Tropical Phenology: Individual-Level Phenological Study of Neem (Azadirachta indica A. Joss.) Occuring in Onitsha, Nigeria

An annual cycle phenological study of Azadirachta indica growing in Onitsha with tropical deciduous vegetation has been carried out to record and document the phenological activities of the species. The following phenological activities were observed: bud break (BB) (both vegetative and reproductive), leaf flushing (LF), inflorescence emergence (IE), fruit development (FD), and fruit ripening (FR). The initiation stages and the peaks in phenophases were recorded. A 2-digit scale was used to include the principal and secondary growth stages and this provided the basis for data collection. From the result of the study, the tree revealed two sub-annual cycles in both vegetative and reproductive activities, and both took place in the wet and dry season. There was no time lag between the onset of leaf-flushing and inflorescence emergence in A. indica, in the sub-annual cycles. The initiation of leafing and flowering in the species in the drought-laden dry season increased the rate of leaf fall and extended the duration of deciduousness more than in the wet season. Also Advance in fruit ripening was observed, and this took place in the drought-laden dry season. Thus, it was recommended that long-term phenological observation and documentation be carried out on the species for future references, especially in tracing the impact of climate change on the plant.