You can typically remove about one-third of the total tree roots with no problem. This is done sometimes when trenches are cut in the soil for burying irrigation lines. But when roots are cut, about one-third of the top should be removed as well.
Bob Morris
Bob Morris is a horticulture expert living in Las Vegas and professor emeritus for the University of Nevada. Visit his blog at xtremehorticulture.blogspot.com. Send questions to Extremehort@aol.com.