| Issue | Data source | Assumptions |
| Establishment cost | | ?/span>3650/ha |
| Subsidies | Sitka spruce (SS) | Establishment Grant: 2860/ha, Maint grant: ?90/ha. Annual premium: ?10/yr (15 yrs) |
| Sph (stems per hectare) | Afforestation Scheme FC static yield model | Spacing dictated by species Reduction in sph over life-cycle |
| Productive area | Afforestation Scheme | 85% |
| Maintenance costs | | Management: ?0/year (yr 6 onwards); Insurance: ?0/yr (yr 6 to 20); Inspection paths: ?5/ha (yr 14) |
| Maincrop (MC), dbh | FC static yield model | FC static yield model |
| Merchantable timber volume Net Realisable Volume | FC static yield model FIVE/ForBES model | Mean tree volume. The model provides a breakdown of volume by product category. MTV net of cost of sales, harvest losses, sph |
| Yield Class | FC static yield | Sitka spruce (SS) yield class 14 - 24 |
| TH vs No TH | FC static yield model | Thinning assumes stable sites without undue risk Thin and No Thin options calculated for all scenarios |
| Thinning yield Unthinned yield | FC static yield model | Stands thinned to (MTT4). |
| Optimal rotations: Silvicultural Reduced MAI Financial max NPV | ForBES/FC static yield model ForBES/FC model ForBES | Rotation of MAI Reduced rotation Max NPV of 30 to 50 year rotations |
| Costs | Establishment and maintenance Harvesting | All costs which occur before the current age are treated as sunk costs. Afforestation: current age = 0 |
| Establishment, maintenance and re-establishment costs | Teagasc Forestry Development Department | Establishment, maintenance and re-forestation costs are representative of those in common use in the farm forestry sector as determined by expert opinion in the Forestry Development Department, Teagasc. |
| Harvest Road costs | Only applicable if thinning | Assume costs covered by grant for farm forests |
| Cost of sales | FIVE/ForBES | Based on % reduction in NRV Thinning: 12, Clearfell: 5 |
| Harvest losses | FIVE/ForBES | Conifers: Include % reduction in NRV. |
| Incomes |
| The model uses price size curves (PSC) based on average tree size plus volume assortments to calculate timber revenues |
| Log optimisation | FIVE/ForBES | The proportion in each product category is based on market knowledge and is for average quality crops. |
| Allocation to assortments (peping) | FC assortment tables ( | The model estimates the volume of large sawlog, pallet, pulp and stake material in thinnings and clearfell (no stake recovery from non-spruce or broadleaved species). |
| Timber prices: -conifers | Coillte 10 year price series based on average tree size | Timber prices and costs keep pace with inflation. Uses price size curves and NRV from FIVE to calculate timber revenues. |
| Timber prices: -broadleaves | Timber price surveys in UK and Ireland | Broadleaf timber prices are based on smaller samples and are not as robust as conifer prices. |
| Subsidies | Forest Service Teagasc Forest Subsidies Model | Current SS subsidies: ?10/ha for 15 years Historic subsidies |
| Price/Cost indices | | Component specific CPI and average CPI applied |
| Discount rate | | 5% |
| Reforestation | | ?500 at end of first rotation |