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We investigated how thinning intensity and rotation length affect radiative forcing, and thus climate warming or cooling, through changes in albedo and carbon stocks in Norway spruce (Picea abies Kart. (L.)) stands. Forest ecosystem model simulations were conducted under the current climate on sub-mesic sites in central Finland (62oN). Even-aged management regime with a business-as-usual (baseline) thinning from below over an 80-year rotation length was used as the reference management regime with which others were compared. Other even-aged management regimes included baseline thinning with ±20 per cent changes in basal area thinning thresholds over rotation lengths of 80, 100 and 120 years. Additionally, we used as a comparison an uneven-aged management regime, with selective cuttings (from above) at ca. 15-year intervals, and no management regime, over the simulation periods of 80–120 years. Under even-aged management, a simultaneous decrease in thinning intensity and extension of rotation length from 80 to 120 years reduced total radiative forcing compared to the reference management regime. Thus, it had an overall net cooling effect. Under even-aged management with baseline thinning and/or higher thinning intensity with rotation lengths of 80–100 years, and under uneven-aged management, there was little net climatic effect. This was because the opposing effects of changes in albedo and ecosystem carbon stocks largely cancelled each other out. No management regime resulted in the highest net cooling effect but provided no harvest income for timber. Thus, proper incentives for forest owners would likely be required to promote such potential cooling effects in forest management. [ABSTRACT FROM AUTHOR]

Climate warming can reduce global soil carbon stocks by enhancing microbial decomposition. However, the magnitude of this loss remains uncertain because the temperature sensitivity of the decomposition of the major fraction of soil carbon, namely resistant carbon, is not fully known. It is now believed that the resistance of soil carbon mostly depends on microbial accessibility of soil carbon with physical protection being the primary control of the decomposition of protected carbon, which is insensitive to temperature changes. However, it is still unclear whether the temperature sensitivity of the decomposition of unprotected carbon, for example, carbon that is not protected by the soil mineral matrix, may depend on the chemical recalcitrance of carbon compounds. In particular, the carbon-quality temperature (CQT) hypothesis asserts that recalcitrant low-quality carbon is more temperature-sensitive to decomposition than labile high-quality carbon. If the hypothesis is correct, climate warming could amplify the loss of unprotected, but chemically recalcitrant, carbon and the resultant CO2 release from soils to the atmosphere. Previous research has supported this hypothesis based on reported negative relationships between temperature sensitivity and carbon quality, defined as the decomposition rate at a reference temperature. Here we show that negative relationships can arise simply from the arbitrary choice of reference temperature, inherently invalidating those tests. To avoid this artefact, we defined the carbon quality of different compounds as their uncatalysed reaction rates in the absence of enzymes. Taking the uncatalysed rate as the carbon quality index, we found that the CQT hypothesis is not supported for enzyme-catalysed reactions, which showed no relationship between carbon quality and temperature sensitivity. The lack of correlation in enzyme-catalysed reactions implies similar temperature sensitivity for microbial decomposition of soil carbon, regardless of its quality, thereby allaying concerns of acceleration of warming-induced decomposition of recalcitrant carbon. [ABSTRACT FROM AUTHOR]

An integrated catchment management project was established at the Whatawhata Research Centre in the late 1990s to study the implications of land use and management change for a typical New Zealand hill country pastoral farm system. The main changes implemented on the 296 ha Mangaotama block in 2001–2002 included production forest plantation (147 ha), indigenous riparian planting (8 ha); intensification of livestock enterprises and spaced-tree planting. The purpose of this study was to estimate the greenhouse gas (GHG) balance for the catchment farm, incorporating recent measurement and modelling over a 100-year period (excl. soil carbon). The changes reduced the GHG intensity of the livestock enterprises from 25 to 15 kg CO2-e kg−1 product and turned the system from a net emission source (c. 1 kt CO2-e y−1) into a long-term net sink (−353 kt CO2-e y−1). This was mainly due to planting of Pinus radiata with high carbon assimilation rates, compared to the smaller areas and slower assimilation rates of indigenous trees (currently 5–17 t CO2-e ha−1y−1). Based on 100-year mean tree carbon stocks, it was estimated that the area of pine forestry required to achieve net zero emissions would be in the order of 36% of the catchment farm. [ABSTRACT FROM AUTHOR]

Determining the magnitude of climate change effects is crucial for informing national economic strategies, forest management and offsetting increasing carbon emissions. This study synthesizes predicted climate change impacts and future biosecurity threats to New Zealand's plantation forests. Projected productivity increases for radiata pine (Pinus radiata D. Don), the main commercial forest species in New Zealand, are slight due to changing climatic conditions. However including photosynthetic effects from increasing CO2, productivity gains across New Zealand averaged 19 per cent by 2040 and 37 per cent by 2090. This increased productivity results in marked increases in wind risk due to trees becoming taller and more slender. The average season length with 'very high and extreme' climatic fire risk increases by 71 per cent up to 2040 and by 83 per cent up to 2090. Currently, the most significant biotic disturbances in New Zealand plantations come from two needle cast diseases, for which climate projections show slight increases or decreases depending on the disease and region. Although insect pests currently cause little damage to New Zealand plantations, damage may increase in the future with projected increases in population and host susceptibility. It has not been possible to fully account for the effects of any new introductions of pests and pathogens and evidence from other countries with a significant resource of planted forests suggest this should not be underestimated. Potentially invasive weedy and damaging tree species are likely to expand their range under climate change and compete more strongly with plantations. [ABSTRACT FROM AUTHOR]

The main components of global carbon budget calculations are the emissions from burning fossil fuels, cement production, and net land-use change, partly balanced by ocean CO2 uptake and CO2 increase in the atmosphere. The remaining difference between these terms is referred to as the residual sink, assumed to correspond to increasing carbon storage in the terrestrial biosphere (ΔB). It is often used to constrain carbon exchange in global earth-system models. More broadly, it guides expectations of autonomous changes in global carbon stocks in response to climatic changes, including increasing CO2, that may add to, or subtract from, anthropogenic CO2 emissions. However, a budget with only these terms omits some important additional fluxes that are important for correctly inferring ΔB. They are cement carbonation and fluxes into increasing pools of plastic, bitumen, harvested-wood products, and landfill deposition after disposal of these products, and carbon fluxes to the oceans via wind erosion and non-CO2 fluxes of the intermediate break-down products of methane and other volatile organic compounds. While the global budget includes river transport of dissolved inorganic carbon it omits river transport of dissolved and particulate organic carbon, and the deposition of carbon in inland water bodies. Each one of these terms is relatively small, but together they can constitute important additional fluxes that would significantly reduce the size of the inferred ΔB. We estimate here that inclusion of these fluxes would reduce ΔB from the currently reported 3.6 down to only about 2.1GtCyr−1 (excluding losses from land-use change). The implicit reduction in the size of ΔB has important implications for the inferred magnitude of current-day biospheric net carbon uptake and the consequent potential of future biospheric feedbacks to amplify or negate net anthropogenic CO2 emissions. [ABSTRACT FROM AUTHOR]