9. Biodiversity

The biodiversity module is a simple structure representing population carrying capacity. The population is represented by global and encompassing all biomes mean species abundance (\(MSA\)). \(MSA\) is increased by species regeneration rate (\(Spec\_Regen\)) and decreased by species extinction rate (\(Spec\_Extn\)). In addition, \(MSA\) approaching species carrying capacity (\(Spec\_Capa\)) limits \(Spec\_Regen\) and intensifies \(Spec\_Extn\). This process is quantified as logistic functions and based on the ratio between \(MSA\) and \(Spec\_Capa\), and the regeneration factor and the extinction factor, respectively.

9.1 Species carrying capacity

\(Spec\_Capa\) is calculated based on reference species carrying capacity (\(Spec\_Capa\_Max\)), representing maximum sustained population size, and influencing factors related to fertilizers consumption (\(Imp\_Fertz\_on\_Biodiv\)), biomass production for energy purposes (\(Imp\_Biom\_on\_Biodiv\)), climate damage (\(Imp\_CC\_on\_Biodiv\)) and land use change (\(Imp\_Land\_on\_Biodiv\)).

\[Spec\_Capa(t) = Spec\_Capa\_Max \times Imp\_Fertz\_on\_Biodiv(t) \times Imp\_Biom\_on\_Biodiv(t) \times Imp\_CC\_on\_Biodiv(t) \times Imp\_Land\_on\_Biodiv(t)\]

(Eq. 9.1)

The four influencing factors are estimated by logistic functions. In detail, \(Imp\_Fertz\_on\_Biodiv\) is a logistic function of fertilizer consumption (including nitrogen, phosphate, and potash fertilizers). \(Imp\_Biom\_on\_Biodiv\) consists of impacts from forest agriculture biomass production, which are logistic functions of related land areas. \(Imp\_CC\_on\_Biodiv\) is adopted from climate impact on economy, as a logistic function of temperature change from preindustrial. \(Imp\_Land\_on\_Biodiv\) takes into consideration changes of agricultural land, forest land, and other land compared to their initial areas.