Carbon Accumulation by Southeastern Forests May Slow

by Zoё Hoyle, SRS Science Delivery Group
The analysis showed that from 2007 to 2015  the largest gains in forest carbon stocks came from younger forests that had no disturbance events or cutting activities. Photo courtesy of the U.S. Forest Service.

The analysis showed that from 2007 to 2015 the largest gains in forest carbon stocks came from younger forests that had no disturbance events or cutting activities. Photo courtesy of the U.S. Forest Service.

Carbon accumulation levels in the southeastern U.S. may be slowing due to forest dynamics and land use changes, according to findings of U.S. Forest Service researchers published in the journal Scientific Reports on Friday, January 23.

The study authored by Forest Service Southern Research Station (SRS) scientists John Coulston, David Wear, and Jim Vose, is the first to isolate the impacts of forest disturbances, such as fire, disease, and cutting, as well as the impacts of land use change using permanent monitoring locations across the Southeast, making it one of the most thorough carbon studies completed.

Researchers show that future carbon accumulation rates are highly sensitive to future land use changes. Land use choices that either reduce the rate of afforestation or increase the rate of deforestation are key factors in future forest carbon accumulation.

“Future land transitions are uncertain but relatively small changes in afforestation from agriculture resulted in substantial decrease in accumulation rates,” said Coulston. “While tree-cutting did cause a decrease, overall forest growth was much greater, partly due to the rapid growth of younger forests.”

The aging of forests in the region was also a significant force behind potential slowing accumulation rates as growth rates are typically lower for older forest.  The study found forests to be fairly resilient to natural disturbances caused by weather, insects, diseases and fires. These disturbances reduced carbon accumulation rates but the losses were compensated by subsequent regrowth and storage in dead material on the site.

“These findings highlight the need for careful assessments of policies that affect forest management and land use changes in rural areas of the Southeast,” said Wear, project leader of the Station’s Center for Integrated Forest Science. “Continued forest carbon accumulation in the region is highly sensitive to land use transitions.”

The impact of land use transition is especially significant in the Southeast where 89 percent of the forested land is privately owned, underscoring the importance of land use policies that provide incentives for keeping lands in a forested condition.

The study estimated impacts on forest carbon accumulation in the region between 2007 and 2012, and projected potential changes out to 2017 based on forest growth and land use change scenarios.

Access the full text of the article.

For more information, email John Coulston at jcoulston@fs.fed.us.

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Posted in Climate Change, Forest Inventory & Analysis, Threats

Sunlight to the Seagrasses

by Sarah Farmer, SRS Science Delivery Group
Healthy seagrass meadows prevent erosion on coasts, store carbon, and provide marine animals with food and habitat. Photo by NOAA.

Healthy seagrass meadows prevent erosion on coasts, store carbon, and provide marine animals with food and habitat. Photo by NOAA.

Just off Florida’s 8,000 miles of coastline and tidal areas, in shallow sunlit waters, over 2 million acres of seagrass meadows waft in the ocean currents. Besides providing food and habitat for manatees, sea turtles, shellfish, and other animals, seagrasses protect coasts from erosion and store vast quantities of carbon dioxide.

“Seagrasses grow off the coast of many other U.S. states, including North Carolina and Virginia, as well as around the world,” says U.S. Forest Service Southern Research Station (SRS) scientist Zanethia Choice. “Globally, their economic value is nearly $4 trillion.”

Although more closely related to lilies than to terrestrial grasses, like most of their distant grass kin, seagrasses require plenty of sunlight. Poor water quality reduces the amount of sunlight that reaches them, and seagrasses around the world are threatened by practices that affect water quality such as wastewater disposal and fertilizer runoff.

Choice, a natural resource specialist at the SRS Center for Bottomland Hardwoods Research, and her colleagues from the University of Florida recently studied light requirements for four common seagrass species along the Florida Gulf Coast. The study was published in Marine Pollution Bulletin.

“We found a direct relationship between the amount of light reaching the ocean floor and the amount and diversity of seagrasses growing there,” says Choice. In 90 percent of sites where 13 years of historic data showed that adequate sunlight had been reaching the ocean floor, researchers found thriving seagrass meadows. However, areas with suitable light but no seagrass were most likely due to unsuitable substrate, temperature, and the amounts of dissolved salts and oxygen.

Seagrasses are adapted to nutrient-poor waters. When nutrients – whether from fertilizer runoff, wastewater disposal, or other human activities – wash into the ocean, they float suspended in the ocean waters. Seagrasses cannot use these suspended nutrients very efficiently, but tiny algae called phytoplankton can. Phytoplankton thrive in nutrient-rich waters, and as they grow, they intercept light and shade the ocean floor. Seagrasses were notably absent from areas with high nutrient levels.

Some seagrasses such as star grass could survive with as little as 8 percent of sunlight reaching the ocean floor, while other species required 25 percent sunlight or more. “Light requirements for all the seagrasses we studied differed from previous findings at other locations,” says Choice. “The differences are probably due to morphological and physiological differences, and adaptation to light histories at specific locations.”

Understanding the light requirements of different seagrass species is essential for coastal managers who want to maintain seagrass habitats, and managing for seagrass health also provides water quality targets that can benefit other marine life.

Read the full text of the article.

For more information, email Zanethia Choice at zdchoice@fs.fed.us

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Posted in Bottomland Hardwoods, Forest Watersheds, Threats

Freshwater Crayfish in Peril Worldwide

SRS scientist co-authors global assessment

by Zoё Hoyle, SRS Science Delivery Group
Procambarus lagniappe, the lagniappe crayfish, from Mississippi. Photo by Chris Lukhaup, courtesy of the U.S. Forest Service.

Procambarus lagniappe, the lagniappe crayfish, from Mississippi. Photo by Chris Lukhaup, courtesy of the U.S. Forest Service.

In early January, scientists led by the Zoological Society of London (ZSL) published results of a global assessment that shows that almost a third of the world’s species of crayfish are threatened with extinction. U.S. Forest Service aquatic ecologist Susie Adams was a co-author on the report and provided important information about North American crayfish species.

Adams was invited to be part of a collaboration with 76 experts from the International Union for Conservation of Nature (IUCN) started in 2010 to review the conservation status of the world’s 590 species of freshwater crayfish. The process led to IUCN Red List assessments of all the species.  Results published in the Philosophical Transactions of the Royal Society B show that 32 percent of all crayfish species are threatened with extinction, a much higher rate than that of most land and marine species.

“Though freshwater ecosystems take up less than one percent of the Earth’s surface, they support some 10 percent of the world’s species,” said Adams, who researches crayfish and other aquatic species for the Forest Service Southern Research Station Center for Bottomland Hardwoods Research in Mississippi.

“The study found that approximately 20 percent of North American crayfish species are threatened, and in the U.S., only two percent of those threatened occur in protected areas, which further highlights the imperiled status of freshwater species in the U.S.”

The project initially used information Adams compiled for status reviews of about 63 species. She was then invited to a work session with other astacologists (crayfish researchers) from the U.S. and Mexico to conduct status reviews of all North American species. Adams wrote or contributed to status reviews for 47 species as well as co-authoring the review paper.

The assessment found that the most common threats facing U.S. and Mexican species result from pollution, urban development, damming/water management, and logging. Though the extinction rate for U.S. species is less than that of North America as a whole, the report highlights a major hotspot of crayfish diversity in the South, notably Tennessee, Alabama, and Mississippi, where 53 percent of U.S. species (189 of 357) can be found in a single state.

“Globally, the greatest number of species for which we have insufficient data to assess conservation status are also in southern U.S., especially in the Gulf Coastal Plain and southern Appalachians,” said Adams. “This means there may be many more threatened species from this area than we know about, and this is especially true for crayfish species that burrow.”

The study notes that despite growing evidence for a freshwater biodiversity crisis, freshwater species, particularly invertebrates such as crayfish, are underrepresented on endangered species lists and in management plans for biodiversity. Only one percent of U.S. freshwater crayfish species, for example, are listed under the U.S. Endangered Species Act, compared to 20 percent of mammals.

Read the full text of the article.

For more information, email Susie Adams at sadams01@fs.fed.us.

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Posted in Bottomland Hardwoods, Fish & Wildlife, Forest Watersheds, Threats