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Eucalypt plantations and climate change

Booth, Trevor H.
Forest ecology and management 2013 v.301 pp. 28-34
Eucalyptus, air temperature, carbon dioxide, climate change, climatic zones, databases, emissions, genotype, photosynthesis, plantations, silvicultural practices, trees, water use efficiency, Australia
Eucalypts are grown in plantations in more than 90 countries, so it is important to assess their vulnerability to climate change. Global mean annual temperature over land has already increased by about 0.9°C in the last century and many countries have agreed that urgent action should be taken to limit the increase in global mean temperature below 2°C. Unfortunately, as emissions are currently tracking at higher levels than the worst case scenario envisaged by the Intergovernmental Panel on Climate Change it appears increasingly unlikely that temperature increase can be limited to 2°C. This paper assesses the vulnerability of eucalypt plantations to climate change. Vulnerability is a function of potential impact, which is related to exposure and sensitivity, and adaptive capacity. Eucalypt plantations total more than 20million hectares and are grown in many countries around the world, so have significant exposure to climate change. About 41% of more than 800 eucalypt taxa grow naturally in Australia within narrow climatic ranges of less than 2°C, so are potentially sensitive to climatic change. Fortunately, the small number of commercially important species tend to have much wider climatic tolerances, but genetic selection to improve growth may well be reducing their climatic adaptability. Efforts have been made to simulate eucalypt growth under changing climatic and atmospheric conditions. If photosynthesis and water use efficiency are increased by increasing atmospheric carbon dioxide levels then some plantations may enjoy significant yield increases. However, recent results from eucalypts growing under elevated CO2 conditions in whole tree chambers suggest there is little if any ‘fertilisation effect’ on photosynthesis, though water use efficiency is increased. Consequently, productivity may increase in some plantations and decrease in others. Fortunately, the adaptive capacity of eucalypt plantations is high. Many eucalypts are grown on short rotations of less than ten years, so changing silvicultural practices and planting different genotypes to match changing climatic conditions is relatively easy. While the vulnerability of eucalypt plantations is only at a medium level it is concluded that sharing information about where particular eucalypt genotypes are grown, identifying potentially marginal climatic areas and recommending genotypes suitable for changing conditions would help to further reduce potential vulnerability. The development of a eucalypt database and mapping system is proposed as a major collaborative project to help to protect one of global forestry’s most valuable resources.