Thursday, March 25, 2010

Where Do You Put 50,000 Trees?

Spring Creek Nature Area
Spring Creek Nature Area

The City of Richardson recently announced a "Tree the Town" program, a 10-year plan to plant 50,000 trees in Richardson, using money and services donated by corporations and civic groups across Richardson. The total value of the program is estimated at $34 million. The Dallas Morning News Richardson blog has details.

After the jump, where will all those trees go?

In the comments of a followup story on the Richardson blog, reader "oopsie" asked for a reality check:

"According to google, Richardson is about 28 square miles of total space. Now, divide 50,000 trees by 28 square miles, and you get about 1,786 trees per square mile. An acre is about 1/640 of a square mile, so we're talking about roughly three trees per acre across the whole town. Except of course, that most of the town is covered by houses, buildings, pavement, concrete, and other trees. Oops, inconvenient truth here Mr. Gore!

"Looking at Google Earth again, It seems clear that there really isn't that much plantable space. Some parks, UTD campus, some undeveloped land, and some slivers in medians, and the big power lines. Certainly not more than 1% of the total land area is plantable, and if UTD won't let us fill their vacant land with trees, or we decide not to cover our ball fields and parks with trees, that number is probably more like .01% So, being charitable, Omar will need to plant his trees about (50,000/(28 * .0001)) * 1/640 = 9500 trees per acre.

"So It would seem, that in order to reach his goal, Mr. Omar will need to stack his trees horizontally in piles 50-100 feet tall, rather than planting them, in order to reach his goal.

"Of course, maybe all these trees could be used to attract some lumber industry economic development."

"You can fool all of the people some of the time, and some of the people all of the time, but you can't fool simple arithmetic."

Could oopsie be right? Will there be so many trees that there's no room to move? Is Richardson's stated goal of planting 50,000 trees totally impractical?

Let's check oopsie's arithmetic. oopsie is right about Richardson's size, 28 square miles. He's right that there are 640 acres per square mile. That does lead to 2.7 trees per acre. oopsie is right that not all that space is available for planting. oopsie uses Google Earth to eyeball an estimate for "plantable" space and decides on .01% of the total land. That should lead him to (2.7 / .0001) = 27,000 trees per "plantable" acre. oopsie somehow calculated 9,500 trees per acre. That's wrong but the correct figure is even more frightening than oopsie's mistaken total.

So, are matters as bad, or even worse, than oopsie warned? Probably not. oopsie's estimate of .01% for plantable space is probably way off. Let's approach it from another angle. According to the City of Richardson's web site, the Parks and Recreation Department maintains 1598 acres, including 956 acres of parkland, 37 acres along US 75, 350 acres of medians, 100 acres of roadside, 12 acres of public building land, and 23 acres of ditches. (That leaves 120 acres unaccounted for, which might be a discrepancy worth tracking down ... some other time. For now, we'll accept the city's total of 1598 acres.) The city's land area of 28 square miles amounts to about 18,000 acres. The 1598 acres maintained by the city parks department amounts to about 9% of the city's total area. Whew! 9% is a lot more than .01%, 900 times more in fact. Assuming all this land is available for planting, we'd have 50,000 / 1598 = 31 trees per acre, or about 1 tree every 30 feet or so.

That sounds reasonable, right? Maybe not. Although oopsie's estimate of .01% for "plantable" space is certainly too small, our own estimate of 9% is certainly too large. A lot of our parkland is covered with ball fields that we never want to plant with trees. A lot of our parkland and roadway medians are already covered in trees (see photo above). So, how mamy of those 1598 acres are really available for the "Tree the Town" program? That's the $34 million question. If only half of the land maintained by the parks department is open, that ups the density to 62 trees per acre. Only a quarter and its 124 trees per acre. That starts getting crowded.

But perhaps trees per acre is the wrong measure. Much of the land is along medians. Medians can support more trees per acre than open park land can (because some of the land around the trees in medians is in the street and doesn't count towards the trees/acre measure). The city of Richardson has about 400 miles of paved streets. Assuming that all 50,000 trees are planted along streets (and not in parks), that amounts to 125 trees per mile or about 1 tree every 42 feet.

That, too, sounds reasonable, right? Maybe not. Not all of our streets have medians. Many of our medians already have trees. How many of those 400 miles are really available for the "Tree the Town" program? That's another $34 million question. If it's only half, that's one tree every 21 feet. Only a quarter and it's one tree every 11 feet. That starts getting crowded again. Even adding Richardson's 23 miles of trails to its 400 miles of roads doesn't spread the trees out all that much. Assuming the city can plant along the sides of the streets and not just in the medians might spread those trees out again, but will it be enough? Many of those curbs are in front of private homes and I doubt the city is planning to plant trees there.

OK, let's look at this from one more angle. A few years ago, Richardson compiled a "tree inventory". The city documented the location of over 4,000 trees. That's a lot of trees already in the ground. But, consider that the "Tree the Town" program proposes to plant 12 times as many new trees as are already in the inventory. That's a lot of trees.

What if, instead of looking at tree density, we looked at the rate these 50,000 trees will have be planted. It's a ten year program. That means we'll be planting 13 trees per day, every day, rain or shine or snow, for the next ten years. That's a lot of good deeds by those Boy Scouts.

No matter how you look at it, 50,000 trees is a huge number of trees for a city the size of Richardson. Still, the program is a good one. Whatever number of trees get planted, they will add value to the city and make Richardson a more enjoyable place to live and work. But 50,000 is almost certainly marketing exaggeration. It has the feel of a number someone (?) grabbed out of the air because it is big enough to grab the public's attention. After all, if you're going to name the program "Tree the Town," you don't want to sound small, right? Otherwise, you might just as well call it Arbor Day.

P.S. I'm not a fan of the city's web mapping application. It's slow. It doesn't quite operate the way I'm used to. Meaning ... it's not Google Maps. So I took the tree location information and loaded it into Google Maps myself. Satellite view. Street view. You get the picture. View it here. Enjoy.

1 comment:

Mark Steger said...

I've learned that the 'Tree the Town' initiative encompasses tree plantings on more than just city-owned property. Trees planted by homeowners, businesses, schools, etc., all would count towards the goal of planting 50,000 trees. I was careful not to assert that that goal is impossible, only huge. With this additional information, it's still large.