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Carbon Offset Verification of Forest Ecosystems

A project funded under the Earth Observation LINK Programme

Global Implications and Rationale of the Project
The United Nations Framework Convention on Climate Change (UNFCCC) and the Kyoto Protocol have identified the need to monitor, preserve and enhance the amount of carbon (carbon dioxide being the most important of the greenhouse gases) stored in the terrestrial biosphere as well as setting tight controls on total fossil fuel combustion. To this aim, the Kyoto Protocol requests countries to report the following statistics regarding their carbon reserves:

(1) reforestation, afforestation and deforestation activities;

(2) carbon stocks since 1990;

(3) land use change and forest inventory.

In response to these requirements which countries must meet under the protocol, a variety of international carbon offset programmes have been initiated, as well as, a consequential series of green house gas (GHG) regulatory bodies to monitor the activities of these burgeoning programmes. Since reliable third party verification of carbon offsets is required by many GHG regulatory bodies, SGS Ltd., the world’s largest international testing, inspection, and monitoring organisation, is offering a service of analysis and verification of carbon offset, or emission reduction, projects. This service was developed together with EcoSecurities Ltd., a firm specialising in policy and environmental technologies and finance. The carbon offset verification service consists of a formal analysis of project concept and design, a risk and uncertainty analysis, ongoing monitoring of project implementation and verification, and the quantification and certification of projected and achieved emission reductions. The service is available to both buyers and sellers of carbon offsets, and is also relevant to GHG regulatory bodies and other interested parties. SGS views the offering of this service as being a risk management tool for all parties in this emerging field.

Analysis of Carbon Storage in forest ecosystems
Although emissions can be reasonably quantified, large uncertainties exist in spatial estimates of biotic carbon pools in the landscape. Even when direct measurements of carbon pools can be made, they usually represent small samples in space and time. In order to quantify the carbon impacts of a forestry project, it is necessary to identify and analyse all relevant carbon stores (carbon pools) that may be affected by the project (Figure 2), and their rates of change (carbon flows) during the lifetime of the project.

Figure 2. Carbon flows likely to be relevant to a monitoring program for the forestry carbon offset project.

Most of the terrestrial carbon stores are bound within forest ecosystems, however, actual measurements of gross carbon budgets for forested areas at regional scales are very difficult to construct (Edwards et al., 1981).Changes in biomass density, resulting from tree growth, stand thinning, mortality and logging, are not easy to monitor because of the need for extensive and regular field surveys and allometry. Photosynthesis and foliage respiration estimates are also difficult to obtain due to the challenge of controlling the environmental conditions in field allometry. In addition, accurate carbon allocation to root biomass density measurements require destructive sampling methods. Even when direct measurements of the carbon pools and fluxes can be made, they usually represent small samples in space and time. For large-area estimates of carbon pools in forest ecosystems, potentially significant errors are introduced when trying to extrapolate point measurements to local and regional scales. The SGS methodology is currently based upon extensive and permanent sampling plots, field measurements and Forestry Commission and other published yield tables. However, the need for a regular surveillance program for verification of project development and certification of achieved offsets or emission reductions, requires periodic verification of carbon achievements through field inspections and allometric monitoring, which is very labour-intensive and time consuming.

The Way Forward With Remote Sensing Techniques
Remote sensing provides an effective non-destructive approach for the estimation of above-ground biomass from forest ecosystems with which to characterise models for carbon partitioning. Exploiting this potential, we have initiated a new research program which will couple techniques for estimating vegetation biophysical and biochemical variables from remote sensing data to the current carbon offset framework developed jointly by SGS Ltd and EcoSecurities Ltd. This project presents a new method for estimating above-ground biomass, and hence carbon stocks of conifer forests utilising remote sensing techniques and carbon partition modelling. Using multi-sensor and multi-temporal Synthetic Aperture Radar, this research will be developed for application at the regional to national scales with great potential for UNFCCC Joint Implementation Projects and compliance with Article 3.3 of the Kyoto Protocol. In recent years, the utility of Synthetic Aperture Radar (SAR) has provided a viable method for monitoring forests' resources at regional and national scales and for developing forest inventory systems. The microwave radiation used by SAR is of sufficiently long wavelengths not to be significantly affected by atmospheric attenuation, resulting in an operating capability which is independent of cloud cover. Importantly, microwave interactions are sensitive to the roughness and physical geometry of forests, an asset which, when combined with the ability of the radiation to penetrate forest canopies, results in the sensitivity of SAR backscatter to key biophysical variables, such as tree density and above ground biomass density (Beaudoin et al., 1994; Baker et al., 1994; Green et al., 1996, Green, 1998). The accuracy with which biophysical parameters can be retrieved from SAR measurements of forests depends considerably upon vegetation structure and ground conditions.

Study Area
Thetford Forest (Figure 3), a well understood temperate plantation, has been adopted as one of the study sites. Extensive fieldwork was carried out at Thetford in 1989 in order to quantify the above-ground biomass density in selected forest stands. A range of biomass densities were characterized at both sites with measurements of tree height, DBH and species. In addition, stand partition information on tree species and planting date were digitised from forest management maps in order to extrapolate the field measurements over a greater number of forest stands (Figure 3)(Luckman and Baker, 1997).

Figure 3. GIS thematic layer of Thetford forest stands

The biomass density was estimated by forming a regression between stand age and the measured biomass density and extrapolating to a large number of stands for which the planting date was provided by the UK Forestry Commission. SAR data used in this early study was L-band polarimetric AIRSAR data from Thetford acquired during the NASA/JPL 1991 MAC-Europe campaign (Figures 4 and 5).

Figure 4. AIRSAR L-band HV imagery of Thetford Forest acquired on 28/7/91 (pixel size 10m).

Figure 5. Thetford Forest ( © CEH, Monkswood)

The relationship between estimated above-ground biomass density and backscattering coefficient showed a reasonable dynamic range with saturation occurring at a stand biomass density of between 60-80 tonnes per hectare (Figure 6).

Figure 6. Relationships between AIRSAR backscattering coefficient and above-ground biomass density.

Further Research
The next stage of the research will be to evaluate the sensitivity of airborne SAR to change in biomass densities of various Thetford site tree species over time by comparing backscatter values derived from the earlier AIRSAR (1991) campaign with a E-SAR Campaign recently flown during 2000 (i.e. 9 years time separation). The E-SAR is an experimental multi-frequency SAR mounted on board a Dornier 228 aircraft and owned by the DLR. Frequencies covered comprise X, L and C with potential for P-band observations. The L-band is fully polarimetric. In addition to the historical ground survey data existing for the study area, a new and comprehensive survey of vegetation structure will be conducted during the E-SAR campaign. All imagery and field data will be referenced to the existing polygon coverage of forest compartments of the Thetford forest in an ARC/INFO GIS. Carbon partitioning estimates will be aggregated for each compartment. A major challenge of this project will be to improve our understanding of remote sensing for estimating the carbon pools and fluxes of forest ecosystems at local to regional scales. Comparison of the AIRSAR (1991) and ESAR (2000) data will test the hypothesis that it is possible to measure change in above-ground biomass densities of various Thetford site tree species over time, which will provide useful information in support of future satellite missions with multi-band, multi-polarization instruments.

Participating Researchers

University of Oxford:

Environmental Change Institute
Dr. Terry Dawson, Principle Investigator
Genevieve Patenaude

Department of Plant Sciences
Brian Briggs
Simon Pryor

Academic Partners:
Heiko Balzter , Center for Ecology and Hydrology, Monks Wood
Adrian Luckman, University of Wales, Swansea
Ronnie Mine, Center for Ecology and Hydrology, Edinburgh

Industrial Partners:
Peter Jones, Biffa Waste Services Ltd.
Pedro Moura Costa, EcoSecurities Ltd.
Gareth Phillips, SGS

Collaborators:
Louise Auckland, EcoSecurities
Pam Berry, Environmental Change Institute, Oxford University
David Gaveau , Center for Ecology and Hydrology, Monks Wood
Frances Gerard, Center for Ecology and Hydrology, Monks Wood
Andrew Hurst, Environmental Change Institute, Oxford University
Conor Linstead, Forum for the Future
Irma Lubrecht, SGS
Paul Saich, Department of Geography, University College London
Laine Skinner, University of Wales, Swansea

Links:

References:

J. R. Baker, P.L. Mitchell, R.A. Cordey, G.B. Groom, J.J. Settle, and M.R. Stileman, "Relationships between physical characteristics and polarimetric radar backscatter for Corsican pine stands in Thetford Forest, UK", International Journal of Remote Sensing, 15, p.p. 2827-2849, 1994.

A. Beaudoin, T. Le Toan, S. Goze, E. Nezry, A. Lopes, E. Mougin, C.C. Hsu, H.C. Han, J.A. Kong and R.T. Shin, "Retrieval of forest biomass from SAR data", International Journal of Remote Sensing, 15, p.p. 2777-2796, 1994.

N.T. Edwards, H.H. Shugart, S.B. McLaughlin, W.F. Harris and D.E. Reichle, "Carbon metabolism in terrestrial ecosystems", In D.E. Reichle (ed.), Dynamic Properties of Forest Ecosystems, Cambridge University Press, Cambridge, p.p. 499-536, 1981.

R.M. Green, N.S. Lucas, P.J. Curran and G.M. Foody, "Coupling remotely sensed data to an ecosystem simulation model – an example involving a coniferous plantation in upland Wales", Global Ecology and Biogeography Letters, 5, p.p. 192-205, 1996.

R.M. Green, "Relationships between polarmetric SAR backscatter and forest canopy and sub-canopy biophysical properties", International Journal of Remote Sensing, 19, p.p. 2395-2412, 1998.

A. Luckman and J.Baker, "A comparison of biomass retrieval using L-band SAR between a temperate coniferous plantation in the UK and semi-natural boreal forest in Sweden", In Guyot, G. and Phulpin, T. (eds.) Physical Measurements and Signatures in Remote Sensing, Balkema, Rotterdam, p.p. 463-470, 1997.