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In this Research Topic, we aim to provide a snapshot of the state-of-the-art of the fields of forest and tree ecology and physiology above and below ground, including forest soils and their microbial communities, with a special focus on plant ecophysiology, (soil) biodiversity, ecosystem functioning, as well as the effects of disturbances, (a-)biotic stresses, and biological invasions.

competition --- disturbance --- functional traits --- forest ecosystem research --- funding priorities --- resource availability --- stressors --- trees

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Trees are among the longest-living organisms. They are sensitive to extreme climatic events and document the effects of environmental changes in form of structural modifications of their tissues. These modifications represent an integrated signal of complex biological responses enforced by the environment. For example, temporal change in stem increment integrates multiple information of tree performance, and wood anatomical traits may be altered by climatic extremes or environmental stress. Recent developments in preparative tools and computational image analysis enable to quantify changes in wood anatomical features, like vessel density or vessel size. Thus, impacts on their functioning can be related to climatic forcing factors. Similarly, new developments in monitoring (cambial) phenology and mechanistic modelling are enlightening the interrelationships between environmental factors, wood formation and tree performance and mortality. Quantitative wood anatomy is a reliable indicator of drought occurrence during the growing season, and therefore has been studied intensively in recent years. The variability in wood anatomy not only alters the biological and hydraulic functioning of a tree, but may also influence the technological properties of wood, with substantial impacts in forestry. On a larger scale, alterations of sapwood and phloem area and their ratios to other functional traits provide measures to detect changes in a tree’s life functions, and increasing risk of drought-induced mortality with possible impacts on hydrological processes and species composition of plant communities. Genetic variability within and across populations is assumed to be crucial for species survival in an unpredictable future world. The magnitude of genetic variation and heritability of adaptive traits might define the ability to adapt to climate change. Is there a relation between genetic variability and resilience to climate change? Is it possible to link genetic expression and climate change to obtain deeper knowledge of functional genetics? To derive precise estimates of genetic determinism it is important to define adaptive traits in wood properties and on a whole-tree scale. Understanding the mechanisms ruling these processes is fundamental to assess the impact of extreme climate events on forest ecosystems, and to provide realistic scenarios of tree responses to changing climates. Wood is also a major carbon sink with a long-term residence, impacting the global carbon cycle. How well do we understand the link between wood growth dynamics, wood carbon allocation and the global carbon cycle? Papers contribution to this Research Topic will cover a wide range of ecosystems. However, special relevance will be given to Mediterranean-type areas. These involve coastal regions of four continents, making Mediterranean-type ecosystems extremely interesting for investigating the potential impacts of global change on growth and for studying responses of woody plants under extreme environmental conditions. For example, the ongoing trend towards warmer temperatures and reduced precipitation can increase the susceptibility to fire and pests. The EU-funded COST Action STREeSS (Studying Tree Responses to extreme Events: a SynthesiS) addresses such crucial tree biological and forest ecological issues by providing a collection of important methodological and scientific insights, about the current state of knowledge, and by opinions for future research needs.

Tree response --- Genetic plasticity --- mechanistic modeling --- wood functional traits --- Extreme climate events --- Ecophysiology --- Manipulation experiments --- forest management

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This eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: frontiersin.org/about/contact

Science: general issues --- Ecological science, the Biosphere --- Biome --- ecosystem function --- functional traits --- vegetation --- evolutionary history --- Biogeographic history --- Biome transitions

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Trees are among the longest-living organisms. They are sensitive to extreme climatic events and document the effects of environmental changes in form of structural modifications of their tissues. These modifications represent an integrated signal of complex biological responses enforced by the environment. For example, temporal change in stem increment integrates multiple information of tree performance, and wood anatomical traits may be altered by climatic extremes or environmental stress. Recent developments in preparative tools and computational image analysis enable to quantify changes in wood anatomical features, like vessel density or vessel size. Thus, impacts on their functioning can be related to climatic forcing factors. Similarly, new developments in monitoring (cambial) phenology and mechanistic modelling are enlightening the interrelationships between environmental factors, wood formation and tree performance and mortality. Quantitative wood anatomy is a reliable indicator of drought occurrence during the growing season, and therefore has been studied intensively in recent years. The variability in wood anatomy not only alters the biological and hydraulic functioning of a tree, but may also influence the technological properties of wood, with substantial impacts in forestry. On a larger scale, alterations of sapwood and phloem area and their ratios to other functional traits provide measures to detect changes in a tree’s life functions, and increasing risk of drought-induced mortality with possible impacts on hydrological processes and species composition of plant communities. Genetic variability within and across populations is assumed to be crucial for species survival in an unpredictable future world. The magnitude of genetic variation and heritability of adaptive traits might define the ability to adapt to climate change. Is there a relation between genetic variability and resilience to climate change? Is it possible to link genetic expression and climate change to obtain deeper knowledge of functional genetics? To derive precise estimates of genetic determinism it is important to define adaptive traits in wood properties and on a whole-tree scale. Understanding the mechanisms ruling these processes is fundamental to assess the impact of extreme climate events on forest ecosystems, and to provide realistic scenarios of tree responses to changing climates. Wood is also a major carbon sink with a long-term residence, impacting the global carbon cycle. How well do we understand the link between wood growth dynamics, wood carbon allocation and the global carbon cycle? Papers contribution to this Research Topic will cover a wide range of ecosystems. However, special relevance will be given to Mediterranean-type areas. These involve coastal regions of four continents, making Mediterranean-type ecosystems extremely interesting for investigating the potential impacts of global change on growth and for studying responses of woody plants under extreme environmental conditions. For example, the ongoing trend towards warmer temperatures and reduced precipitation can increase the susceptibility to fire and pests. The EU-funded COST Action STREeSS (Studying Tree Responses to extreme Events: a SynthesiS) addresses such crucial tree biological and forest ecological issues by providing a collection of important methodological and scientific insights, about the current state of knowledge, and by opinions for future research needs.

Tree response --- Genetic plasticity --- mechanistic modeling --- wood functional traits --- Extreme climate events --- Ecophysiology --- Manipulation experiments --- forest management

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Aim : Erythrophleum species and gene pools, despite being morphologically similar, oc-
cupy contrasted habitats. The aim of this work is to determine if Erythrophleum species
and gene pools respond differently to shade and drought, to understand the underlying
mechanisms that explain these differences by measuring traits on control seedlings, and
finally to understand if these differences can explain their distribution patterns.
Location : Industrial site of Pallisco-CIFM in Mindourou, Cameroon, and two zones
in southern (Dja-and-Lobo department) and central Cameroon (Mba-and-Kim depart-
ment).
Methods : The work consisted of an in situ and a drought and shade experiment. Dur-
ing the in situ experiment, two zones where species or gene pools are coexisting were
sampled. During the drought/shade experiment, two modalities of drought (watered or
non watered) and two modality of light (low light and hight light) were tested on 190
seedlings from two species and six gene pools to compare their response to stress. At the
end of the experiment, functional traits were measured on 56 control seedlings.
Results : Allometric models have been calculated and phenophases compared for field
individuals sampled in the field of two gene pools. Differences of phenophases and crown
shape have been highlighted. No clear difference between species and gene pools were
observed experimentally in seedling survival and response to drought and shade. Differ-
ences of functional traits have been found between species and gene pools, suaW having
more drought-adapted traits than any other pool.
Main conclusions : Dry forests gene pools had more drought tolerant traits than pools
found in wetter forests, but did not show more resistance to drought or more sensitivity
to shade in the drought/shade experiment. A difference exist but is thin because of
the morphological proximity of the pools and species, supporting the ecological gradient
hypothesis.

Tropical forests, Central Africa, Cameroon, Erythrophleum, ecological specialisation, trade-offs, gene pools, functional traits, allometry, diversification, stress tolerance --- Sciences du vivant > Sciences de l'environnement & écologie