Holdridge Life Zones of the World

The Holdridge Life Zones of the World is available from the UNEP GRID Data Collection in Geneva, Switzerland and from the NOAA NGDC Global Environmental Database (GED) in Boulder, Colorado, USA. These data centers provide slightly different versions of this data set, but all are based on the same source: Leemans, Rik. 1990. Possible Changes in Natural Vegetation Patterns Due to a Global Warming. IIASA Working Paper WP90-08 and Publication Number 108 of the Biosphere Dynamics Project. Laxenburg, Austria: International Institute of Applied Systems Analysis. 22 pp.

The UNEP GRID data set shows the Holdridge Life Zones of the World, a combination of climate and vegetation (ecological) types, under current, so-called normal climate conditions, as well as under a presumed doubling of atmospheric CO2. The Life Zones were devised using three indicators: biotemperature (based on the growing season length and temperature); mean annual precipitation; and a potential evapotranspiration ratio, linking biotemperature with annual precipitation to define humidity provinces. The data set has a spatial resolution of one-half degree latitude/longitude, and a total of 38 life-zone classes that are listed on the accompanying legend sheet.

The UNEP GRID Holdridge Life Zones data set includes a total of four data files. The first (HOLDNORM) is as described in the paragraph above; the second (HOLDDOUB) shows how the Life Zones would change given an assumed doubling of atmospheric CO2 (according to a General Circulation Model from the U.K. Office of Meteorology). The third and fourth data files show only those portions of the Life Zones which would undergo changes, that is for both the old classification (HOLDCHFR) before and the new classification (HOLDCHTO) after the theoretical doubling of CO2 (in effect, these areas have the appearance of 'sliver' polygons). The data set is useful for testing the role of climate influence on vegetation patterns, and also as a basis for evaluating future effects of climate change on vegetation.

The GED Holdridge Life Zones data set consists of two global thematic layers: (1) Holdridge Life Zones Classification (as predicted by climate, according to the Holdridge classification method); and (2) Holdridge Life Zones Aggregated Classification (aggregated according to Olson's ecosystem classes). The data are gridded at a resolution of 30 minutes.