Mangroves in a Changing World

Dr. Karen L. McKee

Scientist Emeritus, U.S. Geological Survey

Mangrove ecosystems are subject to a range of climate change factors, including atmospheric CO2, air and sea temperatures, precipitation, and sea-level. Although rising concentrations of atmospheric CO2 may have direct effects on mangrove vegetation, CO2 may interact with other factors such as nutrient availability, flooding or salinity stress, and competition, to alter mangrove structure and function. Mangroves respond to higher CO2 with increased growth, but some studies suggest that other factors such as competition and herbivory may limit the beneficial effects.  Although findings indicate that biological interactions could modify the direct effects of higher CO2, predictions are difficult to make at a global scale due to limited data on mangrove species. Global changes in temperature and rainfall may also modify mangrove distribution patterns, leading to range expansion at their latitudinal limits. Such climate changes, however, may be facilitated by negative effects on competing, temperate vegetation in sub-tropical regions, e.g., the Mississippi River Delta where the black mangrove, Avicennia germinans, has expanded into areas where the temperate salt marsh grass, Spartina alterniflora has succumbed to periodic dieback associated with drought. One of the most important global change factors affecting mangroves is sea-level rise. Recent work has shown how both physical and biological processes influence vertical land building in mangrove forests and how factors affecting organic matter accumulation may lead to changes in elevation trajectories. Analysis of a global dataset revealed that high rates of sedimentation do not guarantee accommodation of sea-level rise because of high rates of subsidence; peat-forming areas are able to keep up because of subsurface expansion driven by root matter accumulation.  Carbon sequestration rates estimated from surface accretion of organic carbon, however, were similar in organic (216 g C m-2 yr-1) and mineral (145 g C m-2 yr-1) soil types, but varied across geographic locations (41 to 591 g C m-2 yr-1), suggesting spatial variation in controls on C deposition.  Subsurface inputs of carbon, which were estimated using measured rates of root matter accumulation and root carbon content, averaged 121 g m-2 yr-1, but exceeded 400 g m-2 yr-1 at several sites.  In summary, changes in atmospheric CO2 concentration, climate, and sea level will lead to complex interactions affecting the structure and function of mangroves.  Predicting the outcome of such interactions will be aided by multivariate approaches that allow simultaneous examination of multiple drivers of change along with internal feedback pathways and linkages among physical and biological components.

We recommend reading justhost review if you would like a quality business hosting for your small company website.