Water Relations of Jamaican Upper Montane Rain Forest Trees

Abstract

We studied the water relations of an upper montane rain forest at an elevation of °1550 m in the Blue Mountains of Jamaica to investigate whether the growth of the forest is limited by water shortage and/or whether the characteristically hard, leathery leaves of tropical montane rain forest trees are an adaptation to water shortage. Daily courses of leaf water potential, leaf relative water content, leaf resistance, and leaf temperature were followed for nine tree species at the driest time of year. The lowest leaf water potential measured was —1.7 MPa. Leaf resistance was usually low and rarely showed increases that might be attributed to water shortage; it was significantly correlated with light levels. Leaf relative water content was always >86% and was not correlated with leaf water potential. Leaf sublethal water deficits (SLD) averaged 27% (12 species). There was no relationship between SLD and leaf structural characteristics. We conclude that water supply rarely, if ever, seriously limits the growth of these montane forests and that their xeromorphic leaves are not an adaptation of water limitation.