GEOGRAPHICAL-DISTRIBUTION OF LEAF LIFE-SPAN AND SPECIES-DIVERSITY OF TREES SIMULATED BY A LEAF-LONGEVITY MODEL

The leaf life span, leaf habit (evergreenness and deciduousness), and species diversity of trees were simulated by a cost-benefit model of l eaf longevity (Kikuzawa 1991), using monthly mean temperature values a nd their decreasing rate with altitude of 6 degrees C with 1000 m of s ites of different latitude and altitude in eastern Asia. Numbers of tr ee species in tropical regions with different lengths of favorable per iod for photosynthesis were also simulated. The following results were obtained by the model simulation. 1. In tropical areas, evergreen for ests predominate from lowlands to the altitudinal limit of forests. 2. However, leaf longevity is shorter in the lowland than that at a high er altitude. 3. Percentages of deciduousness are high in mid latitude, and the percentages of evergreenness again increase in even higher la titude, resulting in a bimodal distribution in percentages of evergree nness with increasing latitudes. 4. Altitudinal distribution of percen tages of evergreenness and deciduousness in mid latitude duplicates th e latitudinal distribution. In low altitudes, percentages of evergreen ness are high. But in mid altitudes, percentages of deciduousness beco me high, in even higher altitudes, however, evergreenness again predom inates. 5. Number of species is highest in the non-seasonal tropical r egion and decreases towards seasonal tropics and higher altitudes and latitudes.