Global convergence in the vulnerability of forests to drought

Abstract

Shifts in rainfall patterns and increasing temperatures associated with climate change are likely to cause widespread forest decline in regions where droughts are predicted to increase in duration and severity. One primary cause of productivity loss and plant mortality during drought is hydraulic failure. Drought stress creates trapped gas emboli in the water transport system, which reduces the ability of plants to supply water to leaves for photosynthetic gas exchange and can ultimately result in desiccation and mortality. At present we lack a clear picture of how thresholds to hydraulic failure vary across a broad range of species and environments, despite many individual experiments. Here we draw together published and unpublished data on the vulnerability of the transport system to drought-induced embolism for a large number of woody species, with a view to examining the likely consequences of climate change for forest biomes. We show that 70% of 226 forest species from 81 sites worldwide operate with narrow hydraulic safety margins against injurious levels of drought stress and therefore potentially face long-term reductions in productivity and survival if temperature and aridity increase as predicted for many regions across the globe. Safety margins are largely independent of mean annual precipitation, showing that there is global convergence in the vulnerability of forests to drought, with all forest biomes equally vulnerable to hydraulic failure regardless of their current rainfall environment. These findings provide insight into why drought-induced forest decline is occurring not only in arid regions but also in wet forests not normally considered at drought risk

Drought and shade deplete nonstructural carbohydrate reserves in seedlings of five temperate tree species

“…2011; Choat et al. 2012). These trends motivate a strong interest in understanding the mechanisms behind tree mortality and the interactions among different types of stress that could inform predictions of tree responses to global change in the future (Fisher et al.…”

In Vivo Visualizations of Drought-Induced Embolism Spread in Vitis vinifera

“…the metabolically active refilling of embolized xylem conduits) in live plants using HRCT, including the growth of water droplets emerging from xylem parenchyma surrounding embolized vessels that eventually led to the dissolution of trapped gas inside the vessels. While we now have a better understanding of embolism repair and the physiological consequences of embolism spread are well documented (Tyree and Zimmermann, 2002;McDowell et al, 2008;Cochard et al, 2009;Zwieniecki and Holbrook, 2009;Choat et al, 2012), the spatial dynamics and biophysics of embolism formation and spread in vivo have yet to be fully explored. Clearly, the spatial organization of xylem conduits plays a critical role in embolism repair and is likely even more influential in embolism spread, as direct connections between conduits are the most likely pathway through the network.…”

“…The resulting spread of embolisms through the xylem effectively reduces the hydraulic conductivity of the network, impairing the capacity to replace transpired water. The consequences of embolism formation can be dramatic, and it is now considered to be one of the major physiological factors driving reductions in forest primary productivity and drought-induced mortality in woody plants (Anderegg et al, 2012;Choat et al, 2012).…”

Forests on the brink

“…But forests occur in a wide range of climatic conditions, so it is a challenge to predict how the vulnerability of trees to changes in water availability compares between different biomes. In a paper published on Nature's website today, Choat et al 3 use a combination of physiological measurements of the vulnerability of trees to drought and of the drought stress they actually experience in their natural habitats to show that forests worldwide are at high risk.…”

“…Choat and colleagues' study 3 of trees across the globe suggests that they are at high risk from even small increases in drought intensity. drought-induced forest die-offs and tree mortality in many ecosystems 4 (Fig.…”