Urban tree root systems and their survival near houses analyzed using ground penetrating radar and sap flow techniques

Root systems of two mature Field maple trees ( Acer campestre L.) growing i n both shaded and non-shaded sites, on clay soil in an urban environment, w ere analyzed by ground penetrating radar (GPR), light microscope and sap fl ow techniques. The ground surface above the root systems was covered by asp halt. However, a small piece of garden existed near the non-shaded tree, an d root area of roots growing in this direction increased significantly, due to a presumed increase in available water and nutrients. However, no garde n was present near the shaded tree, therefore roots remaining under the asp halt surface did not increase in area in any particular direction. Maximum rooting depth of shaded and exposed trees, as determined by GPR, was approx imately 1.4 and 1.7 m, respectively. The trees utilized relatively large am ounts of water for transpiration, i.e. 65-140 l per fine summer day and in average 10 m(3) per growing season. However, transpiration expressed per ro ot surface area (and/or whole root system enveloping area) was practically the same in both trees, i.e. 1 dm(3) m(-2) d(-1) or almost 100 dm(3) m(-2) per growing season. These figures represented about 50% of potential evapot ranspiration when considering projected crown areas. Increased transpiratio n under long-term high evaporation demands may cause occasional local dryin g of soil around roots, associated with soil shrinking in clay, which can b e followed by serious damage to buildings.