Download Carbon sequestration and trading: opportunities for

Carbon sequestration and trading: opportunities for land management
Nigel D Turvey and Mark Burns
The issues of carbon sequestration are new and still under development. The subject requires close
scrutiny before commitment is made to investment in carbon sequestration with an expectation for
returns to be made from trading carbon credits. This paper will examine some of the issues surrounding
the use of forest plantations as carbon sinks, and the role of soil carbon in that process. The issues
include qualification of plantations as sinks, potential debits for harvesting wood, and the place of soil
carbon. Measurement and verification for certification of carbon credits is a high priority and requires
skilled sampling strategies to minimise verification costs at an acceptable level of precision of the
estimate.
Changing land use for the establishment of forest plantations can result in a decline in soil carbon early
in the rotation. This emission will most likely have to be offset against carbon sequestered in the trees
themselves. There is an opportunity to stimulate forest growth through the application of organic waste
high in nutrients such as sewage sludge (biosolids), and increase soil organic matter content along the
way. There may also be an opportunity to apply other organic waste to soil and thereby enhance soil
carbon content, and to use rehabilitation of mine sites as a vehicle for disposal of organic waste and
increasing carbon sinks.
Ownership of and the ability to trade carbon sequestered in trees and soil is not clear, so early investment
must be flexible and based on a no-regrets approach and the stand-alone (without carbon credits)
commercial viability of the investment project.
The Kyoto context
Carbon sequestration in the context of the Kyoto Protocol includes the definition of allowable sinks and
the manner in which functioning of the sinks will be allowed. Carbon sequestration is covered by
subsections of Article 3 of the Kyoto Protocol:
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Article 3.3 allows for afforestation, reforestation and deforestation since 1990.
Article 3.4 provides for a process for the inclusion of additional sink activities such as soils.
Article 3.7 provides for inclusion of emissions from land use change in the 1990 baseline emission.
The rules of operation of the Kyoto Protocol are still being debated and formed by bodies such as the
Intergovernmental Panel on Climate Change (IPCC). It is clear that carbon sequestered by forests
planted since 1990 will be allowed as carbon sinks; these forests are termed ‘Kyoto forests’. Trees
sequester carbon in their early juvenile stages where Net Primary Productivity (NPP) is high and
respiration is only a small proportion of Gross Primary Productivity (GPP). As forests senesce, NPP
declines and almost all energy captured by the plants is used in respiration or maintenance; this results in
negligible additional carbon sequestration. This means that Kyoto forests must be managed and
eventually harvested in order to maintain sequestration of atmospheric carbon. It appears that such
harvesting may be allowed without debit if the extent of the balance of carbon in planted, growing and
harvested forests are such as to keep a reasonably constant rate of carbon sequestration in the landscape.
Commitment period
A period between 2008 and 2012 has been set as the first commitment period by the UNFCCC.
Allowable sink activities such as carbon sequestration by forests planted since 1990 will be counted
towards meeting the emission targets of participating countries. The importance of this period is that a
lead time is required to get trees up to their maximum rate of carbon sequestration. Any early loss of soil
carbon due to changing land use and establishment of plantations will need to be offset by the forest sink
in time for measurement and verification of carbon in sinks for the commitment period.
In order for a healthy and rapidly growing forest with an increasing soil carbon sink to be counted
towards emission reduction, the forests need to be either in the ground now, or being planned to be
planted in the next two years, depending on the fertility, climate and production potential of the
intended site.
What might qualify?
Criteria for qualification of a forest as a carbon sink are yet to be finalised. However, some or all of the
following criteria may be considered when a forest is examined:
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Age: established since 1990.
Land clearing emissions: carbon lost in land clearing prior to establishment counted as a debit.
Species: indigenous species may be preferred for political and environmental reasons (eg Bush for
Greenhouse program of the AGO).
Additionally: that the planted forest is an initiative for carbon sequestration rather than just a part
of routine plantation establishment for timber or pulpwood production.
Longevity: that the life cycle of the products from the forest are long term, with long rotation
plantations for saw logs greatly preferred over short rotation pulpwood plantations.
Harvest: that the forest may or may not be harvested without debit. If harvested during the
commitment period, the debit in wood removed may be greater than the sink counted for the short
duration of the commitment period.
Soil carbon: may or may not be included in total carbon sequestered by the forest. The main
problem is accurate measurement and verification of changes in soil carbon over the life of the
forest.
What can plantations do?
The amount of carbon sequestered by a plantation depends upon the growth rate, age, wood density, and
the apportionment of biomass in parts of the tree with different carbon contents and longevity. A fast
growing and well managed plantation can sequester a total of above and below ground biomass in the
order of 9 t C/ha/yr. In addition, soil carbon can increase due to the death of roots and the
incorporation of litter from the forest floor.
During the establishment phase of a plantation, soil carbon can be lost due to disturbance of the soil and
subsequent mineralisation of organic carbon. Soil carbon may not return to pre-establishment
concentrations until half way through the life of the plantation.
The quantities of carbon in soil under plantation forests and native forests range between 100 and 400
t/ha. This carbon pool can be as great as, and in some cases greater than, the carbon held in the tree
crop. Commonly, more than 70% of the soil carbon in the profile is held in the surface 50 cm of soil
which makes it very vulnerable to loss due to disturbance. In unfertile sandy soils, much of the carbon is
held as organic matter, whereas in more fertile soils dominated by clay fractions, most carbon is bound in
the mineral fraction of the soil and is more resilient to loss.
The nett effect of gains in carbon by a plantation, both above and below ground and including soil
carbon, are dependent upon the:
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previous land use of the site,
fertility of the soil,
climate of the location,
amount of soil disturbance during plantation establishment,
species grown,
growth rate,
length of rotation.
Measurement and verification of carbon sequestered
The quantities of carbon in trees and soil needs to be measured for verification and certification of
carbon sequestered. This measurement will underpin the tradeable instrument such as the physical
carbon, a future, an option or any other derivative. This is especially important for establishing carbon
credits for the commitment periods, and for the informal period leading up to established trading.
The quantity of carbon in trees in a plantation is relatively easy to measure to a high level of precision
using standard forest plantation inventory techniques. However, soil carbon is spatially highly variable.
Soil carbon in unfertile sandy soils with low amounts of soil carbon tend to be spatially highly variable
when compared to soil carbon in more fertile soils, and hence require far more intensive sampling in
order to achieve the same level of precision of the estimate of carbon present. This means that it is easier
and hence cheaper to measure and verify soil carbon to the same precision in more fertile soils.
The costs of verification for certification of carbon sinks will be high for small players: this alone will be a
strong incentive for pooled verification and trading to minimise verification and transaction costs. This
is also an added incentive to maximise plantation growth rates in order to minimise the proportion of
transaction costs deducted from the carbon sink traded.
Assisted carbon sequestration
Application of biosolids
There is a potential opportunity to increase the quantity of soil carbon and to improve tree growth with
the addition of organic waste (dewatered biosolids) to the soil both prior to plantation establishment and
during the growth of the crop.
The benefits of adding organic waste to plantations can result in improved tree growth and carbon
sequestration, and improved soil carbon content. There are examples of plantations close to urban
centres which have benefited from additions of domestic dewatered biosolids. Trees are an obvious
choice of crop to receive sewage sludge because of their size and structure, and the lack of consumer
health issues.
The potential problems of adding biosolids to agricultural soils includes an increasing salt load on the
soil, accumulation of trace metals in the soil, and leaching of nitrate nitrogen and organic phosphorus
through the soil and into groundwater. Nitrate leaching can also result in removal of essential cations
from the soil. Other types of organic waste high in carbon can cause problems of nutrient availability
and trace metal mobility in soils. It is a conundrum that the least fertile soils which would benefit most
from the application of biosolids are often the most vulnerable to losses due to leaching because of low
soil buffering capacities.
Recycling Organics on Mine Sites
Compared to agricultural soils, mine sites offer positive and effective opportunities for the recycling of
organic waste material and the maximisation of carbon sequestration through its use in tree plantations.
Opportunities exist on both recontoured mine spoil and on large peripheral buffer zones which
surround many mines.
Tree establishment in coal mine spoil has increased dramatically on large open cut mines in both New
South Wales and Queensland since 1990. On many sites, trees have been planted (and more recently
sown) directly into overburden where growth has been surprisingly good as a result of minimal weed
competition. This lack of weed competition offers a unique opportunity to channel the benefits of
recycled organics into productive forests biomass without the depleting effects of weeds.
Biosolids have been trialled on both pasture and treed areas in the Hunter Valley coalfields. On treed
areas growth enhancement has been excellent although not always quantified. Broadacre application of
biosolids from Sydney is currently being undertaken on a number of sites at several of these mines. The
relatively high cost of topsoil stripping, stockpiling and respreading has opened up opportunities for the
importation of biosolids as a topsoil substitute from relatively long distances.
Coal mine overburdens are generally deficient in key nutrients (particularly N and P) and in non mineral
carbon (as opposed to carbonaceous material). Spoil material often has unfavourable chemical
characteristics such as high pH, low cation exchange capacity, and can be sodic or saline. These all can
be off-set by the addition of waste organic material such as biosolids. In improving the physical and
chemical soil environment the ability to improve tree growth and consequent carbon sequestration in
plantations is dramatically increased.
The process of tree growth converts the constituents of organic waste into longer term wood and carbon
products which are stored above and below ground within the tree. The carbon within these wood
products can then be included in sequestered carbon calculations for the mining company. Disturbed
mine sites offer considerable opportunity for the addition of organic waste to soil to increase soil carbon
and in turn to increase the potential carbon sink created through plantation establishment.
With selection and matching of sites, soils, waste type and crop type, there is an opportunity to use
organic wastes to increase site carbon for the benefit of both above and below ground carbon sinks.
Dr Nigel Turvey
Managing Director
Greenfield Resource Options (GRO Australia)