Studying Urban Trees With Smartphones and Satellites

Another story in our series on citizen science in California, as part of Redefine's celebration of Citizen Science Day on April 16.

Trees add a lot to a neighborhood. They're beautiful, they can provide habitat for wildlife, the offer shade and shelter from the wind. And by absorbing sunlight to turn into biomass, trees can also cool urban neighborhoods — an especially important gift as climate change increasingly makes itself felt.

But though it's common knowledge that trees provide these services, it's also clear that different trees provide those services in different amounts. In southern California for instance, palms provide almost no shade but offer important habitat for owls and bats, while jacaranda trees offer little in the way of benefits to wildlife but provide lots of shade -- and lots of organic matter for soils in the form of shed flowers. Different tree species require different amounts of water in return for the services they provide, which can be a little hard to measure in SoCal given that those species grow in different mixes from one spot to the next. And given Southern California's wildly varied landscapes, with foggy coastal bluffs just a two-hour drive from searingly hot desert slopes, the effect of urban trees on the landscape can be mind-numbingly complex.

But since 2014 the Los Angeles Focal Trees Project, a citizen science effort, has been trying to untangle that data and give us a better understanding of which trees do more to make our cities livable — among other discoveries.

The Focal Trees Project is spearheaded by the group Earthwatch and researchers at the University of California Riverside, in cooperation with NASA, the L.A. County Natural History Museum, Amigos de Los Rios, The Nature Conservancy, TreePeople, and others. With work provided by a group of trained citizen scientists, the project aims to mesh precisely timed observations of trees on the ground with flyover data collected by NASA on temperatures, atmospheric chemistry and other environmental factors. The result, project leaders hope, will be a deeper picture of just how our urban trees are doing, and what they need in order to keep providing the ecological services they offer.

According to Earthwatch Institute's Ellie Perry, citizen scientists working with the Focal Trees Project go through a bit of training in data collection before they're sent out into the world to document SoCal trees. Participants learn how to document not just the precise location of each tree but also the spread of the trees' canopies, the diameter of each tree's trunk (mearued at "breast height," or four feet six inches off the ground, a standard arborists' measure) and the approximate percentage of surrounding land that is unpaved, and thus porous to rainwater or irrigation. 

"It doesn't take long to train our citizen scientists," Perry told Redefine. "But it's really important that they all follow the same process, so that we get data that's consistent from tree to tree."

This isn't Earthwatch's first dance with citizen scientists: it's pretty much what the 45-year-old environmental science non-profit does. The group has participated in more than 1,300 conservation science research projects in hundreds of countries, and in 2011 marked ten million hours of data collection over the course of its organizational lifespan. As such, the group was a natural choice when reseacher scientsts Peter Ibsen and  Darrel Jenerette at University of California Riverside decided to seek citizen scientists' help in corroborating NASA satellite data coming in from the L.A. Basin and Inland Empire.

For the last two years, the Focal Trees Project, which Earthwatch includes in its broader Urban Resiliency Initiative, has focused on 10 representative species of trees commmon in the Los Angeles Area. They range from natives like the coast live oak and western sycamore to imports such as jacarandas and brush box, with one species — Chitalpa tashkentensis — a garden hybrid that exists nowhere in the wild.

Once trained, volunteer citizen scientists fan out across Southern California on days when NASA satellites are scheduled to collect aerial imagery. This coordination allows researchers to have a sense of just what things looked like on the ground as the satellite data was collected — literally "ground truthing" the NASA data, but also providing a much deeper look into local conditions that is possible from a satellite.

In 2014 and 2015, those satellite readings included ground-level nitrogen, so the volunteers also took leaf samples of their subject trees so that those samples could be measured for their nitrogen content, with that information then used to get a better idea of what the satellite readings were actually, well, reading.

Volunteers submit their observations either in hard copy or through their smartphones, using the increasingly important iNaturalist app. You can see the Focal Trees Project's iNaturalist observations here.

Data collected by the Focal Trees Project is now being studied, and preparations are underway for the 2016 season. (You can find more information on how to participate at Earthwatch's Urban Resiliency website.) In the long term, the project may well help determine which kinds of trees provide the greatest range of ecological services for the water and other resources they require. And that would go a long way to help make our cities more livable in a changing world.

Banner image by Tracie Hall, some rights reserved.