When roots grow under pavement, they tend to grow just beneath the surface where oxygen supply is greatest. Once roots successfully navigate their way under a sidewalk to open ground, the roots on the other side can exploit new moisture and fertility resources. Subsequently, roots thicken up and can exert great pressure on the pavement. Preventing roots from damaging pavement begins with species selection and good design. Choose a small tree species for small spaces.
Root pruning or trenching to correct a problem is costly and often severely affects the tree.
Researchers that have attempted to determine how much of a tree root system may be safely removed have met with mixed results, - probably due to differential sensitivities among tree species. However, without a doubt, major root removal can cause tree decline and often mortality. Preventing root growth by installing some type of barrier has been successful in some cases. Most rigid root barriers are manufactured from plastic and can take the form of solid, molded forms that are placed into planting holes, panels that are fastened together, or continuous sheets of material. The latter two types can be fitted to a planting hole or be used in a linear fashion along one side of a planting.