UK forest carbon inventory

 

The development of a UK forest carbon inventory is being undertaken by Forest Research and is jointly funded by the Forestry Commission and Defra under contract CEPG 1/GA01054 'UK Emissions by Sources and Removals by Sinks due to Land Use, Land Use Change and Forestry Activities'. The research is part of a wider consortium with the project managed and led by CEH (Edinburgh). The current phase of the contract requires the development of the inventory methodology, and its demonstration in two pilot areas.

The need for a forest carbon inventory

The Kyoto Protocol (UNFCCC, 1998) contains a number of stipulations concerning the reporting by participating countries of net changes in greenhouse gas emissions by sources and removals by sinks resulting from direct human-induced land-use change and forestry activities. The Protocol places restrictions on precisely what sources and sinks should be counted as part of a national greenhouse gas balance (notably in terms of any forestry activities initiated before 1990). However there is an implicit requirement for participating countries to develop the capability to periodically monitor and report carbon stocks and stock changes associated with national forests. In particular, countries are required to provide data to establish the level of national forest carbon stocks in 1990 and to enable an estimate to be made of changes in carbon stocks in subsequent years. The Protocol further stipulates that all such monitoring must be undertaken in a transparent and verifiable manner.

Overview of the carbon monitoring network

Estimates of carbon stocks associated with British forests that are derived from the inventory include soil carbon stocks and carbon stocks in standing timber and associated woodland components. The estimates will primarily be based on data recorded in the National Inventory of Woodland and Trees (NIWT) and the Forest Enterprise sub-compartment data-base. Costs prohibit the establishment of a new monitoring network with the sole aim of monitoring national carbon stocks and stock changes in woodland. The proposed network is therefore based on the range of monitoring networks already available in the UK, with the majority operated by Forest Research or the Forestry Commission. 

Any cost-effective system for estimating forest carbon stocks and stock changes will at some level also rely on models. Since direct monitoring of the entire UK forest estate would be impractical, carbon accounting models or statistical estimates will be used for spatial and possibly temporal interpolation and/or extrapolation of carbon stock estimates. In contrast, verification is carried out through direct monitoring of a sample of sites. The suitability of existing monitoring networks and inventory systems for application within such a framework for monitoring and reporting carbon stocks and stock changes has been evaluated in terms of the following criteria:

• Comprehensive/representative
  The extent to which the network/inventory covers the UK forest estate, or constitutes a representative sample.
• Relevant
  Whether data collected in the network/inventory can be used to estimate or infer carbon stocks and stock changes.
• Accurate and/or precise
  The accuracy and precision that might be expected in carbon stock and stock change estimates derived from data currently collected.
• Adaptable and/or extendable
  The potential for adaptation and/or extension of the network/inventory to address carbon monitoring objectives, either to achieve greater comprehensiveness or to improve quality of data on which to base estimates of carbon stocks and stock changes.

The proposed monitoring system is based on four nested methodologies or ‘modules’, with a schematic diagram of the relationships between the individual modules given below. The first of these (Module A) is an inventory-based approach supported by a forest carbon accounting model that generates district-level and national-level estimates of carbon stocks in forest biomass, litter and soil. The other three modules (B-D) supply data and assessments for the verification of estimates generated by module A, or to support development, calibration and validation of the carbon accounting model.

Module A

This will consist of a GIS-based forest cover map (FCM) based on a unification of NIWT, SSWT, SCDB and LCM2000. The FCM will show the location and area of individual forest stands across the UK. Minimal data will be recorded against each individual stand and used as input to a carbon accounting model. The data will include:

• Soil type
• Species composition
• Productivity (yield class and/or stand height and density)
• Age class structure
• Management prescription.

These data will be collected by a number of techniques including ground survey and remote-sensing techniques or assigned on the basis of default assumptions made for districts or grid-squares of the UK. For some stands, it may be possible to transfer data directly from existing systems such as SCDB. The specification of the carbon accounting model is assumed to be based on a combination of upgraded and validated components of CARBINE, CFLOW and ROTHC models. It should be noted that this is not the only option for Module A. The detailed specification for the module and underlying model depend strongly on the requirements implicit in national and international agreements on approaches to forest carbon accounting. For example, if the accounting methodology of Kirschbaum et al. (2001) was to be accepted internationally and adopted in the UK, then the ‘carbon accounting model’ might consist of simple benchmark values of long term carbon stocks associated with particular combinations of site, (possibly) species and management regime. These benchmark estimates may be derived in turn from simulation results for different scenarios obtained using a unified and upgraded version of CARBINE, CFLOW and ROTHC, but this more complex model would not need to be integrated into this module of the forest carbon monitoring system. On the other hand, if ‘real time’ carbon accounting was to be adopted, then a dynamic carbon accounting model such as a combined CARBINE/CFLOW/ROTHC system would need to be integrated directly into Module A.

Module B

This module consists of an extensive forest monitoring network. The main function of the module is to provide broad-scale verification of national and district estimates of carbon stocks derived from carbon accounting models. It will be based on a representative grid, possibly an extension of the 16 x 16 km transnational grid with plot information collected at a relatively low level of precision. Because of the representative nature of the network, it has the potential for providing estimates of carbon stocks and stock changes totally independent of those generated in Module A.

Module C

This module consists of an intermediate forest monitoring network. The main function of the module is to provide data for improving and verifying representation in models of tree and stand biomass / carbon dynamics in response to alternative silvicultural prescriptions. There may be a secondary application for estimates obtained from this network in verifying more coarse-scale carbon stock estimates derived from models from an extensive network (see Module B). Module C is primarily based upon an adapted PSP network, but also with the incorporation of a number of EU L-I plots.

Module D

This module consists of an intensive forest monitoring network. The main function of the module is to provide data for validating estimates of carbon stocks derived from carbon accounting modules or more coarse-scale monitoring networks. Module D would be based on a combination of CFN and L-II plots. An additional role would in aiding the development of dynamic/process models of forest growth which could be used for future projections of carbon stock change taking predictions of environmental change into account.