POPULATION-STRUCTURE AND DISPERSION PATTERN IN MANGROVES OF KARACHI, PAKISTAN

Structural characteristics and dispersion patterns were studied in mon ospecific stands of the mangrove species Avicennia marina (Forssk. ) V ierh. in Karachi, Pakistan. Tree density varied between 6 and 940 with an average of 151.8 trees per 0.1 ha, the basal area varied between 0 .22 and 4.09 with an average of 1.33 m2 per 0.1 ha, and plant cover va ried between 97.74 and 822.6 with an average of 436.63 m2 per 0.1 ha. The observed variation in the three structural attributes is accounted for in the various environmental variables measured, such as salinity , mud content and maximum water-holding capacity. The height of trees decreased invariably with distance from the shore, most probably as a result of increase in soil water salinity. The distribution of seedlin gs varied greatly between sites and they showed a tendency to cluster either around the trees or in depressions protected from water movemen t. The dispersion pattern analysis of trees (greater than 3 cm diamete r at breast height) revealed a small-scale pattern corresponding to a patch size of 72 m2 and a large-scale pattern corresponding to a size of 396 m2, the former presumably being of reproductive origin and the latter a consequence of environmental heterogeneity.