Paradox of leaf phenology:: Shorea robusta is a semi-evergreen species in tropical dry deciduous forests in India

Shorea robusta, widely distributed in moist and dry forests in the tropics, has been paradoxically described as deciduous, semi-deciduous or evergreen species. To assess this contradiction, quantitative documentation of leaf dynamics, flowering and fruiting (by monthly counts on tagged twigs) was made in marked individuals of Shorea in a tropical dry deciduous forest. Annual leaf exchange seems to be a survival strategy in Shorea during the period of seasonal drought; it replaces all old leaves of differing longevity with new leaves to reduce water loss due to transpiration, and simultaneously supports asynchronous flowering. During March (the transitional month for the leafing phenophase) four phenological variants, reflecting considerable functional diversity in conspecific trees, were recorded. These were: variant a, leaf fall completed and leaf flush begins; variant b, leaf fall and leaf flush overlapping; variant c, leaf fall completed but leaf flush delayed, short leaflessness; variant d, leaf fall incomplete (old leaves persist) and leaf flush delayed. Individuals of Shorea responded variously (leaf exchange or evergreenness to leaflessness or deciduousness, but <= 1 year leaf lifespan) to microsite conditions, making it essentially. a semi-evergreen species. It is suggested that semi-evergreenness in Shorea, an indicator of high adaptability, permits its extensive distribution in the tropics, from moist to the dry regions.