Role of site in the mortality and production of Acacia mangium plantations in Indonesia

In Indonesia, Acacia mangium plantations exceed 1.6 Mha contributing approximately 3.5% of the country’s GDP. The viability of these plantations is increasingly threatened by fungal pathogens, insect pests, squirrels, monkeys, elephants and wind damage. Studies indicate that the problem is growing and in some areas, fungal pathogens such as Ganoderma and Ceratocystis species have contributed up to 50% tree mortality by the fourth rotation. Multiple statistical procedures were employed to examine the influence of soil and topographical properties on tree survival (trees ha⁻¹), wood production (m³ ha⁻¹), and mortality associated with Ganoderma root rot, Ceratocystis wilt and by wind. Soil family level was found to be a good indicator of tree mortality. Plots with fine-loamy Typic Kandiudult soils had the highest tree survival and mortality associated with species of Ganoderma and Ceratocystis, but had the lowest incidence of mortality by wind. The degree of association between soil and topographic variables with tree survival, wood production and the cause of mortality were poor and inconsistent. Tree survival was slightly higher on upslope areas away from valley bottoms, and drier mid-slopes, ridges and hilltops, and very low pH (<3.3) soils. Wood production was also lightly higher in drier, elevated locations, away from valley bottoms. Mortality by wind was slightly higher in moist, poorly drained, low-lying valley bottoms and topographically flat areas. Our ability to further pinpoint the influence of topography and soil attributes on wood production and cause of mortality was greatly compromised by the lack of site-specific soil data, and potential misclassification of the cause of mortality. This study could not reliably or consistently relate tree survival, wood production or the cause of mortality to any one, or combination of, soil and topographic variables.