A Study of the Root System of the Beech in Woodland Soils, with Especial Reference to Mycorrhizal Infection

IT is well known that the root system of beech shows a certain plasticity in form according to the type of soil on which it grows. In all localities, however, young seedlings are alike in having a long tap root which comprises the main part of the system. The length of time that this root remains functionally important varies with conditions, especially those arising out of soil variations. Vater (1927) described the root system of beech in Germany, and pointed out that the trees he studied retained their tap roots up to the age of 27 years. As the trees aged, however, the long surface branches became increasingly more important as absorbing organs, and at 80 years shallow outgoing branches of the heart root comprised the greater part of the functional root system. Hilf (1927) also made a study of beech-root systems, noting that in adult trees the system was shallow with occasional deep sinkers. As a rule the majority of the shallow roots remained inside the canopy of the aerial branches of well-grown trees. In soils derived from Bunter sandstone showing litter and humus accumulation, young roots tended to grow upwards and colonize these highly organic surface layers. They also colonized pockets of humic matter derived from the decay of old roots in the soil. Hilf gives interesting data upon the percentage of roots in soil horizons. 77 % of the fine roots were found in the humus layer, while 23 % were found in the top 50 cm. of mineral soil. 12% of the large roots were present in the humus, and 88% in the mineral soil. Watt (1934) has described the roots of beech in the Chilterns and pointed out that in deep soils of the plateau with little humus accumulation the roots go relatively deep, whereas in plateau soils where raw humus accumulates, the majority of the fine roots are to be found in the surface layers. The first study of beech woods in the Chilterns has allowed a classification of the root systems to be made. There are two main types. The first includes shallow root systems which are not only found on soils which are morphologically shallow, but also on raw humus soils which may be described as physiologically shallow. The second type includes deep root systems on the deepest soils of the escarpment and the better plateau soils.