Featured Expert
Jeffery Johnson
Plant Coordinator
Minnesota Landscape Arboretum
Chanhassen, MN

Q: We have a lot with a number of mature trees on it. What type of precautions should we take when we build a new house there?

A: Well, that's a great question, and what we're running into particularly in the metropolitan area again, but specifically in developing areas, is people buying very expensive, wooded lots, coming in, hiring a contractor to build a house, and not paying much respect to the trees that are there that have a lot of value; and protecting them is very important to the homeowner. What we see in three to five years, or maybe even a little longer down the road, is that those trees start to suffer, and it goes to the issue of the roots again. The real heart of a woody plant is in its roots, and when tree roots are disturbed, one of a couple of different things can happen. If you're taking soil away and cutting down into the root zone, you're taking roots away that are required for that plant to absorb water and nutrients necessary for the plant to grow. Those water and nutrients are transported up into the leaves, and then those leaves manufacture food for the tree, and the tree translocates that food back down in the form of sugars into the roots, where the roots are respiring - they're breathing just like we are. We take sugars and we convert them to energy, and we have carbon dioxide as a byproduct. Plant roots do the same thing. They respire, and they need oxygen in order to do that. But what happens when you sever roots is the root to crown ratio is affected, and that can show up in stress in the top of the plant. The other thing that happens commonly is we've got all this construction activity going on around the tree, and the soil gets compacted, which excludes oxygen. We have changes in grade happening on construction sites where we have overfill, which will suffocate those roots as well. And then the grade also changes on particular sites, and the changing grade can suffocate those roots again, particularly if it adds water to a certain area where there are trees, and that water doesn't have anywhere else to go. So, oxygen is really the key to maintaining a healthy root system in trees and shrubs. What I really recommend people do if they're going out and buying an expensive wooded lot and going to build a house on it is hire a consulting arborist to come out on the site and talk to the homeowners before construction begins, and hopefully they can work with the contractor to ensure that construction occurs away from high valued tress on the property. You're not going to be able to protect every tree on a landscape, and certainly a consulting arborist might tell you "These trees are really highly sensitive to damage, particularly with the orientation of the house and the access ways in the construction process. So, let's just take these out now, rather than waiting five or ten years until they die, and then having to take them out, which would maybe be a more expensive process." But that consulting arborist is going to be very familiar with this phenomenon of construction damage on wooded lots, and he or she will be able to help you in that process. The important thing is getting that person involved in the front end of the process, rather than waiting until the problems start showing up five or ten years down the road, when there's very little that can be done, if anything, for those trees at this time.

The University of Minnesota is an equal opportunity educator and employer.
Online Privacy Statement

(none) /pyg/arb/qanda/1400/arb_1409.shtml
Last updated: Tuesday, February 01, 2005