in the BSSP community (51%), whereas overstory NPP comprised the largest fraction of total NPP (86%) for the BSFM community. Overstory LUE was similar (P = 0.87) for the two communities (0.20-0.21 g MJ(-1) annual absorbed photosynthetic active radiation [APAR]), but ecosystem LUE was significantly greater (P = 0.03) for the BSFM community (0.20 g MJ(-1) annual APAR) than the BSSP community (0.15 g MJ(-1) annual APAR). The results from this study demonstrate that all vegetation components must be measured to accurately estimate NPP and LUE of boreal black spruce ecosystems, and community-specific LUE coefficients increase the accuracy of LUE models.