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Bird's Eye View: Understanding Urban Tree Canopy in Hawai‘i
Waianae Canopy April 2022 from Pacific Southwest Region on Vimeo.
What is Tree Canopy?
Imagine you are a Manu o Kū (fairy tern bird) flying over your favorite Monkeypod tree. As you look down from your bird's eye view, you see the tree's canopy - its leaves, branches, and stems that provide coverage over the ground.
Why do we Measure Tree Canopy?
The tree and its canopy are a driving force behind numerous environmental, social, and economic benefits that we rely on every day. On average, the bigger the tree canopy, the bigger the benefits. Trees sequester carbon in their trunks, remove particulate matter from the air, clean stormwater run-off by removing harmful chemicals, cool ambient air by up to 10 degrees on hot days, shelter wildlife, and they create a sense of place. Research also shows that communities that plant trees together grow together- improving social ties and trust among neighbors and communities. Working with programs and partners like i-Tree, we can quantify and put dollar values to many of those benefits.
How do we measure Tree Canopy?
Advances in image resolution and the technology to analyze those images have improved over the last few years to allow us to see and clearly identify an individual tree’s canopy. For Hawaii's tree canopy, artificial intelligence (i.e., a neural network classifier for tree cover) was trained using current and historic landcover data (e.g., MAXAR Vivid imagery and 1-meter resolution LiDAR 2016 or newer). Accuracy was checked against the latest imagery, inventories, and ground-truthing.
How do we measure Urban Tree Canopy?
There are many different ways to define urban areas in a community. Our urban tree canopy was derived using the Canopy layer, 2010 Census Tract Boundaries, and the Carbon Assessment Land Cover dataset compiled by USGS. Urban developed areas were queried out out of Land Cover dataset to embody residential areas, commercial areas, roads, freeways, etc. Canopy was clipped around 2010 census tracts as a boundary layer, and then clipped to examine urban areas.
What have we learned about our Urban Tree Canopy in Hawai‘i?
We are still in the process of analysis but what we do see now is that the urban tree canopy across Hawai‘i is not uniform.
| Island | O’ahu | Hawai‘i island | Kaua‘i | Maui | Moloka‘i | Lana‘i |
|---|---|---|---|---|---|---|
|
Urban Tree Canopy % Estimate per island |
17 | 33 | 31 | 26 | 32 | 15 |
How can I use the Urban Tree Canopy Data and Viewer?
Understanding the extent and location of a tree canopy can help a community design and implement sound management practices to maximize those services: prioritizing locations for tree planting, establishing urban forestry master plans and sustainability plans, and managing threats to canopy loss.
Depending on land cover imagery availability, there are several best practices for assessing your urban tree canopy. Check out this USDA Forest Service synthesis for more information- Urban Tree Canopy Assessment: A Community’s Path to Understanding and Managing the Urban Forest.
The Hawai‘i urban tree canopy viewer combines the canopy layer with other information—such as the extent of impervious surfaces, socioeconomic and health data, and urban heat severity maps, to name a few. You can check out our complete viewer layer list. These layers provide information to help us understand differences in canopy across communities. They can also aid in the process of prioritizing urban greening goals (e.g., tree planting and tree maintenance) with the goal that all communities will experience the benefits that tree canopy offers.
How do I access the Urban Tree Canopy Data and Viewer?
Full and free access to the viewer is available here. For those unfamiliar with ArcGIS interactive maps and who want to learn about example applications, please watch our tutorial here.
We recognize several other ways to use this data which is all available free to download. By downloading the data, you commit to citing and acknowledging your source for any products.
Suggested citation: EarthDefine LLC, US Forest Service, National Oceanic and Atmospheric Administration, HI Division of Forestry and Wildlife. 2021. Hawaiʻi High Resolution 1m Tree Canopy Map [ESRI file geodatabase raster format], 2009-2020. https://www.fs.usda.gov/detailfull/r5/communityforests/?cid=fseprd995876