title: Seasonality constraints to livestock grazing intensity.
abstract: Increasing food production is essential to meet the future food demand of a growing world population. In light of pressing sustainability challenges such as climate change and the importance of the global livestock system for food security as well as GHG emissions, finding ways to increasing food production sustainably and without increasing competition for food crops is essential. Yet, many unknowns relate to livestock grazing, in particular grazing intensity, an essential variable to assess the sustainability of livestock systems. Here, we explore ecological limits to grazing intensity (GI; i.e. the fraction of net primary production consumed by grazing animals) by analysing the role of seasonality in natural grasslands. We estimate seasonal limitations to GI by combining monthly net primary production data and a map of global livestock distribution with assumptions on the length of nonfavourable periods that can be bridged by livestock (e.g. by browsing dead standing biomass, storage systems or biomass conservation). This allows us to derive a seasonality-limited potential GI, which we compare with the GI prevailing in 2000. We find that GI in 2000 lies below its potential on 39% of the total global natural grasslands, which has a potential for increasing biomass extraction of up to 181 MtC/yr. In contrast, on 61% of the area GI exceeds the potential, made possible by management. Mobilizing this potential could increase milk production by 5%, meat production by 4% or contribute to free up to 2.8 Mio km² of grassland area at the global scale if the numerous socio-ecological constraints can be overcome. We discuss socio-ecological trade-offs, which may reduce the estimated potential considerably and require the establishment of sound monitoring systems and an improved understanding of livestock system's role in the Earth system.
authors.affiliation: Institute of Social Ecology Vienna, Alpen-Adria Universitaet Klagenfurt, Wien, Graz, Schottenfeldgasse 29, 1070, Vienna, Austria.
authors.forename: Tamara
authors.initials: T
authors.lastname: Fetzel
authors.affiliation: Ecosystem Services and Management Program, International Institute for Applied Systems Analysis, Schloßplatz 1, 2361, Laxenburg, Austria.
authors.forename: Petr
authors.initials: P
authors.lastname: Havlik
authors.affiliation: Commonwealth Scientific and Industrial Research Organisation, 306 Carmody Road, St Lucia, QLD, 4067, Australia.
authors.forename: Mario
authors.initials: M
authors.lastname: Herrero
authors.affiliation: Institute of Social Ecology Vienna, Alpen-Adria Universitaet Klagenfurt, Wien, Graz, Schottenfeldgasse 29, 1070, Vienna, Austria.
authors.forename: Karl-Heinz
authors.initials: KH
authors.lastname: Erb
mesh_terms: D000818:Animals; D018533:Biomass; D057231:Climate Change; D004463:Ecology; D065948:Grassland; D058751:Livestock
keywords: food security; global livestock systems; grassland management; grazing intensity; natural grasslands; seasonality