Download Carbon Stored in Tropical

Carbon Stored in Tropical-Arid Areas
Research Institute
Hiroyuki Tanouchi (Department of Forest Vegetation)
Hajime Utsugi (CO2 Budget Team, Hokkaido Research Center)
Forestry and Forest Products Research Institute (
Background and Purpose
Arid land on earth, which is not being used by human beings, is arid or semi-arid land. It
accounts for more than 30% of the total land area. A long time ago, most of the original
vegetations were forests. Due to excessive cultivation and grazing, the vegetation were
transformed to a weak arid land （desertification phenomenon）. In such a land, aridification
of one layer of the soil advances, and salt accumulates on the surface soil. If a forest can be
raised in such deserted land, the forest may act as a carbon dioxide sink and carbon storage.
We carried out the following studies in the tropical and subtropical areas of inland
Australia:
(1) Select promising tree species for forestation
(2) Develop the afforestation technology according to soil types
(3) By this technology, estimate possible areas for forestation and carbon fixation
Achievements
(1) Search for trees with a high tolerance for stress and are actively growing
In arid lands, it was necessary to plant the tree that combined the properties of drought
resistance and salt tolerance. Therefore, a strong drought resistant species was used to
examine the tolerance level when irrigated with high salt concentration. In general, an
inverse relationship was found between growth and tolerance. But a kind of Eucalyptus,
Eucalyptus camaldurensis, was found to grow vigorously without dying even with high salt
concentration.
In addition, the concentrated salt accumulated at the topsoil (0-50cm) of the salt
accumulated soil. Because the salt concentration in deeper soil was suitable for tree growth,
trees with roots that can penetrate the topsoil and extend deeper appear promising. To avoid
salt, young trees, E. camaldurensis, were planted in slim pipes, and roots extended quickly by
more than 1m. Although the trees were planted in pipes, the amount of growth (carbon
fixation ability) did not drop back. Based on this study, it is understood that E. camaldurensis
has a high tolerance for stress brought on by salt and aridity and also has a high carbon
fixation ability.
(2) Forestation method in the two soil types
In the target area, two types of arid land are known to exist: hardpan surface soil
and salt accumulated soil. For hardpan surface soil, forestation could be performed after
the physical properties of the soil were improved by blasting the hardpan where roots
could not extend. In the area with the salt accumulated soil, 1m long young trees, which
were planted in pipes, were transplanted. 200 trees/ha were planted for each soil type.
(3) Possible forested area and carbon fixation
By introducing this technology, it was possible to fix 2.5 ton-C/ha each year in the arid
land and salt accumulated land. The target hardpan surface soil and salt accumulated soil
were 419.7 and 326.7 million ha, respectively, which occupy 18% of the global arid area. In
this area, natural vegetation only can fix 0.0-0.2 ton-C/ha, which almost equals to 0. The
additional potential amount of carbon absorption and carbon fixation is enormous by
forestation. The amount is equivalent to 26% (1.87Gton-C/ha/yr) of the carbon
(7.1Gton-C/ha/yr) emitted by humans on earth. In other words, if the unused and
unattended arid land is transformed into a carbon sink and storage, we can expect that
global warming will be reduced. The afforestation technologies are being developed, so we
hope that these technologies can be used in the arid land with different soil types besides the
tropical land.
This study is the result of the GHG-SSCP Project of the Ministry of the Environment and
the NEDO Project on the “Development of Technology for High-Efficiency Conversion of
Biomass and Other Energy”.
(1) Selection of trees
(2) Afforestation technology
(3) Carbon fixation ability
Carbon fixation ability based on arid land type, area, and forest
Arid land type
Area
Hardpan surface
Salt accumulated
soil
soil
Unit
419.7
326.7
Million ha
Amount
Natural forest
0.2
0.0
ton-C/ha/yr
of carbon
Carbon fixation
2.5
2.5
ton-C/ha/yr
fixation
forest
1.1
0.8
Gton-C/yr
Carbon fixation in
each forest (global)