EFFECTS OF SEASONAL RAINFALL ON RADIAL GROWTH IN 2 TROPICAL TREE SPECIES

Seasonal drought may limit primary productivity in most of the tropics , but the determinants of tree growth are not well known. A 10-year st udy of the deciduous trees Cochlospermum vitifolium (Willd.) Spreng. ( Cochlospermaceae) and Cnidoscolus spinosus Lundell (Euphorbiaceae) in southwestern Mexico showed radial growth to be highly correlated (both r>0.85) only with precipitation during an interval of <2 months in th e mid-wet season. Growth was not affected by total annual precipitatio n or by an early starting or late ending of the wet season, or by heav y rainfall in the dry season. Annual mean girth increments ranged from 0.03 to 3.31 cm and -0.1 to 2.01 cm, respectively. The best model for growth (r(2)>0.85) was a linear combination of mid-summer precipitati on (positive coefficient) and total precipitation over the previous 2 years (negative coefficient). Comparison with other species showed het erogeneous responses of wood production to climate variation, and sugg ests that the range of functional types of dry forest trees is still u nknown.