ABSTRACT
It is appropriate that a world study of vegetation and soils should culminate in some account of their distributions on mountains in the tropics. Environmental extremes, from the very hot to the very cold, are here brought into close proximity; tropical rain forest may envelop the lower slopes while the peak is perpetually snow-clad. One might almost expect to find many of the main vegetation zones of the earth repeated here in miniature with tropical forests giving way upwards to sub-tropical forest, mid-latitude forest, boreal forest and, finally, to tundra. Although some suggestion of this kind of sequence is frequently encountered, nature cannot be said to have repeated herself with such absolute faithfulness on any tropical mountain. In spite of the gradual decrease in air temperature with increase in height, one should not expect such analogies. Even on the coldest peaks of tropical mountains, the sun reaches a high elevation at midday throughout the whole of the year. The pronounced division of the year into a relatively warm season and a much cooler one is not experienced and yet it is to such a régime that the plants of higher latitudes have adapted themselves. Furthermore, on many tropical mountains, increase in height entails an increase in precipitation; because of the uplift given to impinging air masses, the slopes at certain heights are inordinately wet. These two factors, along with several others, produce climatic conditions which are peculiar to tropical mountains. These conditions reappear time and time again in characteristic patterns. Plant formations have evolved which are adapted to these climates and adaptation seems to have followed remarkably similar lines in all parts of the tropics. Because of this convergent evolution, some general statements can be made about the peculiarities and patterns of tropical mountain vegetation.
