Christopher Dean

Old-growth forests, carbon and climate change: Functions and management for tall open-forests in two hotspots of temperate Australia

Abstract The prognosis and utility under climate change are presented for two old‐growth, temperate forests in Australia, from ecological and carbon accounting perspectives. The tall open‐forests (TOFs) of south‐western Australia (SWA) are within Australia’s global biodiversity hotspot. The forest management and timber usage from the carbon‐dense old‐growth TOFs of Tasmania (TAS) have a high carbon efflux, rendering it a carbon hotspot. Under climate change the warmer, dryer climate in both areas will decrease carbon stocks directly; and indirectly through changes towards dryer forest types and through positive feedback. Near 2100, climate change will decrease soil organic carbon (SOC) significantly, e.g. by ∼30% for SWA and at least 2% for TAS. The emissions from the next 20 years of logging old‐growth TOF in TAS, and conversion to harvesting cycles, will conservatively reach 66(±33) Mt‐CO2‐equivalents in the long‐term – bolstering greenhouse gas emissions. Similar emissions will arise from rainforest SOC in TAS due to climate change. Careful management of old‐growth TOFs in these two hotspots, to help reduce carbon emissions and change in biodiversity, entails adopting approaches to forest, wood product and fire management which conserve old‐growth characteristics in forest stands. Plantation forestry on long‐cleared land and well‐targeted prescribed burning supplement effective carbon management. Abbreviations: C, carbon; CBS, clearfell, burn and sow; CO2‐e, CO2 equivalents; CWD, coarse woody debris; DOC, dissolved organic carbon; GHG, greenhouse gas; Mt, megatonnes; SOC, soil organic carbon; SWA, south‐western Australia; SWAFR, Southwest Australian Floristic Region; TAS, Tasmania; TOF, tall open‐forest; t‐C ha−1 yr−1, tonnes of carbon per hectare per year

Pre-logging carbon accounts in old-growth forests, via allometry: An example of mixed-forest in Tasmania, Australia

Abstract Uncertainty in past and future anthropogenic carbon emissions obscures climate change modelling. Available allometrics are insufficient for regional-level accounting of old-growth, pre-logging carbon stocks. The project goal was to determine the aboveground carbon (biomass and necromass) for a typical old-growth Eucalyptus delegatensis-dominated mixed-forest in Tasmania. Allometrics were developed for aboveground biomass of Eucalyptus delegatensis and generic rainforest understorey species. A total of 207 eucalypts with DBH 0.21–4.5 m, and 897 rainforest understorey trees with DBH 0.01–2.52 m were measured across 7.7 ha. DBH frequency distribution of E. delegatensis showed at least two age cohorts and distinct positive skew, whereas its DBH carbon distribution showed distinct negative skew. Half of the eucalypt biomass was from trees with DBH > 2.4(0.1) m, and 16% with DBH ≥ 3.5 m (from ∼1.1 trees ha−1) – indicating the importance of allometrics for high DBH. Aboveground carbon was 622(180) Mg ha−1, with ∼20% from understorey and ∼25% from necromass. The carbon in aboveground biomass was above the median value for temperate forests. The long-term aboveground-carbon emissions from clearfelling the same forest type from 1999 to 2009 is likely to be 2.9(±1.3) Tg, depending on the growth and seral stages of the forest logged.

Comment on “Carbon in Trees in Tasmanian State Forest”

Moroni et al. (2010) reported extant, spatially representative carbon stocks for Tasmanias State forest. Their disputation of earlier work, contextual setting, redefinition of carbon carrying capacity (CCC), methods, adoption of ecological concepts and consequent conclusions on carbon flux were investigated. Their reported data was very useful; however, the absence of sufficient context and fundamental equations was atypical of scientific publications; old-growth should have been differentiated from mature forests and wet-sclerophyll from mixed-forest, redefinition of CCC was unwarranted, and several of their arguments and conclusions appeared unwarranted. From their graphs and tables, I estimated that the carbon deficit in State forest biomass (the amount below CCC) due to commercial forestry was conservatively 29(±4) Tg (or 106(±13) Mtonnes CO2-eq; with couped-production forests 29(±6)% below CCC) a greenhouse gas mitigation opportunity—indicating the usefulness of the existing definition of CCC. Also, using their data, earlier work on long-term fluxes accompanying conversion of wet-eucalypt forests to harvesting cycles was found to correspond to 0.56(±0.01) Mha (i.e., >1/3 of State forest), 76(±2)% of which is in the commercial production area—in contrast to their claim that earlier work referred to a small and atypical proportion.

Climate Change Impacts on Soil Processes in Rangelands

Changing climates are expected to increase the vulnerability of the world’s rangelands to ecosystem degradation. Rising temperatures and altered rainfall patterns are likely to substantially affect plant processes and thus the maintenance of healthy soils and functional soil processes. Changing climates are likely to reduce the ability of rangeland soils to sequester carbon, resist erosion and maintain infiltration and nutrient production processes. This chapter describes the projected changes in climate for the world’s major rangelands and the effects on soil processes and ecosystem functions. We use two examples of climate-induced changes in rangelands; woody thickening from the western USA and grassland degradation in eastern Australia to demonstrate the tight interconnections between climate, altered plant and invertebrate communities, and reduced soil function. There is still considerable uncertainty associated with the assessment of soil organic carbon stocks, the magnitude of current emissions and sinks, and the possible flow-on effects to other processes in rangelands. The maintenance of plant cover, including woody cover, will be critical for carbon storage and ecosystem stability in the face of climate change, and as an aid to adaptation to the stressors of forecasted change.

Novel 3D geometry and models of the lower regions of large trees for use in carbon accounting of primary forests

The largest uncertainty in human’s contribution to climate change from land use is the fate of carbon that was below ground in pre-modified forests. We produced high-resolution 3D models of the rarely measured zone near the base of large, mature trees by using photogrammetry. The models led to equations linking the easy-to-measure trunk diameter and ground slope to attributes such as tree buttress shape, humus mound, wood and hollow area, and root volume. The equations can be used for carbon accounting. The 3D models are irreplaceable, being for increasingly rare, large trees, and may be useful to other scientific endeavours.

Creative Carbon Accounting. A reply to “The Wood, the Trees, or the Forest? Carbon in Trees in Tasmanian State Forest: A Response to Comments'

Moroni et al. (2012) made forty claims which misrepresent my earlier reply to their work (Dean, 2011) and if left unrefuted, might mislead all but the most expert reader—I cover seven of the most important ones here. Firstly, in my earlier paper I had calculated a conservative carbon deficit in State forests due to logging of the most-targeted forest types—mature wet-eucalypt—by clearfell, burn and sow to yield even-aged eucalypt regeneration. That deficit was conservative as a range of stand ages were used even though most carbon flux through logging has been from the old-growth subset. It was additionally conservative at the landscape-scale as inclusion of conversion to plantation and logging of other primary-forest types would have yielded a larger carbon deficit, not a smaller one, as implied in Moroni et al. (2012). Secondly, their claim that I applied “carbon saturation” at the landscape-scale is incorrect. Instead I applied carbon carrying capacity at that scale and included different stands ages in its calculation (by definition). Conversely, Moroni et al. (2012) produce the “confusion” which they claim to observe by advocating the use of “carbon saturation” at the landscape-scale, which can have no practical usage.