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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: • • • 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: • • • • • • • 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: • • • • • • • 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)