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\DOI{10.5802/crbiol.192}
\datereceived{2026-02-06}
\dateaccepted{2026-03-24}
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\COI{The author does not work for, advise, own shares in, or receive
funds from any organization that could benefit from this article, and
has declared no affiliations other than their research organization.}

\dateposted{2026-05-21}
\begin{document}

%\dateposted{2026-02-16}

\begin{noXML}

\CDRsetmeta{articletype}{review}

\editornote{Article submitted by invitation}
\alteditornote{Article soumis sur invitation}

\title{Assessing the potential effects of climate change on future
forest composition in France}

\alttitle{\'{E}valuation des effets potentiels du changement climatique
sur la composition future des for\^{e}ts en France}

\author{\firstname{Christian} \lastname{Piedallu}\CDRorcid{0000-0001-7316-1874}}
\address{Universit\'{e} de Lorraine, AgroParisTech, INRAE, Silva, F-54000 Nancy, France}
\email{christian.piedallu@agroparistech.fr}
\curraddr{AgroParisTech, 14 rue Girardet, CS 14216 F-54042 Nancy Cedex, France}

\keywords{\kwd{Climate change}\kwd{Forest composition}\kwd{Tree
species}\kwd{Ecological niche}\kwd{Vulnerability}\kwd{Adaptive
management}}

\altkeywords{\kwd{Changement climatique}\kwd{Composition
foresti\`{e}re}\kwd{Esp\`{e}ces d'arbres}\kwd{Niche \'{e}cologique des
essences}\kwd{Vuln\'{e}rabilit\'{e}}\kwd{Gestion adaptative}}

\begin{abstract}
Climate change is already affecting French forests: rising
temperatures, altered precipitation, and more frequent extreme events
are driving shifts in species distributions, reduced productivity, and
increased tree mortality. Anticipating future forest composition
requires understanding species' exposure to future climatic conditions,
their sensitivity to these conditions, and their capacity to adapt or
migrate. Regional contrasts are marked, with stronger warming and
drying in northeastern and Mediterranean regions, while parts of
western France are comparatively less affected. Observations show high
vulnerability of temperate species such as Fagus sylvatica and
\textit{Picea abies}, whereas Mediterranean species (e.g.\ \textit{Pinus
pinaster}, \textit{P. halepensis}) appear more resistant at present.

Future changes will depend on climate change evolution intensity, site and stand
characteristics, species composition, and adaptive capacity. Initially,
adaptive management---adjusting stand structure, promoting diversity,
and managing density, water, and species selection---can mitigate
impacts and buy time. Under higher vulnerability, species replacement
may become necessary---ideally by favoring drought-tolerant species
already present through natural regeneration, or otherwise through
assisted migration using drought-adapted provenances of native species
or non-native species with suitable traits. Uncertainties about
ecosystem resilience and the effectiveness of management measures
underline the need for integrative, site-specific strategies to sustain
ecosystem services and effectively guide future forest composition
under ongoing climate change.
\end{abstract}

\begin{altabstract}
Le changement climatique affecte d\'{e}j\`{a} les for\^{e}ts
fran\c{c}aises : l'augmentation des temp\'{e}ratures, les modifications
des pr\'{e}cipitations et la fr\'{e}quence accrue des
\'{e}v\'{e}nements extr\^{e}mes entra\^{i}nent des d\'{e}placements
dans la r\'{e}partition des esp\`{e}ces, une baisse de la
productivit\'{e} et une mortalit\'{e} accrue des arbres. Anticiper la
composition future des for\^{e}ts n\'{e}cessite de comprendre
l'exposition des esp\`{e}ces aux conditions climatiques futures, leur
sensibilit\'{e} \`{a} ces conditions et leur capacit\'{e} \`{a}
s'adapter ou \`{a} migrer. Les contrastes r\'{e}gionaux sont
marqu\'{e}s, avec un r\'{e}chauffement et un ass\`{e}chement plus
prononc\'{e} dans les r\'{e}gions du nord-est et
m\'{e}diterran\'{e}ennes, tandis que certaines parties de l'ouest de la
France sont comparativement moins affect\'{e}es. Les observations
montrent une plus forte vuln\'{e}rabilit\'{e} des esp\`{e}ces
temp\'{e}r\'{e}es telles que le h\^{e}tre (Fagus sylvatica) et
l'\'{e}pic\'{e}a (Picea abies), alors que les esp\`{e}ces
m\'{e}diterran\'{e}ennes (par ex. le pin maritime Pinus pinaster, le
pin d'Alep P. halepensis) semblent plus r\'{e}sistantes pour le moment.

Les changements futurs d\'{e}pendront de l'intensit\'{e} de l'\'evolution du climat, des
caract\'{e}ristiques \'{e}cologiques de la station, des peuplements, de
la composition des esp\`{e}ces et de leur capacit\'{e} d'adaptation.
Dans un premier temps, une gestion adaptative agissant sur la structure
des peuplements, le m\'{e}lange, la densit\'{e}, la
ressource en eau, et le choix des esp\`{e}ces, peut att\'{e}nuer les
impacts et faire gagner du temps. L\`{a} o\`{u} la vuln\'{e}rabilit\'{e} est
plus \'{e}lev\'{e}e, le remplacement des esp\`{e}ces peut \^{e}tre
n\'{e}cessaire, de pr\'{e}f\'{e}rence en favorisant les esp\`{e}ces
tol\'{e}rantes \`{a} la s\'{e}cheresse d\'{e}j\`{a} pr\'{e}sentes par
r\'{e}g\'{e}n\'{e}ration naturelle, sinon par migration assist\'{e}e en
utilisant des provenances adapt\'{e}es 
d'esp\`{e}ces indig\`{e}nes ou non indig\`{e}nes, poss\'{e}dant des
traits \'{e}cologiques appropri\'{e}s. Les incertitudes concernant la
r\'{e}silience des \'{e}cosyst\`{e}mes et l'efficacit\'{e} des mesures
de gestion soulignent la n\'{e}cessit\'{e} de strat\'{e}gies
int\'{e}gr\'{e}es adapt\'{e}es aux conditions locales, afin de
maintenir les services \'{e}cosyst\'{e}miques et orienter de fa\c{c}on
pertinente la composition future des for\^{e}ts face au changement
climatique en cours.
\end{altabstract}

%\input{CR-pagedemetas}

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\vspace*{2pt}

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\end{noXML}

\defcitealias{IGN2023}{ibid.}

\section{Introduction}

With a global mean temperature increase of ${+}$1.4~{\textdegree}C
relative to the pre-industrial period, combined with altered
precipitation regimes and a rising frequency of extreme climatic events
\citep{IPCC2022}, climate change is profoundly reshaping ecosystems
across biomes worldwide. Europe is warming faster than the global
average, and France has already experienced an increase of
approximately ${+}$2.1~{\textdegree}C compared to pre-industrial levels
\citep{CCCS2024}, with major consequences for forest ecosystems.\ 
Following a long period of \mbox{expansion} driven by increasing forest
area and ecosystem fertilization---associated with rising atmospheric
CO$_{2}$ concentrations, nitrogen deposition, and a lengthening growing
season---French forests are now increasingly exposed to the adverse
effects of climate change \citep{Olsetal2020}. These impacts are
already observable through shifts in species distributions, declining
productivity, and rising rates of tree dieback across many taxa.

Climate projections indicate that these trends are likely to intensify
over the 21st century, \mbox{leading} to substantial shifts in species'
suitable ranges.\ This~raises critical questions about the ability of
{current} tree species to persist, as well as about which species or
populations may be better suited to future environmental conditions.
Anticipating future forest composition therefore requires understanding
not only species' exposure to climate change, but also their intrinsic
sensitivity and adaptive capacity. It also requires identifying those
species capable of persisting or potentially replacing others under
changing climatic conditions. This evaluation is an essential step for
guiding forest management and conservation strategies. This paper aims
to synthesize current evidence on climate-driven changes in French
forests in order to identify the tree species that may shape tomorrow's
forests under ongoing and future climatic conditions.

\vspace*{-2pt}

\section{Regional heterogeneity in temperature and precipitation
changes in France} \label{sec2}

\vspace*{-2pt}

Across France, significant changes in temperature and precipitation
have already been observed, with marked contrasts between regions and
seasons. The year 2018 marks the onset of a sequence of hot and dry
years, whose intensity varies depending on location
\citep{Schuldtetal2020}. The most pronounced changes
between the
1961--1990 and the 2018--2024 periods occurred during summer, with
temperature increases exceeding 2.5~{\textdegree}C across large parts
of eastern France and locally exceeding 3~{\textdegree}C, as
illustrated in Figure~\ref{fig1}. Summer precipitation changes show a near
spatial pattern, characterized by increased precipitation along the
western fa\c{c}ade of the country and decreases in the eastern and
southern regions (excepted for Corsica), accompanied by strong local
heterogeneity. The combination of these temperature and precipitation
changes results in contrasting trends in water availability for plants,
depending on both the period and the location. Two regions appear to be
particularly affected by these recent changes: northeastern France and
the Mediterranean area. By contrast, Brittany, the southwest, and
Corsica seem to be less affected.

\vspace*{-2pt}

\section{Tree species are shifting their distributions in response to
climate change}\label{sec3}

\vspace*{-2pt}

The distribution of tree species is strongly constrained by these
climatic conditions. Warm, cold, or dry environments define the climatic limits
within which species can establish and persist within their ecological
niche \citep{Hutchinson1957}. In response to changes in climate,
species may migrate, go extinct, or adapt. Over time, climatic
fluctuations have caused shifts in species' distribution ranges, with
tree migrations. Historically, these dynamics occurred over long time
scales, with species' ranges expanding and contracting during glacial
and interglacial cycles \citep{BenitoGarzonetal2014}. For example,
deciduous \textit{Quercus} species, one of the most important genera in
Europe, were nearly absent from France at the end of the last
glaciation but have since expanded substantially
\citep{BirksTinner2016}. The current rate of climate change is
unprecedented compared to these historical fluctuations, raising
questions about species' \mbox{capacity} to survive abrupt changes or
migrate rapidly enough to track suitable habitats
\citep{Loarieetal2009}.

In the absence of adaptation, climate change is expected to drive
shifts in species distributions mainly along latitudinal and
elevational gradients, potentially allowing colonization of colder
margins while reducing regeneration and increasing mortality at the
warm (southern) edges of species' ranges \citep{LenoirSvenning2015}.
Species distribution models (SDMs) are commonly used to estimate
climatically suitable areas for future periods \citep{Franklin2010,
GuisanZimmermann2000}. These models typically project substantial
changes in suitable habitat by the end of the 21st century, with
contractions for temperate and montane species and expansions for
Mediterranean species across much of France \citep{Hanewinkeletal2013,
Maurietal2022}, as illustrated in Figure~\ref{fig2}. While SDMs offer
valuable insights, they assume equilibrium between species
distributions and climate and often neglect demographic processes,
dispersal limitations, biotic interactions, and adaptive capacity,
potentially leading to an overestimation of range shifts
\citep{Buissonetal2010}. They primarily provide long-term perspectives
on potential distributional trends rather than short-term\break dynamics.

\begin{figure*}
\includegraphics{fig01}
\caption{\label{fig1}Evolution of summer temperatures ({\textdegree}C)
and summer precipitation (mm) between the 1961--1990 and the
2018--2024 periods.}
\end{figure*}

\begin{figure*}
\includegraphics{fig02}
\caption{\label{fig2}Example of the projected evolution of suitable
areas for Fagus sylvatica stands (probability of presence) between the
1961--1990 period (left) and the 2071--2100 period under SSP3-7.0
(center) and SSP5-8.5 (right). Shared Socioeconomic Pathways (SSPs) are
standardized scenarios describing alternative trajectories of societal
development. Projections for 2071--2100 correspond to the average of
three General Circulation Models (GCMs): MRI-ESM2-0, IPSL-CM6A-LR, and
GFDL-ESM4.}
\vspace*{1pc}
\end{figure*}

Different studies indicate that tree species' ranges are already
responding to climate warming \citep{Riglingetal2013}. Comparisons of
juvenile and mature tree distributions show shifts toward cooler
conditions at range edges in some regions \citep{MonleonLintz2015}.\ 
Some species, such as \mbox{\textit{Fagus sylvatica},} exhibit distributional
changes along climatic \mbox{gradients} \mbox{consistent} with recent
warming \citep{Klopcicetal2022}. These shifts are especially pronounced
in mountainous regions \citep{Crimminsetal2011}, where species can more
readily move upward than poleward. For instance, \citep{Lenoiretal2008}
reported an upward migration of approximately 29~m per decade since the
beginning of the twentieth century for tree species in France.
\citet{Bertrandetal2011} observed smaller changes in lowland areas,
where longer-distance dispersal is required to maintain species within
their ecological\break niches.

\begin{figure*}
\vspace*{-3pt}
\includegraphics{fig03}
\vspace*{-3pt}
\caption{\label{fig3}Comparison of tree mortality rates across
ecological regions (SER, IGN) for the major tree species in France
during 2009--2017 and 2018--2024 ($n$\ ${=}$\ 1,321,769 trees). Plots
affected by harvesting, wind, or fire damage were excluded (source:
forest inventory, IGN). The year 2018 marks the beginning of a sequence
of hot and dry years.}
\vspace*{-4pt}
\end{figure*}

\section{Climate-driven changes in tree{\hfill\break} demographic
processes} \label{sec4}

Numerous ground observations illustrate that these climate changes are already
affecting demographic processes \citep{McDowelletal2020}. Forest
productivity provides an indicator of tree fitness, even in the absence
of visible symptoms of decline. \mbox{Recent} \mbox{studies} have {documented}
widespread decreases in productivity across large areas of French
forests, with declines occurring earlier and more severely in
Mediterranean regions than in temperate areas \citep{Hertzogetal2024}.
In northern France, the recent decline in forest productivity was
preceded by a period of accelerated growth, driven by fertilization
effects and a longer growing season. In addition, climate change
reduces natural forest regeneration, as heat and drought limit seedling
survival and establishment \citep{Bolteetal2023, Kremeretal2025}. In
Mediterranean and semi-arid regions, these effects are particularly
pronounced, further compromising forest resilience under ongoing
climatic stress \citep{EnriquezdeSalamanca2022}.

Concurrently, a marked rise in forest dieback has been observed,
particularly in the center and north-east of France
(Figure~\ref{fig3}). According to estimates by the French National
Forest Inventory \citep{IGN2024}, nearly 4\% of metropolitan forests
are currently affected by dieback, with the impacted area more than
doubling between 2017 and 2022. These trends are consistent with
observations at the European scale, indicating a marked decline in tree
vitality, with increasing defoliation trends, and approximately one
third of trees exhibiting moderate to severe defoliation in recent
years \citep{Hammondetal2022, MichelSeidling2018}. 

Increasing evidence indicates that tree mortality is not confined to
the warm margins of species' distribution ranges but also occurs within
the core of their ecological niches \citep{Boseetal2024,
CavinJump2017}. Accordingly, we observe high mortality rates in
northeastern France, in regions historically characterized by temperate
climates and non-limiting water availability, but recently exposed to
repeated climatic stresses (Figure~\ref{fig1}). Such mortality patterns
may partly reflect a phenomenon of structural overshoot, whereby forest
biomass that developed under historically favorable climatic conditions
exceeds the level that current environmental conditions can sustainably
support \citep{Jumpetal2017, Zhangetal2024}. Conversely, limited
dieback can be observed in regions with historically warm and dry
climates, likely due to long-term acclimatization
\citep{IsaacRentonetal2018}.

\looseness=1
These changes are influenced by stand charac\-teristics---such as age,
species composition, density, and structural complexity---which are key
drivers of forest dynamics \citep{Manion1981, Taccoenetal2019}, as well
as by the increasing frequency and intensity of biotic
\mbox{disturbances}, often exacerbated by climate change
\citep{Marinietal2017}. The interplay of these multiple factors
complicates the evaluation of species vulnerability, ultimately
resulting in significant ecological consequences. For example, the
combined effects of productivity decrease and mortality increase have
led to a marked reduction in the French forest carbon sink since the
beginning of the twenty-first century \citep{Ciaisetal2026,
CITEPA2023}.

\section{Understanding adaptive capacity of the{\hfill\break} trees is
a key factor} \label{sec5}

The observed spatial patterns of forest dieback may partly reflect
differences in species' adaptive capacity, with populations originating
from historically warmer or drier regions often being more resilient
than those less adapted to climatic stress \citep{Depardieuetal2020}.
Adaptive capacity refers to the ability of a species to persist and
maintain its functions under changing environmental conditions, thereby
mitigating the impacts of climate change. It is shaped by several key
components, including phenotypic plasticity, genetic diversity, and
gene flow within and among populations \citep{Lindneretal2010,
Valladaresetal2014}. Phenotypic plasticity enables trees to adjust
their morphology, physiology, and phenology in response to altered
climatic conditions---for instance, through changes in leaf traits,
stomatal conductance, water-use efficiency, or the timing of budburst
\citep{Aubinetal2016, Nicotraetal2010}. Plastic responses may also
involve adjustments in rooting depth or biomass allocation,
facilitating access to soil water during drought
\citep{SchenkJackson2002}.

Genetic diversity enhances population resilience to environmental
change, while connectivity among populations facilitates the exchange
of traits that improve local adaptive responses
\citep{RoyerTardifetal2021}.\ However, the long lifespan of trees
limits the pace of evolutionary adaptation, increasing the risk of
maladaptation to changing climatic conditions
\citep{delCastilloetal2022}. Early life stages, such as seedlings,
often display higher plasticity and experience stronger selective
pressures, which can promote the persistence of locally adapted
genotypes under novel climatic conditions \citep{Vitasseetal2013}.\ 
High variability in adaptive traits complicates comparisons among
species, and substantial uncertainty remains regarding the capacity of
trees to \mbox{respond} to rapid climate change
\citep{RoyerTardifetal2021}. While adaptive selection may favor
individuals whose traits are better suited to current environmental
conditions, the overall adaptive capacity of tree populations remains
challenging to quantify, particularly in natural forest ecosystems
\citep{Garzonetal2019}.\looseness=-1

\section{Mediterranean tree species appear less{\hfill\break} affected
by climate change} \label{sec6}

In this context of forest shifts, some species are expected to decline,
while others may benefit \citep{Morinetal2008}. Comparing changes in
productivity and mortality rates among species provides a useful
framework to identify those with contrasting sensitivities to ongoing
climatic changes. According to the IGN \citep{IGN2023}, the most
pronounced productivity losses over the 2006--2020 period were observed
for \textit{Picea abies}, \textit{Pseudotsuga menziesii}, and
\textit{Fagus sylvatica}, particularly in northeastern France
\citep{IGN2024}. More moderate declines were reported for
\textit{Quercus} species, slightly more marked for \textit{Quercus
robur} than for \textit{Quercus petraea}. In contrast, Mediterranean
pines---especially \textit{Pinus pinaster} and \textit{Pinus
halepensis}---exhibited stable or even increasing productivity during
the same period \citep{IGN2023}.

Similar global patterns emerge when considering mortality rates between
2009 and 2024, with higher mortality observed for \textit{Picea abies}
and lower rates for the Mediterranean species \textit{Pinus pinaster}
and \textit{Pinus halepensis} (Figure~\ref{fig4}). However, notable
discrepancies between productivity changes and mortality were also
identified for some species. For instance, \textit{Pseudotsuga
menziesii}, despite experiencing substantial productivity losses
\citepalias{IGN2023}, did not show an increase in mortality in recent years
(Figure~\ref{fig4}), while \textit{Fagus sylvatica} exhibited moderate
mortality rates during the 2018--2024 period, despite declining
productivity. Conversely, \textit{Pinus sylvestris}, which displayed
relatively stable productivity, showed comparatively high and
increasing mortality rates. Overall, the most severe dieback occurred
in species subjected to strong biotic pressures, such as
\textit{Castanea sativa} affected by chestnut blight and ink disease,
\textit{Fraxinus excelsior} impacted by ash dieback (chalara), and
\textit{Picea abies}, increasingly damaged by bark beetle outbreaks
\citep{Trugmanetal2021}.

\begin{figure*}
\includegraphics{fig04}
\caption{\label{fig4}Comparison of tree mortality rates between the 31
major tree species in France during 2009--2017 and 2018--2024 ($n$\ ${=}$\ 
1,321,769 trees). Plots affected by harvesting, wind, or fire damage were
excluded (source: national forest inventory, data IGN).}
\end{figure*}

These patterns should be interpreted with caution, as they also reflect
variability among stands, ecological conditions, and differences in the
magnitude of climatic changes or in the intensity of pathogen
outbreaks. Discrepancies between growth and mortality responses further
highlight that the factors promoting tree growth may differ from those
increasing mortality risk \citep{Dasetal2016}. Nevertheless, the
observed gradients support the idea of shifts in species' distribution
ranges toward higher \mbox{altitudes} or latitudes, with taxa
originating from cool and moist environments being more disadvantaged
than thermophilous species \citep{Taccoenetal2022}.

This comparison reveals an apparent resistance of Mediterranean tree
species, especially Mediterranean pines, at the northern limit of their
distribution, despite the pronounced warming observed in southern
France (Figure~\ref{fig1}). However, this resistance may be challenged
in the future by the spread of emerging pathogens, such as the pine
wood nematode, whose impacts can be exacerbated under warmer climatic
conditions \citep{Karmezietal2022}. 

\section{A multi-approach framework to anticipate forest responses to
climate change} \label{sec7}

The significant changes in tree species distributions and demographic
processes already observed are expected to persist or even intensify as
climate warming continues.\ In this context, evaluating potential
species composition to adapt forests to \mbox{future} \mbox{climatic} conditions is
essential \citep{Keenan2012}.\ A~wide range of tools is available to
anticipate forest responses to climate change \citep{Orazioetal2017}.
Given the complexity of forest systems and the high degree of
uncertainty, we recommend combining multiple sources of information and
complementary methods. A five-step methodological framework is proposed
that integrates climate data, species-specific sensitivities, local
environmental characteristics, and various decision-support tools to
assess forest vulnerability and support adaptive management decisions
at spatial scales ranging from small natural regions to the plot level.

\medskip\noindent
Step 1: Characterizing past and future local climate change.

Because the impacts on vegetation dynamics generally increase with the
intensity of climate change, vulnerability assessments should begin by
characterizing climate changes already observed at the local scale,
complemented by projections of future changes under different climate
scenarios. Climate exposure should consider trends in temperature,
\mbox{water} availability, and the frequency and intensity of extreme climatic
events.\ The greater the magnitude and rate of changes, the higher the
exposure of tree species.

\medskip\noindent
Step 2: Evaluating site conditions.

A local assessment of site conditions is necessary to characterize
ecological constraints. Relevant site information includes soil
water-holding capacity (closely related to soil depth), soil fertility,
and the occurrence of waterlogging. Certain topographic features can
also be considered, as they can influence for example water fluxes and
soil moisture redistribution. This information complements climate data
and can be integrated with it, for example, to estimate changes in soil
water availability. Site conditions are generally obtained from field
surveys or existing site-type maps and may be supplemented by spatially
explicit models when ground-based data are unavailable. Together, these
variables refine the assessment of species exposure.

\medskip\noindent
Step 3: Understanding species sensitivity.

Species sensitivity can be assessed using bibliographic information on
species traits, ecological requirements, and tolerance to climatic
constraints, as well as local responses to past climate events. Several
databases synthesize species' ecological traits and climatic
preferences \citep{Choatetal2012, Ellenbergetal1992, Kattgeetal2020}.
In addition, indicators such as regeneration success, tree growth, or
mortality rates can be assessed in the field and compared according to
levels of climatic exposure. These assessments may rely on standardized
protocols to describe the extent of tree decline or on
dendrochronological analyses. They can be based on forest inventory
data, health monitoring networks, or targeted field surveys.

\medskip\noindent
Step 4: Comparison of climate-sensitive decision-support tools for
forest dynamics.

Numerous decision-support tools are currently being developed to guide
species selection and silvicultural practices aimed at improving forest
adaptation to future climatic conditions \citep{Cochardetal2021,
Piedalluetal2023, TimberlakeSchultz2019}. These tools span a gradient
from empirical to process-based models. Empirical models rely on
observed data and are primarily correlative. Among these, species
distribution models are widely used to characterize climatic limits or
ecological niches and to project potential distributions under future
climate scenarios. If the data used to calibrate them adequately
represent the ecological niche, they can be used to assess areas
potentially suitable in the long term \citep{Thuilleretal2005}.\ Other
common approaches focus on modeling and mapping forest dieback or tree
mortality based on stand, soil, and climate variables. It provides a
more realistic short-term perspective of vulnerability patterns,
although extrapolating their results over longer time periods can be
challenging \citep{Piedalluetal2023}.\ In contrast, process-based models
explicitly represent ecological mechanisms and are commonly used to
explore ecosystem responses to changing environmental conditions. Some
can simulate long-term forest dynamics and assess potential impacts on
regeneration, growth, or mortality \citep{ChuineBeaubien2001,
Cochardetal2021, Ogeeetal2003}. Calibrating these models to adequately
capture spatial variability can be challenging. Each modeling approach
has inherent limitations and uncertainties, which should be analyzed in
light of data- and method-related constraints. Although they should be
compared and interpreted with caution, these different models provide
essential guidance for adaptive management and for anticipating forest
responses under changing climatic conditions.

\medskip\noindent
Step 5: Synthesis and recommendations to estimate suitable tree
species.

Assessing forest responses to climate change \mbox{requires}
synthesizing information from these multiple sources.\ This synthesis
could be structured through a new type of guidance framework inspired
by traditional forest site-type catalogues and guides \citep{Gaudin2008}.
This enables the evaluation of species suitability from multiple
perspectives, using complementary methodological approaches. Such a
synthesis requires substantial expertise due to the diversity of local
contexts and the potential for contradictory results across information
sources. The relevance and reliability of each source should be
critically assessed, and unrealistic outcomes identified. The
evaluation of suitable forest composition should also account for
multiple risks, including those directly linked to climate warming and
drying, as well as to forest fires, windstorms, and the emergence of
novel pathogens. {Although} uncertainties may remain high, this
{integrated} approach, which requires specialized expertise, can help
anticipate future changes and support the design of adaptation measures
tailored to local conditions.

\section{A range of scenarios for future forest{\hfill\break}
composition in the face of climate change} \label{sec8}

Forest composition may follow different trajectories depending on the
interaction between species' and stands' exposure to stressors, their
intrinsic sensitivity, and their adaptive capacity \citep{Keenan2015}
(Figure~\ref{fig5}). When vulnerability is low, forests may persist
close to their current state. As vulnerability increases, more
resistant individuals or species may survive at the expense of weaker
ones, potentially altering the composition of existing stands.
Initially, the mortality of some individuals can benefit others by
reducing competition for light and water, thereby accelerating stand
regeneration dynamics. For example, seedlings established under more
stressful conditions may develop traits that enhance their adaptation
to future climatic conditions \citep{Zhangetal2025}. Conversely, if
dieback is severe, the buffering effect of the forest canopy may be
lost, and the microclimate may warm, limiting the success of
regeneration or plantation efforts \citep{Thometal2023}.

\begin{figure*}
\vspace*{.3pc}
\includegraphics{fig05}
\vspace*{.2pc}
\caption{\label{fig5}Potential adaptation pathways under increasing
disturbance intensity.}
\vspace*{.2pc}
\end{figure*}

Adaptive forestry provides strategies to anticipate changes in stands
that are currently minimally affected but potentially vulnerable in the
future \citep{Bolteetal2010}. Key levers include stand structure
adaptation, species mixture, density and water resource management,
known to influence different demographic processes
\citep{Taccoenetal2021}. Reducing basal area decreases competition and
improves soil water balance by limiting rainfall interception and
evapotranspiration \citep{Sohnetal2016}. Species mixtures diversify
risks and mitigate problems from pathogen attacks, while also affecting
tree interactions such as competition, facilitation, nutrient
enhancement, and allelopathy \citep{Jacteletal2021, Pretzschetal2015}.
Depending on the species involved, some trees benefit from these
interactions, while others may be disadvantaged, making mixture effects
highly variable between species \citep{Boseetal2024}. Stand structure
also appears particularly important, with uneven-aged stands often
benefiting more \citep{Searleetal2022}. Additionally, water \mbox{resources}
should be maintained or enhanced through forest practices that limit
soil compaction and promote infiltration. 

When species vulnerability increases to the point of threatening stand
persistence, the question of species replacement arises. Several
options can then be considered, such as promoting secondary species
already present, encouraging their natural regeneration or arrival from
nearby areas, or implementing enrichment planting. The overall
objective is to increase species diversity and favor species or
provenances better adapted to hot and dry climates, while minimizing
reliance on artificial regeneration. When drought-tolerant species are
already present nearby, they can be promoted to increase their
importance within the stand. For example, the upward expansion of oak
can be encouraged at higher elevations when mountain species (such as
fir, spruce, or beech) are threatened by decline. Another solution is
enrichment planting, which allows the diversification of an existing
stand by introducing a limited number of new trees. The choice of
species should be based on their tolerance for shade. For example, in
northeastern France, species recommended for low-light conditions
include \textit{Tilia} spp., \textit{Acer} spp., and \textit{Carpinus
betulus}, whereas \textit{Quercus robur}, \textit{Pinus sylvestris},
and \textit{Larix decidua} are favored in areas with higher light
availability \citep{CNPF0000}. In some situations---particularly when
monospecific stands experience extensive mortality---complete
reforestation may ultimately be required \citep{Fadyetal2021}. This
issue is especially acute in lowland \textit{Norway spruce} forests
that have experienced widespread dieback, where establishing fully
stocked plantations is often required. In this case, the loss of forest
cover further amplifies local temperatures and water stress, and can
significantly complicate natural regeneration and the re-establishment
of a continuous forest canopy.

When species better adapted to future climatic conditions are not
available in the surrounding landscape, assisted migration may be
considered, either by selecting new provenances of native species or by
introducing non-native species with suitable ecological traits
\citep{Aitkenetal2008, Pedlaretal2012}. Meta-analyses and common garden
provenance trials have demonstrated substantial intraspecific variation
in functional traits among tree populations, particularly in their
responses to drought and climatic stress \citep{Albertoetal2013,
Copieetal2025}. Populations originating from historically warmer or
drier regions often exhibit greater drought tolerance, resistance, and
survival under water-limited conditions, reflecting local adaptation of
physiological traits related to water use, phenology, and hydraulic
function \citep{IsaacRentonetal2018}.\ These \mbox{findings} provide a
scientific basis for the selection of appropriate seed sources in
climate-adaptive forest \mbox{management}. 

\looseness=-1
In France, these approaches are currently explored through experimental
and operational programs such as Giono, ClimEssences, and {RENEssence}
\citep{Muschetal2022, ONF2022}. These initiatives aim to evaluate the
performance of alternative provenances and species under current and
future climatic conditions. The ClimEssences
platform\footnote{\url{https://climessences.fr/}.} (CNPF/ONF) provides
detailed species and provenance profiles, including ecological traits,
to guide species selection under future climate scenarios. These
initiatives focus on southern or drought-tolerant provenances of native
species---including, for example, \textit{Quercus} species (\textit{Quercus robur}, 
\textit{Q.~petraea}, \textit{Q.~pubescens}), 
\textit{Fagus sylvatica}, \textit{Abies alba}, and
\textit{Pinus sylvestris}. Experimental plantations within
the Giono project have shown improved survival and drought resistance
of southern provenances of \textit{Fagus sylvativa} and \textit{Quercus
petraea} compared to local material during recent heatwaves and drought
events, particularly on shallow or water-limited soils \citep{ONF2022}.
They also target potentially suitable non-native species such as
\textit{Cedrus atlantica}, \textit{Abies} species (\textit{Abies
bornmuelleriana}, \textit{cephalonica},
\textit{nordmanniana},\,{\ldots}), \textit{Quercus} species
(\textit{Quercus \mbox{cerris} or rubra}), or \textit{Pinus species}
(\textit{Pinus radiata}, \textit{taeda}, \textit{pinaster, rigida,
brutia)}, outside parts of their current distribution range.

Despite these initiatives, assisted migration remains associated with
substantial uncertainties and risks. Species and provenance performance
vary strongly across sites \citep{RoyerTardifetal2021}. Short-term
gains in growth or survival do not necessarily translate into long-term
resilience, especially with respect to late frost sensitivity, pest and
pathogen dynamics, or extreme events \citep{AitkenBemmels2016}. In
addition, the introduction of non-native species raises concerns
regarding potential impacts on native biodiversity, ecosystem
functioning, and biotic interactions. Consequently, current
recommendations emphasize a cautious and adaptive approach based on
limited-scale trials, species mixtures, and diversification strategies
rather than large-scale species replacement. Assisted migration should
therefore be viewed as one component of a broader adaptation strategy,
to be combined with natural regeneration, stand structural adaptation,
and continuous monitoring.

\section{Conclusion} 

Forests are already changing, reflecting the early impacts of climate
change. These changes will continue as long as climate warming
persists, but considerable uncertainties regarding their future
\mbox{trajectories}. Projected climate changes suggest substantial
transformations in vegetation, with a 4~{\textdegree}C temperature
increase by the end of the 21st century potentially shifting temperate
biomes toward Mediterranean-like conditions and profoundly altering
species composition and ecosystem dynamics. Currently, both the
southern range limits and the core areas of species' ecological ranges
appear to be affected by adverse impacts. These result from increased
heat and drought, the proliferation of pathogen attacks, ecosystem
degradation caused by more frequent wildfires, as well as from
wind-related damage. The unprecedented pace of environmental change
leaves little time for experimentation and evaluation of potential
solutions, despite the critical importance of such efforts.

Assessing the composition of future forests remains challenging and
will depend on various factors, including our ability to limit
greenhouse gas emissions and the capacity of species to adapt to new
conditions. While acclimation may provide some buffering capacity,
future forest composition will also depend on our capacity to implement
a diversified set of solutions, involving carefully assessed risks.
Adaptive forest management can offer viable strategies by adjusting
stand structure, diversifying species composition, managing density and
water resources, and promoting natural regeneration, potentially
delaying adverse impacts and buying valuable time for forests to adapt.
Where necessary, better-adapted provenances or species may also be
introduced. Despite all these possibilities, which require substantial
efforts to be implemented and maintained, it is likely that, over time,
a number of forests will reach silvicultural limits, and that, in some
locations, forests may no longer be able to regenerate.

Evaluating potential adaptation strategies will require strong field
expertise, as well as the capacity to effectively use and integrate
diverse decision-support tools. Continued research is essential to
better characterize vulnerable stands, assess adaptive options, and
refine forest management strategies. Forests are of particular
importance. They are not only ecosystems at risk but also key actors in
climate change mitigation through carbon sequestration and the
regulation of ecosystem processes. Preparing today's forests for
tomorrow's climate is therefore an urgent and complex challenge that
calls for immediate, informed, adaptive, and coordinated action.

\section*{Use of artificial intelligence techniques}

The author declares that generative AI was used in the writing process.
In accordance with the GAIDeT taxonomy (2025), the
following tasks were delegated to generative AI (GAI) tools under full
human supervision: Proofreading and editing, \mbox{Translation}. The GAI tools used were: Chat-GPT5 and DeepL. Responsibility for the final manuscript rests entirely with the
authors. GAI tools are not listed as authors and bear no responsibility
for the final \mbox{outcomes}.

%\section*{Declaration of interests}
%The author does not work for, advise, own shares in, or receive funds
%from any organization that could benefit from this article, and has
%declared no affiliations other than their research organizations.
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