Conclusion

In the intact forest, A. germinans seedling and sapling recruitment was three times greater the mortality rate. Additionally, L. racemosa and R. mangle seedling mortality rate was two times greater the recruitment, and sapling mortality was 28 times greater than recruitment rate. In general, growth was low across all life stages within the intact forest compared to the new gaps. These results give insight into how A. germinans becomes a co-dominant to dominant in closed canopy mature (climax) mangrove forest of South Florida (Craighead 1971), and the observation that L. racemosa needs light gaps for sapling to survive to the adult stage (Ball 1980).

The seedling and sapling recruitment rates of A. germinans were > 1.5 times greater than mortality in new lighting-initiated canopy gaps, indicating an increasing population. New gaps also had 2.6 to 10.6 times greater rate of seedling mortality for R. mangle and L. racemosa compared to recruitment, indicating decreases in these populations. Seedling stem elongation was greatest in the new gaps. Taken together, the seedling recruitment rate in new gaps was twice as high as that in the other forest stages. Presumably this recruitment rate will continue to increase as the conditions within the gaps favor propagule establishment (Chapter II). Additionally, new light gaps likely favor A. germinans seedling recruitment in this initial stage of gap succession.

At the growing gap stage of development, seedling mortality rate of R. mangle was 10 times greater and sapling mortality was 13 times greater than recruitment. The recruitment of R. mangle adults was 4 times greater than mortality. The gaps have developed to a phase in which there was reduced stem elongation, sapling and adult growth, and few individuals able to recruit into the adult life stage. Sapling populations are high (~ 1 sapling m²), and seedling populations are low (0.6 seedling m²). R. mangle dominates seedling and sapling stages of the growing gaps and eventually are making the transition to the adult life stage. The end results indicate that at the growing gap stage of succession of the lightning gaps R. mangle stems were being favored as adult trees.

Lightning gaps have been reported as an important disturbance mechanism in many mangrove forests around the world. I found differences in survival, recruitment, and growth by species within and across life stages and these differences changed depending on the forest stage. In summary, these results provide population parameters needed to understand and predict recruitment and survivorship for each of the three dominant species (A. germinans, L. racemosa, and R. mangle) during the gap-phase dynamics of the mangrove forest. Additionally, these growth estimates enable better understanding of intact forest and development within the stages of gap-phase dynamics. The results of this study are of considerable importance in these lightning disturbed systems and for other mangroves systems experiencing gap dynamics mechanisms.