This is the peer reviewed version of the following article: Jump, A. S., Ruiz-
Benito, P., Greenwood, S., Allen, C. D., Kitzberger, T., Fensham, R., Martínez-
Vilalta, J. and Lloret, F. (2017), Structural overshoot of tree growth with climate
variability and the global spectrum of drought-induced forest dieback. Glob
Change Biol, 23: 3742–3757, which has been published in final form at
https://doi.org/10.1111/gcb.13636. This article may be used for non-
commercial purposes in accordance With Wiley Terms and Conditions for self-
archiving.
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Structural overshoot of tree growth with climate variability and the global spectrum of
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drought-induced forest dieback
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Alistair S. Jump
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, Paloma Ruiz-Benito
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, Sarah Greenwood
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, Craig D. Allen
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, Thomas
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Kitzberger
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, Rod Fensham
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, Jordi Martínez-Vilalta
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and Francisco Lloret
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Accepted for publication in Global Change Biology published by Wiley-Blackwell
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1
Biological and Environmental Sciences, University of Stirling, Scotland, FK9 4LA, UK.
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CREAF, Campus de Bellaterra (UAB), Edifici C, Cerdanyola del Vallès 08193, Catalonia,
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Spain.
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Forest Ecology and Restoration Group, Department of Life Sciences, Science Building,
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Universidad de Alcalá, Campus Universitario, 28805 Alcalá de Henares, Madrid, Spain.
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U.S. Geological Survey, Fort Collins Science Center, New Mexico Landscapes Field
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Station, Los Alamos, New Mexico 87544.
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Laboratorio Ecotono, INIBIOMA, CONICET-Universidad Nacional del Comahue,
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Bariloche, 8400 Río Negro, Argentina.
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Queensland Herbarium, Environmental Protection Agency, Mt Coot-tha Road, Toowong,
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Queensland 4066, Australia; School of Biological Sciences, University of Queensland, St
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Lucia, Queensland 4072, Australia
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Autonomous University of Barcelona, Cerdanyola del Vallès 08193, Catalonia, Spain.
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Corresponding author: Alistair S. Jump, Biological and Environmental Sciences,
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University of Stirling, Scotland, FK9 4LA, UK. a.s.jump@stir.ac.uk, +441786467848
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Running title: Tree mortality due to structural overshoot
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Keywords: Climate change, forest dynamics, drought, mortality, extreme events
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Type of article: Review
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Words: 7062 – including tables and figure captions
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Abstract
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Ongoing climate change poses significant threats to plant function and distribution. Increased
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temperatures and altered precipitation regimes amplify drought frequency and intensity,
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elevating plant stress and mortality. Large-scale forest mortality events will have far-reaching
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impacts on carbon and hydrological cycling, biodiversity, and ecosystem services. However,
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biogeographical theory and global vegetation models poorly represent recent forest die-off
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patterns. Furthermore, since trees are sessile and long-lived, their responses to climate
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extremes are substantially dependent on historical factors. We show that periods of
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favourable climatic and management conditions that facilitate abundant tree growth can lead
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to structural overshoot of above-ground tree biomass due to a subsequent temporal mismatch
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between water demand and availability. When environmental favourability declines,
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increases in water and temperature stress that are protracted, rapid, or both, drive a gradient
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of tree structural responses that can modify forest self-thinning relationships. Responses
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ranging from premature leaf senescence and partial canopy dieback to whole-tree mortality
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reduce canopy leaf area during the stress period, and for a lagged recovery window
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thereafter. Such temporal mismatches of water requirements from availability can occur at
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local to regional scales throughout a species geographical range. Since climate change
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projections predict large future fluctuations in both wet and dry conditions, we expect forests
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to become increasingly structurally mismatched to water availability and thus over-built
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during more stressful episodes. By accounting for the historical context of biomass
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development, our approach can explain previously problematic aspects of large-scale forest
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mortality, such as why it can occur throughout the range of a species and yet still be locally
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highly variable, and why some events seem readily attributable to an ongoing drought while
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others do not. This refined understanding can facilitate better projections of structural
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overshoot responses, enabling improved prediction of changes to forest distribution and
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function from regional to global scales.
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Introduction
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Changing climate patterns pose significant threats to plant and ecosystem function and
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species distributions (Kelly & Goulden, 2008). In many areas, increased temperatures and
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altered precipitation regimes combine to exacerbate drought stress from hotter droughts,
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significantly elevating plant mortality, from water-limited Mediterranean forests to tropical
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moist forests (IPCC, 2014; Allen et al., 2015, Greenwood et al., in press). Of particular
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concern are broad-scale forest die-off events where rapid mortality occurs over 10s to 1000s
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of km
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of forest, which could offset any positive tree-growth effects of CO
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fertilisation and
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longer growing seasons from warming temperatures during the second half of the 20
th
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Century (Norby & Zak, 2011; Nabuurs et al., 2013; Ruiz-Benito et al., 2014; van der Sleen et
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al., 2015). Furthermore, widespread forest growth reductions and increases in the extent and
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magnitude of die-off events are anticipated as climate warms and becomes more extreme and
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as current climatic extremes become more frequent (Adams et al., 2009; van Oijen et al.,
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2013; Allen et al., 2015; Frank et al., 2015; Charney et al., 2016; Greenwood et al., in press).
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Extensive forest die-offs would have far-reaching consequences through impacts on carbon
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and hydrological cycling, biodiversity, and goods and environmental services to local human
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populations (Anderegg et al., 2015; Frank et al., 2015; Trumbore et al., 2015).
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Ongoing environmental changes are already altering the distribution of species across the
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globe (Walther et al., 2002; Parmesan, 2006). Contemporary plant range changes have been
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readily identified in woody species, with range expansions and increases in population
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density resulting from enhanced growth and reproduction at the upper and poleward edge of
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species distributions as the climate warms (Sturm et al., 2001; Harsch et al., 2009). Negative
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changes in plant water balance due to elevated temperature and/or decreased precipitation are
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expected to locally constrain productivity and elevate mortality (e.g. Juday et al., 2015), with
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effects being particularly evident at the equatorial and low altitude (or hotter and drier)
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margins of species distributions (Bigler et al., 2007; Sarris et al., 2007; Allen et al., 2010;
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Carnicer et al., 2011; Linares & Camarero, 2011; Sánchez-Salguero et al., 2012). Indeed,
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recent evidence from populations at the equatorial and low altitude range-edge of forest-
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forming tree species has shown elevated mortality and growth decline linked to rising
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temperatures and drought stress over the last half-century (Jump et al., 2006; van Mantgem &
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Stephenson, 2007; Beckage et al., 2008; Piovesan et al., 2008). Drought-linked tree mortality
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might, therefore, be expected to concentrate along already hotter and drier margins of a
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species’ distribution. However, this is not always the case, with recent drought-linked die-off
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also occurring throughout species ranges while some range edge populations can be relatively
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unaffected by regional drought (Jump et al., 2009; Allen et al. 2010; Hampe & Jump, 2011;
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Allen et al., 2015; Cavin & Jump, 2016). Consequently, simple biogeographical explanations
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cannot adequately explain the full range of drought-linked tree mortality patterns observed.
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Despite the recognised effects of intense droughts and increased temperatures on tree
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mortality, the die-off patterns observed worldwide are poorly reproduced by global
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vegetation models (McDowell et al., 2013; Steinkamp & Hickler, 2015). Forests are complex
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ecosystems, and the responses to climate extremes are dependent on a range of factors
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including species composition, species-specific plant functional traits (Anderegg et al.,
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2016a), intraspecific variability, biotic interactions, legacy effects, such as “ecological
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memory” of past climate, management, or natural disturbances (Johnstone et al., 2016), and
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stand structure (Fensham et al., 2005; Allen et al., 2015). Another major factor commonly
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