Forest carbon pool

Another model, first introduced by Moore, et al. (2i), was used to examine the role of terrestrial vegetation and the global carbon cycle, but did not include an ocean component. This model depended on estimates of carbon pool size and rates of CO2 uptake and release. This model has been used to project the effect of forest clearing and land-use change on the global carbon cycle (22, 23, 24). 

Several studies, based on models, examined the effects of land-use change on the global carbon cycle and conclude that there is a net release of carbon due to land clearing. However, the results and conclusions of these studies are based on assumed sizes of vegetation carbon pools which are inputs to the models. For example, Melillo et al. 24) concluded that boreal and temperate deciduous forests of the northern hemisphere are net sources of atmospheric carbon. Their analysis used values for carbon density derived by Whittaker and Likens 19) from work by Rodin and Bazilevich (27). Rodin and Bazilevich extrapolated results of small, unrelated studies in Europe and the USSR to estimate total biomass of Eurasian boreal and temperate deciduous forests. Their estimates have since been extrapolated to forests worldwide and are used often today. 

Table I. Estimation of the global vegetation carbon pool using the latest estimates of total carbon density for forests.

Carbon represents about 50% of the total oven-dried biomass present in forests [32]. Estimation of carbon pools in forests necessarily involves studying the different strata of biomass present in them. In the different studies, the following carbon pools and variables were measured ... 

Dixon R, Brown S, Houghton R, Solomon A, Trexier M, Wisniewski J. Carbon pools and flux of global forest ecosystems. Science, 1994. 263(14) pp. 185-190. 

Bonino E. Changes in carbon pools associated with land-use gradient in the Dry Chaco. Forest Ecology and Management, 2006. 223 pp. 183-189. doi 10.1016/j.foreco. 2005.10.069... 

Rillig, M. C., Wright, S. F., Nichols, K. A., Schmidt, W. F., and Torn, M. S. (2001). Large contribution of arbuscular mycorrhizal fungi to soil carbon pools in tropical forest soils. Plant Soil 233,166-177. 

Schroeder, P. E., and J. K. Winjum. 1995. Assessing Brazil s carbon budget I. Biotic carbon pools. Forest Ecology and Management 75 77-86. 

Previous estimates of biotic carbon pool losses have used forest harvesting as the measure. Bolin [8] using data from Food and Agriculture Organization (FAO) and other sources calculated the net release of CO2 from the harvest of forests globally as 1 Gt of carbon per year. The estimate is indeed on the low side. Figure 1 shows the total dead organic carbon... 

Hu, S., Coleman, D. C., Carroll, C. R., Hendrix, P. F., Beare, M. H. 1997. Labile soil carbon pools in subtropical forest and agricultural ecosystems as influenced by management practices and vegetation types. Agric. Ecosyst. Environ. 65 69-78. 

Czimczik, C., Schmidt, M. W. I., Glaser B., Schulze E.-D. (2000). The inert carbon pool in boreal soils—char black carbon stocks in pristine Siberian Scots pine forest. Proceedings of the Boreal Forest Conference. Edmonton, May 2000. 

The nature of P mineralization in soils is a second factor mediating towards phosphorus availability not constraining tropical forest [CO2] responses. This is because, unlike nitrogen, phosphorus is mineralized independent of carbon in most soils. Thus, it has less potential to be locked up in the larger soil carbon pool that should occur as a result of increased plant productivity at higher [CO2]. 

Carbon pools and flux of global forest ecosystems. Science 263, 185-190. 

Figure 2. The carbon dynamics of a primary forest prior to and following deforestation and slash burning. Arrows represent the relative magnitude of C flux. In the primary forest (represented by the large box at the top of the figure), the C pool is in a dynamic equilibrium with inputs approximately equalling exports. With deforestation and fire, the balance is altered with exports far exceeding imports.

Soil contributes to a greater extent to total carbon storage than do above-ground vegetation in most forests (Johnson and Curtis 2001). The total amount of soil organic carbon (SOC) in the upper meter of soil is about 1500 x 1015 g C (Eswaran et al. 1993 Batjes 1996), and the global atmospheric pool of CO2 is about 750 x 1015 g C (Harden et al. 1992). The CO2 emission from soil into atmosphere is about 68.0-76.5 1015 g C per year, and this is more than 10 times the CO2 released from fossil fuel combustion (Raich and Potter 1995). Variations in SOC pools and SOM turnover rates, therefore, exert substantial impacts on the carbon cycles of terrestrial ecosystems in terms of carbon sequestration in soil and CO2 emission from soil. 

The use of wood in long-life products, such as buildings, ensures that this sequestered carbon is held in a materials pool for a longer time. If the use of renewables is encouraged, then more carbon is stored in this manner. Eventually, of course, such systems will establish equilibrium with the environment, as the materials flow into the pool equals the materials flow out into the environment. The use of wood in this way intervenes in a natural cycle, so that wood use and ultimate disposal replaces the natural cycle of wood decay in the forest (Figure 1.5). 

Figure 1.5 The use of wood products stores carbon in a materials pool, eventual disposal returning the sequestered carbon to the grand carbon cycle to provide for growth of new forest.

If the forest resource is properly managed, then timber can be harvested indefinitely. The use of timber in products represents a means by which atmospheric carbon can be stored in materials pools. 

---