Résumé

Key message Forest disturbance affects the within-population distribution of genetic diversity, but not its overall levels, in a tropical pioneer tree species. In particular, clumps of related saplings with impoverished diversity are found in canopy gaps but not under forest cover. Context Forest disturbances can have long-term consequences on the genetic structure of tree populations, because they can alter the demographic properties of the regeneration process and favour some subpopulations/genotypes, both by stochastic processes and by selection. Intermediate disturbances tend to favour species diversity, at least in highly diverse communities, but their effect on intra-specific diversity is unknown. Aims In this study, we have looked at the genetic consequences of forest disturbance in a stand of the long-lived Neotropical pioneer species, Jacaranda copaia. Methods The study site was experimentally logged in 1984, and the canopy gaps generated by the logging were mapped. Seedlings of J. copaia colonised the gaps, as expected, at a higher density than in the surrounding forest. In 2006, we exhaustively sampled all saplings and adult trees available in a 25-ha area. The samples were genotyped at nine microsatellite loci, and the distribution of genetic diversity was inspected by analyses of spatial autocorrelation, automated Bayesian assignment and comparisons of diversity between cohorts by bootstrap (RaBoT). Results Spatial autocorrelation was found to extend farther in post-disturbance saplings than in the undisturbed population (100 m and beyond versus less than 50 m), and divergent clumps (F ST = 0.05) of related genotypes were found; genetic diversity was found to be impoverished in each clump relative to the global population at about half of the loci. Conclusion Overall, our results suggest that forest disturbance has changed the patterns of distribution of genetic diversity, with potential consequences on long-term population viability.

Auteurs, date et publication :

Auteurs Thomas Leclerc , Ruppert Vimal , Valérie Troispoux , Sophie Périgon , Ivan Scotti

Publication : Annals of Forest Science

Date : 2015

Volume : 72

Issue : 5

Pages : 509–516

Catégorie(s)

#CIRAD #FORET Paracou

Auteurs, date et publication :

Auteurs Stephan Hättenschwiler , Sylvain Coq , Sandra Barantal , Ira Tanya Handa

Publication : New Phytologist

Date : 2011

Volume : 189

Issue : 4

Pages : 950–965

Catégorie(s)

#CIRAD #FORET Paracou

Résumé

Abundant Neotropical canopy-tree species are more resistant to drought-induced branch embolism than what is currently admitted. Large hydraulic safety margins protect them from hydraulic failure under actual drought conditions.

Auteurs, date et publication :

Auteurs Camille Ziegler , Sabrina Coste , Clément Stahl , Sylvain Delzon , Sébastien Levionnois , Jocelyn Cazal , Hervé Cochard , Adriane Esquivel-Muelbert , Jean-Yves Goret , Patrick Heuret , Gaëlle Jaouen , Louis S. Santiago , Damien Bonal

Publication : Annals of Forest Science

Date : 2019

Volume : 76

Issue : 4

Pages : 115

Catégorie(s)

#ANR-Citation #CIRAD #FORET Paracou

Résumé

The sequence of key water potential thresholds from the onset of water stress to mortality, and the timing of stomatal closure with regard to leaf xylem embolism formation are essential to characterizing plant adaptive strategies to drought. This constitutes a critical knowledge gap for tropical rainforest species, which may be less vulnerable to drought than previously thought. We recorded key leaf and stem water potential thresholds, leaf hydraulic safety margins (HSMleaf), leaf stomatal safety margins (SSMleaf) and estimated native embolism levels during a normal-intensity dry season across 18 neotropical rainforest tree species. We also solved a sequence of key water potential thresholds. Additionally, we provide a cross-biome analysis of SSMleaf encompassing 97 species from four major biomes based on a literature survey. In the studied rainforest species, leaf turgor loss point, used as a surrogate for stomatal closure, typically occurred before the onset of leaf xylem embolism. Most species exhibited positive HSMleaf and SSMleaf, with contrasting values across species and nearly absent embolism levels during the dry season irrespective of the experienced midday leaf water potentials. Our results point out that leaf xylem embolism is not routine for Neotropical rainforest tree species. Based on our proposal of the water potential sequence for tropical rainforest trees, we argue that leaf xylem embolism is a rare event for these species. This was supported by the literature survey, indicating that across biomes, most woody species have rather large SSMleaf and that leaves of tropical rainforest trees are not necessarily more vulnerable than in other biomes. However, we found evidence that some tropical rainforest species may be more vulnerable than others to ongoing climate change. Our data provide an opportunity to parametrize tree-based or land-surface models for tropical rainforests. Read the free Plain Language Summary for this article on the Journal blog.

Auteurs, date et publication :

Auteurs Camille Ziegler , Sébastien Levionnois , Damien Bonal , Patrick Heuret , Clément Stahl , Sabrina Coste

Publication : Functional Ecology

Date : 2025

Volume : 37

Issue : 6

Pages : 1717–1731

Catégorie(s)

#CIRAD #FORET Paracou

Résumé

Natural disturbance is a fundamental component of the functioning of tropical rainforests let to natural dynamics, with tree mortality the driving force of forest renewal. With ongoing global (i.e. land-use and climate) changes, tropical forests are currently facing deep and rapid modifications in disturbance regimes that may hamper their recovering capacity so that developing robust predictive model able to predict ecosystem resilience and recovery becomes of primary importance for decision-making: (i) Do regenerating forests recover faster than mature forests given the same level of disturbance? (ii) Is the local topography an important predictor of the post-disturbance forest trajectories? (iii) Is the community functional composition, assessed with community weighted-mean functional traits, a good predictor of carbon stock recovery? (iv) How important is the climate stress (seasonal drought and/or soil water saturation) in shaping the recovery trajectory? Paracou is a large scale forest disturbance experiment set up in 1984 with nine 6.25 ha plots spanning on a large disturbance gradient where 15 to 60% of the initial forest ecosystem biomass were removed. More than 70,000 trees belonging to ca. 700 tree species have then been censused every 2 years up today. Using this unique dataset, we aim at deciphering the endogenous (forest structure and composition) and exogenous (local environment and climate stress) drivers of ecosystem recovery in time. To do so, we disentangle carbon recovery into demographic processes (recruitment, growth, mortality fluxes) and cohorts (recruited trees, survivors). Variations in the pre-disturbance forest structure or in local environment do not shape significantly the ecosystem recovery rates. Variations in the pre-disturbance forest composition and in the post-disturbance climate significantly change the forest recovery trajectory. Pioneer-rich forests have slower recovery rates than assemblages of late-successional species. Soil water saturation during the wet season strongly impedes ecosystem recovery but not seasonal drought. From a sensitivity analysis, we highlight the pre-disturbance forest composition and the post-disturbance climate conditions as the primary factors controlling the recovery trajectory. Highly-disturbed forests and secondary forests because they are composed of a lot of pioneer species will be less able to cope with new disturbance. In the context of increasing tree mortality due to both (i) severe droughts imputable to climate change and (ii) human-induced perturbations, tropical forest management should focus on reducing disturbances by developing Reduced Impact Logging techniques.

Auteurs, date et publication :

Auteurs Bruno Hérault , Camille Piponiot

Publication : Forest Ecosystems

Date : 2018

Volume : 5

Issue : 1

Pages : 2

Catégorie(s)

#CIRAD #FORET Paracou

Résumé

Climate models predict a range of changes in tropical forest regions, including increased average temperatures, decreased total precipitation, reduced soil moisture and alterations in seasonal climate variations. These changes are directly related to the increase in anthropogenic greenhouse gas concentrations, primarily CO2. Assessing seasonal forest growth responses to climate is of utmost importance because woody tissues, produced by photosynthesis from atmospheric CO2, water and light, constitute the main component of carbon sequestration in the forest ecosystem. In this paper, we combine intra-annual tree growth measurements from published tree growth data and the corresponding monthly climate data for 25 pan-tropical forest sites. This meta-analysis is designed to find the shared climate drivers of tree growth and their relative importance across pan-tropical forests in order to improve carbon uptake models in a global change context. Tree growth reveals significant intra-annual seasonality at seasonally dry sites or in wet tropical forests. Of the overall variation in tree growth, 28.7% was explained by the site effect, i.e. the tree growth average per site. The best predictive model included four climate variables: precipitation, solar radiation (estimated with extrasolar radiation reaching the atmosphere), temperature amplitude and relative soil water content. This model explained more than 50% of the tree growth variations across tropical forests. Precipitation and solar radiation are the main seasonal drivers of tree growth, causing 19.8% and 16.3% of the tree growth variations. Both have a significant positive association with tree growth. These findings suggest that forest productivity due to tropical tree growth will be reduced in the future if climate extremes, such as droughts, become more frequent.

Auteurs, date et publication :

Auteurs Fabien Wagner , Vivien Rossi , Mélaine Aubry-Kientz , Damien Bonal , Helmut Dalitz , Robert Gliniars , Clément Stahl , Antonio Trabucco , Bruno Hérault , Morag Mcdonald

Publication : Plos One

Date : 2014

Volume : 9

Issue : 3

Pages : e92337

Catégorie(s)

#CIRAD #FORET Paracou

Résumé

Although ongoing research has revealed some of the main drivers behind global spatial patterns of microbial communities, spatio-temporal dynamics of these communities still remain largely unexplored. Here, we investigate spatio-temporal variability of both bacterial and eukaryotic soil microbial communities at local and intercontinental scales. We compare how temporal variation in community composition scales with spatial variation in community composition, and explore the extent to which bacteria, protists, fungi and metazoa have similar patterns of temporal community dynamics. All soil microbial groups displayed a strong correlation between spatial distance and community dissimilarity, which was related to the ratio of organism to sample size. Temporal changes were variable, ranging from equal to local between-sample variation, to as large as that between communities several thousand kilometers apart. Moreover, significant correlations were found between bacterial and protist communities, as well as between protist and fungal communities, indicating that these microbial groups change in tandem, potentially driven by interactions between them. We conclude that temporal variation can be considerable in soil microbial communities, and that future studies need to consider temporal variation in order to reliably capture all drivers of soil microbiome changes.

Auteurs, date et publication :

Auteurs Johan De Gruyter , James T Weedon , Stéphane Bazot , Steven Dauwe , Pere-Roc Fernandez-Garberí , Stefan Geisen , Louis Gourlez De La Motte , Bernard Heinesch , Ivan A Janssens , Niki Leblans , Tanguy Manise , Romà Ogaya , Mikaell Ottosson Löfvenius , Josep Peñuelas , Bjarni D Sigurdsson , Gaëlle Vincent , Erik Verbruggen

Publication : FEMS Microbiology Ecology

Date : 2020

Volume : 96

Issue : fiaa018

Catégorie(s)

#CIRAD #CNRS #FORET Nouragues #FORET Paracou

Résumé

Unoccupied aerial vehicle laser scanning (UAV-LS) has been increasingly used for forest structure assessment in recent years due to the potential to directly estimate individual tree attributes and availability of commercial solutions. However, standardised procedures for campaign planning are still largely missing. This study investigated scanner properties and flight planning to provide recommendations on minimising forest canopy occlusion and thereby maximise exploration of canopy volume. A flight campaign involving two UAV-LS systems was conducted over a dense, wet tropical forest at the Paracou research station (French Guiana). Four experiments on scanner properties and flight planning were conducted, analysed and recommendations derived. First, the scanner pulse repetition rate (PRR) should be at least 100 kHz per 1 m s−1 flight speed based on 360° FOV for exploration of middle canopy strata (5 m to 20 m). Higher PRR are beneficial for exploration of lower canopy (<5 m) but would need to be increased exponentially to achieve linear improvement. Alternatively, flight speed could be reduced within the constraints given by the inertial measurement unit (IMU), but would increase flight time. Second, the scanner maximum range was identified as a proxy for the laser pulse power, which positively impacts canopy exploration. This was particularly the case when using multi-return capabilities. No saturation could be observed when increasing the laser power, suggesting that this is currently a limiting factor. Additionally, a smaller laser beam divergence and pulse width were plausible reasons for better exploration of the upper canopy just below the top of canopy. Third, off-nadir scanning angles up to 20° were found to result in similar occlusions, suggesting a practical FOV of 40° in the investigated dense forest. This number might be larger for open canopies. UAV-LS systems with viewing geometries that focus laser pulses downwards and within optimal ranges should be preferred. Fourth, using different horizontal flight directions in the mission planning favours minimisation of occlusion. A minimum of two different flight directions is suggested. However, specific optimal yaw angles were not possible to predict before flight. Therefore, including multiple directions ensures coverage of all possible configurations. Many of these investigated features can be optimised independently from each other, and should be considered before acquisition of new UAV-LS systems and flight mission planning. These results support the establishment of general guidelines for the investment in UAV-LS systems and optimal mission planning for forest structure assessment.

Auteurs, date et publication :

Auteurs Benjamin Brede , Harm M. Bartholomeus , Nicolas Barbier , François Pimont , Grégoire Vincent , Martin Herold

Publication : International Journal of Applied Earth Observation and Geoinformation

Date : 2022

Volume : 114

Pages : 103056

Catégorie(s)

#CIRAD #FORET Paracou

Résumé

There is increasing evidence to suggest that soil nutrient availability can limit the carbon sink capacity of forests, a particularly relevant issue considering today’s changing climate. This question is especially important in the tropics, where most part of the Earth’s plant biomass is stored. To assess whether tropical forest growth is limited by soil nutrients and to explore N and P limitations, we analyzed stem growth and foliar elemental composition of the five stem widest trees per plot at two sites in French Guiana after 3 years of nitrogen (N), phosphorus (P), and N + P addition. We also compared the results between potential N-fixer and non-N-fixer species. We found a positive effect of N fertilization on stem growth and foliar N, as well as a positive effect of P fertilization on stem growth, foliar N, and foliar P. Potential N-fixing species had greater stem growth, greater foliar N, and greater foliar P concentrations than non-N-fixers. In terms of growth, there was a negative interaction between N-fixer status, N + P, and P fertilization, but no interaction with N fertilization. Because N-fixing plants do not show to be completely N saturated, we do not anticipate N providing from N-fixing plants would supply non-N-fixers. Although the soil-age hypothesis only anticipates P limitation in highly weathered systems, our results for stem growth and foliar elemental composition indicate the existence of considerable N and P co-limitation, which is alleviated in N-fixing plants. The evidence suggests that certain mechanisms invest in N to obtain the scarce P through soil phosphatases, which potentially contributes to the N limitation detected by this study.

Auteurs, date et publication :

Auteurs Helena Vallicrosa , Laynara F. Lugli , Lucia Fuchslueger , Jordi Sardans , Irene Ramirez‐Rojas , Erik Verbruggen , Oriol Grau , Laëtitia Bréchet , Guille Peguero , Leandro Van Langenhove , Lore T. Verryckt , César Terrer , Joan Llusià , Romà Ogaya , Laura Márquez , Pere Roc‐Fernández , Ivan Janssens , Josep Peñuelas

Publication : Ecology

Date : 2025

Volume : 104

Issue : 6

Pages : e4049

Catégorie(s)

#CIRAD #CNRS #FORET Nouragues #FORET Paracou

Auteurs, date et publication :

Auteurs Mauro Mariotti D'Alessandro , Stefano Tebaldini , Fabio Rocca

Publication : IEEE Transactions on Geoscience and Remote Sensing

Date : 2013

Volume : 51

Issue : 8

Pages : 4430–4437

Catégorie(s)

#CIRAD #FORET Paracou