Assessment of vegetative Phenology with respect to leaf elongation pattern of Avicennia marina and Rhizophora mucronata in Hajambro creek, Indus delta, Pakistan

Zafar Farooqui, Pirzada Jamal Siddiqui

Abstract


Leaves emergence and the rate of elongation have been studied in Hajambro creek in Indus deltaic region, Pakistan. Leaves emergence was found higher during the summer months (mostly pre-monsoon period), that was March April, May and June. Leaves of A. marina that were observed from March to July, till the leaves reached their maximum length (about 77 mm), showed a gradual increase in their length, reaching maximum in April. Leaves of Avicennia marina reached their maximum length (about 77 mm) in about 113 days. The leaves showed gradual increase in their length, reaching maximum in April (0.97mm d-1). The per-day increment in length was 0.54 mm d-1. As reaching their maximum length (77mm), the per-day increment in the length gradually slower down. The leaves of Rhizophora mucronata were observed from February to November. The leaves of Rhizophora mucronata showed elongation rate of 0.24 mm d-1 from the day of the first observation till the leaves reached their maximum length (120 mm). The maximum time required by the leaves to reach their maximum length (120 mm) was 236 days. The rates of elongation of leaves are also fast in summer. The rate of elongation of the leaves was found to be highly correlated with the temperature (p<0.005). It was also found that the leaves grew faster on low salinity (in July and August). During these months, the salinity in the creek waters was the lowest (up to 10-12) when the downstream discharge was the highest. The abscission time was found during September, October, November and December. Therefore, the leaves fall was found highly correlated with the litter fall research as most of the leaves fall was also higher during this drier season. Our results strongly endorsed the previous hypothesis that a fresh water is needed for the fast growth rates of mangroves. The stunted growth of Avicennia marina in the Indus delta, Sindh is due to a negligible amount of fresh water available to the delta, through downstream discharge, only in July. Therefore, better management of water resources is necessary for the conservation and management of the mangrove forest of Indus delta, Pakistan.


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