A quantitative terrestrial vegetation model was produced which consists of:
(1) A world classification of important terrestrial plant growth forms (life forms);
(2) A set of predictive variables representing the main climatic correlates of these forms; and
(3) Empirically obtained hypothetical limiting values defining an ecoclimatic envelope for each plant form (relative to the climatic variables). The model was applied to a world climatic data-base (1 225 sites) in order to substantiate the hypothesized life-form status of the plant types by accurately predicting their actual world distributions. Particular combinations of forms are interpreted as vegetation formation types by reference to growth-form dominance considerations. Model validation was attempted by comparing predicted and actually occurring vegetation at independent sites on all continents. Prediction accuracy of 85% for individual plant types and 50% for vegetation structure (exact combination of actually occurring dominant forms) suggests that general macroclimatic conditions are much more important than any other factors (such as complex specific interactions) in determining general ecological structure on most sites. Subpolar Mixed Woodland * Boreal EG NL Trees (woodland) SG BL Dwarf-Trees (microphyll) NL Treeline Krummholz SG Herbs (polar semi-desert type) Mediterranean Evergreen Forest * Mediterr. EG BL Trees * Long-Needle EG Trees (submed.) Mediterranean Mixed EG Forest * Mediterr. EG BL Trees * Long-Needle EG Trees (submed.