Ecology and ecophysiology of epiphytes in tropical montane cloud forests

Abstract

ABSTRACT Because several reviews of epiphyte ecology and physiology are already available, this chapter focuses on what is particular about epiphyte ecology in cloud forests as opposed to lowland rain forests. The combination of high atmospheric humidity, frequent precipitation and low temperature results in much lower drought stress, which enables a denser colonization of exposed twigs with no “canopy soil” (humus), and the survival of small species, small individuals with little internal water storage, and species with no adaptations to drought. Because juveniles have the highest mortality with drought as the most important factor, water availability in most cases explains why cloud forest epiphytes do not occur in lowland forests. Species not occurring in cloud forests are limited by low temperatures (particularly in sub-tropical and upper montane areas) or excessive humidity (particularly bromeliads). The lower temperatures in cloud forests reduce night-time respiration, resulting in higher growth of non-vascular epiphytes. This, together with lower decomposition rates, leads to the formation of thick layers of canopy soil, providing a rooting substrate for vascular epiphytes. The very high living and dead epiphytic biomass plays an important role in the nutrient and hydrological cycles of tropical montane cloud forests.