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 leaf longevity (Kikuzawa 1991), using monthly mean temperature values and their decreasing rate with altitude of 6°C with 1000 m of sites of different latitude and altitude in eastern Asia. Numbers of tree species in tropical regions with different lengths of favorable period for photosynthesis were also simulated. The following results were obtained by the model simulation.

1. In tropical areas, evergreen forests predominate from lowlands to the altitudinal limit of forests.
2. However, leaf longevity is shorter in the lowland than that at a higher altitude.
3. Percentages of deciduousness are high in mid latitude, and the percentages of evergreenness again increase in even higher latitude, resulting in a bimodal distribution in percentages of evergreenness with increasing latitudes.
4. Altitudinal distribution of percentages of evergreenness and deciduousness in mid latitude duplicates the latitudinal distribution. In low altitudes, percentages of evergreenness are high. But in mid altitudes, percentages of deciduousness become high, in even higher altitudes, however, evergreenness again predominates.
5. Number of species is highest in the non-seasonal tropical region and decreases towards seasonal tropics and higher altitudes and latitudes.