Distribution mapping of world grassland types

Journal of BiogeographyAdam P. Dixon

The World Wildlife Fund and NatureServe have partnered to create a biogeographical characterization of the world's grassland, such as the landscape in Bowdoin, Montana.National and international policy frameworks—such as the European Union’s Renewable Energy Directive—increasingly seek to conserve and reference "highly biodiverse grasslands." However, to date, there is no systematic global characterization and distribution map for grassland types. We propose a systematic definition of grassland that can be applied globally, then integrate the  grassland types identified in the International Vegetation Classification (IVC) a global  classification that characterizes all vegetation types, with the Terrestrial Ecoregions of the World (TEOW)—a spatial regionalization of the earth’s terrestrial biodiversity. This framework is a first step to establishing a comprehensive spatial characterization of each of the world’s grassland types.  We first provide a definition of grassland as a distinct biotic and ecological unit. We use the IVC division level to classify the grassland into major regional types. We use the TEOW as an ecologically meaningful approach to reporting grassland distribution.

Through literature review, input from regional grassland experts, and consultation of geographic datasets, we determined which TEOW contained an IVC division that met our decision rule (at least 10 percent of the ecoregion should historically have been comprised of grassland). We then developed a spatial catalog of IVC divisions by ecoregion. We created a global biogeographic representation of earth’s grassland types and their distribution. We mapped forty-seven taxonomically distinct grassland divisions. Fourteen additional grassland divisions are recognized, which were all limited in total extent, but which were not able be mapped with our approach due to lack of TEOW representation and the fine scale distribution of these grassland types. The framework provided by our geographic mapping effort provides a systematic overview of grasslands, and sets the stage for more detailed classification and mapping at finer scales. Each regional grassland type can be characterized in terms of its range of biodiversity, thereby assisting in definitions of “highly biodiverse grasslands.” Further effort is needed to move from distribution mapping to mapping of current areal extent, including for limited extent grassland types.  Our approach of combining a vegetation classification with spatial ecoregions may support international initiatives and policies which need clarity to advance grassland conservation.

NatureServe Author(s)

Citation

  • Dixon AP, Faber-Langendoen D, Josse C, Loucks CJ, Morrison J. 2014. Distribution mapping of world grassland types. Journal of Biogeography. doi: 10.1111/jbi.12381