Phenology, litterfall and nutrient resorption in Avicennia marina (Forssk.) Vierh in Gazi Bay, Kenya

The phenology and litterfall of the mangrove Avicennia marina were monitored from August 1993 to November 1994 in Gazi Bay, Kenya. Phenological trends in the emergence and fall of leaves were monitored at regular intervals from 200 tagged terminal shoots distributed over 34 different trees randomly selected within three sites in a monospecific stunted A. marina stand. Litterfall data were collected using 23 litter traps randomly distributed in the same stand. The results showed a marked seasonality in leaf emergence in A. marina with a peak of 1.61+/-0.34 leaves per leaves present day(-1) during the rainy season. Most litterfall was recorded at the beginning of the dry season. Average total litterfall amounted to 6.2+/-4.7 ton ha(-1) year(-1) with leaves contributing up to 83% of the total. Peak leaf emergence preceded peak leaf fall by approximately 1 month. Trees produced most new leaves when there were optimal conditions of runoff (nutrients), low evapotranspiration and reduced salinity during the rainy season. The average leaf longevity observed in the present study was approximately 11 months (1.1 turnover per year). Analysis of leaves of different physiological ages showed a nutrient resorption in the A. marina stand of 68% for N and 61% for P. Chloride content did not change with the ageing of leaves.