Bolts in Trees

Question:

 I have several large oaks in my back yard (30" diameter) and live next to a pond. I'd like to put up several wood duck houses in the spring and will hang them on a 5/16"x4 1/2 lag bolt driven/screwed into these live oaks. Would driving these lag bolts into this oaks be harmful to the tree?

Minnesota Master Gardeners say:

 The answer is yes, driving screws or bolts of any kind into live trees causes damage. In a general sense, it is always correct to avoid any intentional injury to valuable trees. When one considers the aesthetic, not to mention monetary value of mature oak trees, it should cause one to appreciate what a wonderful things they are. While the initial damage to your oaks would be slight enough, the open wounding of these trees carries far greater potential for damage. Any wound may act as a point of entry for fungi, which can kill any tree, oaks included. To be even more specific, oak trees in Minnesota are dying by the tens of thousands of a disease called "Oak Wilt'. This is caused by a fungus called Ceratocystis fagacearum, which can be spread through open wounds. It is inadvisable to wound or prune oak trees in April, May, and June, and the summer months that follow are still at least slightly risky months to prune or wound. Go to this Extension site to read about Oak Wilt:
http://www.extension.umn.edu/distribution/naturalresources/DD3174.html

If Oak Wilt isn't frightening enough, there's yet another threat to oak trees. It's called "Two-lined Chestnut Borers", which are insects that may attack and kill oak trees:
http://www.dnr.state.mn.us/treecare/forest_health/twolined_chestnutborers.html

I guess I'm not trying to be an alarmist, but if one considers the value of mature oak trees (think how much you would miss yours if they died) it isn't worth even a slight risk to drive nails, screws or bolts into them. Also, some day those oaks will die of old age, if nothing else, and someone will use a power saw to cut them up for firewood. Large lag bolts could seriously injure whoever was operating a chain saw.

Here is a site that discusses nest box hanging techniques that don't rely upon nails, screws, or bolts:

http://www.roanokewildlife.org/Woodworking%20for%20Wildlife/nest%20box%201.htm
Here's a publication called "Birdhouse basics" from University of Maine Extension:
http://www.umext.maine.edu/onlinepubs/htmpubs/7117.htm