| Outstanding challenges in plant ecology are (1) integrating processes at the leaf, individual, and population levels, (2) understanding how interactions between multiple environmental conditions affect performance, and (3) using eco-physiological and demographic information to sustainably manage harvested populations. Mangroves are used as a model system to address these questions.; Using greenhouse and field studies, this research provides an integrated understanding of the effects of salinity and light on the carbon gain, individual growth, and demography of Avicennia germinans and Rhizophora mangle. Experimentally, there were interactive effects of salinity and light on seedling performance; carbon gain and size increased more with light availability at low than high salinity. In natural populations, adult and sapling growth was lower at high salinity, translating to lower population growth. Seedling growth and transition to saplings increased with light, with lower rates at high salinity. But, there were no interactive effects of salinity and light because naturally-occurring light levels are much lower than the levels at which interactions were detected experimentally. Elasticity analysis indicated that at low salinity, despite higher seedling growth rates at high light, intermediate light Avicennia seedlings were relatively more important to the overall population growth rate, because <30% of the forest had high light. These results suggest that it is inaccurate to assume that the functional effects of salinity and light on individual performance translate directly to populations. Functional effects of environmental conditions on populations can only be understood in a demographic context, which considers the temporal and spatial variation in those conditions.; The undisturbed mangrove population we studied was expanding (λ = 1.067). Elasticity analysis indicated that the most vulnerable demographic element was survivorship of small trees (2–14.9 cm DBH)—precisely the size favored for harvesting. Harvesting intensities ranged from 12 to 100% of small trees. According to modeling simulations, most of the observed harvesting was unsustainable. We believe mangroves can be sustainably harvested, but harvesters must cut at lower intensities and over a broader area. Interviews with harvesters indicate that their perceptions of the sustainability of harvesting did not match the results of our demographic study, suggesting that educational programs are necessary. |
