I just got back from a trip to Pullman where I guest lecture once a year for the Landscape Plant Management class. It’s also a chance to get some new photos for my Wall-O-Shame. Here’s my latest:
Pin oak (Quercus palustris) doesn’t drop its leaves in the winter – instead, they hang on until the following spring. So it’s really easy to see which part of this tree is alive (i.e., has last year’s leaves). It’s apparent that most of the crown has died, with only some lower scaffold branches remaining.
How did this happen? Take a look at how new that concrete is around the base of the tree (and how small the tree well is. This construction was done in 2004:
Note the complete lack of root zone protection. Not only has the majority of the tree’s fine roots been destroyed in preparation for pouring concrete, but only a very small space under the tree is “protected.” I guess the cup at the base represents the irrigation system. To top it off, this construction was done in August, when coincidentally I was there as well. It was blistering (as it usually is in the summer in eastern Washington), and the remaining leaves on this tree were wilted:
So why would anyone be surprised when, 6 years later, this tree looks like crap? And why doesn’t WSU insist on tree protection standards when construction bids are submitted?
In Melbourne, Australia, we had a huge storm about 5 years ago now in which we lost a lot of landscape trees in the inner city parks and gardens. They were mature specimens too, mainly Ulmus spp., some upwards of 150 years old. When looking at maps of the parks which lost trees in the storm a very clear pattern emerged. All of the trees that were lost had been planted along pathways or roads, which had been modified or relayed several times since. All the trees also fell away from the paths. I think when people dig around trees and see fine roots they don’t think they’ll be putting the tree at risk by severing them – which, by Linda’s example as well as mine simply isn’t true. I put it down to the popular conception that trees have ‘taproots,’ so people think cutting fine roots close to the surface with neither harm the health of the tree nor put its stability at risk. Linda, isn’t it something like 90% of a large tree’s root system is in the first foot of soil or so surrounding the tree (and extend beyond the drip line, another myth)? I don’t know if they’re the right figures, but I don’t think I’m that far off.
Jimbo, it’s estimated that a tree or shrub’s root system extends anywhere from 2.5-3 times the diameter of the crown, and the majority of the roots are within the upper 18″ of soil. When you curtail this broad, shallow system, you are going to affect the health and s
tability of the roots. You’re also correct that many people erroneously think that a seedling’s taproot system remains as the tree matures. And there’s the maddening human desire to see symmetry in nature, so still other people assume that a root system simply mirrors the crown upside down and underground.
We had Hurricane Isabel move through here back in 2003. Many street trees blew over. Also, many oaks in forests and other open areas blew over. I think that fueled the myth of a tree’s root system. Most trees had a reason why they blew over, and most seemed to have insufficient roots and/or root rot. Additionally, we had local meteorologists saying the wet soils don’t hold on to their trees. I even recall a little graphic one had comparing trees in wet soil to a champagne glass in a bowl of pudding. All this was after a relatively dry August, though 2003 ended up as our second highest year for rainfall.