1.0    THE CARBON OFFSET VERIFICATION MODEL (COV)
2.0    Preventing Desertification in a drought affected area
3.0    Article 3
4.0    Article 4
5.0    Article 5
6.0    Article 6

INTRODUCTION:

Tropical tree plantations may be an important component of the global carbon cycle because they represent a carbon sink that can be manipulated by humans and they ca mitigate the effects of tropical deforestation, which is the main biotic source of atmospheric carbon (Houghton et al., 1983).

Most forest plantations in the tropics are planted with fast growing trees that culminate in volume and biomass production earlier than natural forests. These high biomass production forests have a high capacity to sequester atmospheric CO2 and hence assist in mitigating global warming. Sequestration of CO2 in plantations occurs in tree biomass (stems, branch, foliage and roots), forest floor and as storage in the soil. Young growing forests are one of the best means to removing CO2 (the gas partially responsible for the greenhouse effect) from the air. Thus planting forests help to reduce the amount of carbon dioxide in the air (by the action of sunlight on the green chlorophyll organic compound, CO2 is absorbed by trees through the small fissures in the leaves or needless, these gases are fixed as biomass).

Therefore the model is designed to assess the above ground-biomass for two even-aged, single species plantations with the same site class (Pinus patula and Eucalyptus saligna) as an attempt to quantify the carbon storage potential of the two species and their possible roles in carbon sequestration and atmospheric carbon dynamics.

MATERIALS AND METHODS

During the study samples were collected from Sao Hill Forest Project - Mafinga area, Iringa, in P.patula and E.saligna stands and trial plots planted adjacent to the project area between 1978 and 1997.Startified random sampling design was used. Sample plots were established in different aged stands of Pines and Eucalyptus. For Pinus patula, the ages include planted stands of 3,10,17 and 22 years. For Eucalyptus saligna, the ages include planted stands of 3,5,10 and 14 years. Stem wood biomass for each age class was calculated as the product of wood density and stem wood volume.

Thinning is done once for P. patula at 25 % removal (Age15) while for E. saligna no thinning at all according to the Forest Management Plan (FMP) (Malimbwi et al., 1998) report. The Stem Basic Density of 410kg/m3 and 504kg/m3 for P.patula and E. saligna respectively was used (Ringo at el., 1980 and Iddi at el., 1998)

Data Analysis:

The following were computed from vegetation data collected:

BD = BODw/BGv
CARBON MASS: = Vol. * BD stemwood * cf. (cf. = 0.45)
BIOMASS FUNCTIONS TO BE FITTED:
InX = a + b In DBH

Where; BD = Basic Density, BODw = Block Oven Dry weight, BGv = Block Green Volume,
Vol = Stem volume, Cf = is the mean fraction of carbon in dry biomass, DBH = Diameter at Breast Height, a, b, … = parameters to be estimated separately from the equation, In = natural logarithm

The Correction factor (mean fraction of carbon in dry biomass) for carbon mass conversion usually range from 0.4 –0.5 as recommended by different researchers. Hence for this case an average of 0.45 is used. The basic density formula has been used since it involves few assumptions and errors compared to the conversion from yield data.

ASSUMPTIONS INVOLVED:

· Carbon without Project case = 10% of carbon with Project case.
· Mortality will vary with tree age for both species.

RESULTS AND DISCUSSION

The amounts of carbon stored in living P. patula trees seem to increase with time. But carbon is lost during the course of rotation as a result of thinning and natural mortality, as shown in Figure 1. The figure show that Carbon will decrease at age 15 where thinning will occur.

Figure 1. Biomass development curve for Pinus patula

Cuevas et al did a study on above and below-ground organic matter storage and production in a tropical pine plantation and a paired broadleaf secondary forest. He found that the Pinus caribaea plantation had significantly more mass aboveground than the secondary forest (94.9 vs 35.6 t/ha for biomass and 10.5 vs 5.0 t/ha for litter. Marland (1998), also asserts that the carbon-sequestration potential of pine plantations ranges between 6 and 18 t/ha/yr, and of eucalyptus plantations between 10 and 24.

The carbon offset curve show that carbon increase with time as shown in Figure 2. Therefore for a Plantation of Pinus patula a total of 115.58 thousands tonsC/ha may be offset in a single rotation.

Figure 2. Carbon offset curve for Pinus patula.

For Eucalyptus saligna, carbon is increasing with time with the total amount of 69.90 thousands tonsC/ ha in a single rotation (15 years) being sequestered. In the course of rotation since no thinning will take place, small amount of carbon will decrease due to natural mortality. The maximum growth age for this case is 15 years but the trend show that carbon will continue to increase up to 25 years where little or no more carbon will be sequestered due to maturity of the trees. (See figure 3.)

Figure 3. Biomass development curve for Eucalyptus saligna.

The carbon offset curve show that carbon seems to increase with time thus, a total amount of 62.91 thousand tons C/ha may be offset in a single rotation as shown in figure 4

Figure 4. Carbon offset curve for Eucalyptus saligna.

The study shows that establishment of Pines and Eucalyptus plantations is seen as an efficient way to create carbon sinks due to rapid increment rate soon after establishment. Brown et al. (1985) predict that the sink function to become more significant in the future, attributed to the increase in the rate of establishment and the large areas of young plantations, which will sequester more carbon as they develop and grow into older age classes.



1. Brown, S., Lugo, A. E & Chapman, J. 1985. Biomass of tropical tree plantations and its implications for the global carbon budget. Canadian journal of forestry Research, 16: 390 – 394.

2. Cuevas, E., S. Brown and A.E. Lugo (1991) Above and below-ground organic matter storage and production in a tropical pine plantation and a paired broadleaf secondary forest. Plant and Soil 135, 257-268.

3. Iddi, S., Hamza, K.F.S. & Mbarouk, A.A. 1998. Basic density and fibre length of Eucalyptus maidenii (F. Muell) and E. saligna (S.M.) grown at Sao Hill, Tanzania. Faculty of Forestry & Nature Conservation, SUA, Record No. 70, 9pp.

4. Ringo, W.N and Klem, G.S. 1980. Basic Density and Heartwood Content in wood of Pinus patula from Sao Hill. Division of Forestry, FAFV, UDSM, Record No. 14, 17pp.

5. Houghton, R. A., H. E. Hobbie, J. M. Melillo, B. Moore, B. J. Peterson, G. R. Shaver and G. M. Woodwell, 1983. Changes in the carbon content of terrestrial biota and soils between 1860-1980: a net release of CO2 to the atmosphere. Ecol. Monograph, 235-262.

6. Marland, G.: 1988, The Prospect of Solving the CO2 Problem Through Global Reforestation, Carbon Dioxide Research Division, U.S. Department of Energy, Washington D.C., U.S.A.