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

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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

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A Future for Freeze-Tolerant Eucalyptus in the South?

Possible water impacts if landowners switch from pine

by Zoё Hoyle, SRS Science Delivery Group
Eight-year-old Eucalyptus stand in south Florida. Photo by Edward Barnard, courtesy of

Eight-year-old Eucalyptus stand in south Florida. Photo by Edward Barnard, courtesy of

Recently published research by U.S. Forest Service scientists provides important first-time analyses of the potential impacts of introducing plantations of freeze-tolerant Eucalyptus into the South.

Eucalyptus, a fast-growing tree native to Australia and Indonesia, is planted across large areas of Asia, Africa, and South America as a major source of hardwood fiber for paper and biofuels. Because of its sensitivity to freezing temperatures, Eucalyptus hasn’t been planted extensively in the U.S., where fiber markets are dominated by softwood from pines grown in the Southeast.

Some paper mills require hardwood fiber, and interest in using small-diameter hardwoods for biofuel pellets is growing. In the southern U.S., hardwood fiber mostly comes from natural stands, and sources are scarce, especially in localized markets. There is increasing interest in the South in the development of a freeze-tolerant Eucalyptus species to grow in plantations as a hardwood fiber source.

The prospect of Eucalyptus plantations also raises concerns, since Eucalyptus is known for using large quantities of water. Will landowners convert their forest land to Eucalyptus to get better returns? If they do, how could this affect southern water resources?

Forest Service Southern Research Station (SRS) scientists recently published companion articles in the journal Forest Science: one estimates the acres and types of land southern landowners might convert to freeze-tolerant Eucalyptus, while the other evaluates possible impacts on the region’s water resources.

The economic and hydrological analyses were led respectively by David Wear and Jim Vose, both project leaders of the SRS Center for Integrated Forest Science in Raleigh, North Carolina.

Wear and North Carolina State University collaborators first defined a study area based on hardiness zones and water availability that spans the southeastern U.S. from east-central Texas to South Carolina. Then they compared net economic returns from potential Eucalyptus plantings with those of existing land uses, exploring how Eucalyptus plantations might develop under different market futures.

They found that Eucalyptus would probably be most competitive with planted pine, as opposed to agricultural and other land uses, and that conversions from pine could be expected on 0.8 to 1.4 million acres, 5 to 9 percent of the current area of planted pine.

“Extending the analysis to the current area of naturally regenerated pine results in as much as 2.8 million acres,” said Wear. “But actual adoption depends on uncertain future markets for cellulose, especially for bioenergy feedstock.”

Vose and fellow scientists from the SRS Center for Watershed Science and the SRS Eastern Forest Threat Assessment Center used the study area developed by Wear to analyze potential impacts on water resources at stand and regional scales. “With one of the highest evapotranspiration rates among tree species, Eucalyptus plantings could have negative effects on water resources and aquatic ecosystems, especially at local scales,” said Vose. “To our knowledge, this study is the first critical analysis of the potential impacts of Eucalyptus on water resources in the U.S. South.”

To analyze effects at the stand level, researchers used a process-based model tied to climate data at five specific locations across the study area, applying the model to a hypothetical Eucalyptus plantation at each site from initial planting through a full rotation.

Precipitation varied widely among the five locations, from about 31 inches per year in the Texas location to about 61 inches per year in Mississippi. Stand-level results showed that Eucalyptus plantations could potentially lower water flow drastically in some locations.

“These effects will depend on the hydrologic conditions of the planting site and on the amount of land planted in Eucalyptus,” said Vose. “Negative impacts might occur in areas with low rainfall or where dry years are likely.”

For the regional analysis, the researchers applied the large-scale water balance model WaSSI at the watershed level, identifying the HUC-12 watersheds across the entire South-wide planting area identified in the Wear study. They simulated replacing different proportions of the existing conifer land cover with Eucalyptus.

The researchers found that at the level of conversion indicated by Wear’s research, effects at the watershed level would be negligible – even lower if plantations were on early rotation schedules.  In contrast, if economic conditions promoted large-scale conversion of existing land cover (such as 50 percent of current conifer cover), there could be regional effects on water availability in areas such as the Florida Panhandle, south Alabama, southwest Georgia, and Mississippi.

Read the full text of the economic analysis by Wear et al.

Read the full text of the hydrologic analysis by Vose et al.

For more information, email David Wear at or Jim Vose at

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Posted in Biomass and Bioenergy, Economics & Policy, Forest Operations, Forest Products, Forest Watersheds, Genetics, Southern Pines