Diversity of leaf phenology in a tropical deciduous forest in India

Patterns of leaf phenological diversity were documented in nine key tree species of a tropical deciduous forest in the Vindhyan region of India. Monthly leaf counts on 160 tagged twigs on fen individuals of each species were made through two annual cycles. Tree species exhibited a gradient of deciduousness (similar to leafless duration), ranging from semi-evergreen species (entire population never becoming leafless) to 7-mo-deciduous species. The semi-evergreen species initiated leaf flush (bud break of vegetative bud) earlier around the spring equinox. In all deciduous tree species synchronous leaf-flush initiation, with low inter-annual variability, occurred during the hot dry summer (May-June, day temperature > 40degreesC). prior to the onset of the rainy season. Based on the quantification of leafless period, leaf-flush duration, and leaf strategy index (leaf-flush rate/leaf-fall rate, proposed in this study) in different species, four plant functional types were recognized: (a) semi-evergreen, spring flushing, showing leaf exchange, with mean leafless period 8 d, leaf-flush duration 6-7 mo and leaf strategy index < 0.5 (Shorea robusta); (b) < 2-mo-deciduous, summer flushing, leafless period 3-8 wk, leaf-flush duration 5-6 mo, and leaf strategy index > 0.5 - < 0. 7 (Anogeissus latifolia, Diospyros melanoxylon and Hardwickia binata): (c) 2-4-mo-deciduous, summer flushing, leafless period 2-3 mo, leaf-flush duration 4-5 mo. and leaf strategy index > 0.8 - < 1.0 (Acacia catechu, Lagerstroeiniaparviflora and Terminalia tomentosa); and (d) > 4-mo-deciduous, summer flushing, leafless period > 4-7 mo, leaf-flush duration 3-4 me, and leaf strategy index 1.0 (Boswellia serrata and Lannea coromandelica). Conspecific trees showed asynchrony with respect to leaf-flush completion, initiation and completion of leaf-fall, and extent of leafless period. Leaf strategy index (indicating rate of resource use and conservation) was strongly related with the leafless period in different species (r = 0.82) and can serve as a useful index in leaf phenological studies and classification of plant functional types.