Summary of global area, annual net primary productivity (NPP), plant carbon content and soil carbon content in broadly categorized terrestrial ecosystems (Table 2 in Amthor, J.S. et al., 1998 - after Ajtay et al., 1979; Botkin and Simpson, 1990; Gorham, 1995; FAO, 1997) Potential carbon gains and losses are semi-quantitative, based on perceived productivity and stimulation due to increasing CO2 and losses that could occur due to warming-stimulated increases in decomposition and reduced productivity due to increasing environmental stress, such as air pollution. The potential gains and losses are weighted toward global responses rather than per ground area at a particular location; they do not account for the effects of coastal inundation due to sea level rise. A key point is that the accumulation of C is in many cases a very slow process, whereas the release can be almost instantaneous, and over the near term (50-100 years) the potential for losses is significantly greater than the potential for storage. Ecosystem Area NPP* NPP* Plant C Plant C Soil C Soil C Potential Potential (10^12 m^2) (gC/m^2/year) (Pg C/year) (g/m^2)* (Pg)* (g/m^2)& (Pg)& C gain rate C loss rate Forest, tropical 14.8 925 13.7 16500 244 8300 123 +++ --- Forest, temperate and plantation 7.5 670 5.0 12270 92 12000 90 ++ -- Forest, Boreal 9.0 355 3.2 2445@ 22@ 15000 135 + --- Woodland, temperate 2.0 700 1.4 8000 16 12000 24 + - Chaparral 2.5 360 0.9 3200 8 12000 30 + - Savanna, tropical 22.5 790 17.7 2930 6 11700 264 ++++ ---- Grassland, temperate 12.5 350 4.4 720 9 23600 295 +++ ---- Tundra, arctic and alpine 9.5 105 1.0 630 6 12750 121 ----- Desert and semidesert scrub 21.0 67 1.4 330 7 8000 168 + - Desert, extreme 9.0 11 0.1 35 0 2500 23 + - Perpetual ice 15.5 - - - - - - Lake and stream 2.0 200 0.4 10 0 - - Wetland 2.8 1180 3.3 4300 12 72000 202 +++ --- Peatland, northern 3.4 - - - - 133800 455 ----- Cultivated and permanent crop 14.8 425 6.3 200 3 7900 117 + - Human area 2.0 100 0.2 500 1 5000 10 + - TOTAL 150.8 391 59.0 3220 486 13640 2057 Footnotes * Assuming that phytomass is 45% carbon. & Values for all biomes except northern peatlands are for the top 1.0 m of soil only. Nepstad et al. (1994) report that stores of carbon below 1 m depth exceed those in the top 1.0 m in an Amazonian forest. Value for all biomes except wetlands and northern peatlands exclude surface litter. Surface litter and standing dead plants may contain from 50 Pg to >200 Pg C globally, with large amounts in some forest ecosystems (see references in Ajtay et al., 1979; Amthor, 1995). @ The value for boreal forest is based on Botkin and Simpson (1990), who claim that living phytomass in boreal forests is only 24% of the value given in Ajtay et al. (1979). References Ajtay, G.L., P. Ketner and P. Duvigneaud (1979) Terrestrial primary production and phytomass. pp. 129-181 In: B. Bolin, E.T. Degnes, S. Kempe and P. Ketner, eds. The Global Carbon Cycle. Wiley, Chichester, UK. Amthor, J.S. (1995) Terrestrial higher-plant response to increasing atmospheric CO2 in relation to the global carbon cycle. Global Change Biology 1, 243-274. Amthor, J.S. and members of the Ecosystems Working Group (1998) Terrestrial Ecosystem Responses to Global Change: a research strategy. ORNL Technical Memorandum 1998/27, Oak Ridge National Laboratory, Oak Ridge, Tennessee. 37 pp. Botkin, D.B. and L.G. Simpson (1990) Biomass of the North American boreal forest. Biogeochemistry 9, 161-174. FAO (1996) Production Yearbook, Volume 50. United Nations Food and Agriculture organization, Rome. Gorham, E. (1995) The biogeochemistry of northern peatlands and its possible responses to global warming. pp. 169-187. In: G.M. Woodwell and F.T. McKenzie, eds. Biotic Feedbacks in the Global Climate System. Oxford University Press, New York. Nepstad, D.C., C.R. de Carvalho, E.A. Davidson, P.H. Jipp, P.A. Lefabvre, G.H. Negreiros, E.D. da Silva, T.A. Stone, S.E. Trumbore and S. Vieira (1994) The role of deep roots in the hydrological and carbon cycles of Amazonian forests and pastures. Nature 372, 666-669.