Scottish Government

Annex 1: Illustrative LCA Spreadsheet Analysis of Biomass Energy System Relevant to Scotland

The results presented in this Annex are adapted from the earlier work of Elsayed et al. (2003) which presented energy and greenhouse gas balances for a range of biofuel options. Among other objectives these results were intended to:

• Propose a standard for the calculation and reporting of such balances, particularly in terms of accessibility, transparency and accounting for uncertainties.
• Serve as a set of consistent 'benchmark' results for the energy and greenhouse gas balances that could be regarded as representative of the typical performance of different biofuel systems in the UK based on current production systems and conversion technologies.

Two essential features of the commitment to accessibility and transparency involved the provision of:

• A complete biomass / process flow diagram for the biofuel system being analysed.
• Detailed reporting of calculations leading to ultimate results in spreadsheet form supported by explanatory notes.

The system considered here is a modified version of that presented in Appendix F of Elsayed et al. (2003, referred to as 'small-scale production of wood chips from woodland management (option B)', which was based on an updating of results presented in the earlier study of Matthews and Mortimer (2000).

In many respects, the original flow diagram and spreadsheets reported in Elsayed et al. (2003) might be viewed as representative of how forest-based wood chip production systems might operate in Scotland currently or in the future, in particular:

• Forestry system was assumed to comprise existing Scots pine stands with an average productivity of 8 m ³ ha ^-1 y ^-1 over a rotation.
• Management of Scots pine stands was assumed to involve either 'retention' of stands on a relatively long rotation of just under 80 years or some form of 'continuous cover' regime.
• Biomass processed into wood chips was assumed to be derived via a mixture of routes, i.e. proportions of small diameter stemwood and/or whole trees produced from early thinnings, branchwood potentially available when felling operations are carried out and offcut material generated in sawmills.
• Wood was assumed to be dried passively using low-technology storage techniques.
• The main timber transport activity was assumed to be a round trip distance of 90 ± 18 km. (For example this would be consistent with the distance from Castle Douglas to Carlisle or Huntly to Inverness.

The assumptions in Elsayed et al. (2003) could therefore represent an example of a Scottish biomass production system. The presentation of ranges on estimates also implies that potential variations in forestry practice or wood processing methods have been accounted for in the assumptions and related calculations. However, it is important to distinguish between variability in the detailed implementation of a particular system being characterised, and the (generally) greater variation that may be observed across a range of systems involving different site types, scales, processing steps and supply chains. The results presented in Elsayed et al. (2003) aim to account for the variety of the first and not the second kind. (This is a possible source of ambiguity in interpretation of such results if the distinction between the two types of variation is not clearly understood.)

In this Annex, the results of Appendix F in Elsayed et al. (2003) have been adapted to account for potential variation across possible forestry-based wood chip production systems in Scotland in two important areas:

• Systems modelled involve wood production from both existing and new-established forest areas, growing on both inorganic and organic soil types. (The results of Elsayed et al. implicitly assumed production from existing forests for which vegetation carbon dynamics could be regarded as making a negligible contribution to the CO₂ and GHG balances.)
• The range assumed for biomass transport distances was greatly increased to represent the shortest to the longest that might be observed within Scotland.

The biomass / process flow diagram presented here is unchanged from that assumed in Appendix F of Elsayed et al. (2003), however significant modifications have been made here compared to the spreadsheets in Appendix F.

In Table A4.1, the energy balance calculations for the main biomass transport activity are based on an assumed round-trip distance of 400 ± 350 km in contrast to the assumption in Elsayed et al. (2003) of 90 ± 18 km. A similar assumption is made in the corresponding calculations for the CO₂ and GHG balances (Tables A4.2 and A4.3 respectively). This greater range encompasses the shortest likely (a round-trip of 50 km) up to the distance between North and South Scotland or North England to mid-Scotland.

The spreadsheets for CO₂ and GHG balances in Tables A4.2 and A4.3 have also been changed to incorporate estimates representing the potential variability in carbon sinks and/or sources due to vegetation carbon dynamics that may occur depending on whether wood production is based on existing or newly-established forests, and whether forests are growing on soils with low or high carbon content. Details of the calculations and underlying data or assumptions are given in the notes to the spreadsheets. Revised spreadsheets for CH₄ and N ₂O balances have not been included in this Annex because, for this example system, the contributions to the GHG balance ultimately derived are small.

The original energy and GHG balances in Appendix F of Elsayed et al. (2003) could be expressed as 360 ± 38 MJ per tonne and 22 ± 2 kg CO₂-e per tonne respectively. These values can be compared with the estimates in Tables A4.1 and A4.3 of 803 ± 393 MJ per tonne and 36 ± 28 kg CO₂-e per tonne. The sensitivity of the results to the assumptions and potential variation in system details is evident - for example the new summary estimate for the energy balance is more than double that reported by Elsayed et al., while the range of uncertainty for the GHG balance (8 to 64 kg CO₂^-e per tonne) covers almost an order of magnitude. However, the critical observation is that, despite this variability, all of the estimates of energy inputs are small relative to the energy available from the biomass produced. This is emphasised if energy and GHG 'requirements' are calculated for a more complete supply chain as considered by Elsayed et al., namely heat (small scale) by the combustion of wood chip from woodland management (option B) as presented in Tables 19 and 23 of their report, where estimates of 0.094 ± 0.006 MJMJ^-1 and 0.007 kg CO₂-e MJ^-1 are reported. If corresponding calculations are made based on the results in Tables A4.1 and A4.3, estimates of 0.14 ± 0.04 MJMJ^-1 and 0.008 ± 0.003 kg CO₂-e MJ^-1 are obtained.

Although greater variability in biomass production systems has been accounted for, including what might be regarded as 'worst case scenarios' the end result on system performance as measured by energy and GHG requirements is marginal. The calculations and results in this Annex illustrate how variation in specific system details might be accounted for, in particular how transparent LCA results such as those presented by Elsayed et al. (2003) night be adapted to explore systems and scenarios relevant to Scottish conditions. Comparison of the results with those of Elsayed et al. also indicates some robustness in the estimates derived by this approach across a wide range of assumptions.

Figure A1.1: Biomass/process flow diagram for small-scale production of wood chips from woodland management

Table A1.1 Spreadsheet for Primary Energy Inputs to Small-Scale Production of Wood Chips from Woodland Management

Biofuel specifications

Density of wood chips (loose) = 168 kg/m ³
Net calorific value of wood chips = 17.8 MJ/kg

Abbreviations

ha.a = hectare year
t hwfn = tonne of harvested wood fuel with needles attached (50% moisture content, wet basis)
t rwc = tonne of raw wood chips (50% moisture content, wet basis)
t dwch = tonne of dried wood chunks (25% moisture content, wet basis)
t dwc = tonne of dried wood chips (25% moisture content, wet basis)

Notes

(a) Diesel fuel consumption of 19 MJ/ha.a used by forestry machinery for mounding and spreading herbicides (Ref. 1) and a gross energy requirement of 1.110 MJ/ MJ for diesel fuel in the UK for 1996 (Ref. 2).

(b) Lubricating oil consumption of 0 MJ/ha.a used by forestry machinery for mounding and spreading herbicides (Ref. 1) and a gross energy requirement of 1.110 MJ/ MJ for motor spirit in the UK for 1996 (Ref. 2).

(c) Application rate for a mixture of herbicides of 0.037 kg/ha.a (Ref. 1) and a total energy requirement for general pesticides, herbicides and fungicides of 274.1 MJ/kg (Ref. 3).

(d) Allocation of part of energy inputs to manufacture of machinery and allowance for consumption of spares of 2 MJ/ha.a (Ref. 1).

(e) Consumption of softwood in construction and maintenance of fences of 1.67 kg/ha.a (Ref. 1) with an assumed stand area of 5 ha, and a total energy requirement for softwood of 0.504 MJ/kg (Ref. 4).

(f) Consumption of steel wire in construction and maintenance of fences of 2.40 kg/ha.a (Ref. 1) with an assumed stand area of 5 ha, and a total energy requirement for steel wire of 137.2 MJ/kg (Ref. 4), and related consumption of mild steel of 0.044 kg/ha.a with a total energy requirement for mild steel of 31 MJ/kg (Ref. 5) and an assumed stand area of 5 ha.

(g) Consumption of wood preservative in construction and maintenance of fences of 0.55 kg/ha.a (Ref. 1) with an assumed stand area of 5 ha, and a total energy requirement for wood preservative of 100 MJ/kg (Ref. 5).

(h) Consumption of tree seedlings in stand establishment and regeneration of 18.3 seedlings/ha.a, based on standard planting densities (Ref. 6) and assuming that half of trees originate from natural regeneration with remainder originating from enrichment planting, and a total energy requirement of 1.319 MJ/seedling (Ref. 5).

(i) Reference system consisting of allowing land to revert to wilderness with no energy inputs.

(j) Land area requirement is 0.718 ha.a/t of dried wood chips available at point of use and allocation of 24.5% to harvested wood fuel. Total production of harvested wood over tree stand life cycle 0.34 odt/ha.a woody residues (for wood fuel), 0.755 odt/ha.a roundwood (for wood fuel) and 1.427 odt/ha.a sawlogs overbark (Refs. 7 to 10), assuming a relative value of sawlogs, roundwood and residues of 4:2:1 which gives an allocation to harvested wood fuel of (0.34 + 2 x 0.755) / (0.34 + 2 x 0.755 + 4 x 1.427) = 24.5%.

(k) Diesel fuel consumption of 33 MJ/ha.a used by forestry machinery for felling and extraction of whole trees as harvested wood fuel (from fuel harvest operations) to roadside, assuming 1.786 litre diesel fuel consumption per tonne of stem wood of trees felled and converted and 0.5 litre diesel fuel consumption per tonne of harvested wood fuel (with attached needles) extracted (Ref. 11) with 0.761 odt/ha.a harvested wood fuel being produced from fuel harvest operations of which 0.517 odt/ha.a is stem wood, and a gross energy requirement of 1.110 MJ/ MJ for diesel fuel in the UK for 1996 (Ref. 2).

(l) Lubricating oil consumption of 0 MJ/ha.a used by forestry machinery for combined tree felling and conversion to products, based on 0.002 litres lubricating oil consumed per litre diesel fuel/motor spirit consumed (Ref. 5), and a gross energy requirement of 1.110 MJ/ MJ for diesel fuel in the UK for 1996 (Ref. 2).

(m) Allocation of part of energy inputs to manufacture of machinery and allowance for consumption of spares of 0 MJ/ha.a (Refs. 1 and 5).

(n) Land area required 0.718 ha.a/t of dried wood chips available at point of use.

(o) Diesel fuel consumption of 12 MJ/ha.a used by forestry machinery for felling, conversion and extraction of roundwood (for harvested wood fuel) and sawlogs (for harvested wood fuel) (from log harvest operations) to roadside, assuming 1.786 litre diesel fuel consumption per tonne of stem wood of trees felled and converted and 0.5 litre diesel fuel consumption per tonne of harvested stem wood extracted (Ref. 11) with 0.137 (+2/-4) odt/ha.a harvested stem wood fuel being produced from a log harvest operation, and a gross energy requirement of 1.110 MJ/ MJ for diesel fuel in the UK for 1996 (Ref. 2).

(p) Lubricating oil consumption of 0 MJ/ha.a used by forestry machinery for combined tree felling and conversion to products, based on 0.002 litres lubricating oil consumed per litre diesel fuel/motor spirit consumed (Ref. 5), and a gross energy requirement of 1.110 MJ/ MJ for diesel fuel in the UK for 1996 (Ref. 2).

(q) Allocation of part of energy inputs to manufacture of machinery and allowance for consumption of spares of 0 MJ/ha.a (Refs. 1 and 5).

(r) Land area requirement is 0.718 ha.a/t of dried wood chips available at point of use and allocation of 41.5% to harvested roundwood (for wood fuel). Production at first log harvest consists of 0.0799 odt/ha.a harvested roundwood and 0.0563 odt/ha.a sawlogs overbark (Refs. 7 to 10), assuming a relative value of sawlogs and harvested wood fuel of 2:1 which gives an allocation to harvested wood fuel of 0.0799 / (2 x 0.0563 + 0.0799) = 41.5%.

(s) Land area requirement is 0.718 ha.a/t of dried wood chips available at point of use and allocation of 31.7% to harvested roundwood (for wood fuel). Production at second log harvest consists of 0.0661 odt/ha.a harvested roundwood and 0.0712 odt/ha.a sawlogs overbark (Refs. 7 to 10), assuming a relative value of sawlogs and harvested wood fuel of 2:1 which gives an allocation to harvested wood fuel of 0.0661 / (2 x 0.0712 + 0.0661) = 31.7%.

(t) Land area requirement is 0.718 ha.a/t of dried wood chips available at point of use and allocation of 21.6% to harvested roundwood (for wood fuel). Production at third log harvest consists of 0.0492 odt/ha.a harvested roundwood and 0.0891 odt/ha.a sawlogs overbark (Refs. 7 to 10), assuming a relative value of sawlogs and harvested wood fuel of 2:1 which gives an allocation to harvested wood fuel of 0.0492 / (2 x 0.0891 + 0.0492) = 21.6%.

(u) Land area requirement is 0.718 ha.a/t of dried wood chips available at point of use and allocation of 17.6% to harvested roundwood (for wood fuel). Production at fourth log harvest consists of 0.0415 odt/ha.a harvested roundwood and 0.0973 odt/ha.a sawlogs overbark (Refs. 7 to 10), assuming a relative value of sawlogs and harvested wood fuel of 2:1 which gives an allocation to harvested wood fuel of 0.0415 / (2 x 0.0973 + 0.0415) = 17.6%.

(v) Land area requirement is 0.718 ha.a/t of dried wood chips available at point of use and allocation of 13.2% to harvested roundwood (for wood fuel). Production at fifth log harvest consists of 0.0312 odt/ha.a harvested roundwood and 0.1024 odt/ha.a sawlogs overbark (Refs. 7 to 10), assuming a relative value of sawlogs and harvested wood fuel of 2:1 which gives an allocation to harvested wood fuel of 0.0312 / (2 x 0.1024 + 0.0312) = 13.2%.

(w) Diesel fuel consumption of 10 MJ/ha.a used by forestry machinery for felling, conversion and extraction of roundwood (for harvested wood fuel) and sawlogs (for harvested wood fuel) (from log harvest operations) to roadside, assuming 1.786 litre diesel fuel consumption per tonne of stem wood of trees felled and converted and 0.5 litre diesel fuel consumption per tonne of harvested stem wood extracted (Ref. 11) with 0.114 odt/ha.a harvested stem wood fuel being produced from a log harvest operation, and a gross energy requirement of 1.110 MJ/ MJ for diesel fuel in the UK for 1996 (Ref. 2).

(x) Lubricating oil consumption of 0 MJ/ha.a used by forestry machinery for combined tree felling and conversion to products, based on 0.002 litres lubricating oil consumed per litre diesel fuel/motor spirit consumed (Ref. 5), and a gross energy requirement of 1.110 MJ/ MJ for diesel fuel in the UK for 1996 (Ref. 2).

(y) Allocation of part of energy inputs to manufacture of machinery and allowance for consumption of spares of 0 MJ/ha.a Ref. 1 and 5).

(z) Land area requirement is 0.718 ha.a/t of dried wood chips available at point of use and allocation of 11.2% to harvested roundwood (for wood fuel). Production at sixth log harvest consists of 0.0230 odt/ha.a harvested roundwood and 0.0918 odt/ha.a sawlogs overbark (Refs. 7 to 10), assuming a relative value of sawlogs and harvested wood fuel of 2:1 which gives an allocation to harvested wood fuel of 0.0230 / (2 x 0.0918 + 0.0230) = 11.2%.

(aa) Diesel fuel consumption of 120 MJ/ha.a used by forestry machinery for felling and conversion of trees to sawlogs, roundwood (for wood fuel) and residues (also for wood fuel), assuming 1.786 litre diesel fuel consumption per tonne of stem wood of trees felled and converted (Ref. 11) with 1.723 odt/ha.a harvested stem wood fuel being produced from the main harvest operation, and a gross energy requirement of 1.110 MJ/ MJ for diesel fuel in the UK for 1996 (Ref. 2).

(bb) Lubricating oil consumption of 0 MJ/ha.a used by forestry machinery for combined tree felling and conversion to products, based on 0.002 litres lubricating oil consumed per litre diesel fuel/motor spirit consumed (Ref. 5), and a gross energy requirement of 1.110 MJ/ MJ for diesel fuel in the UK for 1996 (Ref. 2).

(cc) Allocation of part of energy inputs to manufacture of machinery and allowance for consumption of spares of 0 MJ/ha.a (Ref. 1 and 5).

(dd) Land area requirement is 0.718 ha.a/t of dried wood chips available at point of use and allocation of 12.0% to harvested roundwood (for wood fuel) and residues (for wood fuel). Production at main harvest consists of 0.3694 odt/ha.a retrieved residues (not including mass of attached needles), 0.2438 odt/ha.a harvested roundwood and 1.4792 odt/ha.a sawlogs overbark (Refs. 7 to 10), assuming a relative value of sawlogs, roundwood and residues of 4:2:1 this gives an allocation to harvested wood fuel of (2 x 0.2438 + 0.3694) / (4 x 1.4792 + 2 x 0.2438 + 0.3694) = 12.0%.

(ee) Diesel fuel consumption of 34 MJ/ha.a used by forestry machinery for extraction of sawlogs and roundwood (for wood fuel) to roadside, assuming 0.5 litre diesel fuel consumption per tonne of wood extracted (Ref. 11) with 1.723 odt/ha.a of sawlogs and roundwood fuel being produced from the main harvest operation, and a gross energy requirement of 1.110 MJ/ MJ for diesel fuel in the UK for 1996 (Ref. 2).

(ff) Lubricating oil consumption of 0 MJ/ha.a used by forestry machinery for combined tree felling and conversion to products, based on 0.002 litres lubricating oil consumed per litre diesel fuel/motor spirit consumed (Ref. 5), and a gross energy requirement of 1.110 MJ/ MJ for diesel fuel in the UK for 1996 (Ref. 2).

(gg) Allocation of part of energy inputs to manufacture of machinery and allowance for consumption of spares of 0 MJ/ha.a (Refs. 1 and 5).

(hh) Land area requirement is 0.718 ha.a/t of dried wood chips available at point of use and allocation of 7.6% to harvested roundwood (for wood fuel). Production at main harvest consists of 0.2438 odt/ha.a harvested roundwood and 1.4792 odt/ha.a sawlogs overbark (Refs. 7 to 10), assuming a relative value of sawlogs and harvested wood fuel of 2:1 which gives an allocation to harvested wood fuel of 0.2438 / (2 x 1.4792 + 0.2438) = 7.6%.

(ii) Diesel fuel consumption of 15 MJ/ha.a used by forestry machinery for extraction of residues (for wood fuel) to roadside, assuming 0.8 litre diesel fuel consumption per tonne of wood extracted (Ref. 11) with 0.4956 odt/ha.a of residues fuel being produced from the main harvest operation, and a gross energy requirement of 1.110 MJ/ MJ for diesel fuel in the UK for 1996 (Ref. 2).

(jj) Lubricating oil consumption of 0 MJ/ha.a used by forestry machinery for combined tree felling and conversion to products, based on 0.002 litres lubricating oil consumed per litre diesel fuel/motor spirit consumed (Ref. 5), and a gross energy requirement of 1.110 MJ/ MJ for diesel fuel in the UK for 1996 (Ref. 2).

(kk) Allocation of part of energy inputs to manufacture of machinery and allowance for consumption of spares of 0 MJ/ha.a (Ref. 1 and 5).

(ll) Assumed average round trip distance of 400 ± 350 km (Ref. 1) by bulk road carrier transport with a direct energy requirement of 0.8196 ± 0.0310 MJ/t-km, an indirect energy requirement of 0.2857± 0.0352 MJ/t-km and a total energy requirement of 1.1053 ± 0.0352 MJ/t-km (Ref. 4).

(mm) Harvested wood fuel (with needles) requirement of 1.241 t/t dried wood chips.

(nn) Assumed minimal facilities for storage and passive drying of wood chips with negligible energy inputs.

(oo) Diesel fuel consumption of 41 MJ/t dwf used by machinery in conversion of dried wood fuel to dried wood chips, based on assumed diesel fuel consumption of 0.9 l/t for chipping operations with high efficiency (Ref. 11), and a gross energy requirement of 1.110 MJ/ MJ for diesel fuel in the UK for 1996 (Ref. 2).

(pp) Lubricating oil consumption of 0 MJ/t dwf used by machinery in conversion of dried wood fuel to dried wood chips, based on 0.002 litres lubricating oil consumed by forestry machinery per litre diesel fuel consumed (Ref. 5), and a gross energy requirement of 1.110 MJ/ MJ for diesel fuel in the UK for 1996 (Ref. 2).

(qq) Allocation of part of energy inputs to manufacture of machinery and allowance for consumption of spares of 23 MJ/ha.a (Refs. 1 and 5).

(rr) Dried wood fuel requirement of 0.966 t/t dried wood chips.

(ss) Diesel fuel consumption of 35 MJ/t dwch used by machinery in conversion of dried wood chunks to dried wood chips, based on assumed diesel fuel consumption of 0.9 l/t for efficient chipping operations (Ref. 11), and a gross energy requirement of 1.110 MJ/ MJ for diesel fuel in the UK for 1996 (Ref. 2).

(tt) Lubricating oil consumption of 0 MJ/t dwf used by machinery in conversion of dried wood chunks to dried wood chips, based on 0.002 litres lubricating oil consumed by forestry machinery per litre diesel fuel consumed (Ref. 5), and a gross energy requirement of 1.110 MJ/ MJ for diesel fuel in the UK for 1996 (Ref. 2).

(uu) Allocation of part of energy inputs to manufacture of machinery and allowance for consumption of spares of 0 MJ/ha.a (Refs. 1 and 5).

(vv) Dried wood chunk requirement of 0.034 t/t dried wood chips.

(ww) Assumed average round trip distance of 90 ± 18 km (Ref. 1) by bulk road carrier transport with a direct energy requirement of 0.8196 ± 0.0310 MJ/t-km, an indirect energy requirement of 0.2857± 0.0352 MJ/t-km and a total energy requirement of 1.1053 ± 0.0352 MJ/t-km (Ref. 4).

References

1. "Estimation of Carbon Dioxide and Energy Budgets of Wood-fired Electricity Generation Systems" by R. Matthews and N. D. Mortimer, ETSU Report B/U1/00601/05/REP, Energy Technology Support Unit, Harwell, United Kingdom, 2000.

2. "Methodology for Environmental Profiles of Construction Material, Components and Buildings" Centre for Sustainable Construction at the Building Research Establishment Ltd., CRC Ltd., London, United Kingdom, 2000.

3. "Nachwachsende Energieträger - Grundlagen, Verfaben, Ökologische Bilanzierung" (Renewable Energy Sources, Basis, Processes and Ecological Balance) by M. Kaltschmitt and G. A. Reinhardt (eds), Vieweg, Braunschweig/Weisbaden, Germany, 1997.

4. "Carbon and Energy Modelling of Biomass Systems: Conversion Plant and Data Updates" by N. D. Mortimer and M. A. Elsayed, ETSU Report B/U1/00644/00/00REP, Energy Technology Support Unit, Harwell, United Kingdom, August 2001.

5. "Modelling of Carbon and Energy Budgets of Wood Fuel Coppice Systems" by R. Matthews, R. Robinson, S. Abbott and N. Fearis, ETSU B/W5/00337/REP, Energy Technology Support Unit, Harwell, United Kingdom, 1994.

6. "Forest Management Tables (Metric)" by G. Hamilton and J. Christie, Forestry Commission Booklet 34, HMSO, London, United Kingdom, 1971.

7. "Yield Models for Forest Management" by P. Edwards and J. Christie, Forestry Commission Booklet 48, HMSO, London, United Kingdom, 1981.

8. "The Strength Properties of Timbers" by G. Lavers, Forest Products Laboratory Bulletin 50, HMSO, London, United Kingdom, 1969, Second Edition.

9. "Final Report on the Construction of Functions for the Volume and Dry Mass of Principal Tree Components for a Range of Tree Species in Britain" by J. Taylor, Forest Research Mensuration Internal Report, United Kingdom, 2001.

10. "An Assortment Forecasting Service" by T. Rollinson and J. Gay, Forestry Commission Research Information Note 77/83/MENS, United Kingdom, 1983.

11. Private communications with M.Wihersaari, VTT-Energy, Espoo, Finland, September 2002.

Table A1.2 Spreadsheet for Carbon Dioxide Outputs from Small-Scale Production of Wood Chips from Woodland Management

Biofuel specifications

Density of wood chips (loose) = 168 kg/m ³
Net calorific value of wood chips = 17.8 MJ/kg

Abbreviations

ha.a = hectare year
t hwfn = tonne of harvested wood fuel with needles attached (50% moisture content, wet basis)
t rwc = tonne of raw wood chips (50% moisture content, wet basis)
t dwch = tonne of dried wood chunks (25% moisture content, wet basis)
t dwc = tonne of dried wood chips (25% moisture content, wet basis)

Notes

(a) Assuming conversion from previous land use of pasture, with average grass yield of 10-11 t ha ^-1 and a carbon content of 0.45 (Ref. 1). Woodland established is assumed to be Scots pine with yield class 8 m ³/ha.a managed on 76-year rotation plus on year for stand regeneration, with initial density of 2500 trees/ha. Growth pattern and production assumed to follow estimates presented in Ref 2 for selective thinning regime. Average standing biomass of woodland over rotation estimated using Forestry Commission yield models (Ref. 2) and BSORT model (Ref. 3). Carbon content of biomass assumed to be 0.5 tC/odt (Ref. 4). Equivalent CO₂ calculated using CO₂:C ratio 44/12. Periodic CO₂ changes annualised assuming time horizon of 100 years. Range on estimate calculated based on alternative assumption of either Scots pine with yield class 6 or 10 m ³/ha.a managed on 76-year rotation.

(b) Reported estimate and range based on median of independently derived low and high estimates. Low estimate: assuming conversion from previous land use of pasture (mineral soil). Estimated from 10% loss of soil carbon given in Ref. 5 and mean soil organic carbon reported for European mineral soils. High estimate: assuming conversion from previous land use of pasture (organic soil). Drainage and forest establishment assumed to lead to large CO₂ effluxes from soil in the short term which attenuate over time. Magnitude of CO₂ losses based on default values for temperate organic soils given in Ref 6. Periodic CO₂ changes annualised assuming time horizon of 100 years.

(c) Land area requirement is 0.718 ha.a/t of dried wood chips available at point of use and allocation of 24.5% to harvested wood fuel. Total production of harvested wood over tree stand life cycle 0.34 odt/ha.a woody residues (for wood fuel), 0.755 odt/ha.a roundwood (for wood fuel) and 1.427 odt/ha.a sawlogs overbark, assuming a relative value of sawlogs, roundwood and residues of 4:2:1 which gives an allocation to harvested wood fuel of (0.34 + 2 x 0.755) / (0.34 + 2 x 0.755 + 4 x 1.427) = 24.5%.

(d) Diesel fuel consumption of 19 MJ/ha.a used by forestry machinery for mounding and spreading herbicides (Ref. 7), and a direct carbon requirement 0.0686 kg CO₂/ MJ, an indirect carbon requirement of 0.0081 kg CO₂/ MJ and a total carbon requirement of 0.0767 kg CO₂/ MJ for diesel fuel in the UK for 1996 (Ref. 8).

(e) Lubricating oil consumption of 0 MJ/ha.a used by forestry machinery for mounding and spreading herbicides (Ref. 7), and a direct carbon requirement 0.0743 kg CO₂/ MJ, an indirect carbon requirement of 0.0081 kg CO₂/ MJ and a total carbon requirement of 0.0824 kg CO₂/ MJ for diesel fuel in the UK for 1996 (Ref. 8).

(f) Application rate for a mixture of herbicides of 0.037 kg/ha.a (Ref. 7) and a carbon requirement for general pesticides, herbicides and fungicides of 4.921 kg CO₂/kg (Ref. 9).

(g) Allocation of part of energy inputs to manufacture of machinery and allowance for consumption of spares equivalent to 0 kg CO₂/ha.a (refs. 7, 8 and 10).

(h) Consumption of softwood in construction and maintenance of fences of 1.67 kg/ha.a (Ref. 7) with an assumed stand area of 5 ha, and a total carbon requirement 0.041 kg CO₂/kg (Ref. 11).

(i) Consumption of steel wire in construction and maintenance of fences of 2.40 kg/ha.a (Ref. 7) with an assumed stand area of 5 ha, and a total carbon requirement for steel wire of 6.31 kg CO₂/kg (Ref. 11), and related consumption of mild steel of 0.050 kg/ha.a (Ref. 7) with an assumed stand area of 10 ha, and a total carbon requirement for mild steel of 1.24 kg CO₂/kg (Ref. 10).

(j) Consumption of wood preservative in construction and maintenance of fences of 0.55 kg/ha.a (Ref. 7) with an assumed stand area of 5 ha, and a total carbon requirement for wood preservative of 1.41 kg CO₂/kg (Ref. 10).

(k) Consumption of tree seedlings in stand establishment and regeneration of 18.3 seedlings/ha.a, based on standard planting densities (Ref. 12) and assuming that half of trees originate from natural regeneration with remainder originating from enrichment planting, and a total carbon requirement of 0.0567 kg CO₂/seedling (Ref. 10).

(l) Reference system consisting of allowing land to revert to wilderness with no energy inputs.

(m) Land area requirement is 0.718 ha.a/t of dried wood chips available at point of use and allocation of 24.5% to harvested wood fuel. Total production of harvested wood over tree stand life cycle 0.34 odt/ha.a woody residues (for wood fuel), 0.755 odt/ha.a roundwood (for wood fuel) and 1.427 odt/ha.a sawlogs overbark (Refs. 13 to 16), assuming a relative value of sawlogs, roundwood and residues of 4:2:1 which gives an allocation to harvested wood fuel of (0.34 + 2 x 0.755) / (0.34 + 2 x 0.755 + 4 x 1.427) = 24.5%.

(n) Diesel fuel consumption of 33 MJ/ha.a used by forestry machinery for felling and extraction of whole trees as harvested wood fuel (from fuel harvest operations) to roadside, assuming 1.786 litre diesel fuel consumption per tonne of stem wood of trees felled and converted and 0.5 litre diesel fuel consumption per tonne of harvested wood fuel (with attached needles) extracted (Ref. 17) with 0.761 odt/ha.a harvested wood fuel being produced from fuel harvest operations of which 0.517 odt/ha.a is stem wood, and a direct carbon requirement 0.0686 kg CO₂/ MJ, an indirect carbon requirement of 0.0081 kg CO₂/ MJ and a total carbon requirement of 0.0767 kg CO₂/ MJ for diesel fuel in the UK for 1996 (Ref. 8).

(o) Lubricating oil consumption of 0 MJ/ha.a used by forestry machinery for combined tree felling and conversion to products, based on 0.002 litres lubricating oil consumed by tree processor per litre diesel fuel consumed (Ref. 10), and a direct carbon requirement 0.0743 kg CO₂/ MJ, an indirect carbon requirement of 0.0081 kg CO₂/ MJ and a total carbon requirement of 0.0824 kg CO₂/ MJ for diesel fuel in the UK for 1996 (Ref. 8).

(p) Allocation of part of energy inputs to manufacture of machinery and allowance for consumption of spares equivalent to 0 kg CO₂/ha.a (Refs. 7 and 10).

(q) Land area required 0.718 ha.a/t of dried wood chips available at point of use.

(r) Diesel fuel consumption of 12 MJ/ha.a used by forestry machinery for felling, conversion and extraction of roundwood (for harvested wood fuel) and sawlogs (for harvested wood fuel) (from log harvest operations) to roadside, assuming 1.786 litre diesel fuel consumption per tonne of stem wood of trees felled and converted and 0.5 litre diesel fuel consumption per tonne of harvested stem wood extracted (Ref. 17) with 0.137 (+2/-4) odt/ha.a harvested stem wood fuel being produced from a log harvest operation, and a direct carbon requirement 0.0686 kg CO₂/ MJ, an indirect carbon requirement of 0.0081 kg CO₂/ MJ and a total carbon requirement of 0.0767 kg CO₂/ MJ for diesel fuel in the UK for 1996 (Ref. 8).

(s) Lubricating oil consumption of 0 MJ/ha.a used by forestry machinery for combined tree felling and conversion to products, based on 0.002 litres lubricating oil consumed by forestry machinery per litre diesel fuel consumed (Ref. 4), and a direct carbon requirement 0.0743 kg CO₂/ MJ, an indirect carbon requirement of 0.0081 kg CO₂/ MJ and a total carbon requirement of 0.0824 kg CO₂/ MJ for diesel fuel in the UK for 1996 (Ref. 8).

(t) Allocation of part of energy inputs to manufacture of machinery and allowance for consumption of spares equivalent to 0 kg CO₂/ha.a (Refs. 7 and 10).

(u) Land area requirement is 0.718 ha.a/t of dried wood chips available at point of use and allocation of 41.5% to harvested roundwood (for wood fuel). Production at first log harvest consists of 0.0799 odt/ha.a harvested roundwood and 0.0563 odt/ha.a sawlogs overbark (Refs. 13 to 16), assuming a relative value of sawlogs and harvested wood fuel of 2:1 which gives an allocation to harvested wood fuel of 0.0799 / (2 x 0.0563 + 0.0799) = 41.5%.

(v) Land area requirement is 0.718 ha.a/t of dried wood chips available at point of use and allocation of 31.7% to harvested roundwood (for wood fuel). Production at second log harvest consists of 0.0661 odt/ha.a harvested roundwood and 0.0712 odt/ha.a sawlogs overbark (Refs. 13 to 16), assuming a relative value of sawlogs and harvested wood fuel of 2:1 which gives an allocation to harvested wood fuel of 0.0661 / (2 x 0.0712 + 0.0661) = 31.7%.

(w) Land area requirement is 0.718 ha.a/t of dried wood chips available at point of use and allocation of 21.6% to harvested roundwood (for wood fuel). Production at third log harvest consists of 0.0492 odt/ha.a harvested roundwood and 0.0891 odt/ha.a sawlogs overbark (Refs. 13 to 16), assuming a relative value of sawlogs and harvested wood fuel of 2:1 which gives an allocation to harvested wood fuel of 0.0492 / (2 x 0.0891 + 0.0492) = 21.6%.

(x) Land area requirement is 0.718 ha.a/t of dried wood chips available at point of use and allocation of 17.6% to harvested roundwood (for wood fuel). Production at fourth log harvest consists of 0.0415 odt/ha.a harvested roundwood and 0.0973 odt/ha.a sawlogs overbark (Refs. 13 to 16), assuming a relative value of sawlogs and harvested wood fuel of 2:1 which gives an allocation to harvested wood fuel of 0.0415 / (2 x 0.0973 + 0.0415) = 17.6%.

(y) Land area requirement is 0.718 ha.a/t of dried wood chips available at point of use and allocation of 13.2% to harvested roundwood (for wood fuel). Production at fifth log harvest consists of 0.0312 odt/ha.a harvested roundwood and 0.1024 odt/ha.a sawlogs overbark (Refs. 13 to 16), assuming a relative value of sawlogs and harvested wood fuel of 2:1 which gives an allocation to harvested wood fuel of 0.0312 / (2 x 0.1024 + 0.0312) = 13.2%.

(z) Diesel fuel consumption of 10 MJ/ha.a used by forestry machinery for felling, conversion and extraction of roundwood (for harvested wood fuel) and sawlogs (for harvested wood fuel) (from log harvest operations) to roadside, assuming 1.786 litre diesel fuel consumption per tonne of stem wood of trees felled and converted and 0.5 litre diesel fuel consumption per tonne of harvested stem wood extracted (Ref. 17) with 0.114 odt/ha.a harvested stem wood fuel being produced from a log harvest operation, and a direct carbon requirement 0.0686 kg CO₂/ MJ, an indirect carbon requirement of 0.0081 kg CO₂/ MJ and a total carbon requirement of 0.0767 kg CO₂/ MJ for diesel fuel in the UK for 1996 (Ref. 8).

(aa) Lubricating oil consumption of 0 MJ/ha.a used by forestry machinery for combined tree felling and conversion to products, based on 0.002 litres lubricating oil consumed by forestry machinery per litre diesel fuel consumed (Ref. 10), and a direct carbon requirement 0.0743 kg CO₂/ MJ, an indirect carbon requirement of 0.0081 kg CO₂/ MJ and a total carbon requirement of 0.0824 kg CO₂/ MJ for diesel fuel in the UK for 1996 (based on Ref. 8).

(bb) Allocation of part of energy inputs to manufacture of machinery and allowance for consumption of spares equivalent to 0 kg CO₂/ha.a (Refs. 7 and 10).

(cc) Land area requirement is 0.718 ha.a/t of dried wood chips available at point of use and allocation of 11.2% to harvested roundwood (for wood fuel). Production at sixth log harvest consists of 0.0230 odt/ha.a harvested roundwood and 0.0918 odt/ha.a sawlogs overbark (Refs. 13 to 16), assuming a relative value of sawlogs and harvested wood fuel of 2:1 which gives an allocation to harvested wood fuel of 0.0230 / (2 x 0.0918 + 0.0230) = 11.2%.

(dd) Diesel fuel consumption of 120 MJ/ha.a used by forestry machinery for felling and conversion of trees to sawlogs, roundwood (for wood fuel) and residues (also for wood fuel), assuming 1.786 litre diesel fuel consumption per tonne of stem wood of trees felled and converted (Ref. 17) with 1.723 odt/ha.a harvested stem wood fuel being produced from the main harvest operation, and a direct carbon requirement 0.0686 kg CO₂/ MJ, an indirect carbon requirement of 0.0081 kg CO₂/ MJ and a total carbon requirement of 0.0767 kg CO₂/ MJ for diesel fuel in the UK for 1996 (Ref. 8).

(ee) Lubricating oil consumption of 0 MJ/ha.a used by forestry machinery for combined tree felling and conversion to products, based on 0.002 litres lubricating oil consumed by tree processor per litre diesel fuel consumed (Ref. 10), and a direct carbon requirement 0.0743 kg CO₂/ MJ, an indirect carbon requirement of 0.0081 kg CO₂/ MJ and a total carbon requirement of 0.0824 kg CO₂/ MJ for diesel fuel in the UK for 1996 (Ref. 8).

(ff) Allocation of part of energy inputs to manufacture of machinery and allowance for consumption of spares equivalent to 0 kg CO₂/ha.a (Ref. 7 and 10).

(gg) Land area requirement is 0.718 ha.a/t of dried wood chips available at point of use and allocation of 12.0% to harvested roundwood (for wood fuel) and residues (for wood fuel). Production at main harvest consists of 0.3694 odt/ha.a retrieved residues (not including mass of attached needles), 0.2438 odt/ha.a harvested roundwood and 1.4792 odt/ha.a sawlogs overbark (Refs. 13 to 16), assuming a relative value of sawlogs, roundwood and residues of 4:2:1 this gives an allocation to harvested wood fuel of (2 x 0.2438 + 0.3694) / (4 x 1.4792 + 2 x 0.2438 + 0.3694) = 12.0%.

(hh) Diesel fuel consumption of 34 MJ/ha.a used by forestry machinery for extraction of sawlogs and roundwood (for wood fuel) to roadside, assuming 0.5 litre diesel fuel consumption per tonne of wood extracted (Ref. 17) with 1.723 odt/ha.a of sawlogs and roundwood fuel being produced from the main harvest operation, and a direct carbon requirement 0.0686 kg CO₂/ MJ, an indirect carbon requirement of 0.0081 kg CO₂/ MJ and a total carbon requirement of 0.0767 kg CO₂/ MJ for diesel fuel in the UK for 1996 (Ref. 8).

(ii) Lubricating oil consumption of 0 MJ/ha.a used by forestry machinery for combined tree felling and conversion to products, based on 0.002 litres lubricating oil consumed by forestry machinery per litre diesel fuel consumed (Ref. 10), and direct carbon requirement 0.0743 kg CO₂/ MJ, an indirect carbon requirement of 0.0081 kg CO₂/ MJ and a total carbon requirement of 0.0824 kg CO₂/ MJ for diesel fuel in the UK for 1996 (based on Ref. 8).

(jj) Allocation of part of energy inputs to manufacture of machinery and allowance for consumption of spares equivalent to 0 kg CO₂/ha.a (Refs. 7 and 10).

(kk) Land area requirement is 0.718 ha.a/t of dried wood chips available at point of use and allocation of 7.6% to harvested roundwood (for wood fuel). Production at main harvest consists of 0.2438 odt/ha.a harvested roundwood and 1.4792 odt/ha.a sawlogs overbark (Refs. 13 to 16), assuming a relative value of sawlogs and harvested wood fuel of 2:1 which gives an allocation to harvested wood fuel of 0.2438 / (2 x 1.4792 + 0.2438) = 7.6%.

(ll) Diesel fuel consumption of 15 MJ/ha.a used by forestry machinery for extraction of residues (for wood fuel) to roadside, assuming 0.8 litre diesel fuel consumption per tonne of wood extracted (Ref. 17) with 0.4956 odt/ha.a of residues fuel being produced from the main harvest operation, and a direct carbon requirement 0.0686 kg CO₂/ MJ, an indirect carbon requirement of 0.0081 kg CO₂/ MJ and a total carbon requirement of 0.0767 kg CO₂/ MJ for diesel fuel in the UK for 1996 (Ref. 8).

(mm) Lubricating oil consumption of 0 MJ/ha.a used by forestry machinery for combined tree felling and conversion to products, based on 0.002 litres lubricating oil consumed by forestry machinery per litre diesel fuel consumed (Ref. 10), and a direct carbon requirement 0.0743 kg CO₂/ MJ, an indirect carbon requirement of 0.0081 kg CO₂/ MJ and a total carbon requirement of 0.0824 kg CO₂/ MJ for diesel fuel in the UK for 1996 (Ref. 8).

(nn) Allocation of part of energy inputs to manufacture of machinery and allowance for consumption of spares equivalent to 0 kg CO₂/ha.a (Refs. 7 and 10).

(oo) Assumed average round trip distance of 400 ±350 km by bulk road carrier transport with a direct carbon requirement of 0.0562 ± 0.0021 kg CO₂/t-km, an indirect carbon requirement of 0.0161 ± 0.0017 kg CO₂/t-km and a total carbon requirement of 0.0723 ± 0.0027 kg CO₂/t-km (Ref. 11).

(pp) Harvested wood fuel (with needles) requirement of 1.241 t/t dried wood chips.

(qq) Assumed minimal facilities for storage and passive drying of wood chips with negligible energy inputs.

(rr) Diesel fuel consumption of 41 MJ/t dwf used by machinery in conversion of dried wood fuel to dried wood chips, based on assumed diesel fuel consumption of 0.9 l/t for chipping operations with high efficiency (Ref. 17), and a direct carbon requirement 0.0686 kg CO₂/ MJ, an indirect carbon requirement of 0.0081 kg CO₂/ MJ and a total carbon requirement of 0.0767 kg CO₂/ MJ for diesel fuel in the UK for 1996 (Ref. 8).

(ss) Lubricating oil consumption of 0 MJ/t dwf used by machinery in conversion of dried wood fuel to dried wood chips, based on 0.002 litres lubricating oil consumed by forestry machinery per litre diesel fuel consumed (Ref. 10), and a direct carbon requirement 0.0743 kg CO₂/ MJ, an indirect carbon requirement of 0.0081 kg CO₂/ MJ and a total carbon requirement of 0.0824 kg CO₂/ MJ for diesel fuel in the UK for 1996 (Ref. 8).

(tt) Allocation of part of energy inputs to manufacture of machinery and allowance for consumption of spares equivalent to 1 kg CO₂/ha.a (Refs. 7 and 10).

(uu) Dried wood fuel requirement of 0.966 t/t dried wood chips.

(vv) Diesel fuel consumption of 35 MJ/t dwch used by machinery in conversion of dried wood chunks to dried wood chips, based on assumed diesel fuel consumption of 0.9 l/t for efficient chipping operations (Ref. 17) and a direct carbon requirement 0.0686 kg CO₂/ MJ, an indirect carbon requirement of 0.0081 kg CO₂/ MJ and a total carbon requirement of 0.0767 kg CO₂/ MJ for diesel fuel in the UK for 1996 (Ref. 8).

(ww) Lubricating oil consumption of 0 MJ/t dwf used by machinery in conversion of dried wood chunks to dried wood chips, based on 0.002 litres lubricating oil consumed by forestry machinery per litre diesel fuel consumed (Ref. 10), and a direct carbon requirement 0.0743 kg CO₂/ MJ, an indirect carbon requirement of 0.0081 kg CO₂/ MJ and a total carbon requirement of 0.0824 kg CO₂/ MJ for diesel fuel in the UK for 1996 (Ref. 8).

(xx) Allocation of part of energy inputs to manufacture of machinery and allowance for consumption of spares equivalent to 0 kg CO₂/ha.a (Refs. 7 and 10).

(yy) Dried wood chunk requirement of 0.034 t/t dried wood chips.

(zz) Assumed average round trip distance of 90 ± 18 km (Ref. 7) by bulk road carrier transport with a direct carbon requirement of 0.0562 ± 0.0021 kg CO₂/t-km, an indirect carbon requirement of 0.0161 ± 0.0017 kg CO₂/t-km and a total carbon requirement of 0.0723 ± 0.0027 kg CO₂/t-km (Ref. 11).

References

1. "Fertiliser recommendations for agricultural and horticultural crops (RB209)", Seventh Edition, DEFRA: London, 2000.

2. "Yield Models for Forest Management" by P. Edwards and J. Christie, Forestry Commission Booklet 48, HMSO, London, United Kingdom, 1981.

3. " BSORT: a model of tree and stand biomass development and production in Great Britain ", by R. Matthews and R. Duckworth In Imbabi, M. and Mitchell, C. (eds.), Proceedings of World Renewable Energy Congress ( WREC 2005), Elsevier: Oxford, 2005, 404-409.

4. "The Carbon Content of Trees" by G. Matthews, Forestry Commission Technical Paper 4, Forestry Commission: Edinburgh, 1993.

5. "Soil carbon stocks and land use change: a meta analysis" by L. Guo and R. Gifford, Global Change Biology, vol. 8, pp 345-360, 2002.

6. "Revised 1996 Guidelines for National Greenhouse Gas Inventories Workbook" by Intergovernmental Panel on Climate Change ( IPCC),Cambridge University Press: Cambridge, 1997.

7. "Estimation of Carbon Dioxide and Energy Budgets of Wood-fired Electricity Generation Systems" by R. Matthews and N. D. Mortimer, ETSU Report B/U1/00601/05/REP, Energy Technology Support Unit, Harwell, United Kingdom, 2000.

8. "Methodology for Environmental Profiles of Construction Material, Components and Buildings" Centre for Sustainable Construction at the Building Research Establishment Ltd., CRC Ltd., London, United Kingdom, 2000.

9. "Nachwachsende Energieträger - Grundlagen, Verfaben, Ökologische Bilanzierung" (Renewable Energy Sources, Basis, Processes and Ecological Balance) by M. Kaltschmitt and G. A. Reinhardt (eds), Vieweg, Braunschweig/Weisbaden, Germany, 1997.

10. "Modelling of Carbon and Energy Budgets of Wood Fuel Coppice Systems" by R. Matthews, R. Robinson, S. Abbott and N. Fearis, ETSU B/W5/00337/REP, Energy Technology Support Unit, Harwell, United Kingdom, 1994.

11. "Carbon and Energy Modelling of Biomass Systems: Conversion Plant and Data Updates" by N. D. Mortimer and M. A. Elsayed, ETSU Report B/U1/00644/00/00REP, Energy Technology Support Unit, Harwell, United Kingdom, August 2001.

12. "Forest Management Tables (Metric)" by G. Hamilton and J. Christie, Forestry Commission Booklet 34, HMSO, London, United Kingdom, 1971.

13. "Yield Models for Forest Management" by P. Edwards and J. Christie, Forestry Commission Booklet 48, HMSO, London, United Kingdom, 1981.

14. "The Strength Properties of Timbers" by G. Lavers, Building Research Establishment Report CI/SfB 1976, HMSO, London, United Kingdom, 1983, Third Edition.

15. "Final Report on the Construction of Functions for the Volume and Dry Mass of Principal Tree Components for a Range of Tree Species in Britain" by J. Taylor, Forest Research Mensuration Internal Report, United Kingdom, 2001.

16. "An Assortment Forecasting Service" by T. Rollinson and J. Gay, Forestry Commission Research Information Note 77/83/MENS, United Kingdom, 1983.

17. Private communications with M.Wihersaari, VTT-Energy, Espoo, Finland, September 2002.

Table A1.3 Spreadsheet for Greenhouse Gas Outputs from Small-Scale Production of Wood Chips from Woodland Management

Biofuel specifications

Density of wood chips (loose) = 168 kg/m ³
Net calorific value of wood chips = 17.8 MJ/kg

Abbreviations

ha.a = hectare year
t hwfn = tonne of harvested wood fuel with needles attached (50% moisture content, wet basis)
t rwc = tonne of raw wood chips (50% moisture content, wet basis)
t dwch = tonne of dried wood chunks (25% moisture content, wet basis)
t dwc = tonne of dried wood chips (25% moisture content, wet basis)

Notes

(a) Summation of results from previous spreadsheet (Table A4.2) and corresponding spreadsheets for CH₄ and N ₂O balances (not shown) with conversion using a global warming potential for methane of 24.5 kg eq CO₂/kg CH₄ and a global warming potential for nitrous oxide of 320 kg CO₂/kg N ₂O.

(b) Land area requirement is 0.718 ha.a/t of dried wood chips available at point of use and allocation of 24.5% to harvested wood fuel. Total production of harvested wood over tree stand life cycle 0.34 odt/ha.a woody residues (for wood fuel), 0.755 odt/ha.a roundwood (for wood fuel) and 1.427 odt/ha.a sawlogs overbark, assuming a relative value of sawlogs, roundwood and residues of 4:2:1 which gives an allocation to harvested wood fuel of (0.34 + 2 x 0.755) / (0.34 + 2 x 0.755 + 4 * 1.427) = 24.5%.

(c) Land area required 0.718 ha.a/t of dried wood chips available at point of use.

(d) Land area requirement is 0.718 ha.a/t of dried wood chips available at point of use and allocation of 41.5% to harvested roundwood (for wood fuel). Production at first log harvest consists of 0.0799 odt/ha.a harvested roundwood and 0.0563 odt/ha.a sawlogs overbark, assuming a relative value of sawlogs and harvested wood fuel of 2:1 which gives an allocation to harvested wood fuel of 0.0799 / (2 x 0.0563 + 0.0799) = 41.5%.

(e) Land area requirement is 0.718 ha.a/t of dried wood chips available at point of use and allocation of 31.7% to harvested roundwood (for wood fuel). Production at second log harvest consists of 0.0661 odt/ha.a harvested roundwood and 0.0712 odt/ha.a sawlogs overbark, assuming a relative value of sawlogs and harvested wood fuel of 2:1 which gives an allocation to harvested wood fuel of 0.0661 / (2 x 0.0712 + 0.0661) = 31.7%.

(f) Land area requirement is 0.718 ha.a/t of dried wood chips available at point of use and allocation of 21.6% to harvested roundwood (for wood fuel). Production at third log harvest consists of 0.0492 odt/ha.a harvested roundwood and 0.0891 odt/ha.a sawlogs overbark, assuming a relative value of sawlogs and harvested wood fuel of 2:1 which gives an allocation to harvested wood fuel of 0.0492 / (2 x 0.0891 + 0.0492) = 21.6%.

(g) Land area requirement is 0.718 ha.a/t of dried wood chips available at point of use and allocation of 17.6% to harvested roundwood (for wood fuel). Production at fourth log harvest consists of 0.0415 odt/ha.a harvested roundwood and 0.0973 odt/ha.a sawlogs overbark, assuming a relative value of sawlogs and harvested wood fuel of 2:1 which gives an allocation to harvested wood fuel of 0.0415 / (2 x 0.0973 + 0.0415) = 17.6%.

(h) Land area requirement is 0.718 ha.a/t of dried wood chips available at point of use and allocation of 13.2% to harvested roundwood (for wood fuel). Production at fifth log harvest consists of 0.0312 odt/ha.a harvested roundwood and 0.1024 odt/ha.a sawlogs overbark, assuming a relative value of sawlogs and harvested wood fuel of 2:1 which gives an allocation to harvested wood fuel of 0.0312 / (2 x 0.1024 + 0.0312) = 13.2%.

(i) Land area requirement is 0.718 ha.a/t of dried wood chips available at point of use and allocation of 11.2% to harvested roundwood (for wood fuel). Production at sixth log harvest consists of 0.0230 odt/ha.a harvested roundwood and 0.0918 odt/ha.a sawlogs overbark, assuming a relative value of sawlogs and harvested wood fuel of 2:1 which gives an allocation to harvested wood fuel of 0.0230 / (2 x 0.0918 + 0.0230) = 11.2%.

(j) Land area requirement is 0.718 ha.a/t of dried wood chips available at point of use and allocation of 12.0% to harvested roundwood (for wood fuel) and residues (for wood fuel). Production at main harvest consists of 0.3694 odt/ha.a retrieved residues (not including mass of attached needles), 0.2438 odt/ha.a harvested roundwood and 1.4792 odt/ha.a sawlogs overbark, assuming a relative value of sawlogs, roundwood and residues of 4:2:1 which gives an allocation to harvested wood fuel of (2 x 0.2438 + 0.3694) / (4 x 1.4792 + 2 x 0.2438 + 0.3694) = 12.0%.

(k) Land area requirement is 0.718 ha.a/t of dried wood chips available at point of use and allocation of 7.6% to harvested roundwood (for wood fuel). Production at main harvest consists of 0.2438 odt/ha.a harvested roundwood and 1.4792 odt/ha.a sawlogs overbark, assuming a relative value of sawlogs and harvested wood fuel of 2:1 which gives an allocation to harvested wood fuel of 0.2438 / (2 x 1.4792 + 0.2438) = 7.6%.

(l) Harvested wood fuel (with needles) requirement of 1.241 t/t dried wood chips.

(m) Dried wood fuel requirement of 0.966 t/t dried wood chips.

(n) Dried wood chunk requirement of 0.034 t/t dried wood chips.