Black Mangrove on the Move on the Gulf Coast of Texas

Carl Trettin (left) works with TAMU-CC students on black mangrove sampling. Photo courtesy of TAMU-CC.

Carl Trettin (left) works with TAMU-CC students on black mangrove sampling. Photo courtesy of TAMU-CC.

Some plant species are already migrating due to climate change, moving north into areas that aren’t as cold as they used to be. Along the Gulf Coast of Texas, black mangrove, a small shrubby tree, is expanding into saltmarshes as the intervals between winters with freezing temperatures lengthen.

Easily outcompeting the Spartina cordgrasses that dominate the saltmarshes, black mangrove has started taking over the higher marsh areas. Both mangrove forests and saltmarshes provide important ecosystem services—protection from storm surges, habitat for fish and other aquatic species and carbon sequestration—but little is known about the effects of changing from a grass community to a wood-dominated one.

A unique U.S. Forest Service Southern Research Station (SRS) program has provided funding to study this issue, and to increase the capacity for research on mangroves and forested wetlands worldwide. At the end of 2012, the SRS Director’s Partnership Enhancement Initiative (DPEI) announced funding for three projects on mangrove research, two in Puerto Rico, and the third a collaboration with faculty at Texas A&M University at Corpus–Christi (TAMU-CC), a Hispanic-serving institution, to study the expansion of black mangrove into Texas saltmarshes.

This spring TAMU-CC faculty and graduate students started collecting data on the community structure—plants and animals present—among saltmarsh and mangrove systems on two sets of sites. The first set pairs natural saltmarsh with nearby saltmarsh invaded by black mangrove, while the second set pairs restored sites where mangroves are allowed to grow naturally with those where mangrove has been removed.  In addition to looking at biodiversity, the TAMU-CC researchers are testing the use of genetic markers to determine whether black mangrove is spreading primarily by seeds or by clonal vegetative growth.

“They also started using methods for studying carbon dynamics I’ve been developing with other researchers to study carbon dynamics in the mangrove forests of East Africa,” says Carl Trettin, team leader of the SRS Center for Forested Wetlands Research who serves as technical liaison for the mangrove projects. “By training graduate students, the DPEI projects are also helping to build future research capacity for the expanding SRS Forested Wetlands team and for the international global carbon survey of mangrove and peat swamp forests that we’re part of.”

This June the Corpus Christi group hosted a workshop for principal investigators and students involved in the DPEI mangrove projects to exchange information and explore opportunities for future collaborations. As part of the workshop, Trettin gave a briefing on sampling carbon pools in mangroves and collected soil samples for the Corpus Christi study. Participants also developed a plan for expanding the black mangrove research project and preparing a grant proposal to the National Science Foundation.

In late summer, SRS provided additional funding for James Sanchez, a TAMU-CC graduate student involved in the mangrove project who is also a fellow in the Hispanic Leaders in Agriculture and the Environment program sponsored by the Forest Service.

For more information, email Carl Trettin at ctrettin@fs.fed.us.

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Posted in Climate Change, Forest Watersheds