Ecological Impact on Nitrogen and Phosphorus Cycling of a Widespread Fast-growing Leguminous Tropical Forest Plantation Tree Species, Acacia mangium

Many people tend to have the assumption that all kinds of plants are good for the environment, and hence the types of land use does not matter as long as they see plants in them. However, this case study is a very good example to increase people’s awareness that not all kinds of plants, especially plantations of crops like legumes, or in this case Acacia mangium, may not be environmentally friendly and clearing of forest areas for these plantations can result in negative environmental effects that can affect the element cycles in that region.

Firstly, Acacia mangium is major plantation species in the humid tropical lowlands of Asia, and plantations in Indonesia and Malaysia are the resource base for a large pulp and paper industry. Other uses of Acacia mangium includes fuelwood, timber for building and furniture and particle board.

Acacia mangium is reported to be one of the major fast-growing species that yields 31 to 128 kg ha^-1 year^-1 of nitrogen. According to (Arai S., 2008), Acacia magnum plantations produced 8 times larger amounts of nitrous oxide (N₂O) emitted compared to the secondary forests nearby. In addition, logging of tropical forests can further increase N₂O emissions by promoting soil Nitrogen mineralization. Also, the phosphatase production was shown to be larger in soils under Acacia Mangium than those under secondary forests. Hence, this study, conducted in the Gum Gum Forest Reserve in Sandakan, Sabah, Malaysia, and compared with plantations and forests nearby, reviews the difference in nitrogen and phosphorus retranslation and discuss how Acacia Mangium plantations can influence the regional and global nitrogen and phosphorus cycling.

It was shown that the mean annual nitrogen flux via litter fall of Acacia mangium is 217 kg ha^-1 year^-1 which exceeded the nearby plantation of S. macrophylla which is 137 kg ha^-1 year^-1. However, in contrast to the nitrogen flux, the mean annual phosphorus flux via the litter fall of Acacia mangium is only 3.3 kg ha^-1 year^-1 which was considerably smaller when compared to other plantations and the primary forest nearby. Hence, results have shown that Acacia mangium plantations are likely to move larger nitrogen and smaller phosphorus via litter fall than other forests.

Thus, Acacia mangium produces a large amount of nitrogen in litter fall and enhances the nitrogen availability at the forest floor. Also, Acacia mangium selectively retranslocates a big amount of phosphorus before leaf-fall. Thus large areas of Acacia mangium plantations can alter the cycling of both nutrients and cause a potential nutrient imbalance in the ecosystems, especially at the forest floor.

Hence, this case study highlights the fact that not all plants, especially agricultural crops and many plantations like palm trees or in this case, Acacia mangium, have the same beneficial effect to the environment like primary forests. Some plantations may even have a negative effect on the environment, such as the Acacia mangium plantations, and can, when planted in large areas, cause changes to nutrient cycles in the region and even globally. Thus this stresses the need for concern of people on all three levels, governmental, community and individuals, to bring about changes to lessen the occurrence of primary forests being cleared for other land usage.