18.104.22.168. Specific Issues on Deforestation
In deforestation, an extra component is needed. Not only are estimates of below-ground
biomass at the time of deforestation and any replacement vegetation needed,
so are estimates of the decomposition rates of remaining roots (see Chapter
2, Table 2-3). The Guidelines contain principles
for a general approach to the problem. The approach used for estimating soil
carbon is related to typical changes in organic matter content per area and
averaged over the time (20 years) during which the changes occur. The Reference
Manual (IPCC, 1997, Vol. 3, p. 5.23, footnote 15) focuses on the conversion
of tropical forests to pasture and cropland because this conversion accounts
for the largest share of emissions from forest clearing at the global level.
Under the Kyoto Protocol, all forest-clearing activities could be accounted
for. Improvements to the Guidelines, however, might include the following, although
they may be difficult to implement because of lack of data:
- In the IPCC default approach, the average loss from decay of litter per
year is taken as (linear) 10 percent, so the average rate of clearing over
the previous 10 years is used in the calculation of emissions (IPCC, 1997,
Vol. 3, p. 5.31). In the Protocol context, changes in stock resulting from
decay could be calculated by using a method analogous to that described above
for soil carbon.
- Calculation of the net change in aboveground biomass (biomass before clearing
minus biomass that regrows on the land-any new crop or pasture-plus any original
biomass that was not completely cleared) could be carried out for each relevant
forest type and, if appropriate, by region within a country. Again, these
records could be geo-referenced. To assess carbon stocks prior to deforestation,
data from that area before deforestation could be used. If the estimation
is made after deforestation occurs, control plots could be used.
- The fate and amount of below-ground biomass (coarse woody roots, etc.) (Kurz
et al., 1996; Cairns et al., 1997) could be taken into account
(IPCC, 1997, Vol. 3, pp. 5.12). Such below-ground biomass could be treated
as slash, perhaps with a longer decay time (IPCC, 1997, Vol. 3, pp. 5.53).
The Guidelines provide estimates of root-to-shoot mass ratios for such calculations.
- Given variations in burning practices among regions, users could provide
their own information on the fate of biomass that is cleared to reflect practices
in the country or region (IPCC, 1997, Vol. 3, pp. 5.30).