LEAF-AREA VARIATION IN RHIZOPHORA-MANGLE L (RHIZOPHORACEAE) ALONG A LATITUDINAL GRADIENT IN MEXICO

In this study we demonstrate that there is a significant variation in mean leaf area of Rhizophora mangle L. along a latitudinal gradient (1 5 degrees N to 24 degrees N) in Mexico, and that this variation is sig nificantly correlated with latitude and total annual precipitation per site. Mean leaf area of X. mangle and total annual precipitation incr ease significantly from north to south along the latitudinal gradient (chi(2)=56.57, n=27, P<0.001; chi(2)=15989.96, n=27, P<0.001, respecti vely). There is a significant negative association between latitude an d mean leaf area, and between latitude and total annual precipitation (both, r(2)=-0.5, n-27, P<0.001). Correlation between total annual pre cipitation and leaf area is not as strong r(2)=0.3, n=27, P<0.01). Our results show that mean leaf area of R, mangle increases significantly as latitude decreases and precipitation increases, but it seems impro bable that it would increase continuously if we should continue the la titudinal gradient up to the equator. This is probably due to the comb ined effect of energy optimization and moisture maximization year-roun d, the nonlinear temperature gradient between the equator and the pole s, and to geographical heterogeneity (e.g. proximity of mountain range s, or warm or cold ocean currents).