Abstract
Abstract. Interactions between food demand, biomass energy and forest preservation are driving both food prices and land-use changes, regionally and globally. This study presents a new model called Nexus Land-Use version 1.0 which describes these interactions through a generic representation of agricultural intensification mechanisms within agricultural lands. The Nexus Land-Use model equations combine biophysics and economics into a single coherent framework to calculate crop yields, food prices, and resulting pasture and cropland areas within 12 regions inter-connected with each other by international trade. The representation of cropland and livestock production systems in each region relies on three components: (i) a biomass production function derived from the crop yield response function to inputs such as industrial fertilisers; (ii) a detailed representation of the livestock production system subdivided into an intensive and an extensive component, and (iii) a spatially explicit distribution of potential (maximal) crop yields prescribed from the Lund-Postdam-Jena global vegetation model for managed Land (LPJmL). The economic principles governing decisions about land-use and intensification are adapted from the Ricardian rent theory, assuming cost minimisation for farmers. In contrast to the other land-use models linking economy and biophysics, crops are aggregated as a representative product in calories and intensification for the representative crop is a non-linear function of chemical inputs. The model equations and parameter values are first described in details. Then, idealised scenarios exploring the impact of forest preservation policies or rising energy price on agricultural intensification are described, and their impacts on pasture and cropland areas are investigated.
Highlights
In addition to their traditional role of feeding the world, services expected from natural ecosystems and agriculture have recently extended to broader fields such as offering new energetic options, mitigating climate change or preserving biodiversity
The representation of the production system is chosen to account for biophysical features as well as agronomic practices. This representation relies on three main components: (i) a detailed representation of the livestock production system based on the Bouwman et al (2005) model; (ii) potential crop yields from the Lund-Postdam-Jena dynamic global vegetation model for managed Land (LPJmL, Bondeau et al, 2007); and, (iii) a biomass production function inspired by the crop yield response function to inputs asymptoting toward the potential yield
As the pressure on land grows, in response to – all other things being equal – a rise of energy price and/or food crops domestic demand and/or a reduction of agricultural area, the actual crop yield is increased by higher inputs of fertilisers and pesticides and the intensive livestock production expands towards less fertile land classes
Summary
In addition to their traditional role of feeding the world, services expected from natural ecosystems and agriculture have recently extended to broader fields such as offering new energetic options, mitigating climate change or preserving biodiversity. - Actual yields of 11 crop functional types (1999-2003 mean on a 0.5x0.5° grid) - Global land cover (2000) - Production, trade and uses of edible calories (2001) - Consumption of fertiliser and pesticides by the agricultural sector (2001). These considerations have profoundly affected land-use modelling orientations. The Nexus Land-Use can be used for many purposes, especially: (i) testing the impact of scenarios regarding diverse variables (food diets/preferences, demand for agrofuel and other non-food agricultural products, prices of fossil energy and agricultural chemical inputs, forest policies, trade policies, etc.) on agricultural land-use change across the world and their consequences (on food prices, regional consumption of agricultural inputs, regional trade balances, etc.) and, (ii) assessing climate policies through a linkage with the general equilibrium model Imaclim-R (Crassous et al, 2006). The main hypotheses of the model are discussed
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