Terrestrial habitat types (Level 2)

The documentation of the IUCN habitat classification scheme is unfinished, with ~20% of all class descriptions lacking further elaboration16. In this study we aimed to follow the habitat classification system outlined by IUCN16 to facilitate links with other IUCN data, realizing that other - often more detailed - habitat classification systems exist at national scale66,67, using land cover and climate data of higher spatial and thematic resolution19. For instance, in an expert-based visual assessment of the habitat map we found that the most common error source were mistakes in the underlying global land cover data. Based on a precautionary principle and known limitations (see text file on the data repository), we recommend using the habitat map at a coarsened resolution and supply fractional aggregated maps of each individual class at 1 km resolution with every release56. Furthermore not all habitat types can be adequately mapped spatially, with some being only seasonally present41, having intra-annual sequences68 or being of ‘mixed’ nature, such as lightly-grazed savanna habitats which can be considered grassland, shrubland or forest depending on the vegetation cover. Other IUCN habitat classes are very hard to map spatially, such as ‘16. Introduced vegetation’. Better spatial information on other anthropogenic classes, such as sown pasture/rangelands, are also necessary to better represent this class in the global habitat map. In addition, four terrestrial IUCN habitat classes (four level 2 habitat classes) are not represented in the current version of the global habitat map, i.e. all marine habitats (habitat classes 9 to 13) as well as artificial aquatic habitats (15). We stress that the habitat map will be updated in the future as new or improved ancillary data become available, which will likely also help to improve many mapped classes.