Land use and carbon dynamics in woody ecosystems

Humanity has not yet been able to contain its influence on global average temperatures nor on the carry-over effects of that to the biosphere, namely climate change initiated by our carbon emissions, and positive feedback on temperature is likely to increase. The contribution played by our land use change (LUC) is millennia-old and annually it is currently comparable to that of fossil fuel usage, but it is less precisely known. The key aim of this thesis is to improve the knowledge about carbon emissions from LUC to the atmosphere so that we can control them better (‘climate change mitigation’), and in order to facilitate better climate change modelling. Extremes of intensity and expanse of change in carbon, accompanying LUC, were studied using carbon-dense forests and rangelands respectively. The dynamics were reviewed and re-assessed, and previously discounted carbon pools were quantified. Tools used in the analysis included conceptualisation of carbon dynamics, standard forest mensuration, remote sensing and GIS, soil data collection and carbon assay, terrestrial photogrammetry using innovative software, formulae development, and mathematical modelling including forecasting of carbon flux. Most data were from Australia but the concepts applied, theories developed and thematic results are applicable globally. For intense LUC the focus was on the more carbon-dense forests, especially those in Tasmania which were the major feedstock of the Pacific rim’s hardwood pulpwood market until 2012. For expansive areas the Australian commercially grazed rangeland was studied and two case studies were the States of Queensland and New South Wales. In those, LUC had recently been more intensive, with accompanying greater public scrutiny and consequently more data availability. The findings will contribute towards more precise estimates of carbon fluxes for emission trading schemes, national reports and for climate change modelling from several millennia in the past to two in the future. There were several main areas of knowledge enhancement: 1) increased quantification of anthropogenic influence on C flux in woodyecosystems accompanying logging and rangeland grazing, past and future 2) revealing that the half-lives of wood products need to be increased by nearly an order of magnitude to not lose nearly half the carbon of primary forests when they are converted to secondary forests on harvesting cycles; 3) increased formulaic relations between natural phenomena for use in modelling carbon dynamics; 4) showed how a comprehensive time-space (4D) context of carbon dynamics in woody ecosystems can reveal both higher carbon emissions and higher carbon sequestration for LUC or ecosystem recovery respectively, and how it provides an overarching explanation to relieve points of contention by (e.g. for woody-thickening, deforestation; and forest logging); 5) increased understanding of SOC distribution and change (e.g. development of a robust method to calculate cumulative SOC down a diverse soil profile; finding associated with large trees ~6% more SOC than earlier tallied, the same trees targeted for logging; 6) improved experimental methods, e.g.: use of Photoscan software to quantify large trees, and remote sensing/GIS to locate carbon stock benchmarks in degraded rangeland; 7) discovery of a new natural substance (cunnite) constituting a novel but small carbon pool; and 8) informative, diagrammatic portrayal of a sequence of relationships between land-use, woody ecosystems, and climate, in the carbon cycle. To help increase knowledge it is imperative, for carbon accounting of both forest logging and rangeland commercial grazing, that greater data transfer occurs between industry, government departments and the scientific community.