INDUCTION OF REHYDRATION AND BUD BREAK BY IRRIGATION OR RAIN IN DECIDUOUS TREES OF A TROPICAL DRY FOREST IN COSTA-RICA

Clusters of 2-4 bare, deciduous hardwood trees and woody vines in a dr y upland forest in Costa Rica were surrounded by scaffolding and rehyd ration was induced during the dry season by irrigation of 9-50 m2 plot s with 200 mm water. The resulting changes in water status preceding b ud break were monitored. Following irrigation, stem water potentials i ncreased from < -4 MPa to about -1.5 MPa within 24 h and to > -0.3 MPa within 48 h. Rehydration of stem tissues by lateral transport, measur ed as an increase in electric conductivity, continued for 4-8 days. Te rminal flower buds in Tabebuia ochracea began to expand 48 h after irr igation and trees were in full bloom 4 days later. In all experimental species, lateral vegetative buds began to expand 5-7 days after irrig ation and leaves were fully expanded 2 weeks later. After the first ra ins of the rainy season (100 mm in 48 hr) all trees in the dry forest rehydrated and leaves emerged in synchrony slightly faster than after irrigation. In response to rain or irrigation drought-stressed tropica l hardwood trees thus rehydrated at rates similar to those of desert s ucculents and their development resumed much faster than that of decid uous cold-temperate trees in spring.