EFFECTS OF ABIOTIC AND BIOTIC FACTORS ON THE SEEDLING RECRUITMENT OF <em>HERITIERA</em> <em>FOMES</em> IN THE MANGROVES OF THE SUNDARBANS, BANGLADESH

Abstract

Influences of abiotic and biotic factors on the seedling regeneration of Heritiera fomes Buch.-Ham. were investigated. The average number of seedlings appearing in a year was 6680 ha⁻¹ although recruitment density varied among different parts of the forests and from year to year. Of the many mangrove species in the area, H. fomes alone constituted 24% of the recruits. Salinity of the area apparently influenced the recruitments which decreased with increasing levels of salinity. Seedling half-life values for H. fomes in less, moderate and strongly saline zones were 13.7, 8.8 and 6.3 months respectively. The relationship between seedling recruitment and stand density was insignificant. Similarly, up to 33 months, canopy closure was not found to affect the seedling recruitment and survival. A lower recruitment and survival of seedlings were noticed in areas with higher level of tidal inundation. As regards the biotic factors, the spotted deer (Axis axis) was not found to affect the natural regeneration of H. fomes, rather it might influence the dominance of this mangrove species through its preferential browsing habit. The wild boar (Sus scrofa) did not appear to have any significant impact on regeneration. Crabs were not found to cause mortality of seedlings, while the role of the rhesus macaque (Macaca mulatta) also appeared to be insignificant. However, the black rat (Rattus rattus) caused substantial damage to the new seedlings of H .fomes but only in relatively raised and less saline areas.