The Delta Experimental Forest

Studies on bottomland hardwoods

by Zoё Hoyle, SRS Science Delivery Group
Sweetgum leaves. The dynamics of oak-sweetgum stands are studied on the Delta. Photo by Robert Webb, courtesy of bugwood.org.

Sweetgum leaves. The dynamics of oak-sweetgum stands are studied on the Delta. Photo by Robert Webb, courtesy of bugwood.org.

Located in Washington County, Mississippi, the 2,600-acre Delta Experimental Forest (the Delta) was established in 1945 by the U.S. Forest Service and is owned and managed by Mississippi State University (MSU). The Forest Service Southern Research Station (SRS) Center for Bottomland Hardwoods Research conducts research on the forest under a long-term cooperative agreement. Until the 1970s, the Delta was a working forest with a crew of technicians to establish and maintain research studies conducted by SRS scientists. Timber receipts paid for roads and facilities maintenance on the forest.

Research during the first 30 years involved thinning studies, developing methods for growing quality southern hardwoods, evaluating results of efforts to improve eastern cottonwood clones, and studying the progression of heartrot diseases and the life cycles and impacts of insect borers. Later studies included determining the causes of oak decline and investigating red oak-sweetgum stand dynamics.

These studies provided much of what is now known about growing different tree species in the poorly drained but fertile soils deposited by the Mississippi River. In addition, several eastern cottonwood clones selected during the 1960s and 1970s by SRS geneticists and tested in the Delta are still used by forest industry throughout the South and in Europe, Asia, and South America.

The 1970s brought changes in state priorities that resulted in a decline in both forest operations and new studies on the experimental forest. By the mid-1990s, heartrot had degraded many of the older trees on the site; a devastating ice storm in 1994 damaged the crowns of most canopy trees. Most of the forest on the Delta was cut in the late 1990s to regenerate degraded forest stands. Oak seedlings were planted to supplement natural oak regeneration.

Over the last two decades, the Delta became home for a new round of experiments that combine the expertise of SRS scientists in the bottomland hardwoods unit on subjects ranging from red oak-sweetgum stand dynamics to the ecology of wood-destroying insects.

For more information, email Ted Leininger at tleininger@fs.fed.us.

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Posted in Bottomland Hardwoods, Experimental Forests, Genetics, Insects and Diseases

Bold Moves Needed to Save North America’s Freshwater Mussels

Enigmatic declines add to extinction pressures

by Zoё Hoyle, SRS Science Delivery Group
Plain pocketbook mussel (Lampsilis cardium) showing the lure it uses to draw fish close enough to deposit larvae in their gills as part of its unique reproductive cycle. Photo by Wendell Haag.

Plain pocketbook mussel (Lampsilis cardium) showing the lure it uses to draw fish close enough to deposit larvae in their gills as part of its unique reproductive cycle. Photo by Wendell Haag.

North America’s freshwater mussels are in grave danger of disappearing. Though there’s been progress in learning about freshwater mussel biology and effective techniques developed to propagate mussel species, conservation efforts should focus more directly on bold and aggressive habitat restoration, according to a recently published review paper by U.S. Forest Service researcher Wendell Haag.

In the article, Haag, fisheries research biologist with the Southern Research Station Center for Bottomland Hardwoods Research, and co-author J.D. Williams from the University of Florida Museum of Natural History assess and revisit the goals put forward in the National Strategy for the Conservation of Native Mussels developed in 1997 by representatives from federal, state, and local natural resource agencies, conservation groups, and commercial groups.

North America is home to the world’s greatest variety of freshwater mussel species. About 300 species are currently recognized, but this number is likely to increase as genetic methods allow more precise species identification. Many of these species are gone already or are in danger of going extinct due to the massive loss, deterioration, and fragmentation of their river habitats.

“To put it into perspective, the Mississippi River Basin alone supports three to four times as many mussel species as either the Amazon or Congo River basins, which support the world’s richest freshwater fish faunas,” says Haag. “At the same time, North American freshwater mussels have the highest extinction and imperilment rate of any group of organisms on the planet.”

The widespread destruction of riverine habitat by dams and channelization from the 1920s to the early 1980s directly caused the majority of mussel extinctions to date; most of these species were restricted to the large mainstream rivers that were dammed most extensively. Equally as troubling are the enigmatic declines and crashes of mussel populations that have occurred in the last 30 years in streams that remained unimpounded and continue to support other aquatic life.

“What’s causing these enigmatic declines remains unknown, but their characteristic and rapid effects suggest an extremely virulent and widespread factor mostly specific to mussels,” says Haag. “Although we don’t know the cause of these declines, a growing body of evidence shows that mussels are more sensitive to pesticides and ammonia than other stream organisms.”

In revisiting the goals of the national strategy, the researchers recommended more emphasis on identifying causes of the enigmatic mussel declines that have affected streams across the U.S. and Canada. They also recommended that the ability of individual streams to support mussels could be evaluated directly with in situ survival trials using juvenile mussels propagated in captivity.

Recent advances in captive propagation techniques allow many species to be produced in large numbers in a hatchery environment. The near perfection of these methods has the potential to save many mussel species teetering on the brink of extinction, and it provides a ready supply of juvenile mussels for experimental studies. However, Haag cautions that this tool should be used only with careful planning and primarily to reestablish extirpated populations. The widespread use of propagation to augment existing populations poses potentially serious genetic and ecological risks, and Haag and Williams recommend that this approach be used with particular caution and mainly when a species’ global extinction is imminent.

“The primary emphasis of conservation efforts should be on habitat and mussel community restoration,” says Haag. “A critical first step in restoration is the development of a prioritized list of candidate stream reaches. Such a list should be realistic but bold. For example, removing navigation dams on large rivers such as the Mississippi is unlikely, but specific recommendations can be made on how the operation of these dams can be modified to support aquatic ecosystem values.”

High priority streams for restoration would include those affected by non-functional, unsound, or aging dams, and stream reaches affected by enigmatic declines but with otherwise intact habitat. Of particular importance are stream reaches that have potential to serve as dispersal corridors between existing mussel populations.

“What’s needed is a bold vision that’s not limited to what is perceived to be feasible in the short run, but rather one that allows for unanticipated opportunities in the future,” adds Haag. “The mussel conservation community should be ready to capitalize on the growing momentum and necessity for ecological restoration.”

Access the full text of the article.

For more information, email Wendell Haag at whaag@fs.fed.us.

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

When Does Biodiversity Make a Difference?

by Stephanie Worley Firley
Tree species that are more distinct in terms of their evolutionary past may have uniquely important ecosystem functions in a forest community. Pictured is a diverse oak-hickory forest in North Carolina. Photo by Kevin Potter.

Tree species that are more distinct in terms of their evolutionary past may have uniquely important ecosystem functions in a forest community. Pictured is a diverse oak-hickory forest in North Carolina. Photo by Kevin Potter.

Biodiversity can be like a forest’s insurance policy. The more and varied the tree species that live there, the better the chance that the forest can remain healthy, stable, and resilient through times of disturbance. But as climate change prompts new forest management approaches intended to maximize growth and productivity for carbon storage, bioenergy, and other benefits, U.S. Forest Service and North Carolina State University (NCSU) researchers are wondering: when exactly does biodiversity make a difference?

“Considering biodiversity in policy and management decision making is essential, but there are likely to be times when biodiversity is more important to how forest ecosystems function as a whole,” says Kevin Potter, an NCSU scientist working with the Eastern Forest Environmental Threat Assessment Center. To examine the central research question, Potter collaborated with research forester Christopher Woodall from the Forest Service Northern Research Station. They studied the dynamics at play between tree biodiversity and live aboveground biomass across the contiguous United States and published the results in the journal Forest Ecology and Management.

Biodiversity can be measured in many ways, though. If one thinks of biodiversity only in terms of the numbers of tree species in an ecosystem (species richness), then all species are assumed to have equally important roles in the ecosystem. Potter therefore uses measures of biodiversity that incorporate relationships between tree species on the evolutionary tree of life. Species that are more distinct in terms of their evolutionary past may have uniquely important attributes; evolutionary diversity can therefore predict the diversity of different ecosystem functions present in a forest community, which may translate into enhanced biomass production. For this study, the researchers used four measures of evolutionary diversity as additional indicators of tree species biodiversity and function in order to understand the connection between forest biodiversity and biomass.

The researchers analyzed data from about 79,000 permanent Forest Service Forest Inventory and Analysis (FIA) monitoring plots. Taking into account the environmental conditions present at each plot as well as the stocking of live trees (a rough measure of the development of a forest stand), the researchers saw a pattern: biodiversity was a better predictor of biomass for forest stands located in more difficult growing conditions. “When the tree species growing together in a more stressful environment are more widely distributed across the evolutionary tree of life, they are more likely to use available resources, such as light, water, and nutrients, differently. These different functional attributes allow the trees to make the most efficient use of available resources and therefore be more productive overall,” says Potter. “This doesn’t seem to be the case in more friendly forest environments, though. In those places, fewer species seem to be able to use the resources more efficiently, so the most dominant and highly productive species are able to outcompete other species in those habitats.”

The researchers say that more studies are needed as FIA monitoring plots are remeasured over time, but this research is already providing forest managers with important information. “As managers make decisions about how to help forests adapt to and mitigate impacts of climate change, they’ll need to consider the interactions between tree biodiversity, site conditions, and the stocking of live trees,” says Potter. “The biodiversity measures used in our research can help managers understand forest function and allow them to maximize biomass to maintain healthy forests and meet societal needs.”

For more information, contact Kevin Potter at kevinpotter@fs.fed.us.

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Posted in Climate Change, Forest Inventory & Analysis