Population Dynamics of Epiphytes in a Mexican Humid Montane Forest

1 Aspects of epiphyte population dynamics were studied in a Mexican humid montane forest using repeated photographs of branches to follow the fate of 5124 individuals of 44 epiphyte species over 2 years. The diameter of the supporting branch and the size of the longest leaf of bromeliads were measured. 2 Bromeliads tended to grow on smaller, ferns and orchids on thicker, and Peperomia on intermediate branches. Although most plants showed a non-random distribution, there was much overlap. Small individuals of Tillandsia and Catopsis were more frequently found on small branches than were large plants. 3 The probability of falling with a branch within a year decreased with increasing branch size, from 28% for twigs 12cm. 4 In Tillandsia, mortality from factors other than branchfall declined from 0.33 for plants 15 cm. If branchfall was excluded, mortality of Tillandsia was higher on thick than on thin branches, which may have been caused by the decreasing light level towards the centre of tree crowns. 5 Overall probabilities for all plants registered were 0.840 (survival), 0.082 (birth), 0.071 (mortality from branchfall) and 0.096 (mortality from other factors). This resulted in a negative population balance if branchfall was included, and an almost balanced one if branchfall was excluded. 6 The distribution of epiphytes among branches and trees and the rates of recruitment, growth and mortality of these subpopulations must be determined to understand the population dynamics.