Vegetative and reproductive phenology of the mangrove Bruguiera gymnorrhiza (L.) Lam. on Okinawa Island, Japan

Abstract

Vegetative and reproductive phenology of the subtropical mangrove Bruguieragymnorrhiza was investigated at Manko Wetland, Okinawa Island, Japan. Phenology was assessed using litterfall data over 4 years. Leaf and stipule litterfall occurred throughout the year, with distinct seasonal patterns. Kendall’s coefficient of concordance, W, revealed that the monthly changes in leaf and stipule litterfall were strongly and significantly concordant among years. Leaf litterfall was linked to monthly day length and maximum wind speed, and stipule litterfall was linked to monthly mean air temperature, monthly rainfall, and maximum wind speed. Branch litterfall showed no clear monthly pattern, but tended to vary with monthly maximum wind speed. Mean leaf longevity was 19 months. Mean total litterfall was 10.1 Mg ha−1 year−1, with the largest component being vegetative organs (58 %). Flower and propagule litterfall were highest in autumn and summer, respectively, and lowest in winter. The W values revealed that, of the reproductive organs, only flower litterfall had a significant monthly trend. Flower litterfall was correlated with monthly mean air temperature and relative humidity. The average development periods from flower buds to flowers and from flowers to mature propagules were approximately 1 and 8 months, respectively. It took 9 months to produce mature propagules from flower buds. Except for branches, all vegetative and reproductive components of litterfall had clear annual cycles.