A crucial step in setting out to measure carbon in reforestation plots and old growth rainforest was to find an allometric equation that related physical measurements of Australian rainforest trees to their biomass content. A relevant equation, and one supported by the Australian Greenhouse Office, relating diameter of trees at breast height (DBH) (see Figure 5.3) to above-ground biomass is in Snowdon et al. (2000: Table 1.4). The equation is 1.8967+2.3698 (lnDBH).15
After stratification of reforestation plantations located in the area by age, the next task was to devise a procedure that would minimize sampling error for the stratified sites. To enable a sampling intensity to be ascertained that would deliver results with a 95 percent confidence level and with a confidence interval of 10 percent, that is the mean plus or minus 10 percent, plots were measured in a plantation that was in the middle of the age range (13 years since planting) of the plantations to be measured. Six plots of 10 meters x 10 meters were selected using random numbers on a map of the plantation that had been divided into 10 x 10 meter squares. All trees in the plots with a diameter at breast height (DBH) in excess of 5cm were measured.
Analysis of the trial plot data gave the result that a sample of five
Figure 5.3 Measuring the diameter at breast height (DBH) of trees in an old growth tropical rainforest in north Queensland
Figure 5.3 Measuring the diameter at breast height (DBH) of trees in an old growth tropical rainforest in north Queensland randomized plots would deliver the required level of accuracy. The procedure adopted is detailed in Appendix 5.A. In practice, the number of random plots per age stratum varied between three and six depending on the size of the plantation. A remnant of old growth rainforest was then added to the set of plantations for measurement and estimation of carbon content.
A second part of the research project was to forecast carbon sequestration rates by the plantations and old growth forests using the predictive CAMFor in the NCAS.
Inputted to the toolbox were the site coordinates, the type of forest (in this case mixed native species) and the treatment of the land pre- and post-planting, according to the typical methods adopted for reforestation in the area.16 The plantation is assumed to have established on land cleared before 1990, which makes it an eligible reforestation project under Kyoto Rules. The following carbon pools are forecast by CAMFor:
• Biomass of tree (stem, branches, bark, fine and coarse roots, leaves and twigs);
• Soil (organic matter and inert charcoal);
• Debris (coarse and fine litter, slash, below-ground dead material).
Source: Author's compilation using The National Carbon Accounting System (Australian Government 2007).
Figure 5.4 Tonnes of carbon forecast to be sequestered per hectare in a 2008 reforestation of mixed native rainforest species (the land was cleared prior to 1989) replacing grassland in north Queensland
Most of the carbon is in the biomass of the trees, which increases with growth of the forest. However, soil carbon and carbon in grass diminishes after the establishment of the plantation, as depicted in Figure 5.4.
To aid the decision-making process of plantation developers, CAMFor is capable of exploring the interactions between parameters and sensitivities to uncertainty of carbon estimates. Variables such as weather, site characteristics and the effect of timing of plantation harvesting can be entered (Brack and Richards, 2002).
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