A study of the carbon stocks of Melaleuca forests in the coastal regions of Southern Vietnam and South East Queensland Australia

Abstract

The genus Melaleuca consists of around 260 species. The genus dominates forests that cover more than six million hectares of land globally. Most of that forest occurs in Australia, but there are also smaller areas in countries in South-East Asia and the Caribbean region, and the southern United States of America. Melaleuca forests predominantly occur in wetland and coastal ecosystems and as a result are substantially exposed to the influences of climate change and human development, particularly in regards to impacts on hydrological and soil systems. Like other wetland forest ecosystems, a large amount of carbon is stored in the biomass and soil components of Melaleuca forests. However, up until now very little research has been published on the extent and nature of those carbon stocks. This thesis addresses this gap in the research literature and presents the results of a study that involved collecting data on the carbon stocks of various Melaleuca forests in Australia and Vietnam. A variety of widely recognised data collection methods were used to collect data on the carbon stocks of Melaleuca forests at field sites in Southern Vietnam and South East Queensland, Australia. Data was collected from five ‘typical’ Melaleuca forest stand-types in Vietnam including: primary Melaleuca forests on sandy soil (denoted VS1); regenerating Melaleuca forests on sandy soil (VS2); degraded secondary Melaleuca forests on clay soil with peat (VS3); regenerating Melaleuca forests on clay soil with peat (VS4); and regenerating Melaleuca forests on clay soil without peat (VS5). Data was also collected from four ‘typical’ Melaleuca forest stand-types in Australia including: primary Melaleuca forests under continuous water inundation (A1); primary Melaleuca forests not inundated by water (A2); degraded Melaleuca forests under continuous water inundation (A3); and regenerating Melaleuca forests under continuous water inundation (A4). Carbon stock densities of VS1, VS2, VS3, VS4, and VS5 were found to be 275.98 tC/ha, 159.36 tC/ha, 784.68 tC/ha, 544.28 tC/ha, and 246.96 tC/ha, respectively. Carbon stock densities of A1, A2, A3, and A4 were found to be 381.59 tC/ha, 278.40 tC/ha, 210.36 tC/ha, and 241.72 tC/ha, respectively. In Australia, carbon accumulation in forest litter in wet conditions (A1) was likely to be 6.5 times higher than those in drained and drier conditions (A2). The total carbon stock densities in Melaleuca forests in the wildfire conditions were found to be lost around 45 % of those in primary forests under wetter conditions. Furthermore, the exchangeable sodium percentage of Melaleuca forests in Vietnam on sandy soil (VS1 and VS2) showed high sodicity, while those on clay soils (VS3, VS4, and VS5) varied from low to moderate sodicity. The results of this thesis also show that: (1) the carbon stock densities of Melaleuca forests in Australia are much greater than previously thought and substantially higher than current estimates used in Australia’s national carbon accounting systems; (2) the carbon stock densities of Melaleuca forests on peat lands in Vietnam are large compared to many other forest types around the world; (3) and that Melaleuca forests on sandy soils in Vietnam are tolerant of highly sodic conditions, an important feature considering how climate change and human development in the region is impacting on local hydrological and soil systems. In these regards, the results of this thesis provide important information for the future sustainable management of Melaleuca forests in both Australia and Vietnam, particularly in regards to emerging forest carbon conservation and management initiatives.