The Holdridge Life Zones data set is from the International Institute for Applied Systems Analyses (IIASA) in Laxenburg, Austria. The 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 which are listed on the accompanying legend sheet.

The Holdridge Life Zones data set includes a total of four data files. The first is as described in the paragraph above; the second 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); while the third and fourth files show only those portions of the Life Zones which would undergo changes, both before and after the theoretical doubling of CO2. 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 Holdridge Life Zones data file consists of 360 rows (lines) by 720 columns (elements/pixels/samples) of data, and one byte/eight bits per pixel. Its origin is at 90 degrees North latitude and 180 degrees West longitude, and it covers the entire globe to 90 degrees South latitude and 180 degrees East longitude. At one-half degree spatial resolution, each data file comprises 259.2 kilobytes, and thus all four data files described above together equal 1.04 Mb.

The proper reference to this data set is "Leemans, Rik, 1990. Global data sets collected and compiled by the Biosphere Project, Working Paper, IIASA-Laxenburg, Austria." Another useful description of this data set is found in the March 1990 issue of the IIASA publication known as 'Options', in an article entitled "IIASA's Climate Database" (pages 9-12). The source of this GRID-held data set is IIASA.

GRID LEGEND FOR HOLDRIDGE LIFE ZONES OF THE WORLD (Leemans, 1989)

Class no.	Life Zone title
1	Polar desert
2	Subpolar dry tundra
3	Subpolar moist tundra
4	Subpolar wet tundra
5	Subpolar rain tundra
6	Boreal desert
7	Boreal dry scrub
8	Boreal moist forest
9	Boreal wet forest
10	Boreal rain forest
11	Cool temperate desert
12	Cool temperate desert scrub
13	Cool temperate steppe
14	Cool temperate moist forest
15	Cool temperate wet forest
16	Cool temperate rain forest
17	Warm temperate desert
18	Warm temperate desert scrub
19	Warm temperate thorn scrub
20	Warm temperate dry forest
21	Warm temperate moist forest
22	Warm temperate wet forest
23	Warm temperate rain forest
24	Subtropical desert
25	Subtropical desert scrub
26	Subtropical thorn woodland
27	Subtropical dry forest
28	Subtropical moist forest
29	Subtropical wet forest
30	Subtropical rain forest
31	Tropical desert
32	Tropical desert scrub
33	Tropical thorn woodland
34	Tropical very dry forest
35	Tropical dry forest
36	Tropical moist forest
37	Tropical wet forest
38	Tropical rain forest

Cuming, Michael J. and Barbara A. Hawkins, 1981. TERDAT: The FNOC System for Terrain Data Extraction and Processing. Technical Report Mil Project M-254 (second edition). Prepared for USN/FNOC and published by Meteorology International Inc.