A New View of the Forest Canopy of the Smokies

Researchers map forest structure in the Great Smoky Mountains National Park

Researchers mapped 30 unique vegetation canopy structure classes in forests on the Tennessee side of the Great Smoky Mountains National Park. Image from U.S. Forest Service.
Researchers mapped 30 unique vegetation canopy structure classes in forests on the Tennessee side of the Great Smoky Mountains National Park. Image from U.S. Forest Service.

Researchers working at the U.S. Forest Service Eastern Forest Environmental Threat Assessment Center office in Asheville, North Carolina, are just a short drive away from one of the most biodiverse places on the planet: the Great Smoky Mountains National Park, which straddles 800 square miles of western North Carolina and eastern Tennessee.

Although they and nearby collaborators at Oak Ridge National Laboratory (ORNL) have visited the park many times, they are now seeing its forest cover in a way they’ve never seen it before. Along with researchers from the University of California, Berkeley and the U.S. Fish and Wildlife Service, they’ve devised a technique for crunching large volumes of data from Light Detection and Ranging technology (known as LiDAR) to map and characterize the vertical structure of the forest canopy.

LiDAR is a remote sensing method that uses reflections from an airborne laser to measure distances between an aircraft and ground-level features. It can be used to create three-dimensional pictures of attributes of the earth’s surface, including forests, but the volume of data produced makes raw LiDAR data difficult to process and interpret. This challenge presented an opportunity for the researchers to dig deeper into LiDAR data, visualize them in a more useful format, and gain insight into different types of forest structure, their distribution across the landscape, and their relationship to vegetation composition. The results of their efforts were recently published in the Proceedings of the 15th International Conference on Data Mining.

In a case study of the Tennessee side of the park, the researchers placed LiDAR survey points 30 meters apart on a map and measured LiDAR reflectance at 1.5-meter vertical increments at each point.

“Then we examined the forest like a giant layer cake,” says Bill Hargrove, a research ecologist with the Eastern Threat Center and a co-author of the study. He explains, “We calculated the proportion of total foliage, stems, and branches growing in each height layer to describe the presence of shrubs, understory, mid-canopy, and overstory trees within the forest. This vertical distribution of the forest structure is a vital characteristic of the forest itself, as well as an important characteristic of the forest habitat for many species of plants, birds, and other animals.”

Next, with help from the world’s second fastest supercomputer located at ORNL, they used a statistical method to group cells according to the similarity of their vertical profiles and assigned each profile a unique color on the map to show the location and extent of forests with similar layering of foliage and branches. When they compared the vertical profiles with forest compositional types, they found a strong correspondence between canopy structural types and compositional types across the park’s complex terrain.

It is because of this complex terrain that the park is able to support such great biodiversity. The 95-percent forest cover, abundant rainfall, and wide-ranging elevations create diverse habitats for more than 17,000 documented plant and animal species, including dozens of threatened or endangered species as well as species of concern. And, scientists believe, many more species have yet to be discovered.

But the structure of forest vegetation is changing due to environmental changes such as a lack of the fire that promotes health and regeneration of some species, and introduced invasive pests like the hemlock woolly adelgid, which has resulted in widespread hemlock death. As the Great Smoky Mountains National Park and other U.S. landscapes face a variety of threats, understanding changing conditions is a critical need. Forest structure maps can highlight changes in the richness and distribution of habitat to help forest and natural resource managers monitor, manage, and conserve plant and animal species.

Read the full text of the article.

For more information, email Bill Hargrove at whargrove@fs.fed.us.

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