THE APPLICATION OF SOIL SCIENCE TO FORESTRY IN LAND USE PLANNING AND WATERSHED MANAGEMENT IN SRI LANKA.

Abstract

Allocation of land to forestry in Sri Lanka has hitherto been based an "adhoc" considerations. The over-riding approach has been to allocate the least productive soils to various forms of forestry. Furthermore, even current recommendations of forest species for forestry plantations are made mainly on the basis of climate or geographic region with no recognition given to the occurrence of different kinds of soils within a particular region.

Some very striking and significant soil-vegetation relationships have been observed and described, especially in the dry and intermediate zones of this country by several field scientists and researchers engaged in the Soil Survey of Sri Lanka since the early nineteen sixties. In several recorded instances it has been observed that the nature of soil exerts a profound influence on the growth and performance of some species that make up the 'dry-mixed-evergreen" forest. Some relevant examples are cited and further discussed.

Soil related factors should, therefore, be considered as having a very important bearing on species performance and forest productivity on different kinds of soils occurring within the same agro-ecological region. Meaningful land use planning for forestry should, therefore, be based on a proper understanding of the soil-vegetation relationships. Supporting examples are cited and discussed. An argument is also made for allocating land with better quality soils for commercial forestry plantations.

A proper recognition of the soil water-vegetation-evaporation balance in different environments is considered the key to understanding the role of forests in watershed management both in the dry and the wet zones of this country. Based on studies conducted by the Land Water Use Division of the Department of Agriculture over the last two decades, the selective role of a forest cover in the different environments (dry and wet) of the country are discussed in relation to watershed management.