Phenology and litterfall dynamics structuring Ecosystem productivity in a tropical mangrove stand on South West coast of India

Abstract

This study shows results on litterfall dynamics contributing to Net Primary Productivity (NPP) and phenology in three major mixed mangrove habitats in Cochin estuarine system, south-west coast of India. Eleven true mangrove species and three mangrove associates formed the plant biomass where Avicennia officinalis was abundant in Site 1, Excoecaria agallocha in Site 2 and Avicennia officinalis, Rhizophora mucronata were abundant in Site 3. Total tree density varied from 11760 stems ha−1 in Vypin Island (Site 2); 11440 stems ha−1 in Mangalavanam Bird sanctuary (Site 3) and 7680 stems ha−1, Aroor (Site1). The average stands basal area of the three mangrove habitats were 75.54, 54.85 and 103.26 m2 ha−1. The mean annual litterfall production in Cochin mangroves was 16.57±6.58 t ha−1 y−1 in which leaves (53.90%) contributed more followed by flowers, propagules (28.66%) and twigs (17.44%). The spatial variability in litterfall recorded highest in lower latitudinal mangrove habitat, Site.1 followed by Site 2 and Site 3 (2413.36 ± 873.72, 1295.65 ± 401.09, 1263.28±255.28 g DW m−2y−1). Site differences in litter production were statistically significant (one-way ANOVA p<0.001 for total litterfall and p<0.05 for litter components) between the three mangrove habitats. Litter components and total litterfall showed significant seasonality (p<0.001). Highest litterfall was recorded in pre-monsoon period followed by post-monsoon and least in monsoon period. The temporal trend of litterfall was explained through rainfall and mean atmospheric temperature and a negative correlation was there to rainfall during the period. The mean carbon content in the litterfall was estimated as 42.96% of the dry weight and the primary productivity through litterfall in the study area was estimated to be 7.12±2.81 t C ha−1 y−1. This will act as the major source of carbon input to the mangrove ecosystem and surrounding coastal ecosystems and in turn reflected in NPP.