Studies of the Development of Woodland Conditions Under Different Trees: V. The Mineral Composition of the Ground Flora

Abstract

Woodlands are often classified by their ground floras, the classification being based upon the frequencies of the plant species which are present (Cajander, 1926). The associated vegetation seems to reflect not only primary site factors such as geology, aspect and macroclimate but also those secondary local factors determined by the established tree species. The extent to which the dominant tree species modifies site conditions changes as a plantation matures and corresponding changes occur in the ground flora. It has been possible to trace the successive development of the ground floras under various woodland types from earlier vegetation records made by W. H. Guillebaud* at Bedgebury, and by C. O. Hanson and J. Macdonald at Abbotswood (Ovington, 1955). The reduction of light intensity at ground level by the tree canopy and root competition have been considered as the two main operative factors by which a tree species limits its ground flora (Aaltonen, 1926). Shirley (1929) found that when the light intensity is reduced below 20 per cent of full sunlight by the tree canopy, the dry weight of the ground flora is proportional to light intensity and concluded that light intensity is usually the limiting factor in the growth of vegetation under a forest canopy. The increased luxuriance of the minor vegetation following trenching has demonstrated the intense root competition existing in some woodlands, thus Tuomey and Kienholz (1931) and Korstian and Coile (1938) regard competition for soil moisture as a highly significant factor. The application of mineral fertilizers to the forest floor may also result in a more vigorous growth of the ground flora (Ovington, 1947). Whilst the trees and ground flora can be thought of as complementary (Woodhead, 1906), some authors consider that they are in active competition for soil nutrients (Watt and Fraser, 1933). Agronomists have examined in detail soil conditions and the uptake of nutrients by agricultural crops. It is possible that in a similar way the nutrient content of the woodland flora might be of value in interpreting some of the complex relationships existing in the forest ecosystem. In view of the many records of the plant species in the ground flora of woodlands it is surprising that so little information is available of its weight and chemical composition. This may in part be due to the marked periodicity that occurs in the growth of the ground flora in woodlands so that comparisons are difficult, particularly under deciduous tree species. In a previous paper (Ovington, 1955) plant lists and frequencies were given for the associated vegetations in a series of forest plots at three different localities and the weights of water, dry matter, ash, carbon and nitrogen were recorded. This account is complementary to the earlier paper in that it refers to the mineral composition of these