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.