Joannès Guillemot

Cirad - La recherche agronomique pour le développement | CIRAD · Unité Mixte de Recherche Ecologie Fonctionnelle et Biogéochimie des Sols et des Agro-Écosystèmes (Eco et Sols)

Maximizing initial aboveground woody biomass (AGB) accumulation in order to obtain early payments for carbon stocking is essential for the financial viability of reforestation programs fostered by climate mitigation efforts. Intensive silviculture, i.e., silviculture traditionally used in commercial forestry to maximize productivity and gains, has...

Variations in crown forms promote canopy space‐use and productivity in mixed‐species forests. However, we have a limited understanding on how this response is mediated by changes in within‐tree biomass allocation. Here, we explored the role of changes in tree allometry, biomass allocation and architecture in shaping diversity–productivity relations...

Knowing which restoration approach provides the best returns on investment for accumulating carbon is essential to foster restoration planning, financing, and implementation. Here, we explored the cost-effectiveness and drivers of above-ground and soil carbon accumulation in restored forests across an agricultural landscape of Brazil's Atlantic For...

Climate change impacts forest functioning and dynamics, and large uncertainties remain regarding the interactions between species composition, demographic processes and environmental drivers. There are few robust tools available to link these processes, which precludes accurate projections and recommendations for long‐term forest management. Forest...

Understanding how evolutionary history and the coordination between trait trade-off axes shape the drought tolerance of trees is crucial to predict forest dynamics under climate change. Here, we compiled traits related to drought tolerance and the fast-slow and stature-recruitment trade-off axes in 601 tropical woody species to explore their covari...

Potassium (K) availability constrains forest productivity. Brazilian eucalypt plantations are a good example of the K limitation of wood production. Here, we built upon a previously described model (CASTANEA-MAESPA-K) and used it to understand whether the simulated decline in C source under K deficiency was sufficient to explain the K limitation of...

Purpose of Review Increasing the diversity of commercial tree plantations is a promising approach to adapt forests to climate change, but it may complicate management. Here, we evaluate stakeholders’ perspectives about tree-species diversity in plantations and explore policy alternatives to make mixed plantations a viable strategy for climate chang...

Forest ecosystems are increasingly threatened by anthropogenic pressures, especially by the increase in drought frequency and intensity. Tree species mixtures could improve resilience to diverse global anthropogenic pressures. However, there is still little consensus on how tree diversity affects water stress. Although some studies suggest that mix...

Vapor Pressure Deficit (VPD, atmospheric drought) and soil water potential (Ψsoil, soil drought) have both been reported to affect terrestrial plant water stress, plant functions (growth, stomatal conductance, transpiration) and vulnerability to ecosystem disturbances (mortality or vulnerability to wildfires). Which of atmospheric drought or soil d...

Intraspecific variability (IV) has been proposed to explain species coexistence in diverse communities. Assuming, sometimes implicitly, that conspecific individuals can perform differently in the same environment and that IV increases niche overlap, previous studies have found contrasting results regarding the effect of IV on species coexistence. W...

Mixed-species forests are promoted as a forest management strategy for climate change adaptation, but whether they are more resistant to drought than monospecific forests remains contested. Particularly, the trait-based mechanisms driving the role of tree diversity under drought remain elusive. Using tree cores from a large-scale biodiversity exper...

Forest landscape restoration (FLR) commitments have been established in the past years to restore over 200 million hectares, as part of the global Bonn Challenge goal, mostly through the implementation of several different restorative practices in degraded lands, ranging from commercial tree monocultures to restoration plantings. The potential of s...

The extent of the potassium (K) limitation of forest productivity is probably more widespread than previously thought, and K-limitation could influence the response of forests to future global changes. To understand the effects of K-limitation on forest primary production, we have developed the first ecophysiological model simulating the K cycle an...

Potassium availability constrains forest productivity. Brazilian eucalypt plantations are a good example of the K-limitation of wood production. Here, we built upon a previously described model (CASTANEA-MAESPA-K) and used it to understand whether the simulated decline in C-source under K deficiency was sufficient to explain the K-limitation of woo...

Key message Plantations of two multipurpose legume species markedly differ in stand development and functioning. The sustainability of tree plantations can be inferred from their ecological strategies along the fast-slow economic spectrum. Abstract Growing plantations with native trees is crucial for ecosystem restoration and wood and non-wood pro...

Context: Intraspecific variability (IV) has been proposed to explain species coexistence in diverse communities. Assuming, sometimes implicitly, that conspecific individuals can perform differently in the same environment and that IV blurs species differences, previous studies have found contrasting results regarding the effect of IV on species coe...

THIS PREPRINT IS A DUPLICATE OF 10.1101/2022.03.16.484259 Context: Intraspecific variability (IV) has been proposed to explain species coexistence in diverse communities. Assuming, sometimes implicitly, that conspecific individuals can perform differently in the same environment and that IV blurs species differences, previous studies have found co...

Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we...

Ecosystem restoration is a global priority, currently promoted by several ambitious commitments. Most of the research to guide restoration practices was so far put on the recovery of above‐ground functions and services, although soil health is increasingly recognized as a fundamental condition to restoration success. Soil restoration is particularl...

Remote sensors, onboard orbital platforms, aircraft, or unmanned aerial vehicles (UAVs) have emerged as a promising technology to enhance our understanding of changes in ecosystem composition, structure, and function of forests, offering multi-scale monitoring of forest restoration. UAV systems can generate high-resolution images that provide accur...

Recent methodological advances have opened new perspectives for tropical dendrochonological studies by facilitating the visualization, delimitation, and analyses of tree-rings. One of those improvements was brought by X-ray densitometry, which allows building radial wood density profiles at microscopic scale. Furthermore, recent methods allow for c...

Potassium (K) is essential for a wide range of physiological functions in plants, and a limiting element for wood productivity in numerous forest ecosystems. However, the contribution of each of the K-sensitive physiological processes to the limitation of wood productivity is poorly known. In trees, K deficiency acts both on the source and the sink...

As of 2020, the world has an estimated 290 million ha of planted forests and this number is continuously increasing. Of these, 131 million ha are monospecific planted forests under intensive management. Although monospecific planted forests are important in providing timber, they harbor less biodiversity and are potentially more susceptible to dist...

Fertilization is commonly used to increase growth in forest plantations, but it may also affect tree water relations and responses to drought. Here, we measured changes in biomass, transpiration, sapwood-to-leaf area ratio (As:Al) and sap flow driving force (ΔΨ) during the 6-year rotation of tropical plantations of Eucalyptus grandis under controll...

Understanding the processes that underlie the effects of tree diversity on primary production is of foremost importance to enhance climate change mitigation by tropical forests. Here, we investigated the effects of tree diversity on light interception over space and time in two tropical tree experiments, located in Panama— Sardinilla site (monocult...

Research in environmental science relies heavily on global climatic grids derived from estimates of air temperature at around 2 meter above ground1-3. These climatic grids however fail to reflect conditions near and below the soil surface, where critical ecosystem functions such as soil carbon storage are controlled and most biodiversity resides4-8...

Aims Belowground interactions are still poorly understood in mixed-species forests. We investigated the effects of soil fertility on belowground processes in mixed planted forests. Methods The dynamics and traits of Eucalyptus and Acacia mangium fine roots (diameter < 2 mm) in plantations with 50% of each species were studied in a randomized bloc...

Climate change impacts forest functioning and dynamics, and large uncertainties remain regarding the interactions between species composition, demographic processes, and environmental drivers. There are few robust tools available to link these processes, which precludes accurate projections and recommendations for long-term forest management. Fores...

Potential time lags between human-mediated disturbances and the subsequent responses of ecosystems are critical for planning and implementing conservation and restoration actions. In this context, decoupling between the temporal trajec-tories of ecosystems structure and functions is particularly critical. Here, we stand out the need to differentiat...

Climate change is expected to increase the frequency of droughts in most tropical regions in the coming decades. A passive phenomenon called hydraulic redistribution (HR) allows some plant species to take up water from deep and wet soil layers and redistribute it in the upper dry layers where other plants and soil biota can benefit from it. In addi...

Carbon and water budgets of forest plantations are spatially and temporally variable and hardly empirically predictable. We applied G'DAY, a process-based ecophysiological model, to simulate carbon and water budgets and stem biomass production of Eucalyptus plantations in São Paulo State, Brazil. Our main objective was to assess the drivers of spat...

Stemwood productivity in forest ecosystems depends on the amount of light absorbed by the trees (APAR) and on the Light Use Efficiency (LUE), i.e. the amount of stemwood produced per amount of absorbed light. In fertilized Eucalyptus plantations of Brazil, growth is expected to be strongly limited by light absorption in the first years after planti...

Functional specialization of fine roots was found for Eucalyptus grandis trees at harvesting age (6 years) on tropical soils. Aiming to elucidate whether functional specialization is a ubiquitous feature of eucalypts, we focused on its changes with ontogeny, tree nutrient status and soil depth. We studied the potential uptake of N, K and Ca by 2-ye...

Global climatic changes may deeply affect the functioning ofEucalyptusplantations, es-pecially through the increase in frequency and duration of droughts and storms. However,the long-term responses of trees to the interactions of the different changing environmentalfactors remain largely unknown. It is therefore crucial to gain knowledge on the dri...

The ongoing introduction of the exotic Grevillea robusta tree species into agroforestry systems (AFS) of the Indian Western Ghats could become a threat to both climate change mitigation and tree diversity conservation. Here, we quantified carbon (C) storage and shade tree diversity in native forests and coffee AFS under contrasted management (nati...

In agroforestry systems, shade trees strongly affect the physiology of the undergrown crop. However, a major paradigm is that the reduction in absorbed photosynthetically active radiation is, to a certain extent, compensated by an increase in light‐use efficiency, thereby reducing the difference in net primary productivity between shaded and non‐sh...

The timing of leaf phenophases greatly influences the functioning of trees. Phenological traits are thus considered major components of tree fitness, and are expected to be strongly selected under environmental or biotic pressures. To date, most phenological studies have been conducted at the population scale, with comparatively very few works at t...

We aimed to evaluate the importance of modulations of within-tree carbon (C) allocation by water and low-temperature stress for the prediction of annual forest growth with a pro- cess-based model. A new C allocation scheme was implemented in the CASTANEA model that accounts for lagged and direct environmental controls of C allocation. Different ap...

Aims In human‐dominated ecosystems, the presence of a given species is the result of both the ecological suitability of the site and human impacts such as land‐use choices. The influence of land‐use choices on the predictions of species distribution models (SDMs) has, however, been often neglected. Here, we provide a theoretical analysis of the lan...

Among population trait diversity (Qst) and within-population genetic diversity (Hs) evolve under natural selection in an heterogeneous environment. Local adaptation occurs very quickly during the first few generations while genetic diversity decreases only slowly, buffered by sexual reproduction. Thus, selection does not directly result in the eros...

Key message With a retrospective growth analysis over 20 years, we showed that silviculture (in particular thin- ning) of Cedrus atlantica (Manetti) could to some extent mitigate the effects of drought episodes. Severe reductions ofdensityresultedinfasterrecoveryofradialgrowthafter severe drought episodes. Context Climatechangeisexpectedtoincreaset...

The processes that underlie forest productivity and C allocation dynamics in trees are still poorly understood. Forest growth has for long been thought to be C limited, through a hypothesized causal link between C supply and growth (source control). This C-centric paradigm underlies most of the C allocation rules formalized in process-based models...

The extent to which wood growth is limited by carbon (C) supply (i.e. source control) or by cambial activity (i.e. sink control) will strongly determine the responses of trees to global changes. Nevertheless, the physiological processes that are responsible for limiting forest growth are still a matter of debate. The aim of this study was to evalua...

Key message. We demonstrate that, beyond leaf phenology, the phenological cycles of wood and fine roots present clear responses to environmental drivers in temperate and boreal trees. These drivers should be included in terrestrial ecosystem models. Context. In temperate and boreal trees, a dormancy period prevents organ development during adverse...

The extent to which forest growth is limited by carbon (C) supply (source control) or by cambial activity (sink control) will condition the response of trees to global changes. However, the physiological processes responsible for the limitation of forest growth are still under debate. The aim of this study is to evaluate the key drivers of the annu...

Background and AimsThe structure of a forest stand, i.e. the distribution of tree size features, has strong effects on its functioning. The management of the structure is therefore an important tool in mitigating the impact of predicted changes in climate on forests, especially with respect to drought. Here, a new functional-structural model is pre...

Les paiements pour services environnementaux (PSE) sont aujourd'hui largement considérés comme un instrument économique majeur de la lutte contre la déforestation. Les projets d'application, de même que les critiques développées autour de cet outil, apparaissent de plus en plus nombreux dans le monde entier, mettant en lumière de fortes divergences...

Résistant à la sécheresse, doté d’une bonne croissance et d’une bonne valeur économique, le cèdre apparaît comme un recours intéressant face au réchauffement climatique. Ce projet vise à profiter de l’expérience acquise en région méditerranéenne, tirer les enseignements des essais d’installation dans le nord de la France et analyser les données réc...

Carbon (C) sequestration of Arabica and Robusta agroforestry systems (AFS) was assessed with respect to adjacent reference forest patches in the Kodagu district, the most important coffee region of the Western Ghats, one the world hotspots of biodiversity. Results indicate that coffee AFS with native species sequester large amount of C (190-200 t/h...