Ask Mr. Smarty Plants

Roots of trees generally extend at least as far out as the shadow of the canopy of the tree. This area is referred to as the Protected Root Zone (PRZ). Covering this area with concrete is likely to cause the death of the tree by physically damaging the roots and by inhibiting oxygen and water from reaching the roots. Additionally, the roots of the tree have the potential to damage/crack the concrete as they grow trying to reach water and oxygen.

There are a number of permeable paving materials that you might consider instead of concrete. These include such materials as paving bricks, flagstones or patio blocks as long as they are laid without mortar. You can find more types of permeable pavers here. Another possibility is a raised wooden deck that could go right up to the edge of the tree with no harm as long as its foundation didn't damage the roots of the tree.

You can read more about protecting trees from damage during construction projects and advice about placement of pavement in the area of trees in Landscaping Around Established Trees from University of Nebraska-Lincoln Extension Service and Protecting Trees from Construction Damage: A Homeowner's Guide from the University of Minnesota Extension Service.

You can find a list a Landscape Professionals near your area who could advise you on permeable paving materials in our National Suppliers Directory. You might also try your local library or bookstores for books on alternatives materials for patios (e.g., Taunton's Deck & Patio Idea Book or Sunset Ideas for Great Patios and Decks).