A Census for the Trees


This year, as the American people are being counted, San Franciscans are also counting trees. A collaboration spearheaded by the nonprofit Friends of the Urban Forest has taken on the ambitious goal of not only quantifying but mapping the city's arboreal residents. Funded by a grant from the State of California, the project aims to update tree databases, some as many as 20 years old, by deputizing the public as "citizen scientists" and giving out reporting and identification tools through a publicly edited website, or wiki.

Doug Wildman, Friends of the Urban Forest project director, spoke to The Atlantic about engaging citizens online and why we need to count trees in the first place.

wildman.jpgWhere did the idea for an Urban Forest Map come from, and how are you creating it?

A staffer here at Friends of the Urban Forest, Amber Bieg, had the idea. We're using teams built up of people who know their stuff about trees combined with those who don't.

We are also having Mrs. Jones go out in front of her home and identify that tree using a plant key we've provided on our site, take the diameter of the tree at chest height using a string, and enter that data on the wiki. Then we plug it into the survey and it's there for everyone to see. Mrs. Jones's data is also crosschecked by the team that's counting trees in her area.

In addition, we are looking at data collection from aerial imagery and comparing all these sources for their accuracy and efficiency. The survey is going to be a sampling, and we're in partnership with the research station at the University of California Davis to do that.

What will the map accomplish?

We're trying to get people thinking about urban forestry and its benefits. One of the things we've learned over time with Dutch elm disease is that if you have a high percentage of trees that are all the same species or genus or even family, you have the potential of losing them to certain diseases. You want to balance out the species in your population in case a pest or disease comes your way. For instance, We'd better not plant anymore elms. We've reached our max.

Invasive species might be another thing. If you're really looking carefully at not invading other nearby natural areas you might look at your tree population and begin to reduce some of those invasive species.

And we're trying to build a snapshot in time reflecting what's really out there. A tree that Friends of the Urban Forest planted 20 years ago may not be there anymore, and that property may have paved it over but we don't know any better until the property owner tells us. Then, once we've deleted the original from our records, they can request a new tree.

So you're saying that in the last 20 years there has been nothing to verify the trees that are -- or are not -- in the ground?

That's right. And drawing in the public to help us do that might be the beginning of doing surveys of our urban forest effectively and inexpensively.

What's the advantage of doing this project as a wiki?

I think it has the potential to enable communities to be active and plug in the information that is so tedious for city crews and others to plug in. In a way it is a census, but we have the public logging on and helping. Of course, the data is only as good as whoever's are putting it in -- you might say, "that's a pine tree!" when it's really a London plane tree -- but we're looking at how to verify that and keep up with the data that goes in.

The idea is to see what kind of person you need to collect the data. Could it be anyone? Maybe, if you give them the tools. Or is it more efficient to have people that know a little more?

Or can you do most of it from the air? Aerial surveys use spectroscopy, a sampling of color to that lets us make generalizations about tree species. That gives us pretty good data, but you need to "ground-truth" that -- go out there and check, say, five different color images to ensure that you're on track. The purpose of this grant is to see what works, the most efficient and cost-effective way to get an accurate assessment of your urban forest.

How long do you see the project taking?

We've got a couple more months to dial in the Urban Forest Map website, and then our survey should be done over the summer.

What role has the local government played?

The city is really into it. They've got tech people who are really geeky and interested and are helping us do it. We also wrote a grant and got funding from the State of California, from a bond to improve urban forest management. This is a million-dollar project, we got $500,000 to build the Urban Forest Map site and get it going. So the state has an absolute interest in the outcome of the project.

Let's picture all the cities in California -- if we all had the same open-source mapping program and it was working, then we'd be comparing apples and apples. For example, you have Fresno in the San Joaquin Valley, with its hot, hot, hot climate, against our coastal, maritime, cool San Francisco. Fresno would get a huge bang for their buck on shade trees in the summer, while San Francisco, with our storm water, benefits by getting broad-leaf evergreen trees in the winter. In Fresno, you get to see the benefits of shade when you're not turning on your air-conditioning unit, and in San Francisco your benefits are in storm water retention. Both sides are getting their highest ecosystem service benefit.

It sounds like this could be applied nationally, in fact.

Wouldn't it be fun to hack around, going from city to city, comparing them all in real time? In fact, there should probably an overall site that does that for all cities. It's a dream. It could certainly be something national -- we just want it to work right now in San Francisco. We want get the bugs out of it, have people go to the site and enter data. 

What has the response been like from the public? And have you had inquiries from other municipalities?

Almost 400 people have signed up on our site so far, and people are engaged--identifying, counting, measuring, photographing trees. We're getting comments from people as far away as Toronto saying they want to have an Urban Forest Map in their city. In fact we had a meeting with the Sacramento Tree Foundation we last week, and they were thrilled with it. So other cities are definitely looking at it.

Image credit: David Paul Ohmer/Flickr