CONVERSION OF NATURAL, MIXED-SPECIES FORESTS TO CONIFER PLANTATIONS -IMPLICATIONS FOR DEAD ORGANIC-MATTER AND CARBON STORAGE

Aboveground carbon storage of stands of natural forest was compared wi th that of conifer plantations of various age in New Brunswick, Canada . The stands of natural forest were dominated by balsam fir (Abies bal samea), red spruce (Picea rubens), red maple (Acer rubrum), and yellow birch (Betula alleghaniensis). The plantations were dominated by plan ted black spruce (Picea mariana). The stands of natural forest ranged in age From 55 to 105 years, while the plantations represented a chron osequence of 3 to 21 years. Carbon storage in the aboveground living t ree biomass of mature natural stands averaged 74.9 t C/ha(-1) (range 5 7.1 to 92.7 t C/ha(-1)), compared with a projected 82.5 t C ha(-1) in a 60-year-old spruce plantation. Forest-floor biomass was similar amon g stands of natural forest and plantations (overall average 20.4 t C/h a(-1)). Woody detrital biomass (snags and coarse woody debris) in matu re natural stands averaged 19.1 t C/ha(-1), considerably more than in the older plantations studied (0.20 t C/ha(-1) in a 21-year-old planta tion). Because of clear-cut harvesting and precommercial and commercia l thinning, the plantations receive few inputs of snags or coarse wood y detritus. The longer-term paucity of these biomass components in pla ntations has important implications for carbon storage. Overall, our s tudy suggests that a landscape managed as a shifting mosaic of plantat ions on a 60-year rotation would store only about 22% as much abovegro und carbon (i.e., in live trees, snags, coarse woody debris, and the f orest floor) as a landscape covered in older-growth natural forest in which gap-phase disturbance dynamics were the primary mechanism of dis turbance.