Water relations in dry tropical forest trees: the case of Enterolobium cyclocarpum

The water relations of Enterolobium cyclocarpum trees of the Santa Rosa National Park, Costa Rica, were studied during different moments of the daily courses and along different periods of the year. The most outstanding feature of this species was its capacity to flush the leaves during the dry season and under conditions of high evaporative demand. The results showed decreased water potentials in stems and coarse roots during early flushing, from -0.3 MPa to -0.55MPa, evidencing the contribution of stem and root water stores in supporting shoot expansion. It was determined that newly flushed leaves constitute a major factor to restrict water loss and to maintain the water balance during the dry season, as observed in the measurements of the stomatal conductance and the leaf water potential (gs de 50 mmol m-2 s-1;square H de -0.75 MPa). Total daily sap flow showed substantial variations during the year, with daily transpirations of 300 liters during the rainiest months. Simultaneous changes in branch, stem and coarse root sap flow in response to sudden changes in solar radiation indicated that different tree organs were tightly coupled and were highly responsive to environmental changes. This study shows the importance of implementing ecophysiological studies for the best understanding of the processes that occur in forestry systems.