Tree canopy and house size

I will take a controversial position: trees are good. Given the amount of needless tree destruction we see, I sometimes feel in a minority. The City recently took the elm in front of our house, diminishing our shade. It was nearing end of life, and I assume diseased or at risk of disease. They have not planted any replacement yet.

Of course, many people like trees. That is why most of us live under a canopy of trees, even in relatively urban areas. We constrain our houses to be two or three stories to fit under trees, so that we may get shade, reducing summer cooling costs and to a lesser extent winter heating costs. Commensally, we benefit many of the trees we keep because we send trees the extra water runoff that does not get absorbed by our houses’ impervious roofs, and our houses radiate excess heat, keeping the trees warmer.

The City of Minneapolis has a tree canopy of 31.5% (11,569 acres), according to a recent University study. Coincidentally, that is the city’s goal. That goal is too small.

The study says trees could cover an additional 37.5% of possible UTC (urban tree canopy, not university transportation center), including grass and impervious surfaces. Minneapolis has about 200,000 boulevard trees on over 1000 miles of street, leaving aside trees on private property. I believe we should as a society raise our target, maximize tree cover, so much so that during the summer we can hardly see the city from an airplane for the coverage.

There are other benefits to trees. Each tree we plant absorbs one ton of carbon in its lifetime. A carbon calculator tells me I need to plant 17.7 trees to offset one year of driving a gasoline-powered fuel efficient car (1000 miles per month). Fortunately I walk, because that seems like a heckuva a lot of trees to offset driving, certainly more than I could do on my own property (assuming they refer to full size trees). PBS tells me “Densely vegetated areas of a city can create cool islands within an urban center. Plus, shady sidewalks encourage people to walk rather than drive.” Those all seem good things.

Montgomery County, Maryland gives trees to qualifying CBD property owners. There the market failure seems to be the more general problem of private provision of a public good, namely sidewalks. People have little incentive to upkeep beyond the minimum required by law. What if property owners were required to build roads and the public took care of sidewalks?

Chicago pays people to grow trees through its Sustainable Backyards program. Is it really necessary to pay people for trees in their own yard? The main benefits to planting trees should be captured by property owners directly through lowered energy (heating/cooling costs). While I will admit there are some externalities (see Carbon paragraph above), they are small relative to the purported personal benefits of tree planting. Not every good idea should be a government program.

Trees have their risks. In Florida, palm trees can act like missiles during hurricanes. But they also have benefits, such as slowing erosion.

Improve your street, plant a tree.


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9 Responses to Tree canopy and house size

  1. Evan Roberts
    Exiled Antipodean November 19, 2012 at 5:02 am #

    Hear, hear. Unfortunately Minneapolis city government seems complacent about the urban forest. We're more treeful than some other Midwestern cities, but we could do a lot better. There are a lot of parks and other small open spaces that could have more trees.

  2. Reuben Collins
    Reuben Collins November 19, 2012 at 5:28 am #

    I certainly agree that we need more trees. I generally think the park board does a decent job with the boulevard trees around town, although, there are certainly streets around town that have been unnecessarily without boulevard trees for many years.

    Trees & utilities often compete for the same scarce boulevard space. Overhead utilities leave the ground free for trees, but then Xcel "prunes" (brutalizes) them every 5 years. Underground utilities are more difficult and costly when they must compete with trees for underground space.

    There are a few costs that trees impose that you didn't mention. For example, if we all plant a couple trees in our front lawns, half of us will have to replace our sewer laterals in 15 years because the roots destroyed them (which may or may not require removing the tree). Also, trees sometimes fall over onto houses – the bigger they are, the more potential damage.

    I like the newer strains of trees that naturally limit their own height and trunk diameter so as not to destroy the adjacent curbs & sidewalks. Elms, while beautiful in many ways, were probably never a great choice for urban areas in the first place, even if disease wasn't an issue.

  3. Julie Kosbab November 19, 2012 at 5:49 am #

    Another challenge, beyond that of Dutch elm and the (needed) decimation of diseased boulevard trees, is that very often when trees are planted where there are no trees, there is a bias to fast growth trees. Many of the fast growth trees aren't necessarily great long-term trees. They aren't trees that stand there 100 years and become beloved, like the maple tree in my yard in St. Paul.

    The house I live in right now was built in the mid-80s, as were its neighbors. We've lost a bunch of the trees planted during the build of this neighborhood, because they chose quick-growth, shallow-rooted trees. We had an ash go down in a storm, for instance. The gingko trees planted in that era are presently weedy and sad. I am advocating to my husband that we destroy them in favor of fruit trees, because I like fruit and don't like sad weedy trees.

  4. Brendon Slotterback
    Brendon Slotterback November 19, 2012 at 7:23 am #

    In 2011, the "City" planted over 6,000 trees. But we're still dealing with Dutch Elm to a limited extent and the new threat of Emerald Ash Borer, which could have a profound impact on our canopy. 32% will be very difficult to maintain if a lot of ash come down.

    While the U of M study does estimate what could be covered, it's difficult to force private property owners to plant trees. Likewise, many property owners do not want to rip up parking lots to plant trees.

    All that being said, we should increase the canopy. Some of the biggest challenges will be planting (and making sure trees survive) in very built-up areas (downtown, etc). There are infrastructure solutions (like tree trenches and silva cells), but they are expensive. Boulevard space is also not usually increasing.

    Here is a map that allows you to explore tree canopy coverage by neighborhood and parcel.

  5. Jessica Schoner November 19, 2012 at 11:41 am #

    That LA shuttle situation was terrible. When I lived there, you already could guess the racial, ethnic, and economic composition of a neighborhood based on how many trees the City of LA bothered to plant and maintain, so of course the shuttle trees came out of South LA and Inglewood.

    Re: "Is it really necessary to pay people for trees in their own yard?" Yes. Maybe the middle class residents in a single family home that they own wouldn't really need the payment program, but many other residents probably need the assistance. Landlords in high-demand areas or with tenants with few choices have little incentive to plant and maintain trees. Lower income residents might not have the cash flow to pay for a tree, even if the long-term cost savings exceed the initial cost. So Chicago's program, being a reimbursement and not needs-based, might just be a transfer of city funds to those who would have planted trees anyway. But some sort of city program to fund trees in people's yards would probably be worthwhile. Especially programs that support fruit trees. (City of Anaheim specifically excludes fruit trees.)

  6. Dimitri D November 20, 2012 at 3:57 am #

    One thing the city could do– allow home owners to plant boulevard trees. We moves into our house in 2002, and clearly a boulevard tree had just been removed (new grass, indent in sidewalk to accommodate the tree that was once there). After years of waiting for he city to replace it, I put a buckeye in, since they weren't going to do anything. Did the same thing on the other side (corner lot), with a tree we got through the city, ignoring the instructions to "not plant it on a boulevard". We did our homework, and made sure that the one that went under the line to our streetlight has a projected height of 15-20 feet, so shouldn't affect the line.

    • Ian Bicking November 24, 2012 at 4:31 am #

      Technically you are supposed to ask the Forestry department for permission to plant your own trees. I haven't tried that, but we have communicated with Forestry about pruning and they were fairly easy to communicate with.

  7. Joshua November 20, 2012 at 7:19 am #

    The city of Minneapolis should give people trees to plant in their yard. It makes fiscal sense to allow people to place them where they can do the most good for the property owner and not waste taxpayer money on city crews. Also trees should not be planted along sidewalks and roads. Roots heave asphalt and concrete making dangerous walking and driving hazards. Roots also get into pipes causing infrastructure problems.

  8. Janne November 23, 2012 at 10:12 am #

    If you want a boulevard tree — or want one that was recently removed replaced — CALL THE PARK BOARD AND ASK FOR ONE. They'll come put one in for you at no cost. You can even influence the species. 612-370-4900

    http://www.minneapolisparks.org/default.asp?PageI

    And, the City DOES give out heavily subsidized trees, although not many. They do this in partnership with Tree Trust most every spring.