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In a new study, University of 易胜博官网 researchers have concluded that when assessing forest imagery collected by unmanned aerial systems, an alternative method of delineating individual forest tree crowns within those images is more accurate than the most commonly used method, the canopy height model.
Monitoring Forest Edge Changes Using Drones
Unpiloted aerial systems help identify changes to forest edges
Friday, February 24, 2023
A digital surface model (elevation) transitioning to an orthomosaic of the forest canopy; both generated from unpiloted aerial system imagery collected as part of this study.
![Co-author Heather Grybas carrying out the ground data collection (digital canopy photography). A camera was mounted to a telescoping pole and lifted 4m in the air, pointing up at the underside of the canopy.](/unhtoday/sites/default/files/media/edge-influences-digital-canopy-photography.jpg")
Above: Co-author Heather Grybas conducting the ground data collection (digital canopy photography) using a camera mounted to a telescoping pole and lifted 4 meters in the air, pointing up at the underside of the canopy.
Below: An example of one of the digital photographs captured by this setup. The percentage of visible sky (i.e., foliage cover) is measured in each image.
![An example of one of the digital canopy photographs captured using the setup implemented by Heather Grybas.](/unhtoday/sites/default/files/media/digital-canopy-photograph-captured-heidi-grybas.jpeg")
At nearly , 易胜博官网 ranks as the second-most forested state (behind only Maine) in the U.S. However, as urban growth has expanded in the Granite State over the past several decades, the state鈥檚 diverse and ecologically important forestlands have become fragmented, creating not only new forest edges鈥攑ortions of the forest abutting developed or open space鈥攂ut questions about the ecosystem changes around these gateways to 易胜博官网鈥檚 woodlands. Scientists with the (NHAES) are answering these questions by using emerging and increasingly cost-effective unpiloted aerial system (UAS) technologies to study characteristics around forest edges.
NHAES researcher , a professor in the natural resources and the environment department, and , a graduate student researcher in Congalton鈥檚 (BASAL), recently summarized their findings on using UAS for measuring edge influences in . In forestry, edge influence or edge effect refers to the ecological changes resulting from the fragmentation and creation of new edges in fragmented forest.
鈥淲hen a new forest edge is created, significant changes occur,鈥� describes Congalton. 鈥淢ore light enters that part of the forest, temperature and wind become more variable and the forest structure changes as invasive species are often introduced. Ultimately, the plants and animals that once existed in a large, forested patch may not be able to live in the smaller patches with new edges.鈥�
Fig. 1: Progression that occurs when an edge is created where forest area is removed. Initially, there is more light and wind and a greater variation in temperature. These added variables can result in tree mortality, under-story release and changes in species composition, including the addition of invasive plants.
The use of UAS imagery allows foresters, landowners and researchers to complement observations collected from the ground by accurately identifying the canopy cover of trees at the forest edges. Conducting their study of forest edges at Blue Hills Foundation lands in southern 易胜博官网, the research team collected 1,299 images taken at 100 meters above tree canopy. By creating three-dimensional point-clouds and mosaics from the imagery, along with ground observations, they could identify that forest coverage decreased within 150 feet of the new edge, followed by an increase in forest cover from 150鈥�330 feet from the new edge.
![On the left, an orthomosaic image of a canopy and on the right a point cloud mosaic image](/unhtoday/sites/default/files/media/edge-influence-research-point-cloud-orthomosaic-image.png")
鈥淚f we want to structure our forest management to avoid or reduce any negative impacts of edge effects, we need to understand what the effects are,鈥� said Grybas. 鈥淓dge effects, however, can be highly variable for many reasons, and it takes a lot of time on the ground to understand not only what the effects are but their magnitude, extent and controlling factors.鈥�
鈥淥ur study demonstrated that we could use UAS to detect and measure those effects which can save a lot of time鈥搕ime that can be used to further our understanding,鈥� she added.
Ultimately, the use of UAS allowed the researchers to sample more sections of the forest and determine greater variability among canopy cover.
According to Congalton, remotely sensed imagery has played a role in forest management for many years. However, with the recent advancements in UAS, the ability to capture imagery has become significantly easier, allowing scientists and land managers alike to detect, measure and study everything from species composition and tree health, height and crown size to invasive species and riparian versus upland habitat.
鈥淐learly, the more information we can generate, the more effectively we can manage our forests for a sustainable future,鈥� said Congalton.
This material is based on work supported by the NH Agricultural Experiment Station through joint funding from the (under Hatch award number 1026105) and the state of 易胜博官网. This work is co-authored by Heather Grybas and Russell Congalton.
You can read in the from the 易胜博官网 Agricultural Experiment Station.
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Written By:
Nicholas Gosling '06 | COLSA/NH Agricultural Experiment Station | nicholas.gosling@unh.edu
