Can hydraulic traits be used to predict sensitivity of drought-prone forests to crown decline and tree mortality?

Abstract

Water availability is a major factor influencing the distribution and abundance of plant species in several communities (Allen and Breshears 1998; Engelbrecht et al. 2007). Most terrestrial ecosystems are subjected to seasonal droughts and global climate change models predict an increase in frequency and intensity of drought events in several regions of the world (Allen et al. 2010). These extreme drought events will likely induce widespread tree mortality and cause major shifts in plant community composition and ecosystem functioning (Nepstad et al. 2007). Understanding the diversity of plant drought responses and the mechanisms responsible for tree death is therefore of paramount importance to forecasting climate change impacts on the Earth’s biodiversity and ecosystem’s resilience (Anderegg et al. 2012; McDowell et al. 2008). These questions have recently become top priorities for global change research, because widespread and rapid drought-induced tree mortality is already an emerging global phenomenon, threatening the integrity of numerous ecosystems (Breshears et al. 2009; Phillips et al. 2010). Mediterranean-type ecosystems are especially vulnerable to climate change as global climate models predict rainfall reductions with a high degree of certainty in the near future for these regions (IPCC 2007). These wet-winter, dry-summer ecosystems harbor an enormous plant biodiversity. Of particular interest is south-western Australia, one of the world’s biodiversity hotspots and recently reported as one of the most vulnerable ecosystems to tipping points in Australia (Laurance et al. 2011). Can we predict the responses of plants from this species-rich flora to future drier climates? How resistant are different tree species to predicted increases in drought intensity and frequency? Can we predict with confidence changes in species distribution in response to climate change? Providing definite answers to these questions is neither simple nor straightforward, because of the numerous biotic and abiotic drivers that affect the performance of individual plants and the non-linear responses of ecosystems to climatic forcing. An ideal approach to address these questions would require a substantial multi-scale and multidisciplinary research effort. However, recent efforts have suggested that compiling functional trait variation along natural environmental gradients can substantially improve the mechanistic models used to Plant Soil DOI 10.1007/s11104-012-1508-9