佐々木 ノピア

Various demands for forestlands, wood, goods and services to meet the rapid economic development and fast growing population have put great pressures on tropical forests. Although forest clearing for agricultural land and pasture, and commercial logging coupled with government' policy failures are generally recognized as the major causes of deforestation, other causes have not been well documented. As a case study, this article aims at documenting forestry development and analysing the causes of deforestation and forest degradation in Cambodia. Forestry development in six different political regimes, namely, before 1970; 1970 to 1975; 1975 to 1979; 1979 to 1989; 1989 to 1993 and 1993 to the present was studied. Based on our analyses, we concluded that deforestation in Cambodia may have caused by intensive bombardments during the war time, forest clearing for resettlements, wood extraction for re-construction of war-devastated infrastructures, agricultural cultivation, and indiscriminate logging in recent years. Additional to deforestation, forest degradation may have resulted from indiscriminate felling and overexploitation. Cambodia would lose its important natural resource if immediate actions to stop deforestation and forest degradation is no undertaken.

The purpose of this study was to explore the stand dynamics of dipterocarp species in evergreen forest as a basis for devising suitable management systems for Cambodia's forests. The data for this study were obtained from a two-year UNDP-funded forest inventory project in Sandan district of Kampong Thom province. A sample of 18 clusters located in evergreen forest were analyzed. Based on the average stand volume per hectare, this evergreen forest was further divided into poor (less than 200m^3), medium (200-300m^3) and rich (greater than 300m^3) forests. Dipterocarps contributed 50m^3 (36%), 109m^3 (43%) and 163m^3 (53%) in poor, medium and rich forests, respectively. The dominant dipterocarps species were CHBG (Dipterocarpus turbinatus), CRMS (Vatica astrotricha) and PHDK (Anisoptera glabra). To estimate the forest potential and allowable cut of dipterocarps stands, trees of DBH greater than 45cm were analyzed. Cambodia's silvicultural treatment prescribes that only 30% of stands are extracted on a selective felling cycle of 25-30 years. On the basis of this silvicultural treatment and management experience in Southeast Asia, the harvest potential of Cambodia's forest was estimated to vary from 20m^3/ha (6 trees) to 54m^3/ha (13 trees) ; approximately 65% of which was dipterocarps. These figures are more than double the current harvest rate of 10m^3/ha. However, applying such a new management system might cause forest degradation if there is no long-term political commitment to management and research from the government and parties involved. Permanent and regular research on stand dynamics and other influential factors are required to ensure the sustainability of forest resources. Forest management can no longer be concerned solely with timber production ; thus, harvesting and research in non-timber forest products should also be included in the management plan.

A fast growing population and the need for food and forest products coupled with the great demand for wood and rapid economic development in the developing world have brought sustainable forest management under continuous uncertainty. Deforestation in the developing world has been relatively high. But recently, it has been more widely recognized that over-exploitation of forest products and non-forest products is prejudicing the sustainability of the world's forests. Cambodia has been chosen as a case study to test this hypothesis regarding sustainable forest management. There are two main types of forests in Cambodia, namely dryland and edaphic forests, covering a total area of 10.59 million ha or 58% of the total land area. It had been reduced from 12.32 million ha in 1973 as a result of wars and political instability over the last 25 years. Against a background of government instability, great domestic and foreign demands for wood in recent years have resulted in Cambodia's forests being over-exploited. To prove this, a selective 25-year felling cycle system used by F Company was analyzed with the aid of various statistical tools. The analysis shows that although the growing stock of F's evergreen forest is as low as 82 m^3/ha due to illegal logging, the company has exploited 7 m^3/ha or 9% of the total stock. This was 6 percentage points higher than the sustainable cutting rate of Cambodia's evergreen forest. This supports the hypothesis of over-exploitation. The result also shows that there is still a large number of residual trees with diameter less than 45 cm, which are available for extracting over the next 25 years if they are properly managed. Strong enforcement mechanisms for forest monitoring and control are needed to stop illegal logging, to prevent over-exploitation and to manage the residual trees for long-term availability of forest resources.