Connecticut’s forests have been transformed over the years to meet the needs of its inhabitants. Before the arrival of European settlers, Native Americans burned forests in order to clear underbrush and create habitat for the game species they hunted. In the early 1800s, when European settlers arrived in large numbers, forests were cut down to make room for agricultural production and wood was used to build structures, create products and burned for heat. By 1820, the state’s forest cover was reduced to 25 percent. With the decline of agriculture in the state and the passage of conservation acts, Connecticut’s forests have regrown and now cover an estimated 70 percent of the land.

Fahey and colleagues from Purdue and Virginia Commonwealth Universities collecting lidar data

Fahey and colleagues from Purdue and Virginia Commonwealth Universities collecting LiDAR data.

Robert Fahey, assistant professor in the Department of Natural Resources and the Environment, notes that while it would appear that some of these returning forests are unused, they are serving as a carbon sink. This refers to the ecosystem’s ability to absorb, or sequester, carbon from the atmosphere and store it.

Connecticut trees are part of a vast regrowth of forest in the northern US and Canada. As these forests begin to mature, scientists know little about how the aging of these trees will change the ecosystem’s capacity to continue storing carbon or if they might begin to emit carbon into the atmosphere.

“Over the past hundred years or so the forests of the Northeastern US have been a carbon sink, meaning that they have been pulling carbon dioxide out of the atmosphere, offsetting some anthropogenic emissions. But these forests are aging and their potential to continue to be a carbon sink is questionable at best,” says Fahey.

In order to understand how the structure of forest ecosystems affects carbon storage, Fahey, who has a joint appointment in UConn’s Center for Environmental Science and Engineering, is studying forest canopy structure through examination of the specific arrangement of leaves. He believes canopy structural complexity is a prime indicator of efficiency in the ecosystem, which can shed light on how the environment functions.

Forest canopy

Forest canopy.

Canopy structural complexity is a characteristic that can help determine the functionality and resiliency of forests. The amount of sunlight the canopy absorbs has a strong impact on photosynthetic capacity – the ability of the canopy to turn solar energy into growth. A more complex canopy has increased light use efficiency, with more photosynthetic capacity per unit solar radiation absorbed. The configuration of the canopy can also affect how it responds to storm disturbances such as wind and ice. Thus canopy structure is important not only for determining carbon sequestration and effects on climate, but also understanding the link between canopy structure and ecosystem function and resilience could affect the way people manage forest for silvicultural purposes.

“If we understand how different treatments affect complexity of the canopy then we can focus on achieving specific outcomes,” says Fahey. “For instance, we’ll know which forest management practices change the canopy, and therefore the ecosystem, in a particular way. We can then apply that knowledge to achieve ecological or production benefits. Managing a forest for timber production would not necessarily resemble one that stresses ecological solutions.”

“When people talk about complexity of a forest they might refer to the range and diameters of trees, the diversity of species, what function it serves, or how much dead wood, snags and downed logs are creating habitat. The way you quantify it often depends upon your goals. Canopy complexity could be the best way to quantify complexity of the entire ecosystem and to most accurately consider the effects of different practices and their outcomes.”

3D model of UConn Stormwise research site developed using terrestrial laser scanner

3D model of UConn Stormwise research site developed using terrestrial laser scanner.

Grants from the National Science Foundation and the USDA are funding Fahey’s research. To conduct his research, he is utilizing the National Ecological Observatory Network (NEON), an organization that collects data across the continent at eighty-one field sites. NEON gathers all available information from these locations, spanning biological, ecological and meteorological findings and makes those data freely accessible. Through these downloadable data sets, scientists, students, decision makers and the public are better able to study and observe environmental changes spanning the country. The use of Light Detection and Ranging (LiDAR) is another valuable tool in his research. LiDAR uses laser light and is able to create 3-D models of the canopy.

This information is employed to map forests and their canopies and can also be used to track changes over time. “Areas can be scanned and observed again after treatment options to predict changes. Then we can follow how the canopy changes in response and see how trees grow into spaces that are opened up. This information could change treatment practices. For instance, if trees begin to grow lopsided into an opening then we probably want to reconsider that treatment,” says Fahey.

Being able to quantify canopy structural complexity to predict changes can have additional applications, particularly to roadside management. Fahey works on the Stormwise team and is interested in using this research to continue reducing power disruptions from tree failure.

“The next step in Stormwise is monitoring utility trimming to understand how trees grow following trimming and study those effects. If we open the canopy up and there’s more wind, trees may move more but over a few years they’ll develop wind firmness and acclimate. We can then monitor those trees over time and this will help determine how to set trim cycles and what kind of trimming should take place,” says Fahey.

“This research all comes down to finding a better way to measure complexity in forests. By looking at canopy structural complexity, it will give us the best understanding of what is happening in the ecosystem. Once we learn how canopy structural complexity relates to forest productivity and wind disturbance, we can use that to examine silviculture practices to achieve the best results for our needs.”

By Jason M. Sheldon