Documenting Tree Density: With a Swipe of Your Mouse, See How They Grow

Canopy cover, or the measure of mature tree crowns, is an important way to assess the growth of a Tree for All project. We need to know the area and height of the plants at a site not only to check that site preparation and stewardship efforts are paying off, but also to understand the impact of the plants on wildlife habitat and stream temperature. 

And yet measuring canopy cover can be a challenge, particularly when you’re working at a large scale, as we do in the Tualatin River Watershed. Counting plants by hand using GPS technology is tedious and can result in less precise data collection. But in the past decade, the technology known as Light Detection and Ranging—or LiDAR —has addressed these challenges, greatly aiding in the efficiency and accuracy of canopy cover measurement. 

In 2007, just a few years after the inception of Tree For All, Clean Water Services (CWS) joined with a group of partner organizations to hire a contractor to fly LiDAR equipment over the entire Tualatin River Watershed. Ben Protzman, an engineering technician at CWS, explains, “LiDAR works by bouncing beams of light off the ground, and off objects like trees and buildings, in rapid succession, each beam hitting a specific point. These points can then be combined into what’s called a ‘point cloud,’ which can be used to create a detailed topographical surface.” Another round of data collection took place in 2014, and a third is planned for 2019. Tree for All partners use this LiDAR data to make decisions about how to adjust existing projects, and how to proceed with new projects. 

Now, visitors to the Tree for All website can see the data, too—in the form of interactive maps. You’ll find LiDAR links near the end of about half of the project briefs we’ve published so far. Just click on the screenshot of the aerial map, and you’ll find yourself on a new page with an interactive map. (It’s hosted by the ArcGIS Online arm of the mapping tech company Esri.) Look for the icon in the upper left corner that looks like an elevator door. Click on it, and you’ll get a slider bar that you can move back and forth to see how mature canopy cover has changed over time. The 2007 mature canopy is in purple—and as you move the slider, you’ll see it “light up” with orange, representing the new mature canopy detected in 2014.
What counts as “mature canopy”? Ben Protzman explains, “We have processed the LiDAR data using GIS to show only vegetation more than 20 feet tall, excluding man-made features such as powerlines and buildings.

Watch our new video to hear more from Tree for All partners about using LiDAR and other innovative technologies to conduct restoration at an unprecedented scale.

Click here to explore the map.  

Questions about the data or how to use the map? Email us.