Biomass Chronosequences of United States Forests: Implications for Carbon Storage and Forest Management

Forests account for a large fraction of the carbon stored in global soils and vegetation (Dixon et al. 1994). Accordingly, considerable effort has been devoted to understanding the impact of land use and forest management on carbon sequestration, and thus on climate change (Harmon et al. 1990; Lugo and Brown 1992; Heath and Birdsey 1993; Dixon et al. 1994; Houghton et al. 1999; Caspersen et al. 2000; Fang et al. 2001; Pacala et al. 2001; Birdsey et al. 2006). The optimal strategy for forest management aimed at carbon sequestration is controversial. On the one hand, logging diminishes the pool of standing carbon and can result in a large net transfer of carbon to the atmosphere (Harmon et al. 1990; Vitousek 1991; Schulze et al. 2000; Harmon 2001; Harmon and Marks 2002). On the other hand, if the harvested wood has a sufficiently long residence time or is used to offset fossil fuel emissions, repeated harvest and regrowth can effectively sequester carbon (Vitousek 1991; Marland and Marland 1992; Marland and Schlamadinger 1997). For a given parcel of land, the relative merits of plantation forestry vs old-growth protection or restoration depends, in part, on the late-successional carbon storage trajectory. Classical models of ecosystem development propose that live biomass density (biomass per unit area) increases over time to an asymptote (Kira and Shidei 1967; Odum 1969). In contrast, reviews of biomass dynamics in the forest ecology literature tend to emphasize the variety of patterns that can ensue over the course of succession (Peet 1981, 1992; Shugart 1984). In the context of forest management aimed at carbon sequestration, of particular interest is the possibility that live biomass density may decline late in succession in some ecosystems (Loucks 1970; Bormann and Likens 1979). For example, data in Canada’s National Forest Biomass Inventory indicate that biomass declines are common in some types of ‘overmature’ stands, and these declines are accounted for in the Carbon Budget Model of the Canadian Forest Sector (Kurz and Apps 1999). The expected trajectory of live biomass density over time does not in itself determine the optimal strategy for carbon sequestration. Additional factors that must be considered include (1) the impacts of management on other forest carbon