Nicolas Picard

In the context of global change, it is essential to quantify and monitor the carbon stored in forests. Allometric equations are mathematical models that predict the biomass of a tree from dendrometrical characteristics that are easier to measure, such as tree diameter, height, or wood density. Various model forms have been proposed for allometric e...

The development of high-resolution mapping models for forest attributes based on remote sensing data combined with machine or deep learning techniques has become a prominent topic in the field of forest observation and monitoring. This has resulted in the availability of multiple, sometimes conflicting, sources of information, but, at face value, i...

The density of wood is a key indicator of the carbon investment strategies of trees, impacting productivity and carbon storage. Despite its importance, the global variation in wood density and its environmental controls remain poorly understood, preventing accurate predictions of global forest carbon stocks. Here we analyse information from 1.1 mil...

Reconstructing past ecological population dynamics and demographic events is crucial for understanding the dynamics of ecological processes, evaluating the impact of environmental changes and making informed conservation decisions. In forest ecosystems, retrodiction (i.e. the backward projection of ecological populations) plays a pivotal role in un...

A decade of French support to Mediterranean forests under the FAO committee Silva Mediterranea has resulted in establishing strategic approaches for Mediterranean forests, improving stakeholder engagement, consolidating information on Mediterranean forests, and developing and implementing several regional projects in line with the priorities set ou...

In a context of global change, it is essential to quantify and monitor the carbon stored in forests. Allometric equations are mathematical models that predict the biomass of a tree from dendrometrical characteristics that are easier to measure, such as tree diameter, height or wood density. Various model forms have been proposed for allometric equa...

A vast silvicultural experiment was set up in 1982 nearby the town of M’Baïki in the Central African Republic to monitor the recovery of tropical forests after disturbance. The M’Baïki experiment consists of ten 4-ha Permanent Sample Plots (PSPs) that were assigned to three silvicultural treatments in 1986 according to a random block design. In eac...

The development of high-resolution mapping models for forest attributes based on remote sensing data combined with machine or deep learning techniques, has become a prominent topic in the field of forest observation and monitoring. This has resulted in an extensive availability of multiple sources of information, which can either lead to a potentia...

The understanding of tree growth processes is crucial for promoting sustainable forest management strategies. This is a challenging task in highly biodiverse ecosystems where many tree species are observed on very few individuals and the small sample sizes hinder a good fit of species‐specific models. We propose the use of finite mixture of random...

The emergence of alternative stable states in forest systems has significant implications for the functioning and structure of the terrestrial biosphere, yet empirical evidence remains scarce. Here, we combine global forest biodiversity observations and simulations to test for alternative stable states in the presence of evergreen and deciduous for...

Introduction Mounting evidence suggests that geographic ranges of tree species worldwide are shifting under global environmental changes. Little is known, however, about if and how these species’ range shifts may trigger the range shifts of various types of forests. Markowitz’s portfolio theory of investment and its broad application in ecology sug...

ID Article | Alain-Ref1-2-18ajiras220224 | RESUME Introduction : Les forêts tropicales jouent un rôle clé dans la lutte contre le changement climatique en stockant d'importantes quantités de biomasse et de carbone. Cependant, l'estimation de la biomasse totale des peuplements forestiers reste incertaine car certains compartiments ne sont pas toujou...

Many allometric models to predict tree aboveground biomass have been developed in tropical moist forests, but few models are available for tree belowground biomass. Theory predicts that belowground biomass scales in an isometric way with aboveground biomass. Estimates of belowground biomass could then be derived from aboveground biomass using the r...

The density of wood is a key indicator of trees’ carbon investment strategies, impacting productivity and carbon storage. Despite its importance, the global variation in wood density and its environmental controls remain poorly understood, preventing accurate predictions of global forest carbon stocks. Here, we analyze information from 1.1 million...

Forests are a substantial terrestrial carbon sink, but anthropogenic changes in land use and climate have considerably reduced the scale of this system¹. Remote-sensing estimates to quantify carbon losses from global forests2–5 are characterized by considerable uncertainty and we lack a comprehensive ground-sourced evaluation to benchmark these est...

Understanding what controls global leaf type variation in trees is crucial for comprehending their role in terrestrial ecosystems, including carbon, water and nutrient dynamics. Yet our understanding of the factors influencing forest leaf types remains incomplete, leaving us uncertain about the global proportions of needle-leaved, broadleaved, ever...

Determining the drivers of non-native plant invasions is critical for managing native ecosystems and limiting the spread of invasive species1,2. Tree invasions in particular have been relatively overlooked, even though they have the potential to transform ecosystems and economies3,4. Here, leveraging global tree databases5-7, we explore how the phy...

The Governing Missions and Mission-Oriented Research and Innovation in the European Union guidelines promoted by the European Commission (EC) are helpful as a starting place for creating the enabling environment for BioCities which follow the principles of natural ecosystems to promote life (Mazzucato 2018, 2019). The strength of mission-oriented p...

A broad consensus has been reached on the need to adapt the management of our forests to the context of the rapidly changing climate, which resulted in the development of numerous models capable of simulating the impact of the climate change on the forest. The primary goal of this specific endeavor is to propose a novel framework of comparative ana...

1. Biodiversity is an important component of natural ecosystems, with higher species richness often correlating with an increase in ecosystem productivity. Yet, this relationship varies substantially across environments, typically becoming less pronounced at high levels of species richness. However, species richness alone cannot reflect all importa...

A study based on spatial distribution of Scorodophloeus zenkeri was performed in the device 400ha Biaro forest. Both specie has multiple uses, including industrial exploitation by the quality of wood. An inventory of the forest potential of these specie were made based on values in abscissa (x) and ordonna (y) for all individuals. At the end of thi...

Tree height and crown area are important predictors of aboveground biomass but difficult to measure on the ground. Numerous allometric models have been established to predict tree height from diameter (H–D) and crown area from diameter (CA–D). A major challenge is to select the most precise and accurate allometric model among existing ones, dependi...

Marginal and peripheral populations are important for biodiversity conservation. Their original situation in a species’ geographic and ecological space often confers them genetic diversity and traits of high adaptive value. Yet theoretical hypotheses related to marginality are difficult to test because of confounding factors that influence marginal...

The latitudinal diversity gradient (LDG) is one of the most recognized global patterns of species richness exhibited across a wide range of taxa. Numerous hypotheses have been proposed in the past two centuries to explain LDG, but rigorous tests of the drivers of LDGs have been limited by a lack of high-quality global species richness data. Here we...

Purpose of Review Recognizing that in the context of global change, tree genetic diversity represents a crucial resource for future forest adaptation, we review and highlight the major forest genetics research achievements of the past decades in biodiversity-rich countries of the Mediterranean region. For this, we conducted a bibliometric analysis...

One of the most fundamental questions in ecology is how many species inhabit the Earth. However, due to massive logistical and financial challenges and taxonomic difficulties connected to the species concept definition, the global numbers of species, including those of important and well-studied life forms such as trees, still remain largely unknow...

Significance Tree diversity is fundamental for forest ecosystem stability and services. However, because of limited available data, estimates of tree diversity at large geographic domains still rely heavily on published lists of species descriptions that are geographically uneven in coverage. These limitations have precluded efforts to generate a g...

Le plan France Relance lancé en septembre 2020 prévoit des mesures forestières sur 2 ans, avec un accent sur la reconstitution des peuplements forestiers sinistrés, affaiblis par les sécheresses ou attaqués par les scolytes. Cependant la crise forestière liée au changement climatique est partie pour durer et les efforts sur les connaissances à acqu...

When ordinating plots of tropical rain forests using stand-level structural attributes such as biomass, basal area and the number of trees in different size classes, two patterns often emerge: a gradient from poorly to highly stocked plots and high positive correlations between biomass, basal area and the number of large trees. These patterns are i...

Several of the Sustainable Development Goals (SDGs) defined in the 2030 Agenda for Sustainable Development of the United Nations are relevant for Mediterranean pine and mixed forests, especially those related to the restoration of degraded forest ecosystems and to climate change mitigation and adaptation. Because Mediterranean forests are an import...

General patterns that are observed in forests irrespective of their ecological biome or species composition are indicators of general biological processes that drive forest dynamics. Modelling can be used to infer these processes by identifying the minimum set of rules that generate the observed patterns. The regular spatial pattern of the largest...

• Key message A recent paper by Ceccherini et al.( 2020a ) reported an abrupt increase of 30% in the French harvested forest area in 2016–2018 compared to 2004–2015. A re-analysis of their data rather led us to conclude that, when accounting for the singular effect of storm Klaus, the rate of change in harvested area depended on the change year use...

Mapping aboveground forest biomass is central for assessing the global carbon balance. However, current large-scale maps show strong disparities, despite good validation statistics of their underlying models. Here, we attribute this contradiction to a flaw in the validation methods, which ignore spatial autocorrelation (SAC) in data, leading to ove...

La consommation par la France de produits agricoles importés est susceptible d'induire une demande de terres agricoles supplémentaires dans les pays producteurs, donc de la conversion de forêts en terres agricoles : c'est la déforestation importée. La mise en œuvre de la Stratégie nationale de lutte contre la déforestation importée (SNDI) mise en p...

The impacts of logging on the recovery of timber stocks are still largely unknown in Central Africa due to the lack of data on the dynamics of the tree populations concerned. This is particularly the case for Azobé, Lophira alata, a commercially valuable timber species. This study had a twofold aim: (i) to quantify the effects of the forest type an...

The impacts of logging on the recovery of timber stocks are still largely unknown in Central Africa due to the lack of data on the dynamics of the tree populations concerned. This is particularly the case for Azobé, Lophira alata, a commercially valuable timber species. This study had a twofold aim: (i) to quantify the effects of the forest type an...

Tropical rain forests worldwide are affected by anthropogenic disturbances, and secondary forests that develop afterwards are often dominated by pioneer tree species, but the consequences of different anthropogenic disturbances on nutrient cycling are poorly understood. Because most nutrient cycling in tropical rain forests occurs through litterfal...

New IUFRO Task Force presentation at the Iufro Board Enlarged Meeting, held in Curitiba (Brasil) on 26-27 September 2019.

In this Letter, a middle initial and additional affiliation have been added for author G. J. Nabuurs; two statements have been added to the Supplementary Acknowledgements; and a citation to the French National Institute has been added to the Methods; see accompanying Author Correction for further details.

Forests bear the historical legacies of human activities over thousands of years, including agriculture, trade, disease and resource extraction. Many of these activities may represent indices of the proposed geological epoch of the Anthropocene. Modifications to soil, topography and vegetation evidence anthropogenic influences. Yet studies of veget...

Questions We examined the spatial patterns of dominant canopy species in a tropical forest to investigate: 1) what is the niche occupancy of canopy species with respect to topographic gradients? 2) what are the dominant ecological processes that explain their distribution? 3) what are the interactions among the most prevalent canopy species? and 4)...

The architecture (here, the size distribution combined with the spatial pattern of individuals) of natural forest at demographic equilibrium can be used to infer the demographic processes that drive the forest dynamics. In particular, a constant growth rate and a constant mortality rate for all trees would generate an exponential distribution of th...

2019, The Author(s), under exclusive licence to Springer Nature Limited. In this Letter, the middle initial of author G. J. Nabuurs was omitted, and he should have been associated with an additional affiliation: ‘Forest Ecology and Forest Management Group, Wageningen University and Research, Wageningen, The Netherlands’ (now added as affiliation 18...

A spatially explicit global map of tree symbioses with nitrogen-fixing bacteria and mycorrhizal fungi reveals that climate variables are the primary drivers of the distribution of different types of symbiosis.

Impacts of climate change on the future dynamics of Central African forests are still largely unknown, despite the acuteness of the expected changes and the extent of these forests. The high diversity of species and the potentially equivalent diversity of responses to climate modifications are major difficulties encountered when using predictive mo...

The spatial distribution of biomass is key to optimize forest inventory designs to estimate forest aboveground biomass. Point process theory sets an appropriate mathematical framework to model the spatial distribution of trees, then to derive analytical expressions for the relationship between the variance of biomass in plots and the characteristic...

The estimation and monitoring of the huge amount of carbon contained in tropical forests, and specifically in the above-ground biomass (AGB) of trees, is needed for the successful implementation of climate change mitigation strategies. Its accuracy depends on the availability of reliable allometric equations to convert forest inventory data into AG...

This chapter aims to demonstrate the particular relevance of Mediterranean forests to the global agenda and how they can contribute, in view of their particularities, to fulfilling international commitments on the environment.

The State of Mediterranean Forests 2018 analyzes the circum-Mediterranean region, a territory encompassing thirty-one countries and a wide range of political, economic, social and environmental contexts. The region has an extremely rich natural and cultural heritage. Here, human and economic development is largely dependent on at times scarce natur...

Species distribution maps are often lacking for scientific investigation and strategic management planning at international level. Here, we present the range-wide, natural distribution maps of twenty-four Mediterranean and European forest-tree species of key ecological and economic importance in the Mediterranean. Dataset access: https://doi.org/10...

Tree allometric equations that are used to predict the biomass of a tree from its dendrometrical characteristics are key elements for the estimation of forest carbon stocks. Few equations compared to the diversity of forest ecosystems are currently available for the tropical forests of the Congo Basin. Pantropical equations are available but a pend...

The Mediterranean region includes 13 countries among Europe, Near Orient, and Africa. This area is a huge "hot spot" of cultures, religions, socio-economical situations, and of habitats and biodiversity. The report illustrates the geographical and ecological features of the region. Forest ecosystems and vegetation traits, with particular focus on f...

Details on how the maps were produced are given in a published report: N. Wazen, B. Fady (2016) Geographic distribution of 24 major tree species in the Mediterranean and their genetic resources, FAO and Plan Bleu, ISBN 978-92-5-109469-3 This data set received financial support from the French Facility for Global Environment (FFEM) under the regiona...

Griffith et al. do not question the quality of our analysis, but they question our results with respect to the definition of forest we employed. In our response, we explain why the differences we report result from a difference of technique and not of definition, and how anyone can adapt-as we did-our data set to any forest definition and tree cove...

De la Cruz et al. question the reliability of our results, claiming that we do not refer to the most appropriate spatial extent of drylands. In our response, we explain why we chose an existing and internationally recognized delineation of drylands among several options, and why our findings are due to a difference of remote sensing technique and n...

In the Congo Basin where nearly 20 million ha of concessions are exploited according to management plans, improved forest management (IFM) has become a strategy of prime importance when setting up the REDD+ mechanism. For logging companies, REDD+ projects provide the opportunity to compensate a voluntary reduction of the logging intensity by valuin...

Schepaschenko et al. question our findings, claiming that we did not refer to all existing maps and that we did not account for all sources of uncertainty. In our response, we detail our selection criteria for reference maps, which clarify why the work of Schepaschenko et al. was not used, and we explain why our uncertainty assessment is complete a...

Drivers of forest structure in central African rain forests are largely unknown. Using forest inventory data (3024 0.4-ha plots) in a forest concession of 154 456 ha in north-eastern Gabon covering an altitudinal gradient (from 485 to 1009 m asl), relationships between above-ground plot biomass and environmental variables (soil type, altitude, slop...

In order to circumscribe the breeding sites of stomoxes in the Makokou region, eight potentially favorable environments were sampled from January to June 2007 in three habitats: primary and secondary forest (natural environments) and the anthropic environment (artificial or disturbed areas). In the primary forest, three types of substrates were col...

Mapping the world's dry forests The extent of forest area in dryland habitats, which occupy more than 40% of Earth's land surface, is uncertain compared with that in other biomes. Bastin et al. provide a global estimate of forest extent in drylands, calculated from high-resolution satellite images covering more than 200,000 plots. Forests in drylan...

Patterns in above-ground biomass of tropical forests over short altitudinal gradients are poorly known. The aim of this study was to investigate the variation of above-ground biomass with altitude in old-growth forests and determine the importance of changes in floristic composition as a cause of this variation. We used a dataset from 15 1-ha perma...

Global biodiversity and productivity The relationship between biodiversity and ecosystem productivity has been explored in detail in herbaceous vegetation, but patterns in forests are far less well understood. Liang et al. have amassed a global forest data set from >770,000 sample plots in 44 countries. A positive and consistent relationship can be...

Tropical forests in Africa store large amounts of carbon and there is an urgent need for accurate methods to estimate this important carbon stock. One method to achieve this is by allometric equations but in many forest ecosystems in Africa these have not been developed. This study combined biomass data of 896 trees from five tropical countries in...

Key message Liocourt’s legacy for the law on steady-state uneven-aged forests has been questioned. We propose a new interpretation of his results published in 1898 and refer to a manuscript dated 1900 to clarify that he established this law. Context Liocourt’s law states that in steady-state uneven-aged forests, the number of trees in successive di...

The implementation of forest-based projects to mitigate greenhouse gas emissions requires the estimation of emission factors (here the difference in biomass stocks between two forest types). The estimation of these quantities using forest inventory data and allometric models implies different sources of errors that need to be prioritized to improve...

The choice of biomass and volume models is one of the main sources of uncertainty in forest biomass assessment. The quality of the dataset used to develop the equations, the statistical procedures used for modelling and the accuracy in reporting the results vary greatly among the models. Recent studies highlighted that about 25% of the published eq...

Estimating tree and forest biomass is a cornerstone of forest resource assessment. In addition to its application in forest-related commerce, forest resource assessment is becoming increasingly crucial in light of continued global deforestation and climate change. The most frequently used methods for estimating forest biomass involve allometric equ...

Key message Improving the precision of forest biomass estimates requires prioritizing the different sources of errors. In a tropical moist forest in central Africa, the choice of the allometric equation was found to be the main source of error. Context When estimating the forest biomass at the landscape level using forest inventory data and allo...

Motivated by the analysis of the impact of ecological processes on spatial distribution of tree species, we introduce in this paper a novel approach to detect spatial cluster of points. Our procedure is based on an iterative transformation of the distance between points into a measure of closeness. Our measure has the advantage of being independent...

While attention on logging in the tropics has been increasing, studies on the long-term effects of silviculture on forest dynamics and ecology remain scare and spatially limited. Indeed, most of our knowledge on tropical forests arises from studies carried out in undisturbed tropical forests. This bias is problematic given that logged and disturbed...

Many forest growth models use plot-level variables, such as stem density or basal area, as predictors. Even if these variables are area-based, so that their expectations do not change with plot size when expressed per unit of area, a change in plot size may induce a prediction bias if the growth model is nonlinear with respect to these variables. I...

Understanding how environmental factors could impact population dynamics is of primary importance for species conservation. Matrix population models are widely used to predict population dynamics. However, in species-rich ecosystems with many rare species, the small population sizes hinder a good fit of species-specific models. In addition, classic...

A large proportion of the tropical rain forests of central Africa undergo periodic selective logging for timber harvesting. The REDD+ mechanism could promote less intensive logging if revenue from the additional carbon stored in the forest compensates financially for the reduced timber yield. Carbon stocks, and timber yields, and their associated v...

Matrix population models are widely used to study population dynamics but have been criticized because their outputs are sensitive to the dimension of the matrix (or, equivalently, to the class width). This sensitivity is concerning for the population growth rate ([Formula: see text]) because this is an intrinsic characteristic of the population th...

Predicting the biomass of a forest stand using forest inventory data and allometric equations involves a chain of propagation of errors going from the sampling error to the tree measurement error. Using a biomass data set of 101 trees in a tropical rain forest in Gabon, we compared two sources of error: the error due to the choice of allometric equ...