KUL. Faculteit landbouwkundige en toegepaste biologische wetenschappen. Departement landbeheer. Laboratorium voor bos, natuur en landschap
In order to preserve natural tropical forests, one tends to favour the establishment of forest reserves for conservation and plantations for the production of merchantable timbers. On the other hand, both conservation and production can be implemented in sustainable forest management systems. The development of such systems is hampered by the lack of accurate knowledge on the ecology of different indigenous tree species. In the deciduous forest of Ban Pong, near Chiang Mai in Northern Thailand, research was conducted to reveal the ecological constraints for the growth and natural regeneration of Dalbergia (Fabaceae). Sample plots were laid out in different deciduous forest stands. The presence of Dalbergia-trees and some characteristic dipterocarps, Shorea and Dipterocarpus (Dipterocarpaceae) was related to a number of ecological stand characteristics, such as intensity of light, chemical and biological soil properties and species composition of the vegetation.
In a first stage of the research project, the assessed vegetation data was used to differentiate a number of forest types. The Royal Forest Department (1962) has established a classification of the forests of Thailand. Deciduous forests are of two types: mixed deciduous and deciduous dipterocarp forest. Results of this study suggest that the latter should be subdivided into a xeric or dry phase, an intermediate phase and a moist or mesic phase. Each of these phases is marked by a typical association of dominant xerophytic dipterocarps. The differentiation of forest types is controlled by edaphic factors, first of all soil moisture and effective soil depth. In addition, soil, structure and species composition of the different deciduous forests are affected by human impacts, first of all the annual burning of the ground layer. Furthermore, light climate, dendrometric parameters and diversity vary significantly among forest types and are related to soil factors as well.
In a second stage, the ecological constraints for the growth of Dalbergia were investigated. The research yielded some significant site differences for the examined Dalbergia-types, although no direct relation between Dalbergia type and forest type was found. On the level of individual species or types, additional research is required.