COMMON OAK (QUERCUS-ROBUR) ROOT-SYSTEM ORGANIZATION DEVELOPED WITHOUT RESTRICTING EDAPHIC CONDITIONS (COLLUVIAL LEACHED BROWN SOIL)

The root density, slope, and the lateral and depth extension of root spreading have been measured in 150-yr old common oaks (Quercus robur) growing on colluvial leached brown soil. A parallel study was also performed on the clayey silt then silty clay soil materials, which had accumulated to a depth of 4 m above karstified calcareous rock The soil and the underlying layers permitted the root system to develop without any physical or chemical constraints as far as the rock. The root system of common oak can be divided into 2 parts: the surface system which spreads between 0-60 cm in depth; and the deep system below 60 cm. In a 3-m radius around the tree at the surface system level rooting was intensive and consisted of roots of varying diameters (from < 1 mm to > 10 cm), with a maximum root density. Roots sloped at an angle of 80-85-degrees-C with respect to the vertical The extensive rooting could spread up to 20 m from the tree. The deep system spread 2-2.5 m and was composed of subvertical roots (tap roots). It can be divided in 2 parts: the intensive deep system, from 60-120 cm; and the extensive deep system, from 120 cm to > 400 cm. The volumes of the intensive and extensive soil examined were estimated at 17 and 800 m3 respectively