without metabolic dysfunction (Ball, 1988). There are
four primary mechanisms by which mangroves cope with
the overabundance of ions in saline water (see Krauss
et al., 2008). The first is at the root, where mangroves
exclude at least 90 % of external salts. The second is to
store salt ions in vacuoles within the cells of the leaves.
A third mechanism is to increase succulence of the leaf
to maintain ionic balance (e.g., Ceriops tagal, Xylocarpus
spp., Osbornia spp.). Finally, some species (e.g., Acanthus, Aegialitis, Aegiceras, Avicennia) excrete salt via
glands on their leaves (Ball, 1988).
Climate change impacts
Mangroves are very susceptible to shifts in distribution that
will result from increasing temperatures and sea-level rise.
Rising air and ocean temperatures will likely increase mangrove growth rates and may allow them to expand their
global distribution where they will encroach into salt marsh
habitats (Traill et al., 2011). At the local scale, the effects of
sea-level rise will vary depending on a variety of
co-occurring environmental factors including tidal range,
sedimentation and accretion (i.e., increase in soil surface
elevation) rates, and local and regional subsidence. Biological feedback mechanisms, which vary depending upon
species composition and growth rates, will also affect relative sea-level rise via sediment trapping and/or enhanced
root growth (McKee, 2011). For instance, in many Australian mangrove forests, the rate of accretion equals or
exceeds the rate of relative sea-level rise (Lovelock et al.,
2011). Given continued seedling recruitment and adequate
growth, the potential for landward migration of mangroves
into new intertidal areas is strong. However, many mangrove communities occur near prime real estate areas;
migration landward is restricted where human and natural
barriers block their expansion.
Summary
Tidal freshwater forested wetlands are found along rivers
at the uppermost extent of tidal influence, whereas mangroves are found nearest the ocean in the lowermost portion of the intertidal zone. Both systems are regulated
largely by hydrology. Tidal freshwater forested wetlands
will not persist where average annual porewater salinity
exceeds 2 g/L, whereas mangroves can tolerate a wide
range of salinities. However, mangroves are intolerant to
freezing, and the adaptations necessary for mangroves to
survive in saline conditions often limit their growth rates
and ability to outcompete salt marsh species. Rising temperatures associated with climate change will likely
expand the range of mangroves globally, at the detriment
of salt marsh species in some cases. Sea-level rise is forcing the migration of both forested wetland habitats. Both
forested wetland types have done this successfully, but
levees and other barriers (natural and anthropogenic) will
ultimately limit their expansion.
Bibliography
Almeida, S. S., Amaral, D. D., and Silva, A. S. L., 2004. Floristic
analysis and structure of tidal flooded forests in the Amazonian
estuary. Acta Amazonica, 34, 513–524.
Alongi, D. M., 2009. The Energetics of Mangrove Forests.
New York: Springer.
Ball, M. C., 1988. Ecophysiology of mangroves. Trees-Structure
and Function, 2, 129–142.
Boto, K. G., and Wellington, J. T., 1983. Phosphorus and nitrogen
nutritional status of a northern Australian mangrove forest.
Marine Ecology Progress Series, 11, 63–69.
Brinson, M. M., Bradshaw, H. D., and Jones, M. N., 1985. Transitions in forested wetlands along gradients of salinity and
hydroperiod. Journal of the Elisha Mitchell Scientific Society,
101, 76–94.
Cattanio, J. H., Anderson, A. B., and Carvalho, M. S., 2002. Floristic composition and topographic variation in a tidal floodplain
forest in the Amazon estuary. Revista Brasileira De Botanica,
24, 419–430.
Conner, W. H., Doyle, T. W., and Krauss, K. W. (eds.), 2007.
Ecology of Tidal Freshwater Forested Wetlands of the
Southeastern United States. Dordrecht: Springer.
Courtwright, J., and Findlay, S. E. G., 2011. Effects of
microtopography on hydrology, physiochemistry, and vegetation in a tidal swamp of the Hudson River. Wetlands, 31,
239–249.
Craft, C., Clough, J., Ehman, J., Joye, S., Park, R., Pennings, S.,
Guo, H., and Machmuller, M., 2009. Forecasting the effects of
accelerated sea-level rise on tidal marsh ecosystem services.
Frontiers in Ecology and the Environment, 7, 73–78.
Doyle, T. W., Krauss, K. W., Conner, W. H., and From, A. S., 2010.
Predicting the retreat and migration of tidal forests along the
northern Gulf of Mexico under sea-level rise. Forest Ecology
and Management, 259, 770–777.
Duberstein, J. A., and Conner, W. H., 2009. Use of hummocks and hollows by trees in tidal freshwater forested wetlands along the Savannah River. Forest Ecology and Management, 258, 1613–1618.
Duke, N. C., Ball, M. C., and Ellison, J. C., 1998. Factors influencing biodiversity and distributional gradients in mangroves.
Global Ecology and Biogeography Letters, 7, 27–47.
Ellison, A. M., 2004. Wetlands of Central America. Wetlands
Ecology and Management, 12, 3–55.
Hackney, C. T., Avery, G. B., Leonard, L. A., Posey, M., and
Alphin, T., 2007. Biological, chemical, and physical characteristics of tidal freshwater swamp forests of the Lower Cape Fear
River/Estuary, North Carolina. In Conner, W. H., Doyle, T. W.,
and Krauss, K. W. (eds.), Ecology of Tidal Freshwater Forested
Wetlands of the Southeastern United States. Dordrecht: Springer,
pp. 183–221.
Krauss, K. W., and Ball, M. C., 2013. On the halophytic nature of
mangroves. Trees-Structure and Function, 27, 7–11.
Krauss, K. W., Lovelock, C. E., McKee, K. L., Lopez-Hoffman, L.,
Ewe, S. M. L., and Sousa, W. P., 2008. Environmental drivers in
mangrove establishment and early development: a review.
Aquatic Botany, 89, 105–127.
Krauss, K. W., Duberstein, J. A., Doyle, T. W., Conner, W. H., Day,
R. H., Inabinette, L. W., and Whitbeck, J. L., 2009. Site condition, structure, and growth of baldcypress along tidal/non-tidal
salinity gradients. Wetlands, 29, 505–519.
Lovelock, C., Bennion, V., Grinham, A., and Cahoon, D., 2011. The
role of surface and subsurface processes in keeping pace with sea
level rise in intertidal wetlands of Moreton Bay, Queensland,
Australia. Ecosystems, 14, 745–757.
McKee, K. L., 2011. Biophysical controls on accretion and elevation change in Caribbean mangrove ecosystems. Estuarine,
Coastal and Shelf Science, 91, 475–483.
FORESTED WETLAND HABITAT
337
four primary mechanisms by which mangroves cope with
the overabundance of ions in saline water (see Krauss
et al., 2008). The first is at the root, where mangroves
exclude at least 90 % of external salts. The second is to
store salt ions in vacuoles within the cells of the leaves.
A third mechanism is to increase succulence of the leaf
to maintain ionic balance (e.g., Ceriops tagal, Xylocarpus
spp., Osbornia spp.). Finally, some species (e.g., Acanthus, Aegialitis, Aegiceras, Avicennia) excrete salt via
glands on their leaves (Ball, 1988).
Climate change impacts
Mangroves are very susceptible to shifts in distribution that
will result from increasing temperatures and sea-level rise.
Rising air and ocean temperatures will likely increase mangrove growth rates and may allow them to expand their
global distribution where they will encroach into salt marsh
habitats (Traill et al., 2011). At the local scale, the effects of
sea-level rise will vary depending on a variety of
co-occurring environmental factors including tidal range,
sedimentation and accretion (i.e., increase in soil surface
elevation) rates, and local and regional subsidence. Biological feedback mechanisms, which vary depending upon
species composition and growth rates, will also affect relative sea-level rise via sediment trapping and/or enhanced
root growth (McKee, 2011). For instance, in many Australian mangrove forests, the rate of accretion equals or
exceeds the rate of relative sea-level rise (Lovelock et al.,
2011). Given continued seedling recruitment and adequate
growth, the potential for landward migration of mangroves
into new intertidal areas is strong. However, many mangrove communities occur near prime real estate areas;
migration landward is restricted where human and natural
barriers block their expansion.
Summary
Tidal freshwater forested wetlands are found along rivers
at the uppermost extent of tidal influence, whereas mangroves are found nearest the ocean in the lowermost portion of the intertidal zone. Both systems are regulated
largely by hydrology. Tidal freshwater forested wetlands
will not persist where average annual porewater salinity
exceeds 2 g/L, whereas mangroves can tolerate a wide
range of salinities. However, mangroves are intolerant to
freezing, and the adaptations necessary for mangroves to
survive in saline conditions often limit their growth rates
and ability to outcompete salt marsh species. Rising temperatures associated with climate change will likely
expand the range of mangroves globally, at the detriment
of salt marsh species in some cases. Sea-level rise is forcing the migration of both forested wetland habitats. Both
forested wetland types have done this successfully, but
levees and other barriers (natural and anthropogenic) will
ultimately limit their expansion.
Bibliography
Almeida, S. S., Amaral, D. D., and Silva, A. S. L., 2004. Floristic
analysis and structure of tidal flooded forests in the Amazonian
estuary. Acta Amazonica, 34, 513–524.
Alongi, D. M., 2009. The Energetics of Mangrove Forests.
New York: Springer.
Ball, M. C., 1988. Ecophysiology of mangroves. Trees-Structure
and Function, 2, 129–142.
Boto, K. G., and Wellington, J. T., 1983. Phosphorus and nitrogen
nutritional status of a northern Australian mangrove forest.
Marine Ecology Progress Series, 11, 63–69.
Brinson, M. M., Bradshaw, H. D., and Jones, M. N., 1985. Transitions in forested wetlands along gradients of salinity and
hydroperiod. Journal of the Elisha Mitchell Scientific Society,
101, 76–94.
Cattanio, J. H., Anderson, A. B., and Carvalho, M. S., 2002. Floristic composition and topographic variation in a tidal floodplain
forest in the Amazon estuary. Revista Brasileira De Botanica,
24, 419–430.
Conner, W. H., Doyle, T. W., and Krauss, K. W. (eds.), 2007.
Ecology of Tidal Freshwater Forested Wetlands of the
Southeastern United States. Dordrecht: Springer.
Courtwright, J., and Findlay, S. E. G., 2011. Effects of
microtopography on hydrology, physiochemistry, and vegetation in a tidal swamp of the Hudson River. Wetlands, 31,
239–249.
Craft, C., Clough, J., Ehman, J., Joye, S., Park, R., Pennings, S.,
Guo, H., and Machmuller, M., 2009. Forecasting the effects of
accelerated sea-level rise on tidal marsh ecosystem services.
Frontiers in Ecology and the Environment, 7, 73–78.
Doyle, T. W., Krauss, K. W., Conner, W. H., and From, A. S., 2010.
Predicting the retreat and migration of tidal forests along the
northern Gulf of Mexico under sea-level rise. Forest Ecology
and Management, 259, 770–777.
Duberstein, J. A., and Conner, W. H., 2009. Use of hummocks and hollows by trees in tidal freshwater forested wetlands along the Savannah River. Forest Ecology and Management, 258, 1613–1618.
Duke, N. C., Ball, M. C., and Ellison, J. C., 1998. Factors influencing biodiversity and distributional gradients in mangroves.
Global Ecology and Biogeography Letters, 7, 27–47.
Ellison, A. M., 2004. Wetlands of Central America. Wetlands
Ecology and Management, 12, 3–55.
Hackney, C. T., Avery, G. B., Leonard, L. A., Posey, M., and
Alphin, T., 2007. Biological, chemical, and physical characteristics of tidal freshwater swamp forests of the Lower Cape Fear
River/Estuary, North Carolina. In Conner, W. H., Doyle, T. W.,
and Krauss, K. W. (eds.), Ecology of Tidal Freshwater Forested
Wetlands of the Southeastern United States. Dordrecht: Springer,
pp. 183–221.
Krauss, K. W., and Ball, M. C., 2013. On the halophytic nature of
mangroves. Trees-Structure and Function, 27, 7–11.
Krauss, K. W., Lovelock, C. E., McKee, K. L., Lopez-Hoffman, L.,
Ewe, S. M. L., and Sousa, W. P., 2008. Environmental drivers in
mangrove establishment and early development: a review.
Aquatic Botany, 89, 105–127.
Krauss, K. W., Duberstein, J. A., Doyle, T. W., Conner, W. H., Day,
R. H., Inabinette, L. W., and Whitbeck, J. L., 2009. Site condition, structure, and growth of baldcypress along tidal/non-tidal
salinity gradients. Wetlands, 29, 505–519.
Lovelock, C., Bennion, V., Grinham, A., and Cahoon, D., 2011. The
role of surface and subsurface processes in keeping pace with sea
level rise in intertidal wetlands of Moreton Bay, Queensland,
Australia. Ecosystems, 14, 745–757.
McKee, K. L., 2011. Biophysical controls on accretion and elevation change in Caribbean mangrove ecosystems. Estuarine,
Coastal and Shelf Science, 91, 475–483.
FORESTED WETLAND HABITAT
337