McDonald, Kerrine O.; Webber, Dale F.; Webber, Mona K.
Author Affiliation, Ana.
Department of Life Sciences
Mangrove forest structure under varying environmental conditions
Bulletin of Marine Science
Date of Publication
Vegetation assessments were carried out in three mangrove forests undergoing different levels of anthropogenic stress and varying environmental factors. These forests were in Hunts Bay, Fort Rocky Lagoon (part of the Port Royal mangroves on the south shore of Kingston Harbour), and Wreck Bay (Hellshire). The vegetation assessments included the determination of species composition, floristics, and leaf litter production of the mangrove trees. Selected environmental and biological conditions were also investigated at each site. The hypothesized gradient of environmental factors, eutrophication and disturbance was Hunts Bay > Fort Rocky Lagoon > Wreck Bay. With the exception of light on the forest floor, the soil and water column parameters were all significantly different among sites, but the values did not always follow the expected environmental gradient. For example, nitrate/nitrite values were maximum at Wreck Bay (34.4 ýM), followed by Hunts Bay (12.41 ýM) and Fort Rocky Lagoon (10.0 ýM), and phosphates ranked with maximum at Fort Rocky Lagoon (9.69 ýM), then Hunts Bay (4.41 ýM) and Wreck Bay (1.24ýM). Of the vegetation characteristics, only average leaf litter production and percentage cover were significantly different among sites, with a ranking similar to the hypothesis (i.e. Hunts Bay > Fort Rocky Lagoon > Wreck Bay). The most important factors influencing the distribution of productivity and percentage cover among forests were soil salinity, soil NO3, especially the nitrate to phosphate ratio, soil moisture content and soil temperature with R2 values of 0.77 for litter production and 0.64 for percentage cover. Other factors such as diameter at breast height and tree height were not significantly different among forests and showed a weak relationship with edaphic factors. Overall results indicated that the forests were very different with respect to physico-chemical and edaphic factors, and there was a clear gradient of eutrophication. However, the effect of anthropogenic stress and varying environmental conditions is most reliably demonstrated in the productivity and percentage cover of the forests.....