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Woody plant performance in a changing climate.

A similar number of scientific papers, up until 1996, resulted from searching the web of science, for ‘trees’ and the general topic ‘climate change’, or one of the most important consequences thereof, ‘drought’ (Fig. 1); these increased in parallel until the ‘century drought’ of 2003. From then onwards and until 2012, the number of papers dealing with the integrative term ‘climate change’ associated with ‘trees’ doubled compared to those for ‘drought’ (Fig. 1). The number of published papers following the climate change debate was summarised by the Intergovernmental Panel on Climate Change (IPCC), which was founded in November 1988 with the aim of establishing a comprehensive, internationally accepted overview of current scientific information about the increased risk of climate change resulting from human activity. In the first IPCC assessment report (1990), a climate warming of about 3 °C by the end of the 21st century was predicted – this being based on an increase in mean global temperature over the last 100 years. Measurements from ice cores, going back 160,000 years, showed that the Earth’s temperature reflected the amount of CO2 in the atmosphere. Considering such natural processes, the authors are certain that human activity has enhanced the global temperature through increased CO2 emissions since preindustrial times (<1750). Because long-lived woody plants may grow in a climate to which they are not adapted, new forest management practices are required. In the second IPCC assessment report (1996), a stabilization of CO2 emissions at the level of 1994 was calculated to result in a CO2 concentration of 550 ppm by the end of the 21st century. As a consequence, not only changes in temperature but also in water availability were considered to affect forests, particularly at high latitudes. In the third IPCC assessment report (2002), the anthropogenic CO2 increase was confirmed, a temperature increase over the last 50 years, particularly since 1990, was reported, and a temperature rise of 1.5–4.5 °C from 1990 to 2100 estimated. The impact of drought was judged as uncertain because of a lack of systematic data (more than decades). Eventually, in the fourth IPCC assessment (2007) report, increasing CO2 was noted as the most radiative forcing component (having increased from a preindustrial of 280 ppm to 379 ppm in 2005), together with a contribution of CH4 and a minor contribution from ozone. An increase in tree growth between 1995 and 2005 was interpreted as a consequence of the change in temperature. Although FACE studies suggested an acclimation of plants to elevated CO2, global timber supply was projected to increase because of air warming. Modelling studies suggest, however, that the increasing frequency of crop loss due to extreme events such as drought and heavy precipitation may out-weigh the positive effects of a moderate temperature increase. Our concern about climate change is even more troubling because most of the suitable arable land is already in use and world population is still growing. A better understanding of plant response to climate change will therefore be important in optimising the growth and productivity of future managed crop production and conservation of natural resources. This applies especially to woody plants, which possess limited adaptive responsiveness to climate change due to their exceptionally long life span and slow regeneration cycles. The idea of promoting a special issue of Plant Biology on ‘Woody Plant Performance in a Changing Climate’ was born during the final meeting of participants in the model ecosystem experiment ‘Querco’, which was carried out from 2007 to 2009 at the Swiss Federal Institute for Forest, Snow and Landscape Research. Eleven papers report different aspects of this experiment, which together with three other papers, led to an emphasis on the droughtand thermo-tolerant genus Quercus in this special issue. Nine papers provide reports on species of other genera, including trees, shrubs and small woody perennials. The open call for papers did not result in a comprehensive response to the title. However, the special issue covers a wide range of interdisciplinary research on woody plants within the realm of climate change. Studies include plant responses to the greenhouse gas CO2 and its interaction with elevated temperature, as well as plant responses to salinity, which are often associated with climate change. The following is a short résumé of the interesting results from this Plant Biology Special Issue. The driving force of climate change, elevated CO2, was addressed by Pintó-Marijuan et al. (2012), who studied the CO2 effect on the response of photosynthetic leaf traits and stress-related defence mechanisms to incremental increases in temperature. In re-sprouting Holm oak grown with twice the ambient CO2 concentration, they observed a down-regulation of foliar gas exchange but a striking up-regulation of specific photo-protective and anti-oxidant substances, which was evident even under severe heat stress conditions. This finding is discussed by the authors as an ameliorative effect of CO2 on the thermo-tolerance of Holm oak re-sprouts that may have