Question
Hello, my husband is building a raised patio and needs to dig up some roots from our fruitless mulberry tree which is over 20 years old. He will have to dig roots on two sides. Can he safely do this and still have the tree thrive. It is a wonderful shade tree and I would hate to lose it. How close to the tree can he dig these roots before it causes damage? I have not been able to find an answer anywhere.
Thank you.

Answer
The roots of a tree extend out about 1 1/2 times the width of the foliage. Generally up to 25% of the trees roots can be cut without seriously damaging the tree. If you are talking about digging holes for the support of the raised patio you more than likely will not damage enough roots to cause much damage. You may get a little die back of some of the limbs due to the cutting but the tree will adjust. BUT if you are talking about a footing that cuts two sides of the tree's roots you will cut enough roots to significantly damage the tree and cause a great deal of die back of the foliage.
The other problem will be protecting the remaining root system during construction--do not drive on this system during construction, do not pile up soil/sand or construction materials on the area around the tree's roots. These will cause compaction of the soil damaging the remaining roots.

The tree grows roots to support the manufacture of foliage and if some of the roots are cut the the tree's roots system can not support the amount of foliage it once could so some of the limbs will die to compensate for the lost roots.

Here is a web link to a site that gives more information on construction damages to trees.
http://www.treesaregood.com/treecare/avoiding_construction.aspx