Background/Question/Methods At mid-Florida latitudes mangroves adapt or acclimate to temperate conditions; and, they must interact with salt marsh species.  In experiment 1 we studied the importance of local adaptation and maternal genotype on the red mangrove (Rhizophora mangle).  Factors included genotype ( n=86) nested within embayment of origin (n=5), elevation as an indication of desiccation stress (n=2), and island planted (n=5).  In experiment 2 we assessed the importance of salt marsh plants on mangrove colonization.  Treatments included monocultures, all possible pairs, and 3-4 species combinations of Spartina alterniflora, S. patens, Sesuvium portulcastrum, Distichlis spicata, and Juncus roemerainus, and species richness. Response variables were survival and growth of planted R. mangle, and natural colonization.
Results/Conclusions In experiment 1, R. mangle survival was dependent on genotype, elevation, and island planted (logit modeling, p < 0.0005, Rho²= 0.29, n=1,492 records for analysis). Growth over 3 years was affected by genotype x elevation (MANOVA Wilks Lambda _{237, 1371.5} =1.33) and genotype x island (Wilks Lambda _{822, 1371.9} = 1.32) interactions as well as all of the main effects. Univariate comparisons indicated that plant height (p< 0.05) and canopy area (p<0.06) were affected by genotype x environment interactions, but not trunk diameter.  Elevation accounted for 21% of the overall variation in growth, maternal genotype for 4%, and all two- and-three-way interaction terms with genotype accounted for 17%.  Overall, we found that a possible trade-off exists in size (larger providing better growth and perhaps competitive edge) and numbers of propagules (smaller requiring less maternal investment which should allow the production of more propagules/tree).
In experiment 2, at 1 year monocultures of salt marsh species reduced growth, but increasing marsh species richness resulted in greater growth. The average effect of different marsh plant species combinations on growth of R. mangle was marginal (ANOVA F_{11, 58}, p<0.071).  Bare (unvegetated by salt marsh) ground, S. alterniflora, and S. patens inhibited the colonization by Avicennia germinans (GENMOD, log-link function, p < 0.05), but colonization was greatly enhanced by the three species combination S. alterniflora+S. patens+S. portulacastrum (p < 0.012).
These experiments show that there are different survival and growth responses of mangrove seedlings from different maternal genotypes to environmental pressures; and, that mangroves must simultaneously cope with interactions with salt marsh species. This suggests that tropical species expanding their range as climate warms will experience unique selection regimes that can affect community dominance.