The Altitudinal Belts of the Vegetation in the Central Mexican Highlands and Their Climatic Conditions

Lauer, Wilhelm

The vegetation belts at high altitudes in the Central Mexican Highlands are not exclusively tropical in character. This is especially true of the "tierra fria." Even the main part of the "tierra templada" contains a considerable variety of holarctic floristic elements. The timberline in the Mexican Highlands (approximately 4,000 m) is formed by one species of pine (Pinus hartwegii), and the slopes to the Caribbean side are characterized down to an altitude of 1,200 m by a number of boreal species among them many oaks and a Mexican beech species (Fagus mexicana). The climatic conditions suggest that this region should be considered rim-tropical. Using the three-dimensional weather system classification of D. Klaus it is demonstrated that dynamically the Central Mexican plateau bears only rim-tropical character. Only under summer conditions does the tropical circulation of atmosphere form a part of the trade wind regime; in winter atmospheric conditions largely derive their genetic impulse from extra-tropical sources of circulation. The temperature pattern of the Mexican plateau shows both tropical and extratropical conditions. By comparing vertical temperature gradients within the area of the Central Mexican upland it is possible also to demonstrate the influence here of the extratropical elements of circulation. The vegetation has largely adapted to climatic conditions, especially to the minimum factor of the cooler season.

The Altitudinal Belts of the Vegetation in the Central Mexican Highlands and Their Climatic Conditions

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