Jean-Paul Laclau

• Managing Director at French Agricultural Research Centre for International Development

In tropical humid Africa, sandy soils under periodically burnt herbaceous savannas exhibit generally low carbon (C) content and nitrogen (N) availability. Savanna afforestation may overcome these limitations through changes in soil functioning, yet these processes still need to be explored. In this study, we investigated whether changes in the comp...

This Policy Brief by Cirad develops the concept of social-ecological system (SES) health, which considers the relations between stakeholders within a given territory, their activities, and human, plant, animal and ecosystem health.

Realistic representations of plant carbon exchange processes are necessary to understand the growth and productivity of forests and to understand how plants will behave in future climate change scenarios. These processes are known to vary over depending on environmental and genetic factors. Here, we used the model by Farquhar et al. (Plant 149:78–9...

Carbon sequestration by forest plantations, for commercial or restoration purposes, is a nature-based solution to mitigate the impacts of climate change. One of the methodologies suggested by IPCC to quantify carbon sequestration in biomass by forest plantations is to use biomass expansion factors. These factors derive aboveground (BEF) and belowgr...

Soil erosion on agricultural land is a major threat for food and raw materials production. It has become a major concern in rubber (Hevea brasiliensis) plantations introduced on sloping ground. Alternative agroecological crop management practices must be investigated. One aim of our study was to assess the ability of logging residues (i.e., trunks,...

While soil salinization is a major concern for agriculture worldwide, the application of sodium (Na) can stimulate growth in many plant species, due to its ability to replace potassium (K) in some physiological functions. We present an overview of the potential and risks associated with replacing KCl fertilizer with a mixture of KCl and NaCl in tro...

FAO’s most recent global synthesis on planted forests was released in 2009 and the last Unasylva on planted forests was published in 2005. Developed together with a coalition of external partners, including the International Union of Forest Research Organizations (IUFRO) task force on planted forests and the TreeDivNet network, Issue 254 hereby res...

Soil animal communities include more than 40 higher-order taxa, representing over 23% of all described species. These animals have a wide range of feeding sources and contribute to several important soil functions and ecosystem services. Although many studies have assessed macroinvertebrate communities in Brazil, few of them have been published in...

Eucalyptus plantations are commonly fertilized at planting to sustain high biomass production over successive rotations in nutrient-poor soils. However, the dynamics of nutrient uptake by tree roots in the early stages of stand development, depending on the lateral distance from the trees and the depth in the soil, are poorly documented. We assesse...

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...

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...

We hypothesized that the nitrogen-fixing tree Acacia mangium could improve the growth and nitrogen nutrition of non-fixing tree species such as Eucalyptus. We measured the N-mineralization and respiration rates of soils sampled from plots covered with Acacia, Eucalyptus or native vegetation at two tropical sites (Itatinga in Brazil and Kissoko in t...

Most Eucalyptus plantations in Brazil are located in regions currently experiencing periods of water shortage, where fertilizers such as potassium (K) are intensively used to achieve high productivity. In a changing environment , improving our understanding of the effects of K nutrition on tree growth rates and xylem plasticity across tree ages as...

Atmospheric deposition of dissolved organic carbon (DOC) to terrestrial ecosystems is a small, but rarely studied component of the global carbon (C) cycle. Emissions of volatile organic compounds (VOC) and organic particulates are the sources of atmospheric C and deposition represents a major pathway for the removal of organic C from the atmosphere...

This presentation dealt with the restoration of soil health after heavy disturbances in rubber tree plantations in Ivory Coast. We showed that the restitution of logging residues (i.e. the crop residues of the previous rubber stand), combined with a legume cover, made it possible to quickly restore soil functioning.

Soil erosion causes major problems of land degradation in agricultural systems leading to losses of soil fertility. Rubber tree is one of the main tropical perennial crops with about 13 million hectares of plantations worldwide in 2018. In the early stage of a rubber plantation, soil is especially vulnerable to degradations given the low canopy cov...

Eucalyptus is the tree most widely planted in tropical countries to satisfy growing demand for wood products, but high yields require high fertilizer inputs. Introducing N2-fixing trees (NFT), such as Acacia mangium, has been proposed to improve soil fertility and aboveground tree biomass in Eucalyptus plantations. In addition to N inputs, NFT spec...

We evaluated differential expression of genes in leaf and xylem tissues for three Eucalyptus clones in the field using Illumina sequencing, under four contrasting fertilization regimes: a control combining nitrogen (N), phosphorus (P), and potassium (K) and three regimes with N, K, and P deficiency. The field results showed significantly better per...

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...

In a climate change context, changing temperature and precipitation patterns are expected to have strong impacts on Brazilian eucalypt plantations. Implementing adaptive water-efficient management practices is thus becoming necessary to maintain high levels of productivity while preserving the water resources. This paper investigates the ability of...

Dans cette présentation, nous montrons dans un premier temps la forte perturbation des fonctions du sol induite par la phase de replantation (coupe rase, sous-solage, etc.) entre 2 cycles de plantations d'hévéas en Côte d'Ivoire. Dans un deuxième temps, le bénéfice de la restitution des résidus d'abattage et de l'implantation d'une légumineuse sur...

The savannas (called Cerrado) are the second-largest vegetation formation in Brazil after the Amazon rainforest, with about 2 million km². Roots have been found in very deep soil layers in Cerrado ecosystems, which suggests a crucial role of deep rooting in the supply of water and nutrients over dry periods. The aim of our study was to gain insight...

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...

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...

While a recent study showed that significant amounts of the nitrogen (N) requirements of young Eucalyptus trees can be provided by nitrogen-fixing trees (NFTs) in mixed-species plantations through short-term belowground N transfer, the consequences of soil fertility on this facilitation process remain unknown. We assessed the effect of fertilizatio...

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Rubber trees are the main source of natural rubber (NR). The area occupied by rubber plantations rose from 3.9 million ha in 1961 to 12.5 million ha in 2018. Both the expansion of rubber plantations in marginal zones (prone to biotic and abiotic stress), and long-term rubber tree cultivation in traditional areas, raise questions about the sustainab...

Background & Aims Better understanding of belowground interactions in agroforestry systems is crucial for the success of plant co-existence. Beyond root competition, associated arbuscular mycorrhizal (AM) fungi can also be involved in plant to plant interactions. Thus far, the contribution of each agroforestry component (trees, herbaceous vegetatio...

Almost half of the total organic carbon (C) in terrestrial ecosystems is stored in forest soils. By altering rates of input or release of C from soils, forest management activities can influence soil C stocks in forests. In this review, we synthesize current evidence regarding the influences of 13 common forest management practices on forest soil C...

While the number of studies dealing with fine root dynamics in deep soils layers (depth > 1 m) has increased sharply recently, the phenology, the morphology, the anatomy and the role of deep fine roots are still poorly known in forest ecosystems. This review summarizes the current knowledge on fine root production, mortality and longevity in deep s...

Many studies have shown that introducing N2-fixing trees (e.g. Acacia mangium) in eucalypt plantations can increase soil N availability as a result of biological N2 fixation and faster N cycling. Some studies have also shown improved eucalypt P nutrition. However, the effects of N2-fixing trees on P cycling in tropical soils remain poorly understoo...

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...

O objetivo do presente trabalho foi avaliar as correlações entre produtividade e resposta à seca (RS) do eucalipto entre os atributos do solo em dois tipos climáticos distintos no Brasil. Para isto, foram instalados 24 experimentos no Brasil com 4 clones comuns em todos os experimentos para obter fortes contrastes edafoclimáticos, e, desse modo, me...

Forest soil fertility can be defined as a combination of physical, chemical and biological factors characterising the biomass production capacity of the soil. However, numerous ecological variables affect tree growth and the aim of the present study was to investigate the specific influence of soil chemical properties on tree productivity at 49 aci...

Many forest ecosystems are developed on acidic and nutrient-poor soils and it is not yet clearly understood how forests sustain their growth with low nutrient resources. In forestry, the soil chemical fertility is commonly defined, following concepts inherited from agronomy, as the pool of plant-available nutrients in the soil at a given time compa...

Oil palm (Elaeis guineensis Jacq.) is currently cultivated on 19 million ha, and palm oil represents more than one‐third of the global vegetable oil market. Addition of nitrogen (N) via legume cover crop and fertilizers is a common practice in industrial oil palm plantations, however, there is a tendency for N loss, thus contributing significantly...

Brazilian roundwood industry is one of the most important and productive in the world, with Eucalyptus plantations alone representing 73% of the total planted forests. Deep rooting in these plantations represents a more common phenomena than generally expected. However, there is still a lack of information on environmental factors that drive root g...

Despite the strong ecological importance of ectomycorrhizal (ECM) fungi, their vertical distribution remains poorly understood. To our knowledge, ECM structures associated with trees have never been reported in depths below 2 meters. In this study, fine roots and ECM root tips were sampled down to 4-m depth during the digging of two independent pit...

Belowground niche complementarity between deep-rooted and shallow-rooted species in mixed forests may result in a more complete exploitation of soil resources than in monocultures. Our study aimed to assess 1) the maximum distance (horizontally and vertically) where the fine roots from common Cerrado species take up mobile nutrients in deep Ferrals...

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...

While potassium fertilization increases growth yield in Brazilian eucalyptus plantations, it could also increase water requirements, making trees more vulnerable to drought. Sodium fertilization, which has been shown to promote eucalyptus growth compared to K-deficient trees, could partially mitigate this adverse effect of potassium. However, littl...

Agroforestry systems (AFS) are complex to model mainly due to the high spatial variability induced by the shade trees. Recently, the microclimate and light heterogeneity issue in AFS has been addressed using the 3D ecophysiological process-based model MAESPA (Charbonnier et al., 2013; Vezy et al., 2018). MAESPA surpassed the classical sun/shade dic...

Wood production in fast‐growing Eucalyptus grandis trees is highly dependent on both potassium (K) fertilization and water availability but the molecular processes underlying wood formation in response to the combined effects of these two limiting factors remain unknown. E. grandis trees were submitted to four combinations of K‐fertilization and wa...

In a climate change context, changing temperature and precipitation pattern are expected to have strong impacts on Brazilian eucalyptus plantations. Implementing adaptive water-efficient management practices is thus becoming necessary to maintain high levels of productivity while preserving the water resources. This paper investigates the ability o...

The rapid expansion of rubber tree plantations in recent decades has been accompanied by dramatic negative ecological and social impacts. Rubber sector stakeholders consequently engaged in sustainable production of rubber. Despite the lack of harvest during the immature stage following planting, this period plays a key role in future yields. Manage...

Mixing N-fixing trees with eucalypts is an attractive option to improve the long-term soil N status in fast-growing plantations established in tropical soils. A randomized block design was replicated at four sites in Brazil to compare the biogeochemical cycles in mono-specific stands of Eucalyptus (100E) and Acacia mangium (100A) with mixed-species...

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...

Harvest residue management is a key issue for the sustainability of Eucalyptus plantations established on poor soils. Soil microbial communities contribute to soil fertility by the decomposition of the organic matter (OM), but little is known about the effect of whole-tree harvesting (WTH) in comparison to stem only harvesting (SOH) on soil microbi...

This study investigates how *Eucalyptus urograndis* fine roots uptake mobile nutrients in deep Ferralsols during the dry season, considering tree age and social status. Using **¹⁵N-NO₃⁻** injections at varying depths (0.1 to 15 m) in commercial plantations, the research found that dominant trees absorbed nitrates from deeper soil layers (up to 6 m)...

Extreme climatic events and depletion of phosphorus and potassium reserves threaten the productivity and survival of crops and planted forests. Deep root exploration is crucial for adaptation, as studies in Brazil show Eucalyptus roots reaching up to 17 m. Various methods, including isotopic tracers and modeling, revealed that low-density deep fine...

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 major factors driving greenhouse gas exchanges in forest soils (substrate supply, temperature, water content) vary with soil depth. Our study aimed to assess the effects of clear-cutting and drought on the temporal variability of CO2, CH4 and N2O fluxes throughout very deep soil profiles in Brazilian eucalypt plantations conducted in coppice. S...

No sudeste do Brasil, as mudanças climáticas têm-se refletido em alterações nos padrões de precipitação, aumentando a frequência e duração dos períodos secos. Por outro lado, a maior parte das áreas plantadas de Eucalyptus estão localizados em regiões submetidas a longos períodos de déficit hídrico. Como consequência, a produtividade dessas plantaç...

Background and aimsFine-root functioning is a major driver of plant growth and strongly influences the global carbon cycle. While fine-root over-yielding has been shown in the upper soil layers of mixed-species forests relative to monospecific stands, the consequences of tree diversity on fine-root growth in very deep soil layers is still unknown....

Key message: Inter-specific interactions with eucalypts in mixed plantations increased N2fixation rate of acacia trees compared to monocultures. N2fixation was higher during the wet summer than during the dry winter both in acacia monocultures and in mixed plantations. Context: Introducing N-fixing trees in fast-growing tropical plantations may con...

Although large amounts of potassium (K) are applied in tropical crops and planted forests, little is known about the interaction between K nutrition and water supply regimes on water resources in tropical regions. This interaction is a major issue because climate change is expected to increase the length of drought periods in many tropical regions...

Background and aims While the role of deep roots in major ecosystem services has been shown for tropical forests, there have been few direct measurements of fine root dynamics at depths of more than 2 m. The factors influencing root phenology remain poorly understood, creating a gap in the knowledge required for predicting the effects of climate ch...

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Expressiva área das plantações florestais de eucalipto de rápido crescimento no Brasil e em outras regiões do mundo encontra-se sob o efeito das mudanças climáticas, do estresse hídrico e da baixa fertilidade do solo, afetando o crescimento e a qualidade do lenho das árvores. O presente trabalho teve como objetivo avaliar a densidade aparente a 12%...

Climate models predict that the frequency, intensity and duration of drought events will increase in tropical regions. Although water withdrawal from deep soil layers is generally considered to be an efficient adaptation to drought, there is little information on the role played by deep roots in tropical forests. Tropical Eucalyptus plantations man...

Producing more food with less impact on ecosystem services such as the biogeochemical cycles of nutrients is a major challenge ahead of us. Some solutions to design a sustainable intensification of agroecosystems pertain in the understanding of rhizosphere ecology and biogeochemistry, as the root-soil interface is a major hotspot of biological acti...

Supplementary information from doi: 10.1111/1365-2435.12727

Background and Aims Fine roots play a major role in the global carbon cycle through respiration, exudation and decomposition processes, but their dynamics are poorly understood. Current estimates of root dynamics have principally been observed in shallow soil horizons (<1 m), and mainly in forest systems. We studied walnut (Juglans regia × nigra L....

Climatic conditions stimulates the cambial activity of plants, and cause significant changes in trunk diameter growth and wood characteristics. The objective of this study was to evaluate the influence of climate variables in the diameter growth rate of the stem and the wood density of Eucalyptus grandis trees in different classes of the basal area...

Understanding the consequences of changes in climatic and biological drivers on tree carbon and water fluxes is essential in forestry. Using a metamodeling approach, sensitivity and uncertainty analyses were carried out for a tree-scale model (MAESPA) to isolate the effects of climate, morphological and physiological traits, and intertree competiti...

Tropical tree plantations are rapidly expanding to meet the growing demand for wood and nonwood forest products. Current research—combining ecophysiology, genetics and functional genomics—aims to enhance the climate change mitigation role of these plantations and their adaptation. The positive effect of the increase in atmospheric carbon dioxide co...

Tropical tree plantations are rapidly expanding to meet the growing demand for wood and nonwood forest products. Current research-combining ecophysiology, genetics and functional genomics-aims to enhance the climate change mitigation role of these plantations and their adaptation. The positive effect of the increase in atmospheric carbon dioxide co...

Introduction Fine root dynamics control plant growth and development and play a major role in the global carbon cycle through the uptake of water and nutrients as well as respiration and decomposition processes. Fine root elongation rates and lifespan are in direct relation with soil water availability and soil temperature likely depending on seaso...

Potassium (K) is an important limiting factor of tree growth, but little is known of the effects of K supply on the long-distance transport of photosynthetic carbon (C) in the phloem and of the interaction between K fertilization and drought. We pulse-labelled 2-year-old Eucalyptus grandis L. trees grown in a field trial combining K fertilization (...