The Forest Family: Relationships among Tree Species

by Sarah Farmer
Conifers, such as these longleaf pines, tended to be more distantly related than expected by chance. Photo by David Stephens, courtesy of Bugwood.org.

Conifers, such as these longleaf pines, tended to be more distantly related than expected by chance. Photo by David Stephens, courtesy of Bugwood.org.

Like all species, forest trees have their own web of relationships among themselves. Studying these evolutionary ties is the main focus of phylogenetics, and can assist in forest health assessment.

“Understanding relationships among tree species can show how they interact with each other and with the environment,” says North Carolina State University scientist Kevin Potter. “Phylogenetics can be used to assess forest health from the perspective of biodiversity and resilience to stress.” Potter, a research cooperator with the Forest Service Southern Research Station (SRS) Eastern Forest Environmental Threat Assessment Center, is lead author of a new study that analyzes forest phylogenetics across the entire United States. The study was coauthored by SRS scientist Frank Koch, and was recently published in Forest Science.

Potter and Koch studied forest trees across a network of more than 100,000 plots across the United States. The plots are part of the Forest Inventory and Analysis Program, which provides a continual census of forest status and trends.

Over most of the ecoregions studied, the researchers found that trees – except conifers – were more closely related than could be explained by mere chance. “This can mean that many of the trees in that particular environment are able to co-exist because they have similar adaptations to the environmental niches there,” says Potter.  “At the same time, tree species that are closely related can be susceptible to similar threats, whether insect infestations, diseases, or climate change.”

In some areas, including in the Rocky Mountain region, tree species were more distantly related than expected. These results can be somewhat more difficult to interpret, because there are two processes that can lead forest communities to consist of tree species that are more distantly related. First, competition between closely related species for similar resources can result in the survival of only one of them. Second, distantly related species sometimes have evolved similar traits that allow them to be adapted to similar environmental conditions. “The ecological integrity of such communities may be less at risk because they may encompass a wider variety of evolutionary adaptations,” says Potter.

The researchers also found patterns of relatedness along environmental gradients. In harsh environments, such as at high elevations or in dry areas, tree species tended to be more distantly related than expected. In more favorable environments, tree species tended to be more closely related. “These results have implications for broad-scale forest health monitoring,” says Potter. “The relatedness of forest tree species may be connected to their susceptibility to threats such as climate change, nonnative plant invasion, and insect and disease infestation.”

Read the full text of the article.

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

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Posted in Climate Change, Forest Inventory & Analysis, Genetics, Threats

American Chestnut, Past and Future

by Sarah Farmer, SRS Science Delivery Group

American chestnut catkins starting to bloom. Photo by Keith Kanoti, courtesy of Bugwood.org.

The Silvics of American Chestnut , a general technical report (GTR) available from the U.S. Forest Service Southern Research Station (SRS), describes the habitat, life history, special uses, genetics, and restoration of the American chestnut (Castanea dentata).

The publication is the result of collaboration between G. Geoff Wang, the lead author, his colleagues at Clemson University, and Stacy Clark, a research forester with the SRS Upland Hardwood Ecology and Management unit.

Until the early 20th century, American chestnut was one of the most ecologically, culturally, and economically significant trees of the eastern United States. However, the accidental introduction of an exotic pathogen, the chestnut blight (Cryphonectria parasitica), devastated the chestnut population, causing the species to become functionally extinct.

Because of American chestnut’s long absence from the landscape, standard silvicultural handbooks such as the USDA Woody Plant Seed Manual have not included complete information about the species’ life history and growth habits. This publication supplements silvicultural handbooks by summarizing information about American chestnut that will be important to future restoration efforts.

The GTR’s authors point out that restoring chestnut on most sites will require artificial regeneration—growing the blight-resistant trees recently developed in a greenhouse or nursery and planting them as seedlings–rather than starting from seed. They also caution that even if the chestnut trees prove to be blight-resistant, the effects of damaging agents other than blight, including root rot disease and insects that defoliate leaves or damage roots, may represent real barriers to restoration.

American chestnut was once a dominant and widespread canopy tree through many parts of the country, its range stretching from Mississippi to Maine. Its nuts were consumed by animals and people alike, and it was widely used as timber. “Chestnut’s demise is regarded as the most tragic ecological event in the post-glacial history of eastern North American forests,” says Clark. Its return from the brink of extinction would be one of the greatest success stories in the history of forest management.”

For more information, email Stacy Clark at stacyclark@fs.fed.us

Access the full text in PDF format on the SRS website.

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Posted in Genetics, Insects and Diseases, Restoration, Upland Hardwoods

Crash and Burn: How Tornado Damage Affects Fire Behavior

by Sarah Farmer, SRS Science Delivery Group
Aerial view of simulated tornado damage at the Piedmont National Wildlife Refuge near Round Oak, Georgia. Photo by U.S. Forest Service.

Aerial view of simulated tornado damage at the Piedmont National Wildlife Refuge near Round Oak, Georgia. Photo by U.S. Forest Service.

Tornadoes and fires are powerful natural disturbances that can kill trees and cause long lasting changes in community composition. “However, most disturbances are neither rare nor catastrophic,” says U.S. Forest Service scientist Joseph O’Brien. “There is a continuum of disturbance severity in most ecosystems, although the interactions among these disturbances haven’t received much study.”

One of the most obvious interactions between wind damage and fire is that fallen trees become fuel, and can increase the likelihood or intensity of fire. “The impacts of simultaneous wind and fire disturbances are poorly understood,” says O’Brien, a research ecologist at the Southern Research Station Center for Forest Disturbance Science. O’Brien and his colleagues recently studied interactions between wind damage and fire behavior. The study was led by Jeffery Cannon of the University of Georgia, and was recently published in Forest Ecology and Management.

The researchers established six study plots in a pine-oak stand in the Piedmont National Wildlife Refuge in central Georgia. Half the sites were left untouched as a control, while tornado damage in the other half was simulated by pulling trees down with a winch. “In this area, tornadoes typically come from the south,” says O’Brien. “We winched the trees to fall towards the north, as if they had been toppled by the wind.” O’Brien and his colleagues also winched the trees during tornado season (between March and May) and created gaps of about 40 yards across.

The downed trees were left in place, and after about a year, a prescribed fire was conducted. The simulated tornado damage dramatically changed fire behavior, but the differences were not due simply to the extra fuels. Many of the large downed tree trunks were not even consumed in the fire, probably due to its low intensity. “Our study suggests that subtle changes in the types of fuel and its physical arrangement led to changes in combustion patterns,” says O’Brien.

The simulated tornado disturbance caused finer, more flammable fuels such as small branches in the tree crowns to clump together. During the prescribed fire, these areas burned hotter and more fuels were consumed. The largest ecological effects of fire were probably centered on these areas of intense fire. The study shows that wind damage and fire influence each other in a variety of ways, some of which are not immediately obvious. For example, the timing of fire could interact with environmental conditions such as drought and cause larger fuels, like the tree trunks, to also burn. This would probably amplify the patterns O’Brien and his colleagues identified.

“We found that wind and fire interact synergistically,” says O’Brien. “Together, these disturbances can create the potential for more intense fires.”

Read the full text of the article.

For more information, email Joseph O’Brien at jjobrien@fs.fed.us.

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Posted in Fire, Southern Pines, Threats