Local biodiversity of farms in TCA
To enable the required species richness calculations in TCA, data on farm level are required (in contrast to the 100 km x 100 km grid of the global map at webpage eco-costs of land use). For many western countries, maps are available at a gid of 1 km x 1 km or 5 km x 5 km, which might be applied instead of an actual measurement at the farm itself. Fig. 6.2 shows an example are the maps of the species richness in the Netherlands, see Florbase species map
To determine the eco-costs of biodiversity, the equivalent Species-Area Relationship (SAR) power function of Arrhenius S=cAz must be applied, where S is the species richness, A is the Area and z = 0.15. The resulting equivalent data for the biodiversity factor and eco-costs are shown in Table 6.2.
In E-LCA it is common practice to assume that, when land-use is changed from a natural area to an agricultural area, the loss of biodiversity is 100% (neglecting the small biodiversity that is left by conventional farming), since it is incorporated in the standard databases. It makes sense to do the same in TCA. However, when land-use is changed from natural area to organic farmland, it makes sense to take the difference between the two. In the eco-costs system, the biodiversity of the natural situation (the default norm) is the biodiversity of the Global Map of Barthlott , or Table 2.5 at eco-costs of land-use.