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Trends in U.S. Mangrove Area Over the Past 35 years

Paper Reviewed
Giri, C. and Long, J. 2016. Is the geographic range of mangrove forests in the conterminous United States really expanding? Sensors 16: doi:10.3390/s16122010.

Mangrove forests consist of plants that are capable of tolerating saline waters and are found in tropical and subtropical coastal regions of the planet. Recently, however, concerns have been expressed that these important ecosystems might be at risk due to projected negative effects of CO2-induced climate change, (e.g., increasing temperatures, rising sea levels, more frequent and extreme storms). But is this really the case?

A good first assessment of their health in the face of ongoing natural and anthropogenic factors was recently conducted by Giri and Long (2016). Using satellite data, aerial photographs, digital elevation model and field inventory data, the pair of U.S. researchers was able to examine mangrove dynamics for the conterminous United States over the period 1980-2015, which period covers the so-called unprecedented modern rise of global temperature. And what did those dynamics reveal?

According to Giri and Long, and as shown in the figure below, mangrove area increased by 4.3 percent. This increase was not the product of the forests expanding their range northward (poleward toward cooler latitudes). Rather, it was attributed to an inward or landward expansion up-river and/or away from the coast.

As for the cause of the area increase, Giri and Long note there are likely "multiple factors" that are responsible, including "sea level rise, absence or presence of sub-freezing temperatures, land use change, impoundment/dredging, changing hydrology, fire, storm, sedimentation and erosion, and mangrove planting." Whatever the combination, one thing seems sure -- coastal mangroves in the conterminous U.S. have fared well over the past three and a half decades, notwithstanding alarmist concerns of their demise due to CO2-induced global warming.

Figure 1. Areal extent of mangrove forests in the conterminous United States every five years from 1980 to 2015. Source: Giri and Long (2016).

Posted 4 May 2017