Old-growth forests as global carbon sinks

Abstract

Old-growth forests remove carbon dioxide from the atmosphere at rates that vary with climate and nitrogen deposition. The sequestered carbon dioxide is stored in live woody tissues and slowly decomposing organic matter in litter and soil. Old-growth forests therefore serve as a global carbon dioxide sink, but they are not protected by international treaties, because it is generally thought that ageing forests cease to accumulate carbon. Here we report a search of literature and databases for forest carbon-flux estimates. We find that in forests between 15 and 800 years of age, net ecosystem productivity (the net carbon balance of the forest including soils) is usually positive. Our results demonstrate that old-growth forests can continue to accumulate carbon, contrary to the long-standing view that they are carbon neutral. Over 30 per cent of the global forest area is unmanaged primary forest, and this area contains the remaining old-growth forests. Half of the primary forests (6 x 10(8) hectares) are located in the boreal and temperate regions of the Northern Hemisphere. On the basis of our analysis, these forests alone sequester about 1.3 +/- 0.5 gigatonnes of carbon per year. Thus, our findings suggest that 15 per cent of the global forest area, which is currently not considered when offsetting increasing atmospheric carbon dioxide concentrations, provides at least 10 per cent of the global net ecosystem productivity. Old-growth forests accumulate carbon for centuries and contain large quantities of it. We expect, however, that much of this carbon, even soil carbon, will move back to the atmosphere if these forests are disturbed.

Potential for forest vegetation carbon storage in Fujian Province, China, determined from forest inventories

“…The results of this study show significantly greater effects of mature, broadleaved and state-owned forests on carbon storage than young and middle-aged, coniferous and community-owned forests. These results are consistent with the results from Luyssaert et al (2008). They also suggest an important management direction for Fujian Province in the design of future reforestation programs and further enhancement of vegetation carbon sequestration potentials.…”

Stand age and species richness dampen interannual variation of ecosystem-level photosynthetic capacity

“…While young forests established on former agricultural lands, or burned and harvested forests for several years cannot compensate for the initial carbon loss nor contribute to CO 2 sequestration from the atmosphere, old forest stands retain their capacity to sequester CO 2 for long periods 31,32 . We show that the photosynthetic capacity and therefore the gross primary production of old growth forests are more resilient to climate variability than young forests.…”

“…In addition, our study suggests that species-rich forest stands offer a larger potential for maintaining a stable photosynthetic capacity across time than species-poorer stands. Therefore, preserving our current forest (with old forests covering 15% of Earth's surface 32 ) and their species diversity may attenuate the annual fluctuations of global forest---atmosphere CO 2 exchange.…”

Environmental Services Provided from Riparian Forests in the Nordic Countries

“…Eventually, an unmanaged RF zone will reach a stage where net biomass accumulation becomes slow or even negative. What happens with SOC is not well understood, but it has recently been shown that old-growth upland forests generally are C sinks long after their net aboveground C storage has gone down (Luyssaert et al 2008).…”