全球变化知识资源中心

Meeting expected surges in global biomass demand while protecting pristine ecosystems likely requires intensification of current croplands. Yet many uncertainties relate to the potentials for cropland intensification, mainly because conceptualizing and measuring land use intensity is intricate, particularly at the global scale. We present a spatially explicit analysis of global cropland use intensity, following an ecological energy flow perspective. We analyze (a) changes of net primary production (NPP) from the potential system (i.e. assuming undisturbed vegetation) to croplands around 2000 and relate these changes to (b) inputs of (N) fertilizer and irrigation and (c) to biomass outputs, allowing for a three dimensional focus on intensification. Globally the actual NPP of croplands, expressed as per cent of their potential NPP (NPP_act%), amounts to 77%. A mix of socio-economic and natural factors explains the high spatial variation which ranges from 22.6% to 416.0% within the inner 95 percentiles. NPP_act% is well below NPP_pot in many developing, (Sub-) Tropical regions, while it massively surpasses NPP_pot on irrigated drylands and in many industrialized temperate regions. The interrelations of NPP losses (i.e. the difference between NPP_act and NPP_pot), agricultural inputs and biomass harvest differ substantially between biogeographical regions. Maintaining NPP_pot was particularly N-intensive in forest biomes, as compared to cropland in natural grassland biomes. However, much higher levels of biomass harvest occur in forest biomes. We show that fertilization loads correlate with NPP_act% linearly, but the relation gets increasingly blurred beyond a level of 125 kgN ha⁻¹. Thus, large potentials exist to improve N-efficiency at the global scale, as only 10% of global croplands are above this level. Reallocating surplus N could substantially reduce NPP losses by up to 80% below current levels and at the same time increase biomass harvest by almost 30%. However, we also show that eradicating NPP losses globally might not be feasible due to the high input costs and associated sustainability implications. Our analysis emphasizes the necessity to avoid mono-dimensional perspectives with respect to research on sustainable intensification pathways and the potential of integrated socio-ecological approaches for consistently contrasting environmental trade-offs and societal benefits of land use intensification.