Land Evaluation and Species-Site Suitability Determination for Forest Plantation Establishment

Abstract of a presentation conducted by

Sohani Vithanage

Department of Forestry and Environmental Science

University of Sri Jayewardenepura, Sri Lanka

Decisions about the use of land have always been a part of human society. Forestry planning has always taken account of the influence of conditions of land in taking management decisions. The approach and methods of land evaluation were developed in order to provide a systematic framework for assessing the effects of land on potential benefits of each land use. Land evaluation is based upon a comparison between land use and land type. Land use related to forestry can be broadly categorized as production forestry, conservation forestry, recreational forestry and community forestry. These major land uses can be further described in detail according to tree species, silvicultural methods, harvesting practices etc. The focus of land evaluation is to access the requirements and limitation of each of this land use and to compare this with the properties of land.

In the process of land evaluation land use requirements for each identified land utilization type is defined. Simultaneously, land qualities and characteristics of each land unit is described using literature surveys and ground surveys. These data is then coupled with economic and social data to develop a comprehensive comparison of land use with land. The outputs of land evaluation can be presented in terms of land suitability classifications or land suitability maps. At present, this procedure can be carried out with the help of computerized land evaluation systems and geographic information systems. In determining the species site suitability for forest plantation establishment, three aspects have to be considered. They are purpose of plantation, species availability and environmental conditions. For this process, depending on the species and sites, information survey can extend from local level to international level.

Land Evaluation and Species-Site Suitability Determination for Forest Plantation Establishment

Abstract of a presentation conducted by

Sohani Vithanage

Department of Forestry and Environmental Science

University of Sri Jayewardenepura, Sri Lanka

Decisions about the use of land have always been a part of human society. Forestry planning has always taken account of the influence of conditions of land in taking management decisions. The approach and methods of land evaluation were developed in order to provide a systematic framework for assessing the effects of land on potential benefits of each land use. Land evaluation is based upon a comparison between land use and land type. Land use related to forestry can be broadly categorized as production forestry, conservation forestry, recreational forestry and community forestry. These major land uses can be further described in detail according to tree species, silvicultural methods, harvesting practices etc. The focus of land evaluation is to access the requirements and limitation of each of this land use and to compare this with the properties of land.

In the process of land evaluation land use requirements for each identified land utilization type is defined. Simultaneously, land qualities and characteristics of each land unit is described using literature surveys and ground surveys. These data is then coupled with economic and social data to develop a comprehensive comparison of land use with land. The outputs of land evaluation can be presented in terms of land suitability classifications or land suitability maps. At present, this procedure can be carried out with the help of computerized land evaluation systems and geographic information systems. In determining the species site suitability for forest plantation establishment, three aspects have to be considered. They are purpose of plantation, species availability and environmental conditions. For this process, depending on the species and sites, information survey can extend from local level to international level.

Establishment of relationships of growth with site factors and some selected soil parameters of a selected 7 years old mahogany plantation in Eheliyag

Establishment of relationships of growth with site factors and some selected soil parameters of a selected 7 years old mahogany plantation in Eheliyagoda DS, using GIS as a tool

B.Sc. Dissertation

Himesha Randeni and Upul Subasinghe

Mahogany (Swietenia macrophylla) is an exotic tree, which is heavily adapted to the climatic conditions of wet and intermediate zones of Sri Lanka. Although the state sector manages mahogany with longer rotations, private sector expects to achieve the maximum timber yield within a shorter period. Due to the land scarcity, many of these mahogany plantations have been established in barren and rubber uprooted lands which were heavily degraded. Therefore the soil conditions and site factors directly affect the growth of the mahogany within short rotations.

The present study was carried out in a 7 years old mahogany monoculture plantation established in Gomaragala, in low country wet zone of Sri Lanka to find out the effect of soil and site factors to the mahogany tree growth. Extent of this forest is 20.7 ha and it is managed by a private plantation company. This forest has been divided into 2 lots for the purpose of administration. However, for the sales purposes it has been divided into 240 plots.

In order to identify the relationships, tree dbh and tree height as growth parameters; slope and terrain were selected as geographical factors as well as soil texture, soil organic carbon level and soil pH levels were selected as soil parameters. The growth parameters (i.e.dbh and height) were measured of all the trees in plantation. Slope and terrain as geographical parameters were measured of all 240 plots in the entire plantation. Soil parameters namely soil pH, soil organic carbon and soil texture were measured for systematically selected 50 plots out of 240 plots to represent the entire plantation. There are some qualitative parameters namely tree growth, terrain, presence of bedrock, included into the present study. These were usually assessed to give a single value for each plot.

Since the regression based methods was not adequate for both qualitative as well as quantitative parameter analysis, GIS based analysis was decided to use for the present study, because it serves as an analytical and decision supporting tool. ArcView 3.3 was used for this purpose. In order to create digital maps, the survey plan of the selected forest was digitized and georeferanced by main 10 ground control points collected by a GPS data receptor. Then the georeferanced base map was digitized to demarcate all the plots and other land marks. After that different maps were prepared in vector form separately for each parameter. However, for the analysis, all these vector layers were converted to raster layers. Raster layers were then reclassified and overlaid two or three layers at a time with the growth parameters to identify the effects. Then map analysis was completed to make decisions regarding tree growth in different site factors and soil conditions with similar other environmental conditions. Since the soil pH, soil organic carbon level and soil texture were measured in selected 50 plots out of 240 plots, the raster layers were interpolated for entire area.

Results of the present study revealed that there are significant relationships between tree growth with the selected parameters. However, the best conditions for the mahogany tree growth in the particular area are the slope between 11⁰-24⁰, soil pH level bellow 4.0, soil organic carbon range between 9.0%-14.0%, soil with sand between 50%-70%, shallow bedrock prevalence and stony terrain.