Environmental controls on ground cover species composition and productivity in a boreal black spruce forest

Boreal black spruce forests typically have a dense ground cover of bryophyt es. The two main bryophyte groups in boreal black spruce forests, feathermo ss and Sphagnum, have ecophysiological characteristics that influence the b iogeochemical cycles of black spruce forests differently. The objective of this study was to examine the environmental controls of ground cover compos ition and net primary production (NPP) of feathermoss and Sphagnum in a bor eal black spruce forest in central Saskatchewan. The fraction of Sphagnum g round cover was positively correlated to canopy photosynthetically active r adiation (PAR) transmittance (r(2)=0.48, P=0.03), but the fraction of feath ermoss ground cover was negatively correlated to canopy PAR transmittance i n plots where Sphagnum was present (r(2)=0.87, P <0.0001). Sphagnum presenc e was inversely correlated (P=0.0001) to water table index, defined as wate r table depth relative to the peat layer, while feathermoss occurred in a w ider range of microenvironments. Average NPP for 1998 was more than three t imes greater for Sphagnum (77 g C m(-2) year(-1)) than feathermoss (24 g C m(-2) year(-1)), but the average bryophyte NPP for 1998 was 25 g C m(-2) ye ar(-1) because feathermoss was the dominant ground cover. The large, but di ffering, peat carbon content of Sphagnum- versus feathermoss-dominated bore al forests and peatlands necessitates the need to accurately quantify fract ion ground cover. Additional validation of the empirical models between env ironmental variables and fraction ground cover of bryophytes is necessary, but the reported relationships offer an approach to model carbon dynamics o f bryophytes in boreal forests and peatlands.