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 dry upland forest in Costa Rica were surrounded by scaffolding and rehydration was induced during the dry season by irrigation of 9-50 m2 plots with 200 mm water. The resulting changes in water status preceding bud break were monitored. Following irrigation, stem water potentials increased 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, measured as an increase in electric conductivity, continued for 4-8 days. Terminal flower buds in Tabebuia ochracea began to expand 48 h after irrigation and trees were in full bloom 4 days later. In all experimental species, lateral vegetative buds began to expand 5-7 days after irrigation and leaves were fully expanded 2 weeks later. After the first rains 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 tropical hardwood trees thus rehydrated at rates similar to those of desert succulents and their development resumed much faster than that of deciduous cold-temperate trees in spring.