Forest Ecology and Management 260 (2010) 1623–1639 Contents lists available at ScienceDirect Forest Ecology and Management journal homepage: www.elsevier.com/locate/foreco Review Responses of forest trees to single and multiple environmental stresses from seedlings to mature plants: Past stress history, stress interactions, tolerance and acclimation Ülo Niinemets ∗ Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, Kreutzwaldi 1, Tartu 51014, Estonia article info Article history: Received 23 February 2010 Received in revised form 9 June 2010 Accepted 13 July 2010 Keywords: Single and interacting stresses Non-structural carbon pools Ontogeny Photosynthesis Plasticity Stress diagnosis Volatile organic compounds abstract Forest trees are exposed to a myriad of single and combined stresses with varying strength and duration throughout their lifetime, and many of the simultaneous and successive stress factors strongly interact. While much progress has been achieved in understanding the effects of single stresses on tree perfor- mance, multiple interacting stress effects cannot be adequately assessed from combination of single factor analyses. In particular, global change brings about novel combinations of severity and timing of different stresses, the effects of which on tree performance are currently hard to predict. Furthermore, the combinations of stresses commonly sustained by trees change during tree ontogeny. In addition, tree photosynthesis and growth rates decline with increasing tree age and size, while support biomass in roots, stem and branches accumulates and the concentrations of non-structural carbohydrates increase, collectively resulting in an enhancement of non-structural carbon pools. In this review, tree physiolog- ical responses to key environmental stress factors and their combinations are analyzed from seedlings to mature trees. The key conclusions of this analysis are that combined stresses can influence survival of large trees even more than chronic exposure to a single predictable stress such as drought. In addition, tree tolerance to many environmental stresses increases throughout the ontogeny as the result of accu- mulation of non-structural carbon pools, implying major change in sensing, response and acclimation to single and multiple stresses in trees of different size and age. © 2010 Elsevier B.V. All rights reserved. Contents 1. Introduction ........................................................................................................................................ 1624 2. Stress in forests .................................................................................................................................... 1624 2.1. Occurrence of single and multiple stresses ................................................................................................ 1624 2.2. Stress combinations, interactions and implications for reaction norms .................................................................. 1626 3. Stress responsiveness of trees in the current and future climates: tolerance, acclimation and stress history ................................... 1626 3.1. Tolerance of single and multiple limitations .............................................................................................. 1626 3.2. Influence of acclimation, stress priming and stress sequence on the resistance to multiple stress episodes ............................ 1627 3.3. Global change and multiple stresses: CO 2 , temperature and drought interactions ....................................................... 1627 3.4. Multiple stresses in trees: use of storage carbon to gauge and predict stress responsiveness ........................................... 1628 4. Stress in forest trees: from seedlings to mature plants ........................................................................................... 1628 4.1. Variation in stress combinations throughout tree ontogeny .............................................................................. 1628 4.2. Effects of ontogeny on stress sensitivity ................................................................................................... 1629 4.3. Determinate vs. indeterminate growth as an explanation for variations in stress tolerance with ontogeny ............................ 1630 5. Towards adequate diagnosis of stress in forest trees: from single plant to ecosystem responses ............................................... 1631 5.1. Complexity of assessing stress in trees .................................................................................................... 1631 5.2. Traditional methods to diagnose stress .................................................................................................... 1632 5.3. Monitoring volatile organic compounds: a promising method for stress studies ........................................................ 1633 ∗ Tel.: +372 53457189. E-mail addresses: ylo.niinemets@emu.ee, ylo@emu.ee. 0378-1127/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.foreco.2010.07.054