Forest Stand Characteristics and Their Correlation with Carbon Stock in Sarawak Forest

Afifi, Bin Nazeri (2025) Forest Stand Characteristics and Their Correlation with Carbon Stock in Sarawak Forest. PhD thesis, Universiti Malaysia Sarawak.

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Abstract

Borneo’s primary rainforest is one of the world’s oldest and most extensive forests. Heterogeneity in the environment and biogeography made these forests rich in tree species composition and diversity. It has been recognized that forests have proven to be a significant contributor to recovering the excessive carbon in the atmosphere into ecosystem pools. Forest carbon stock is directly linked to forest biomass. Factors that increase tree biomass such as tree diameter, basal area, wood density, and species composition will subsequently increase carbon storage. This study examined the influence of forest stand structure attributes and species composition on forest carbon stock. Two logged-over forests, namely Bukit Durang and Saremas 1 Div 5 and two primary forests, Lambir Hills National Park and Kubah National Park, were selected for this study. Vegetation analysis and the line transect sampling method were carried out in all study areas. Twenty-five 20 m x 20 m quadrates were established in each study area. All trees above DBH of 10 cm and above were enumerated. Forest stand structures and vegetation indices were determined. Aboveground biomass (AGB) of all enumerated trees was calculated using a non-destructive method and converted to carbon stock. The Pearson correlation analysis was performed to determine the correlation between carbon stock forest stand attributes and species composition. The forest structure among the study areas has no variation regarding tree density, number of families and number of genera. However, they differ in terms of basal area and number of species. The highest basal area was recorded in Lambir Hills National Park, while Saremas 1 Div 5 and Kubah National Park exhibited the greatest number of species. The study areas are dominated by the family Dipterocarpaceae, followed by Euphorbiacae. Other families that are commonly found in the study areas include Burseraceae, Anacardiaceae, Lauraceae and Moraceae. The only dominant genus is Shorea, and other genera vary between the study areas. The dominant species varies among the study areas. Higher species diversity indices were computed for Bukit Durang and Saremas 1 Div 5. The logged-over forests were found to have a high number of fast-growing species compared to the primary forests. Tree diameter distributions revealed the reverse J-pattern indicative of all the forest areas studied in a state of equilibrium that can regenerate naturally. Dipterocarpaceae and the genus Shorea recorded the highest carbon stock among all the families and genera. Pearson correlation analyses revealed positive correlations between carbon stock and tree diameter, suggesting that large trees store large amounts of carbon. A weak correlation was also observed between carbon stock and species composition. However, other factors influencing the forest carbon stock are likely possible. Thus, further studies are recommended to include more variables.

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