## 5 Discussion
### Estimating Results in Terms of Global Hectares  
For purposes of comparison with the existing method, the expanded sequestration footprint was translated into global hectares. While the equivalence factors necessary to translate specific land types at global productivity into global hectares are already published [1], the yield factors necessary to first translate national areas into specific land areas of world average productivity must be estimated. The 2004 _World Academic Footprint Account_[41] estimates that global annual forest increment and grassland yields are 1.84 m\({}^{3}\)/ha/yr and 2.23 tonnes of dry matter (t DM)/ha respectively. A value of 10.5 t DM/ha/yr for average grass yields was estimated based on data from [15] and [41], while an average forest increment of 9.9 m\({}^{3}\)/ha/yr was estimated based on the BFC yield tables [21] and the national species distribution [17]. These estimates resulted in a yield factor of 4.7 and 5.4 for forestry and pastureland, respectively. The direct energy footprint (in terms of global hectares) was recalculated using an overall sequestration estimate measured in global hectares. This was calculated by allocating the forest sequestration and corrected grassland NEE estimate, yield and equivalence factors to the relative area of both forest and grassland. The overall value was calculated at 1.82 gha/cap, or 65% of the calculated value, when global forestry is translated into global hectares (_i.e._, reduced by 35%).  
As can be seen from Figure 2, calculation of the ecological footprint resulting from domestic fuel consumption, in terms of actual hectares, results in less value than the estimate from current standardized footprint methods. However, as such values represent different units--Irish hectares and global hectares, respectively--they are not strictly comparable. It could be argued that actual footprints, representing a very specific area, have little comparative value on their own and should only be presented in association with a footprint calculated using the standardized method and expressed in global hectares.  
Figure 2: Comparison of footprint results: comparing actual and global hectares.  
Perhaps more interesting is that translating the forest and NEE based footprint into global hectare equivalents results in a lower value than if the global hectares are calculated normally (using the sequestration estimate of global forestry and the associated equivalence factor.) This may be due to the fact that although Irish grassland and forestry are significantly more productive (resulting in a large yield factor) than the global average, pasture land has a lower equivalence factor than forestry. While Irish forestry and grassland incur a similar cost (_i.e._, an increase in the footprint) when translated into global forestry and global grassland, grassland has an equivalence factor that is approximately one-third of the equivalent value for forestry. As suggested earlier, there is no guarantee that the same relationship between biomass and litter/deadwood accumulation will be evident on a geographic scale or when translating forest areas into global hectares. Also, the inclusion of soil processes challenges the notion of the energy footprint as an optimal area. It is unlikely that any area devoted to carbon capture will function wholly as a carbon sink; certain areas within a 'carbon footprint' area will occasionally function as a carbon source.