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[hal-02434220] TRY plant trait database – enhanced coverage and open access
Plant traits-the morphological, anatomical, physiological, biochemical and phenological characteristics of plants-determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration , biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait-based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits-almost complete coverage for 'plant growth form'. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait-environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives.
ano.nymous@ccsd.cnrs.fr.invalid (Jens Kattge) 09 Nov 2020
https://amu.hal.science/hal-02434220
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[hal-02541780] Carbon-nitrogen interactions in European forests and semi-natural vegetation - Part 1: Fluxes and budgets of carbon, nitrogen and greenhouse gases from ecosystem monitoring and modelling
The impact of atmospheric reactive nitrogen (Nr) deposition on carbon (C) sequestration in soils and biomass of unfertilized, natural, semi-natural and forest ecosystems has been much debated. Many previous results of this dC∕dN response were based on changes in carbon stocks from periodical soil and ecosystem inventories, associated with estimates of Nr deposition obtained from large-scale chemical transport models. This study and a companion paper (Flechard et al., 2020) strive to reduce uncertainties of N effects on C sequestration by linking multi-annual gross and net ecosystem productivity estimates from 40 eddy covariance flux towers across Europe to local measurement-based estimates of dry and wet Nr deposition from a dedicated collocated monitoring network. To identify possible ecological drivers and processes affecting the interplay between C and Nr inputs and losses, these data were also combined with in situ flux measurements of NO, N2O and CH4 fluxes; soil NO−3 leaching sampling; and results of soil incubation experiments for N and greenhouse gas (GHG) emissions, as well as surveys of available data from online databases and from the literature, together with forest ecosystem (BASFOR) modelling.
ano.nymous@ccsd.cnrs.fr.invalid (Chris Flechard) 15 Jul 2020
https://hal.inrae.fr/hal-02541780
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[hal-02650649] Long-term thermal sensitivity of Earth’s tropical forests
The sensitivity of tropical forest carbon to climate is a key uncertainty in predicting global climate change. Although short-term drying and warming are known to affect forests, it is unknown if such effects translate into long-term responses. Here, we analyze 590 permanent plots measured across the tropics to derive the equilibrium climate controls on forest carbon. Maximum temperature is the most important predictor of aboveground biomass (−9.1 megagrams of carbon per hectare per degree Celsius), primarily by reducing woody productivity, and has a greater impact per °C in the hottest forests (>32.2°C). Our results nevertheless reveal greater thermal resilience than observations of short-term variation imply. To realize the long-term climate adaptation potential of tropical forests requires both protecting them and stabilizing Earth’s climate.
ano.nymous@ccsd.cnrs.fr.invalid (Martin J P Sullivan) 29 May 2020
https://hal.umontpellier.fr/hal-02650649
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[hal-03778635] The FLUXNET2015 dataset and the ONEFlux processing pipeline for eddy covariance data
The FLUXNET2015 dataset provides ecosystem-scale data on CO 2 , water, and energy exchange between the biosphere and the atmosphere, and other meteorological and biological measurements, from 212 sites around the globe (over 1500 site-years, up to and including year 2014). These sites, independently managed and operated, voluntarily contributed their data to create global datasets. Data were quality controlled and processed using uniform methods, to improve consistency and intercomparability across sites. The dataset is already being used in a number of applications, including ecophysiology studies, remote sensing studies, and development of ecosystem and Earth system models. FLUXNET2015 includes derived-data products, such as gap-filled time series, ecosystem respiration and photosynthetic uptake estimates, estimation of uncertainties, and metadata about the measurements, presented for the first time in this paper. In addition, 206 of these sites are for the first time distributed under a Creative Commons (CC-BY 4.0) license. This paper details this enhanced dataset and the processing methods, now made available as open-source codes, making the dataset more accessible, transparent, and reproducible.
ano.nymous@ccsd.cnrs.fr.invalid (Gilberto Pastorello) 16 Sep 2022
https://hal.science/hal-03778635
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[hal-02942642] Sensitivity of gross primary productivity to climatic drivers during the summer drought of 2018 in Europe
In summer 2018, Europe experienced a record drought, but it remains unknown how the drought affected ecosystem carbon dynamics. Using observations from 34 eddy covariance sites in different biomes across Europe, we studied the sensitivity of gross primary productivity (GPP) to environmental drivers during the summer drought of 2018 versus the reference summer of 2016. We found a greater drought-induced decline of summer GPP in grass- lands (−38%) than in forests (−10%), which coincided with reduced evapotranspiration and soil water content (SWC). As com- pared to the ‘normal year’ of 2016, GPP in different ecosystems exhibited more negative sensitivity to summer air temperature (Ta) but stronger positive sensitivity to SWC during summer drought in 2018, that is, a stronger reduction of GPP with soil moisture deficit. We found larger negative effects of Ta and vapour pressure deficit (VPD) but a lower positive effect of photosynthetic photon flux density on GPP in 2018 compared to 2016, which contributed to reduced summer GPP in 2018. Our results demonstrate that high temperature-induced increases in VPD and decreases in SWC aggravated drought impacts on GPP.
ano.nymous@ccsd.cnrs.fr.invalid (Zheng Fu) 18 Sep 2020
https://hal.inrae.fr/hal-02942642
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[hal-02610246] Species mixing reduces drought susceptibility of Scots pine (Pinus sylvestris L.) and oak (Quercus robur L., Quercus petraea (Matt.) Liebl.) - Site water supply and fertility modify the mixing effect
Tree species mixing has been widely promoted as a promising silvicultural tool for reducing drought stress. However, so far only a limited number of species combinations have been studied in detail, revealing inconsistent results. In this study, we analysed the effect of mixing Scots pine and oak (pedunculate oak and sessile oak) trees on their drought response along a comprehensive ecological gradient across Europe. The objective was to improve our knowledge of general drought response patterns of two fundamental European tree species in mixed versus monospecific stands. We focused on three null hypotheses: (HI) tree drought response does not differ between Scots pine and oak, (HII) tree drought response of Scots pine and oak is not affected by stand composition (mixture versus monoculture) and (HIII) tree drought response of Scots pine and oak in mixtures and monocultures is not modified by tree size or site conditions. To test the hypotheses, we analysed increment cores of Scots pine and oak, sampled in mixed and monospecific stands, covering a wide range of site conditions. We investigated resistance (the ability to maintain growth levels during drought), recovery (the ability to restore a level of growth after drought) and resilience (the capacity to recover to pre-drought growth levels), involving sitespecific drought events that occurred between 1976 and 2015. In monocultures, oak showed a higher resistance and resilience than Scots pine, while recovery was lower. Scots pine in mixed stands exhibited a higher resistance, but also a lower recovery compared with Scots pine in monocultures. Mixing increased the resistance and resilience of oak. Ecological factors such as tree size, site water supply and site fertility were found to have significant effects on the drought response. In the case of Scots pine, resistance was increased by tree size, while recovery was lowered. Resistance of oak increased with site water supply. The observed mixing effect on the tree drought response of Scots pine and oak was in some cases modified by the site conditions studied. Positive mixing effects in terms of resistance and resilience of oak increased with site water supply, while the opposite was found regarding recovery. In contrast, site fertility lessened the positive mixing effect on the resistance of Scots pine. We hypothesise that the observed positive mixing effects under drought mainly result from waterand/or light-related species interactions that improve resource availability and uptake according to temporal and spatial variations in environmental conditions.
ano.nymous@ccsd.cnrs.fr.invalid (M. Steckel) 16 May 2020
https://hal.inrae.fr/hal-02610246
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[hal-02527995] Distribution of soil properties along forest-grassland interfaces: Influence of permanent environmental factors or land-use after-effects?
Soil properties vary spatially according to land use; both because land users have selected specific soil properties for specific land uses, and land uses modify the soil properties. However, permanent environment factors and land-use effects are unlikely to display the exact same spatial patterns. Study of the spatial and historical patterns of distribution of soil properties could help to separate between these two causes. In this aim, we studied 22 forest-grassland interfaces with controlled historical configurations in northeast France. In each land use (forest and grassland), three distances to the edge (edge, periphery and core) and two land-use histories (ancient and recent) were studied.Along forest-grassland interfaces, forests were usually located slightly upslope of grasslands, and mainly because this non-random topographic position the topsoil texture was significantly more silty in forests, and clayey in grasslands. After statistically controlling for the effects of topography and soil texture, we observed two main gradients of variation in soil properties according to the distance-to-edge (acidity in forest and nutrient content in grassland). In forest, pH and Ca dropped from the edges to the peripheries (15 m distance), while in grassland, C, N, P and Na sharply increased from the edges to the cores (25 m distance). These results demonstrate, through the edge effect, the strong influence of the land use on a part of soil properties. Furthermore, less than two centuries after grassland afforestation or deforestation, we observed that soil properties in recent forests and recent grasslands were respectively closer to their current land use than to their former land use. These results demonstrate a rapid change in soil properties after land-use change. However, recent forests and recent grasslands kept a legacy of soil texture from their former land use, respectively. Recent grasslands also kept a lower soil density, N and Na content compared to ancient grasslands.Hence, this study of forest-grassland interfaces show strong and short-scale relationships between land use and soil properties and suggest that they express both original choices of land users for specific soil properties and land-use after-effects. The non-random topographic position of the forest-grassland interfaces indicates a conscious choice of this positioning by the land users, for agronomic reasons. Beyond that, land use, through vegetation composition and management practices, also has a strong impact on soil properties. The fact that land-use changes affect most soil properties after only a few decades confirms the existence of land-use effects over time.
ano.nymous@ccsd.cnrs.fr.invalid (Maxime Burst) 21 Dec 2021
https://hal.inrae.fr/hal-02527995
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[hal-03051411] Energy, water and carbon exchanges in managed forest ecosystems: description, sensitivity analysis and evaluation of the INRAE GO+ model, version 3.0
The mechanistic model GO+ describes the functioning and growth of managed forests based upon biophysical and biogeochemical processes. The biophysical and biogeochemical processes included are modelled using standard formulations of radiative transfer, convective heat exchange, evapotranspiration, photosynthesis, respiration, plant phenology, growth and mortality, biomass nutrient content, and soil carbon dynamics. The forest ecosystem is modelled as three layers, namely the tree overstorey, understorey and soil. The vegetation layers include stems, branches and foliage and are partitioned dynamically between sunlit and shaded fractions. The soil carbon submodel is an adaption of the Roth-C model to simulate the impact of forest operations. The model runs at an hourly time step. It represents a forest stand covering typically 1 ha and can be straightforwardly upscaled across gridded data at regional, country or continental levels. GO+ accounts for both the immediate and long-term impacts of forest operations on energy, water and carbon exchanges within the soil–vegetation–atmosphere continuum. It includes exhaustive and versatile descriptions of management operations (soil preparation, regeneration, vegetation control, selective thinning, clear-cutting, coppicing, etc.), thus permitting the effects of a wide variety of forest management strategies to be estimated: from close to nature to intensive. This paper examines the sensitivity of the model to its main parameters and estimates how errors in parameter values are propagated into the predicted values of its main output variables.The sensitivity analysis demonstrates an interaction between the sensitivity of variables, with the climate and soil hydraulic properties being dominant under dry conditions but the leaf biochemical properties being most influential with wet soil. The sensitivity profile of the model changes from short to long timescales due to the cumulative effects of the fluxes of carbon, energy and water on the stand growth and canopy structure. Apart from a few specific cases, the model simulations are close to the values of the observations of atmospheric exchanges, tree growth, and soil carbon and water stock changes monitored over Douglas fir, European beech and pine forests of different ages. We also illustrate the capacity of the GO+ model to simulate the provision of key ecosystem services, such as the long-term storage of carbon in biomass and soil under various management and climate scenarios.
ano.nymous@ccsd.cnrs.fr.invalid (Virginie Moreaux) 10 Dec 2020
https://hal.inrae.fr/hal-03051411
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[hal-02927318] How does contemporary selection shape oak phenotypes?
Most existing forests are subjected to natural and human-mediated selection pressures, which have increased due to climate change and the increasing needs of human societies for wood, fibre and fuel resources. It remains largely unknown how these pressures trigger evolutionary changes. We address this issue here for temperate European oaks (Quercus petraeaandQ. robur), which grow in mixed stands, under even-aged management regimes. We screened numerous functional traits for univariate selection gradients and for expected and observed genetic changes over two successive generations. In both species, growth, leaf morphology and physiology, and defence-related traits displayed significant selection gradients and predicted shifts, whereas phenology, water metabolism, structure and resilience-related traits did not. However, the direction of the selection response and the potential for adaptive evolution differed between the two species.Quercus petraeahad a much larger phenotypic and genetic variance of fitness thanQ. robur. This difference raises concerns about the adaptive response ofQ. roburto contemporary selection pressures. Our investigations suggest thatQ. roburwill probably decline steadily, particularly in mixed stands withQ. petraea, consistent with the contrasting demographic dynamics of the two species.
ano.nymous@ccsd.cnrs.fr.invalid (Hermine Alexandre) 01 Sep 2020
https://hal.inrae.fr/hal-02927318
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[hal-03029648] Diversity and potentiality of multi-criteria decision analysis methods for agri-food research
AbstractThere is a growing demand for moving towards sustainable agri-food systems which per nature covers a complex network of activities and domains; such systems will benefit from multi-criteria decision analysis (MCDA) methods. Although some reviews on MCDA in agri-food research have been published, none of them covered the whole value chain. In this article, a corpus of 954 articles published by INRA scientists from 2007 to 2017 was used to study the diversity and potentiality of MCDA techniques. For the first time, experts from more than 10 agri-food domains worked altogether to annotate the articles, carry out a multivariate analysis, and finally interpret the statistical results to identify the specificities of certain domains and the complementarities between domains and to suggest avenues for future agri-food research. One-third of the studies were based only on a list of indicators, even when their purpose was to choose, sort, or rank options. Regardless of the scientific discipline in the agri-food sector, MCDA studies rarely considered temporal dynamics, spatial scale changes, or stakeholder contributions. As the agri-food system becomes increasingly sustainable in the near future, the use of MCDA methods will accelerate. To become more effective, they will have to include ecosystem services, even outside the scope of ecological studies. Similarly, MCDA studies will need to include participatory science to involve stakeholders (i.e., public authorities, governmental agencies) and end-users (i.e., farmers, producers, industrials, consumers) in the construction of the multi-criteria evaluation but also in the resulting decisions.
ano.nymous@ccsd.cnrs.fr.invalid (Geneviève Gésan-Guiziou) 22 Nov 2021
https://hal.inrae.fr/hal-03029648
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[hal-03014264] Snow cover duration trends observed at sites and predicted by multiple models
Abstract. Thirty-year simulations of seasonal snow cover in 22 physically based models driven with bias-corrected meteorological reanalyses are examined at four sites with long records of snow observations. Annual snow cover durations differ widely between models but interannual variations are strongly correlated because of the common driving data. No significant trends are observed in starting dates for seasonal snow cover, but there are significant trends towards snow cover ending earlier at two of the sites in observations and most of the models. A simplified model with just two parameters controlling solar radiation and sensible heat contributions to snowmelt spans the ranges of snow cover durations and trends. This model predicts that sites where snow persists beyond annual peaks in solar radiation and air temperature will experience rapid decreases in snow cover duration with warming as snow begins to melt earlier and at times of year with more energy available for melting.
ano.nymous@ccsd.cnrs.fr.invalid (Richard Essery) 05 Jan 2021
https://hal.science/hal-03014264v2
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[hal-03038406] How does oak mast seeding affect the feeding behavior of sympatric red and roe deer?
Oak reproduction is characterized by mast seeding with high inter-annual fluctuations in fruit production. Such resource pulses can greatly affect ecosystem functioning and may cause seed consumers to alter their mobility, demography, or diet. Consequences of mast seeding for seed consumers remain poorly understood as their long timescale makes them difficult to study. We investigated impacts of oak mast seeding on the feeding behavior of two sympatric European deer species: red deer (Cervus elaphus) and roe deer (Capreolus capreolus). We analyzed their rumen content over a 31-year period in tandem with 10 years of data on oak fructification (i.e. 8 years of field monitoring and two modelled years). Acorn production is strongly correlated with consumption by both deer species. In years of high fructification, acorns represent more than 50% and 35% of red and roe deer diet, respectively, confirming assumptions that deer favor acorns when these are available. Red deer eat more acorns than roe deer both between and within years. High acorn production in mast years appears to saturate the capacity of deer to consume acorns. As the proportion of acorns increase in their diet, red deer eat more grasses and less conifer browse. No dietary shift was found for roe deer. By inducing dietary shifts in consumers, oak mast seeding can have cascading effects on ecosystem processes, notably on the damages on conifers caused by red deer and the consequences for forest dynamics.
ano.nymous@ccsd.cnrs.fr.invalid (Julien Barrere) 22 Aug 2022
https://hal.inrae.fr/hal-03038406
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[hal-02938719] In situ 13CO2 labelling of rubber trees reveals a seasonal shift in the contribution of the carbon sources involved in latex regeneration
Rubber trees (Hevea brasiliensis) are the main source of natural rubber, extracted from latex, which exudes from the trunk after tapping. Tapped trees require large amounts of carbon (C) to regenerate the latex after its collection. Knowing the contribution of C sources involved in latex biosynthesis will help in understanding how rubber trees face this additional C demand. Whole crown 13CO2 pulse labelling was performed on 4-year-old rubber trees in June, when latex production was low, and in October, when it was high. 13C content was quantified in the foliage, phloem sap, wood, and latex. In both labelling periods, 13C was recovered in latex just after labelling, indicating that part of the carbohydrate was directly allocated to latex. However, significant amounts of 13C were still recovered in latex after 100 d and the peak was reached significantly later than in phloem sap, demonstrating the contribution of a reserve pool as a source of latex C. The contribution of new photosynthates to latex regeneration was faster and higher when latex metabolism was well established, in October, than in June. An improved understanding of C dynamics and the source–sink relationship in rubber tree is crucial to adapt tapping system practices and ensure sustainable latex production.
ano.nymous@ccsd.cnrs.fr.invalid (Ornuma Duangngam) 15 Sep 2020
https://hal.science/hal-02938719
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[hal-02948828] Microgeographic local adaptation and ecotype distributions: The role of selective processes on early life‐history traits in sympatric, ecologically divergent Symphonia populations
Trees are characterized by the large number of seeds they produce. Although most of those seeds will never germinate, plenty will. Of those which germinate, many die young, and eventually, only a minute fraction will grow to adult stage and reproduce. Is this just a random process? Do variations in germination and survival at very young stages rely on variations in adaptations to microgeographic heterogeneity? and do these processes matter at all in determining tree species distribution and abundance?We have studied these questions with the Neotropical Symphonia tree species. In the Guiana shield, Symphonia are represented by at least two sympatric taxa or ecotypes, Symphonia globulifera found almost exclusively in bottomlands, and a yet undescribed more generalist taxon/ecotype, Symphonia sp1. A reciprocal transplantation experiment (510 seeds, 16 conditions) was set up and followed over the course of 6 years to evaluate the survival and performance of individuals from different ecotypes and provenances.Germination, survival, growth, and herbivory showed signs of local adaptation, with some combinations of ecotypes and provenances growing faster and surviving better in their own habitat or provenance region. S. globulifera was strongly penalized when planted outside its home habitat but showed the fastest growth rates when planted in its home habitat, suggesting it is a specialist of a high‐risk high‐gain strategy. Conversely, S. sp1 behaved as a generalist, performing well in a variety of environments.The differential performance of seeds and seedlings in the different habitats matches the known distribution of both ecotypes, indicating that environmental filtering at the very early stages can be a key determinant of tree species distributions, even at the microgeographic level and among very closely related taxa. Furthermore, such differential performance also contributes to explain, in part, the maintenance of the different Symphonia ecotypes living in intimate sympatry despite occasional gene flow.
ano.nymous@ccsd.cnrs.fr.invalid (Niklas Tysklind) 30 Sep 2020
https://hal.science/hal-02948828
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[hal-02610238] Stand growth and structure of mixed-species and monospecific stands of Scots pine (Pinus sylvestris L.) and oak (Q. robur L., Quercus petraea (Matt.) Liebl.) analysed along a productivity gradient through Europe
Past failures of monocultures, caused by wind-throw or insect damages, and ongoing climate change currently strongly stimulate research into mixed-species stands. So far, the focus has mainly been on combinations of species with obvious complementary functional traits. However, for any generalization, a broad overview of the mixing reactions of functionally different tree species in different mixing proportions, patterns and under different site conditions is needed, including assemblages of species with rather similar demands on resources such as light. Here, we studied the growth of Scots pine and oak in mixed versus monospecific stands on 36 triplets located along a productivity gradient across Europe, reaching from Sweden to Spain and from France to Georgia. The set-up represents a wide variation in precipitation (456-1250 mm year-1), mean annual temperature (6.7-11.5 °C) and drought index by de Martonne (21-63 mm °C-1). Stand inventories and increment cores of trees stemming from 40- to 132-year-old, fully stocked stands on 0.04-0.94-ha-sized plots provided insight into how species mixing modifies stand growth and structure compared with neighbouring monospecific stands. On average, the standing stem volume was 436 and 360 m3 ha-1 in the monocultures of Scots pine and oak, respectively, and 418 m3 ha-1 in the mixed stands. The corresponding periodical annual volume increment amounted to 10.5 and 9.1 m3 ha-1 year-1 in the monocultures and 10.5 m3 ha-1 year-1 in the mixed stands. Scots pine showed a 10% larger quadratic mean diameter (p is smaller than 0.05), a 7% larger dominant diameter (p is smaller than 0.01) and a 9% higher growth of basal area and volume in mixed stands compared with neighbouring monocultures. For Scots pine, the productivity advantages of growing in mixture increased with site index (p is smaller than 0.01) and water supply (p is smaller than 0.01), while for oak they decreased with site index (p is smaller than 0.01). In total, the superior productivity of mixed stands compared to monocultures increased with water supply (p is smaller than 0.10). Based on 7843 measured crowns, we found that in mixture both species, but especially oak, had significantly wider crowns (p is smaller than 0.001) than in monocultures. On average, we found relatively small effects of species mixing on stand growth and structure. Scots pine benefiting on rich, and oak on poor sites, allows for a mixture that is productive and most likely climate resistant all along a wide ecological gradient. We discuss the potential of this mixture in view of climate change.
ano.nymous@ccsd.cnrs.fr.invalid (Hans Pretzsch) 16 May 2020
https://hal.inrae.fr/hal-02610238
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[hal-03045938] Natura 2000 forest habitats: climatic debt in lowlands and thermophilization in highlands
Natura 2000 is a European network of sites dedicated to the conservation of vulnerable habitats. The definitions of Natura 2000 habitats are mainly based on plant communities. We investigated if the increase of the dominance of warm-adapted species observed in plant communities, described as thermophilization, had already led to measurable changes in Natura 2000 forest habitats. We created 5701 pairs of neighboring forest plots by gathering plots surveyed before 1987 and after 1997 to reflect historical and recent climatic conditions. A Natura 2000 habitat type was assigned to each vegetation plot using an automatic classification program. We calculated a temperature index that synthesized the temperature range of each habitat, and compared the habitat temperature indexes of the recent and historical plots of each pair. We highlighted a significant overall shift of 4.8% ± 1.78 (CI 95%) of the pairs toward warmer habitats over the studied period. While the shift was not significant in lowlands, 11.1% ± 3.0 (CI 95%) of the pairs evolved toward warmer habitats in highlands. The excess of pairs with a warmer habitat in the recent period was interpreted as thermophilization of Natura 2000 forest habitats. Therefore, global warming has been strong enough to induce actual changes at the coarse-grained habitat resolution specifically targeted by public policies. The absence of significant results in lowlands suggests the existence of unrealized potential habitat changes, which can be considered as a climatic debt. These results call for differential prioritization levels and implementations of public policies for nature conservation in lowlands and highlands.
ano.nymous@ccsd.cnrs.fr.invalid (Lise Maciejewski) 21 Apr 2023
https://hal.science/hal-03045938
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[hal-02949790] A standard protocol for reporting species distribution models
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ano.nymous@ccsd.cnrs.fr.invalid (Damaris Zurell) 12 Nov 2020
https://hal.inrae.fr/hal-02949790
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[hal-03038558] Dernières innovations sur la plantation forestière. Contribution de la R&D pour accompagner les évolutions attendues dans les pratiques.
[...]
ano.nymous@ccsd.cnrs.fr.invalid (Catherine C. Collet) 03 Dec 2020
https://hal.inrae.fr/hal-03038558
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[hal-02963149] Le profil cultural : une méthode d'observation pour analyser les impacts de la préparation mécanisée du site sur la structure du sol
Face à la problématique du renouvellement forestier en stations contraignantes, la R&D s’attache à concevoir, tester et évaluer des techniques appropriées de préparation mécanisée du sol avant plantation. L’évaluation s’appuie légitimement sur la survie et la croissance des plants. Mais pour interpréter les résultats, il faut aussi pouvoir caractériser et analyser les effets sur le sol et ses propriétés. C’est l’objet d’une méthode développée en agronomie et qu’on peut adapter au milieu forestier : le profil cultural. Voyons de quoi il s’agit.
ano.nymous@ccsd.cnrs.fr.invalid (Florian Vast) 14 Oct 2020
https://hal.science/hal-02963149
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[hal-02544340] Comment l'Office national des forêts anticipe les effets du changement climatique ?
En charge de la gestion de onze millions d'hectares de forêts publiques, dont 4,6 millions d’hectares en métropole, l’Office national des forêts (ONF) est un acteur majeur de la filière forêt-bois en France. Depuis 2005, le changement climatique s’est imposé à l’ONF comme une priorité de recherche et de développement. Pour adapter les forêts au climat de demain et préserver les stocks de carbone, son département « Recherche développement et innovation » s’est rapproché des acteurs de la recherche en France. Dans cet article, les auteurs font le point des travaux et actions menés au cours des quatorze dernières années et de leur appropriation par les services de gestion.
ano.nymous@ccsd.cnrs.fr.invalid (Myriam Legay) 21 Apr 2020
https://hal.science/hal-02544340
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[hal-02544285] La croissance des forêts et les changements environnementaux
Les forêts de l’hémisphère nord sont plus productives qu’il y a plusieurs décennies. Telle est la tendance observée et quantifiée dans différentes études menées depuis les années 1970 et qui mettent en cause plusieurs facteurs : les modifications des régimes pluviothermiques, les dépôts azotés et l’augmentation de la concentration atmosphérique en dioxyde de carbone. À partir de données de l’inventaire forestier national, les auteurs de cet article se sont penchéssur l’évolution des forêts françaises. Leurs résultats à des échelles plus fines mettent en évidence des variations extrêmes (négative et positive) liées aux espèces et au contexte environnemental local qu’il conviendrait de suivre en « temps réel » compte tenu des grandes incertitudes futures liées au climat.
ano.nymous@ccsd.cnrs.fr.invalid (François F. Lebourgeois) 21 Apr 2020
https://hal.science/hal-02544285
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[hal-03794287] A la recherche de la structure d'attache entre la truffe d'été et son hôte
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ano.nymous@ccsd.cnrs.fr.invalid (Aurélie Deveau) 03 Oct 2022
https://hal.inrae.fr/hal-03794287
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[hal-03179773] Temporal trends in tree defoliation and response to multiple biotic and abiotic stresses
The vitality of forests depends on multiple biotic and abiotic stresses that can act in an interactive way. Tree defoliation levels are therefore subject to long-term changes and shorter-term hazards that need to be monitored in the context of ongoing climate change. In this study, we analysed the combined effects of drought, insect attack and tree nutritional status on the level of defoliation in three major hardwood species in Europe: European beech (Fagus sylvatica), sessile oak (Quercus petraea) and pedunculate oak (Quercus robur). The forest condition data set was collected in the long-term intensive monitoring network in France (RENECOFOR). The average level of defoliation observed was 20% but varied considerably between plots and trees. From 1997 to 2015, beech defoliation worsened by 10% while oak defoliation stabilized over time. For the three tree species, crown defoliation was generally higher in the event of insect attack (increased by 2.6% to 7.5% depending on the tree species) and under drought (increased by 5.9%), while the effect of the tree nutritional statue was less consistent (from - 5.6% to + 10%) these factors acting synergistically. This study highlights the fact that the different stresses a tree species undergoes act in a complex and interactive way, with species-specific responses. In a context of increasing abiotic and biotic stresses, their combined analysis appears to be a necessity at a time when forest owners need to adapt their management to cope with climate change, particularly through the choice of tree species to be favoured in the future.
ano.nymous@ccsd.cnrs.fr.invalid (Maude Toïgo) 25 Aug 2022
https://hal.inrae.fr/hal-03179773
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[hal-02995533] Ecosystem transpiration and evaporation: Insights from three water flux partitioning methods across FLUXNET sites
We apply and compare three widely applicable methods for estimating ecosystem transpiration (T) from eddy covariance (EC) data across 251 FLUXNET sites globally. All three methods are based on the coupled water and carbon relationship, but they differ in assumptions and parameterizations. Intercomparison of the three daily T estimates shows high correlation among methods (R between .89 and .94), but a spread in magnitudes of T/ET (evapotranspiration) from 45% to 77%. When compared at six sites with concurrent EC and sap flow measurements, all three EC‐based T estimates show higher correlation to sap flow‐based T than EC‐based ET. The partitioning methods show expected tendencies of T/ET increasing with dryness (vapor pressure deficit and days since rain) and with leaf area index (LAI). Analysis of 140 sites with high‐quality estimates for at least two continuous years shows that T/ET variability was 1.6 times higher across sites than across years. Spatial variability of T/ET was primarily driven by vegetation and soil characteristics (e.g., crop or grass designation, minimum annual LAI, soil coarse fragment volume) rather than climatic variables such as mean/standard deviation of temperature or precipitation. Overall, T and T/ET patterns are plausible and qualitatively consistent among the different water flux partitioning methods implying a significant advance made for estimating and understanding T globally, while the magnitudes remain uncertain. Our results represent the first extensive EC data‐based estimates of ecosystem T permitting a data‐driven perspective on the role of plants’ water use for global water and carbon cycling in a changing climate.
ano.nymous@ccsd.cnrs.fr.invalid (Jacob Nelson) 07 Jun 2022
https://hal.univ-lorraine.fr/hal-02995533
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[hal-03048253] Vegetation unit assignments: phytosociology experts and classification programs show similar performance but low convergence
Aims: Assigning vegetation plots to vegetation units is a key step in biodiversity management projects. Nevertheless, the process of plot assignment to types is usually non-standardized, and assignment consistency remains poorly explored. To date, the efficiency of automatic classification programs has been assessed by comparing them with a unique expert judgment. Therefore, we investigated the consistency of five phytosociology expert judgments, and the consistency of these judgements with those of automatic classification programs. Location: Mainland France. Methods: We used 273 vegetation plots distributed across France and covering the diversity of the temperate and mountainous forest ecosystems of Western Europe. We asked a representative panel of five French organizations with recognized expertise in phytosociology to assign each plot to vegetation units. We provided a phytosociological classification including 228 associations, 43 alliances and eight classes. The assignments were compared among experts using an agreement ratio. We then compared the assignments suggested by three automatic classification programs with the expert judgments. Results: We observed small differences among the agreement ratios of the expert organizations; a given expert organization agreed with another one on association assignment one time in four on average, and one time in two on alliance assignment. The agreement ratios of the automatic classification programs were globally lower, but close to expert judgments. Conclusions: The results support the current trend toward unifying the existing classifications and specifying the assignment rules by creating guiding tools, which will decrease inter-observer variation. As compared to a pool of phytosociology experts, programs perform similarly to individual experts in vegetation unit assignment, especially at the alliance level. Although programs still need to be improved, these results pave the way for the creation of habitat time series crucial for the monitoring and conservation of biodiversity.
ano.nymous@ccsd.cnrs.fr.invalid (Lise Maciejewski) 03 May 2022
https://hal.science/hal-03048253
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[hal-02504844] Selective and taxon-dependent effects of semi-feral cattle grazing on tree regeneration in an old-growth Mediterranean mountain forest
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ano.nymous@ccsd.cnrs.fr.invalid (Xavier Fortuny) 11 Mar 2020
https://univ-lyon1.hal.science/hal-02504844
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[hal-03005990] Tree mode of death and mortality risk factors across Amazon forests
The carbon sink capacity of tropical forests is substantially affected by tree mortality. However, the main drivers of tropical tree death remain largely unknown. Here we present a pan-Amazonian assessment of how and why trees die, analysing over 120,000 trees representing > 3800 species from 189 long-term RAINFOR forest plots. While tree mortality rates vary greatly Amazon-wide, on average trees are as likely to die standing as they are broken or uprooted—modes of death with different ecological consequences. Species-level growth rate is the single most important predictor of tree death in Amazonia, with faster-growing species being at higher risk. Within species, however, the slowest-growing trees are at greatest risk while the effect of tree size varies across the basin. In the driest Amazonian region species-level bioclimatic distributional patterns also predict the risk of death, suggesting that these forests are experiencing climatic conditions beyond their adaptative limits. These results provide not only a holistic pan-Amazonian picture of tree death but large-scale evidence for the overarching importance of the growth–survival trade-off in driving tropical tree mortality.
ano.nymous@ccsd.cnrs.fr.invalid (Adriane Esquivel-Muelbert) 17 Nov 2020
https://hal.science/hal-03005990
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[hal-02948747] Contrasting patterns of tree species mixture effects on wood δ13C along an environmental gradient
Establishing mixed-species stands is frequently proposed as a strategy to adapt forests to the increasing risk of water scarcity, yet contrasted results have been reported regarding mixing effects on tree drought exposure. To investigate the drivers behind the spatial and temporal variation in water-related mixing effects, we analysed the delta C-13 variation in 22-year tree ring chronologies for beech and pine trees sampled from 17 pure and mixed pine-beech stands across a large gradient of environmental conditions throughout Europe. In the pure stands, average delta C-13 values were lower for beech (-27.9 parts per thousand to -22.2 parts per thousand) than for pine (-26.0 parts per thousand to -21.1 parts per thousand), irrespective of site conditions. Decreasing SPEI values (calculated over June to September) were associated with an increase in delta C-13 for both species, but their effect was influenced by stand basal area for pine and site water availability for beech. Mixing did not change the temporal constancy of delta C-13 nor the tree reaction to a drought event, for any of the species. While the mixing effect (Delta delta C-13 = delta C-13 pure stands - delta C-13 mixed stands) was on average positive for beech and non-significant for pine across the whole gradient, this effect strongly differed between sites. For both species, mixing was not significant at extremely dry sites and positive at dry sites; on moderately wet sites, mixing was positive for beech and negative for pine; at sites with permanent water supply, no general patterns emerge for any of the species. The pattern of mixing effect along the gradient of water availability was not linear but showed threshold points, highlighting the need to investigate such relation for other combinations of tree species.
ano.nymous@ccsd.cnrs.fr.invalid (G. de Streel) 25 Oct 2023
https://hal.inrae.fr/hal-02948747
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[hal-03207504] Altered energy partitioning across terrestrial ecosystems in the European drought year 2018
Drought and heat events, such as the 2018 European drought, interact with the exchange of energy between the land surface and the atmosphere, potentially affecting albedo, sensible and latent heat fluxes, as well as CO 2 exchange. Each of these quantities may aggravate or mitigate the drought, heat, their side effects on productivity, water scarcity and global warming. We used measurements of 56 eddy covariance sites across Europe to examine the response of fluxes to extreme drought prevailing most of the year 2018 and how the response differed across various ecosystem types (forests, grasslands, croplands and peatlands). Each component of the surface radiation and energy balance observed in 2018 was compared to available data per site during a reference period 2004–2017. Based on anomalies in precipitation and reference evapotranspiration, we classified 46 sites as drought affected. These received on average 9% more solar radiation and released 32% more sensible heat to the atmosphere compared to the mean of the reference period. In general, drought decreased net CO 2 uptake by 17.8%, but did not significantly change net evapotranspiration. The response of these fluxes differed characteristically between ecosystems; in particular, the general increase in the evaporative index was strongest in peatlands and weakest in croplands. This article is part of the theme issue ‘Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale’.
ano.nymous@ccsd.cnrs.fr.invalid (Alexander Graf) 25 Apr 2021
https://hal.inrae.fr/hal-03207504
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[hal-02959147] Drought effects on resource partition and conservation among leaf ontogenetic stages in epiphytic tank bromeliads
Studying the response to drought stress of keystone epiphytes such as tank bromeliads is essential to better understand their resistance capacity to future climate change. The objective was to test whether there is any variation in the carbon, water and nutrient status among different leaf ontogenetic stages in a bromeliad rosette subjected to a gradient of drought stress. We used a semi-controlled experiment consisting in a gradient of water shortage in Aechmea aquilega and Lutheria splendens. For each bromeliad and drought treatment, three leaves were collected based on their position in the rosette and several functional traits related to water and nutrient status, and carbon metabolism were measured. We found that water status traits (relative water content, leaf succulence, osmotic and midday water potentials) and carbon metabolism traits (carbon assimilation, maximum quantum yield of photosystem II, chlorophyll and starch contents) decreased with increasing drought stress, while leaf soluble sugars and carbon, nitrogen and phosphorus contents remained unchanged. The different leaf ontogenetic stages showed only marginal variations when subjected to a gradient of drought. Resources were not reallocated between different leaf ontogenetic stages but we found a reallocation of soluble sugars from leaf starch reserves to the root system. Both species were capable of metabolic and physiological adjustments in response to drought. Overall, this study advances our understanding of the resistance of bromeliads faced with increasing drought stress and paves the way for in-depth reflection on their strategies to cope with water shortage.
ano.nymous@ccsd.cnrs.fr.invalid (Mia Svensk) 06 Oct 2020
https://hal.science/hal-02959147
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[hal-02557077] Mining ecophysiological responses of European beech ecosystems to drought
The most accurate understanding of forest functioning during drought is crucial to improve the forecast of future forest productivity. Here we investigate the ecophysiological responses (i.e. primary production, evapotranspiration and water use efficiency) of European beech to drought events with the ecosystem model MuSICA, using as benchmark the observed fluxes at the experimental forest Hesse (France). We show that MuSICA is able to realistically simulate observed drought-induced limitations. Subsequently we use simulation experiments to provide: (1) a quantification of the reduction of ecosystem fluxes during the 2003 drought, (2) a partitioning of heat stress and water limitations during droughts, (3) an analysis of the impact of specific drought trajectories, and (4) an evaluation of the potential impact of projected climate change on the studied forest and (5) over the beech distributional range. Our results show that the 2003 drought resulted in a 17% reduction of annual gross primary production and in a 21% reduction of evapotranspiration at Hesse. The studied forest ecosystem is mostly sensitive to negative precipitation anomalies (82% of the reduced forest productivity in 2003) and almost insensitive to heat stress due to high temperatures (16%). Moreover, we show that the ecosystem fluxes are limited more by fast drought onsets in the early growing season (June-July) than by onsets later in the season. Deciphering the impact of future climate change on beech productivity is complicated by large uncertainties in projected future precipitation and in the severity of extreme dry years. Drastic reduction of ecosystem fluxes is only predicted with climate projections that show marked reductions in precipitation. However, increased CO2 fertilization in the future will counterbalance negative drought impacts. This modelling-based study improves our understanding of the functioning of an emblematic European tree species during extreme events and informs on potential future forest responses to projected climate change.
ano.nymous@ccsd.cnrs.fr.invalid (Fabio Gennaretti) 21 Dec 2021
https://hal.inrae.fr/hal-02557077
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[hal-02549007] Limiting factors of aspen radial growth along a climatic and soil water budget gradient in south-western Siberia
Understanding how climate and soil hydrology control tree growth is critical to predict the response of Siberian ecosystems to climate change. The general aim of this study was to (i) characterize the soil water budget and identify the factors controlling aspen (Populus tremula L.) radial growth in south-western Siberia, and (ii) assess its potential response to future climate change. Along a gradient of climate and soil hydrological conditions, soil water budgets were reconstructed by modeling at four sites, and dendrochronological analyses were performed. Aspen growth potential was simulated in response to different climate change scenarios represented by shifts in soil water budgets. Simulated soil water budgets varied with climate variables, specifically increased temperature and drier summer combined with varying winter precipitation occurring as snowfall.. We show that plant-available soil water and drainage gradually increased while stress decreased from the warmest and driest (south, forest-steppe zone) site to the coldest and wettest (north, southern taiga zone) site. Aspen radial growth was mainly limited by summer temperature in the north and by summer water deficit in the south. Surprisingly, we did not find clear evidence of snow level impact on radial growth, either positively in the south (water supply and protection against soil freezing) or negatively in the north (water-logging and drainage). In the context of climate change, water stress intensity could increase dramatically in the south inhibiting aspen growth; in those places summer soil water content depends on the refilling that occurs at snow-melt and increasing winter precipitation could alleviate stress levels. Conversely, in the north, aspen growth may mostly benefit from rising temperature.
ano.nymous@ccsd.cnrs.fr.invalid (Félix Bredoire) 21 Apr 2020
https://hal.inrae.fr/hal-02549007
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[hal-03046910] Do tree rings record changes in soil fertility? Results from a Quercus petraea fertilization trial
Through the variations in their dimension, density, anatomy or isotopes composition, tree rings have provided invaluable proxies to evaluate past changes in the environment. Whereas long-term records of changes in soil fertility are particularly desired for forest ecosystem studies, the use of the chemical composition of tree rings as potential marker is still controversial. Dendrochemistry has sometimes been considered as a promising approach to study past changes in soil chemistry, whereas some authors stated that element translocations in the wood preclude any possibility of reliable retrospective monitoring. Here, we aimed at testing whether the wood elemental content of fertilized oaks (Quercus petraea) differed from control trees >30 years after a NPKCaMg fertilization and, if so, if the date of fertilization could be retrieved from the ring analysis. The contents in N, Mg, P, K, Ca and Mn were measured for each of the 43 sampled trees and in every ring of the 58-year long chronology with a non-destructive method coupling a Wavelength Dispersive Spectroscope (WDS) with a Scanning Electron Microscope (SEM).The results showed significantly higher contents in Ca and lower contents in Mn in fertilized compared to control trees. However, there was no difference in elemental content between the rings of the fertilized trees built in the 20 years before and those built after fertilization. Thus, whereas the effect of fertilization on increasing ring width was dramatic, immediate and relatively short-lasting, the elemental composition of the entire ring sequence was impacted, precluding the dating of the event. These results question the possibility to reconstruct long-term changes in soil fertility based on dendrochemistry.
ano.nymous@ccsd.cnrs.fr.invalid (Maxime Durand) 07 Mar 2022
https://hal.inrae.fr/hal-03046910
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[hal-02975249] Early effects of temperate agroforestry practices on soil organic matter and microbial enzyme activity
Aims: A field experiment was conducted to evaluate the effects of alley cropping systems on microbial activity and soil organic matter (SOM) pools. We hypothesized that enzyme activity and labile pools of SOM are early and sensitive indicators of changes induced by tree introduction in the cropping systems. Methods: Poplar-alfalfa and alder-gramineous (cereal or ryegrass) associations and their respective control systems (alfalfa and gramineous) were compared in terms of soil carbon (C), nitrogen (N) and water contents, SOM labile pools, NIRS-MIRS spectra and microbial enzyme activity in the topsoil (0–15 cm) for 4 years after tree planting. Results: After 1 year, tree introduction induced a decrease in soil water content, microbial biomass N and some enzyme activities under alfalfa system. After 4 years, tree introduction resulted in higher soil water contents in both systems (alfalfa and gramineous); higher microbial biomass N and lower C:N in alfalfa-poplar plots compared to control plots. MIRS-NIRS analyses showed a greatest differentiation in SOM quality between alfalfa-based systems. Conclusions: The effects of temperate agroforestry systems on SOC in the topsoil are relatively weak in the first years after tree introduction. Observed effects were more pronounced in the alfalfa-poplar system, probably due to higher tree growth. Further studies will provide insights into the longer-term effects of these systems on soil functioning.
ano.nymous@ccsd.cnrs.fr.invalid (Hugues Clivot) 26 Apr 2022
https://hal.science/hal-02975249
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[hal-03197983] Year-to-year crown condition poorly contributes to ring width variations of beech trees in French ICP level I network
Since the 1980-90's episodes of decline in Central European Forests, forest condition has been surveyed thanks to the trans-national network the International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests). It has been traditionally accepted that leaf loss is directly related to impairment of physiological condition of the tree. A few studies tried to correlate crown condition and growth trends while others concentrated on linking annual growth with crown observation at one date clustered into fertility classes. However, none focussed on the high frequency synchronism between leaf loss from annual network observations and annual radial growth issued from dendrochronology. Therefore, we jointly studied annual leaf loss observations and tree-ring width measurements on 715 common beech (Fagus sylvatica L.) trees distributed in the French part of the ICP monitoring network. Detrended inter-annual variations of leaf loss and tree-ring width index were used as response variables in the machine-learning algorithm Random Forest to investigate a common response to abiotic (current and lagged) and biotic hazards, to test the extent to which leaf loss helped to predict inter-annual variations in radial growth. Using Random Forest was effective to identify a common sensitivity to soil water deficit at different time lags. Previous-year climatic variables tended to control leaf loss while radial growth was more sensitive to current-year soil water deficit. Late frost damages were observed on crown condition in mountainous regions but no impact was detected on radial growth. Few significant biotic damages were observed on growth or leaf loss. Leaf loss series did not show a clear common signal among trees from a plot as did radial growth and captured fewer pointer years. Radial growth index did not fall below normal until a 20% leaf loss was reached. However, this threshold is driven by a few extreme leaf loss events. As shown by our joint analysis of leaf loss and radial growth pointer years, no relationship occurred in cases of slight or moderate defoliation. Crown condition is a poorer descriptor of tree vitality than radial growth.
ano.nymous@ccsd.cnrs.fr.invalid (Clara Tallieu) 22 Aug 2022
https://hal.inrae.fr/hal-03197983
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[hal-04168537] Microgeographic adaptation and the effect of pollen flow on the adaptive potential of a temperate tree species
In species with long-distance dispersal capacities and inhabiting a large ecological niche, local selection and gene flow are expected to be major evolutionary forces affecting the genetic adaptation of natural populations. Yet, in species such as trees, evidence of microgeographic adaptation and the quantitative assessment of the impact of gene flow on adaptive genetic variation are still limited. Here, we used extensive genetic and phenotypic data from European beech seedlings collected along an elevation gradient, and grown in a common garden, to study the signature of selection on the divergence of eleven potentially adaptive traits, and to assess the role of gene flow in resupplying adaptive genetic variation. We found a significant signal of adaptive differentiation among plots separated by < 1 km, with selection acting on growth and phenological traits. Consistent with theoretical expectations, our results suggest that pollen dispersal contributes to increase genetic diversity for these locally differentiated traits. Our results thus highlight that local selection is an important evolutionary force in natural tree populations and suggest that management interventions to facilitate movement of gametes along short ecological gradients would boost genetic diversity of individual tree populations, and enhance their adaptive potential to rapidly changing environments.
ano.nymous@ccsd.cnrs.fr.invalid (Julie Gauzere) 21 Jul 2023
https://hal.inrae.fr/hal-04168537
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[hal-02948749] The global distribution of leaf chlorophyll content
Leaf chlorophyll is central to the exchange of carbon, water and energy between the biosphere and the atmosphere, and to the functioning of terrestrial ecosystems. This paper presents the first spatially-continuous view of terrestrial leaf chlorophyll content (Chl(Leaf)) at the global scale. Weekly maps of Chl(Leaf) were produced from ENVISAT MERIS full resolution (300 m) satellite data using a two-stage physically-based radiative transfer modelling approach. Firstly, leaf-level reflectance was derived from top-of-canopy satellite reflectance observations using 4-Scale and SAIL canopy radiative transfer models for woody and non-woody vegetation, respectively. Secondly, the modelled leaf-level reflectance was input into the PROSPECT leaf-level radiative transfer model to derive Chl(Leaf). The Chl(Leaf) retrieval algorithm was validated using measured Chi(Leaf) data from 248 sample measurements at 28 field locations, and covering six plant functional types (PFTs). Modelled results show strong relationships with field measurements, particularly for deciduous broadleaf forests (R-2 = 0.67; RMSE = 9.25 mu g cm(-2); p < 0.001), croplands (R-2 = 0.41; RMSE = 13.18 mu g cm(-2); p < 0.001) and evergreen needleleaf forests (R-2 = 0.47; RMSE = 10.63 mu g cm(-2); p < 0.001). When the modelled results from all PFTs were considered together, the overall relationship with measured Chl(Leaf )remained good (R-2 = 0.47, RMSE = 10.79 mu g cm(-2); p < 0.001). This result is an improvement on the relationship between measured Chl(Leaf) and a commonly used chlorophyll-sensitive spectral vegetation index; the MERIS Terrestrial Chlorophyll Index (MTCI; R-2 = 0.27, p < 0.001). The global maps show large temporal and spatial variability in Chl(Leaf), with evergreen broadleaf forests presenting the highest leaf chlorophyll values, with global annual median values of 54.4 mu g cm(-2). Distinct seasonal Chl(Leaf) phenologies are also visible, particularly in deciduous plant forms, associated with budburst and crop growth, and leaf senescence. It is anticipated that this global Chl(Leaf) product will make an important step towards the explicit consideration of leaf-level biochemistry in terrestrial water, energy and carbon cycle modelling.
ano.nymous@ccsd.cnrs.fr.invalid (H. Croft) 25 Oct 2023
https://hal.inrae.fr/hal-02948749
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[hal-03006193] The pantropical response of soil moisture to El Niño
The 2015-2016 El Nino event ranks as one of the most severe on record in terms of the magnitude and extent of sea surface temperature (SST) anomalies generated in the tropical Pacific Ocean. Corresponding global impacts on the climate were expected to rival, or even surpass, those of the 1997-1998 severe El Nino event, which had SST anomalies that were similar in size. However, the 2015-2016 event failed to meet expectations for hydrologic change in many areas, including those expected to receive well above normal precipitation. To better understand how climate anomalies during an El Nino event impact soil moisture, we investigate changes in soil moisture in the humid tropics (between +/- 25 degrees) during the three most recent super El Nino events of 1982-1983,1997-1998 and 2015-2016, using data from the Global Land Data Assimilation System (GLDAS). First, we use in situ soil moisture observations obtained from 16 sites across five continents to validate and bias-correct estimates from GLDAS (r(2) = 0.54). Next, we apply a k-means cluster analysis to the soil moisture estimates during the El Nino mature phase, resulting in four groups of clustered data. The strongest and most consistent decreases in soil moisture occur in the Amazon basin and maritime southeastern Asia, while the most consistent increases occur over eastern Africa. In addition, we compare changes in soil moisture to both precipitation and evapotranspiration, which showed a lack of agreement in the direction of change between these variables and soil moisture most prominently in the southern Amazon basin, the Sahel and mainland southeastern Asia. Our results can be used to improve estimates of spatiotemporal differences in El Nino impacts on soil moisture in tropical hydrology and ecosystem models at multiple scales.
ano.nymous@ccsd.cnrs.fr.invalid (Kurt C Solander) 15 Nov 2020
https://hal.inrae.fr/hal-03006193
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[hal-03040768] Water potential control of turgor‐driven tracheid enlargement in Scots pine at its xeric distribution edge
The extent to which water availability can be used to predict the enlargement and final dimensions of xylem conduits remains an open issue. We reconstructed the time course of tracheid enlargement in Pinus sylvestris trees in central Spain by repeated measurements of tracheid diameter on microcores sampled weekly during a 2 yr period. We analyzed the role of water availability in these dynamics empirically through time-series correlation analysis and mechanistically by building a model that simulates daily tracheid enlargement rate and duration based on Lockhart's equation and water potential as the sole input. Tracheid enlargement followed a sigmoid-like time course, which varied intra- and interannually. Our empirical analysis showed that final tracheid diameter was strongly related to water availability during tracheid enlargement. The mechanistic model was calibrated and successfully validated (R-2 = 0.92) against the observed tracheid enlargement time course. The model was also able to reproduce the seasonal variations of tracheid enlargement rate, duration and final diameter (R-2 = 0.84-0.99). Our results support the hypothesis that tracheid enlargement and final dimensions can be modeled based on the direct effect of water potential on turgor-driven cell expansion. We argue that such a mechanism is consistent with other reported patterns of tracheid dimension variation.
ano.nymous@ccsd.cnrs.fr.invalid (Antoine Cabon) 04 Dec 2020
https://hal.inrae.fr/hal-03040768
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[hal-02942674] Observing and modeling the isotopic evolution of snow meltwater on the southeastern Tibetan Plateau
Observing the isotopic evolution of snow meltwater helps in understanding the process of snow melting but remains a challenge to acquire in the field. In this study, we monitored the melting of two snowpacks near Baishui Glacier No. 1, a typical temperate glacier on the southeastern Tibetan Plateau. We employed a physically based isotope model (PBIM) to calculate the isotopic composition of meltwater draining from natural snowpacks. The initial condition of the PBIM was revised to account for natural conditions, i.e., the initial δ 18 O stratigraphy of snow layers before melting. Simulations revealed that the initial heterogeneity of δ 18 O in snow layers as well as ice-liquid isotopic exchange were responsible for most variations of δ 18 O in snow meltwater, whereas new snow and wind drift could result in sudden changes of the isotopic composition of the meltwater. The fraction of ice involved in the isotopic exchange (f) was the most sensitive parameter for the model output. The initial δ 18 O in the snowpack is mirrored in meltwater in case of small f and is smoothed with a large exchange fraction f. The other unknown parameter of the PBIM is the dimensionless rate constant of isotopic exchange, which depends on water percolation and initial snow depth. The successful application of the PBIM in the field might not only be useful for understanding snow melting process but might also provide the possibility of predicting the isotopic composition of snow meltwater and improve the accuracy of hydrograph separation. Plain Language Summary Understanding the process of snow melting is vital for water resources management and protection in the mountainous regions of the Tibetan Plateau. Variations of stable isotopes of oxygen and hydrogen in snow meltwater might give important insights into the process of snow melting. Here we observed and simulated the isotopic composition of snow meltwater of two snowpacks near Baishui Glacier No. 1, which is on the southeastern Tibetan Plateau. The simulations indicate that the isotopic heterogeneity in snow layers as well as ice-liquid isotopic exchange accounts for most of the isotopic variations in meltwater. The successful simulation of isotopic evolution in meltwater provides the possibility of simulating the isotopic composition in natural snow meltwater, which is important for hydrograph separation and paleoclimate studies.
ano.nymous@ccsd.cnrs.fr.invalid (Tao Pu) 18 Sep 2020
https://hal.inrae.fr/hal-02942674
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[hal-03048264] EUNIS Habitat Classification: Expert system, characteristic species combinations and distribution maps of European habitats
Aim: The EUNIS Habitat Classification is a widely used reference framework for European habitat types (habitats), but it lacks formal definitions of individual habitats that would enable their unequivocal identification. Our goal was to develop a tool for assigning vegetation-plot records to the habitats of the EUNIS system, use it to classify a European vegetation-plot database, and compile statistically-derived characteristic species combinations and distribution maps for these habitats. Location: Europe. Methods: We developed the classification expert system EUNIS-ESy, which contains definitions of individual EUNIS habitats based on their species composition and geographic location. Each habitat was formally defined as a formula in a computer language combining algebraic and set-theoretic concepts with formal logical operators. We applied this expert system to classify 1,261,373 vegetation plots from the European Vegetation Archive (EVA) and other databases. Then we determined diagnostic, constant and dominant species for each habitat by calculating species-to-habitat fidelity and constancy (occurrence frequency) in the classified data set. Finally, we mapped the plot locations for each habitat. Results: Formal definitions were developed for 199 habitats at Level 3 of the EUNIS hierarchy, including 25 coastal, 18 wetland, 55 grassland, 43 shrubland, 46 forest and 12 man-made habitats. The expert system classified 1,125,121 vegetation plots to these habitat groups and 73,188 to other habitats, while 63,064 plots remained unclassified or were classified to more than one habitat. Data on each habitat were summarized in factsheets containing habitat description, distribution map, corresponding syntaxa and characteristic species combination. Conclusions: EUNIS habitats were characterized for the first time in terms of their species composition and distribution, based on a classification of a European database of vegetation plots using the newly developed electronic expert system EUNIS-ESy. The data provided and the expert system have considerable potential for future use in European nature conservation planning, monitoring and assessment.
ano.nymous@ccsd.cnrs.fr.invalid (Milan Chytrý) 09 Dec 2020
https://hal.science/hal-03048264
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[hal-02949021] Impacts of a partial rainfall exclusion in the field on growth and transpiration: consequences for leaf-level and whole-plant water-use efficiency compared to controlled conditions
• Water use efficiency (WUE), oftentimes estimated as transpiration efficiency (TE): the amount of biomass produced with regard to the water used, has not yet been used as a breeding trait to select poplar genotypes with simultaneously high productivity and conservation of water. Before its application as a selection target, evidence must be presented showing that WUE or its estimators remain constant with age and across environmental conditions. • We conducted a rainfall exclusion experiment in the field on two Populus euramericana (Moench.) and two Populus nigra (L.) genotypes, and assessed leaf-level (A/g s) and whole-plant WUE (DMT/WU as well as their components and related traits. Then, we aimed to compare these results with the same poplar genotypes grown in a glasshouse under contrasting water availability. • Despite a reduction of soil water content and whole-plant transpiration, growth was stimulated in the rainfall exclusion plot, likely as a result of an increased nitrogen assimilation. However, TE values between the glasshouse and the field were similar, and genotype ranking remained fairly constant for transpiration, carbon isotopic discrimination (∆, as a proxy for Wi) and TE. Moreover, even though the drivers of WUE in both experiments were different, increases of WUE measured as ∆ or TE was not associated with lower biomass production. Relatively good agreement was found between ∆ and TE in the field, absence of a similar correlation in the glasshouse is discussed. • These results suggest that ∆ may be a good proxy for TE, and could be used, both as a breeding target for genotype selection in glasshouses without impacting biomass production when planted in the field. However, reduced water availability modified the genotype ranking more significantly than between the field/glasshouse experiments, suggesting a diversity of poplar response to drought that should be considered in breeding strategies. ABBREVIATIONS WUE water use efficiency Wi leaf intrinsic water use efficiency measured by leaf gas exchange (A/g s) TE whole-plant transpiration efficiency (biomass production over water used, DM T /WU) ∆ carbon isotope discrimination δ carbon isotope composition A net CO 2 assimilation C i internal CO 2 concentration g s stomatal conductance to water vapor WU whole plant water use E daily whole-plant transpiration per unit area VPD vapor pressure deficit Vc max maximum CO 2 carboxylation rate J max maximum photosynthetic electron flux A max net CO 2 assimilation measured under saturating atmospheric CO 2 concentration SWC soil water content Ψ p predawn leaf water potential H tree height https://doi.
ano.nymous@ccsd.cnrs.fr.invalid (Maxime Durand) 21 Jul 2022
https://hal.inrae.fr/hal-02949021
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[hal-02942657] Higher than expected CO 2 fertilization inferred from leaf to global observations
Several lines of evidence point to an increase in the activity of the terrestrial biosphere over recent decades, impacting the global net land carbon sink (NLS) and its control on the growth of atmospheric carbon dioxide (ca). Global terrestrial gross primary production (GPP)—the rate of carbon fixation by photosynthesis—is estimated to have risen by (31 ± 5)% since 1900, but the relative contributions of differ- ent putative drivers to this increase are not well known. Here we identify the rising atmospheric CO2 concentration as the dominant driver. We reconcile leaf-level and global atmospheric constraints on trends in modeled biospheric activity to reveal a global CO2 fertilization effect on photosynthesis of 30% since 1900, or 47% for a doubling of ca above the pre-industrial level. Our historic value is nearly twice as high as current estimates (17 ± 4)% that do not use the full range of available constraints. Consequently, under a future low-emission scenario, we project a land carbon sink (174 PgC, 2006–2099) that is 57 PgC larger than if a lower CO2 fertilization effect comparable with current estimates is assumed. These findings suggest a larger beneficial role of the land carbon sink in modulating future excess anthropogenic CO2 consistent with the target of the Paris Agreement to stay below 2°C warming, and underscore the importance of preserving terrestrial carbon sinks.
ano.nymous@ccsd.cnrs.fr.invalid (Vanessa Haverd) 25 Oct 2023
https://hal.inrae.fr/hal-02942657
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[hal-03209287] Photoperiod and temperature as dominant environmental drivers triggering secondary growth resumption in Northern Hemisphere conifers
Wood formation consumes around 15% of the anthropogenic CO 2 emissions per year and plays a critical role in long-term sequestration of carbon on Earth. However, the exogenous factors driving wood formation onset and the underlying cellular mechanisms are still poorly understood and quantified, and this hampers an effective assessment of terrestrial forest productivity and carbon budget under global warming. Here, we used an extensive collection of unique datasets of weekly xylem tissue formation (wood formation) from 21 coniferous species across the Northern Hemisphere (latitudes 23 to 67°N) to present a quantitative demonstration that the onset of wood formation in Northern Hemisphere conifers is primarily driven by photoperiod and mean annual temperature (MAT), and only secondarily by spring forcing, winter chilling, and moisture availability. Photoperiod interacts with MAT and plays the dominant role in regulating the onset of secondary meristem growth, contrary to its as-yet-unquantified role in affecting the springtime phenology of primary meristems. The unique relationships between exogenous factors and wood formation could help to predict how forest ecosystems respond and adapt to climate warming and could provide a better understanding of the feedback occurring between vegetation and climate that is mediated by phenology. Our study quantifies the role of major environmental drivers for incorporation into state-of-the-art Earth system models (ESMs), thereby providing an improved assessment of long-term and high-resolution observations of biogeochemical cycles across terrestrial biomes.
ano.nymous@ccsd.cnrs.fr.invalid (Jian-Guo Huang) 27 Apr 2021
https://hal.inrae.fr/hal-03209287
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[hal-02934348] Sacrificing growth and maintaining a dynamic carbohydrate storage are key processes for promoting beech survival under prolonged drought conditions
Key message In case of a prolonged drought, the stored carbohydrates in trees were remobilized to fuel survival functions until their nearly depletion at death stage. Abstract Dynamic global vegetation models project forest tree mortality in response to the recurrent severe droughts likely in the future. However, these models should better take into account the physiological processes involved in tree mortality. Faced with severe drought, the Fagus sylvatica L. tree strongly limits its cambial growth. This suggests that readjustments in carbon (C) allocation among sink functions are taking place in response to the lack of water and this could allow tree's survival. For 3 years, we induced a water shortage on 8-year-old beech trees in a rain exclusion system. During this period, we analysed the consequences of severe drought on survival rate, growth, and non-structural carbohydrate (NSC) dynamics in the aboveground and belowground compartments of control, water-stressed living, and dead trees. The survival rate after 3 years of drought was 87%, while primary and secondary growth was strongly reduced. The first 2 years, NSC concentrations increased in all tree compartments (stem, branches, and roots) in response to drought. However, during the third year, starch dropped markedly in water-stressed trees, while soluble sugar concentrations remained similar to control trees. All the compartments in dead trees were virtually empty of starch and soluble sugars. Maintaining an active C storage function at the expense of growth was certainly key to F. sylvatica survival under prolonged extreme drought conditions. Process-based models predicting mortality should better take into account C storage and remobilization processes in forest trees.
ano.nymous@ccsd.cnrs.fr.invalid (Pierre-Antoine Chuste) 09 Sep 2020
https://hal.science/hal-02934348
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[hal-03006008] Soil properties explain tree growth and mortality, but not biomass, across phosphorus-depleted tropical forests
We observed strong positive relationships between soil properties and forest dynamics of growth and mortality across twelve primary lowland tropical forests in a phosphorus-poor region of the Guiana Shield. Average tree growth (diameter at breast height) increased from 0.81 to 2.1 mm yr−1 along a soil texture gradient from 0 to 67% clay, and increasing metal-oxide content. Soil organic carbon stocks in the top 30 cm ranged from 30 to 118 tons C ha−1, phosphorus content ranged from 7 to 600 mg kg−1 soil, and the relative abundance of arbuscular mycorrhizal fungi ranged from 0 to 50%, all positively correlating with soil clay, and iron and aluminum oxide and hydroxide content. In contrast, already low extractable phosphorus (Bray P) content decreased from 4.4 to <0.02 mg kg−1 in soil with increasing clay content. A greater prevalence of arbuscular mycorrhizal fungi in more clayey forests that had higher tree growth and mortality, but not biomass, indicates that despite the greater investment in nutrient uptake required, soils with higher clay content may actually serve to sustain high tree growth in tropical forests by avoiding phosphorus losses from the ecosystem. Our study demonstrates how variation in soil properties that retain carbon and nutrients can help to explain variation in tropical forest growth and mortality, but not biomass, by requiring niche specialization and contributing to biogeochemical diversification across this region.
ano.nymous@ccsd.cnrs.fr.invalid (Jennifer Soong) 24 Jun 2022
https://hal.science/hal-03006008
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[hal-03043589] Contrasting Dependencies of Photosynthetic Capacity on Leaf Nitrogen in Early- and Late-Successional Tropical Montane Tree Species
Differences in photosynthetic capacity among tree species and tree functional types are currently assumed to be largely driven by variation in leaf nutrient content, particularly nitrogen (N). However, recent studies indicate that leaf N content is often a poor predictor of variation in photosynthetic capacity in tropical trees. In this study, we explored the relative importance of area-based total leaf N content (N tot) and within-leaf N allocation to photosynthetic capacity versus light-harvesting in controlling the variation in photosynthetic capacity (i.e. V cmax , J max) among mature trees of 12 species belonging to either early (ES) or late successional (LS) groups growing in a tropical montane rainforest in Rwanda, Central Africa. Photosynthetic capacity at a common leaf temperature of 25˚C (i.e. maximum rates of Rubisco carboxylation, V cmax25 and of electron transport, J max25) was higher in ES than in LS species (+ 58% and 68% for V cmax25 and J max25 , respectively). While N tot did not significantly differ between successional groups, the photosynthetic dependency on N tot was markedly different. In ES species, V cmax25 was strongly and positively related to N tot but this was not the case in LS species. However, there was no significant trade-off between relative leaf N investments in compounds maximizing photosynthetic capacity versus compounds maximizing light harvesting. Both leaf dark respiration at 25˚C (+ 33%) and, more surprisingly, apparent photosynthetic quantum yield (+ 35%) was higher in ES than in LS species. Moreover, R d25 was positively related to N tot for both ES and LS species. Our results imply that efforts to quantify carbon fluxes of tropical montane rainforests would be improved if they considered contrasting within-leaf N allocation and photosynthetic N tot dependencies between species with different successional strategies.
ano.nymous@ccsd.cnrs.fr.invalid (Camille Ziegler) 07 Dec 2020
https://hal.science/hal-03043589
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[hal-03043585] Traits controlling shade tolerance in tropical montane trees
Tropical canopies are complex, with multiple canopy layers and pronounced gap dynamics contributing to their high species diversity and productivity. An important reason for this complexity is the large variation in shade tolerance among di erent tree species. At present, we lack a clear understanding of which plant traits control this variation, e.g., regarding the relative contributions of whole-plant versus leaf traits or structural versus physiological traits. We investigated a broad range of traits in six tropical montane rainforest tree species with di erent degrees of shade tolerance, grown under three di erent radiation regimes (under the open sky or beneath sparse or dense canopies). The two distinct shade-tolerant species had higher fractional biomass in leaves and branches while shade-intolerant species invested more into stems, and these di erences were greater under low radiation. Leaf respiration and photosynthetic light compensation point did not vary with species shade tolerance, regardless of radiation regime. Leaf temperatures in open plots were markedly higher in shade-tolerant species due to their low transpiration rates and large leaf sizes. Our results suggest that interspeci c variation in shade tolerance of tropical montane trees is controlled by species di erences in whole-plant biomass allocation strategy rather than by di erence in physiological leaf traits determining leaf carbon balance at low radiation.
ano.nymous@ccsd.cnrs.fr.invalid (Elisée Bahati Ntawuhiganayo) 07 Dec 2020
https://hal.science/hal-03043585
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[hal-02948755] Impacts of Degradation on Water, Energy, and Carbon Cycling of the Amazon Tropical Forests
Selective logging, fragmentation, and understory fires directly degrade forest structure and composition. However, studies addressing the effects of forest degradation on carbon, water, and energy cycles are scarce. Here, we integrate field observations and high‐resolution remote sensing from airborne lidar to provide realistic initial conditions to the Ecosystem Demography Model (ED‐2.2) and investigate how disturbances from forest degradation affect gross primary production (GPP), evapotranspiration (ET), and sensible heat flux (H). We used forest structural information retrieved from airborne lidar samples (13,500 ha) and calibrated with 817 inventory plots (0.25 ha) across precipitation and degradation gradients in the eastern Amazon as initial conditions to ED‐2.2 model. Our results show that the magnitude and seasonality of fluxes were modulated by changes in forest structure caused by degradation. During the dry season and under typical conditions, severely degraded forests (biomass loss ≥66%) experienced water stress with declines in ET (up to 34%) and GPP (up to 35%) and increases of H (up to 43%) and daily mean ground temperatures (up to 6.5°C) relative to intact forests. In contrast, the relative impact of forest degradation on energy, water, and carbon cycles markedly diminishes under extreme, multiyear droughts, as a consequence of severe stress experienced by intact forests. Our results highlight that the water and energy cycles in the Amazon are driven by not only climate and deforestation but also the past disturbance and changes of forest structure from degradation, suggesting a much broader influence of human land use activities on the tropical ecosystems.
ano.nymous@ccsd.cnrs.fr.invalid (Marcos Longo) 13 Oct 2020
https://hal.inrae.fr/hal-02948755
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[hal-02948750] Validation of Space-based albedo products from upscaled tower-based measurements over Heterogeneous and Homogeneous landscapes
Surface albedo is a fundamental radiative parameter as it controls the Earth’s energy budget and directly affects the Earth’s climate. Satellite observations have long been used to capture the temporal and spatial variations of surface albedo because of their continuous global coverage. However, space-based albedo products are often affected by errors in the atmospheric correction, multi-angular bi-directional reflectance distribution function (BRDF) modelling, as well as spectral conversions. To validate space-based albedo products, an in situ tower albedometer is often used to provide continuous “ground truth” measurements of surface albedo over an extended area. Since space-based albedo and tower-measured albedo are produced at different spatial scales, they can be directly compared only for specific homogeneous land surfaces. However, most land surfaces are inherently heterogeneous with surface properties that vary over a wide range of spatial scales. In this work, tower-measured albedo products, including both directional hemispherical reflectance (DHR) and bi-hemispherical reflectance (BHR), are upscaled to coarse satellite spatial resolutions using a new method. This strategy uses high-resolution satellite derived surface albedos to fill the gaps between the albedometer’s field-of-view (FoV) and coarse satellite scales. The high-resolution surface albedo is generated from a combination of surface reflectance retrieved from high-resolution Earth Observation (HR-EO) data and moderate resolution imaging spectroradiometer (MODIS) BRDF climatology over a larger area. We implemented a recently developed atmospheric correction method, the Sensor Invariant Atmospheric Correction (SIAC), to retrieve surface reflectance from HR-EO (e.g., Sentinel-2 and Landsat-8) top-of-atmosphere (TOA) reflectance measurements. This SIAC processing provides an estimated uncertainty for the retrieved surface spectral reflectance at the HR-EO pixel level and shows excellent agreement with the standard Landsat 8 Surface Reflectance Code (LaSRC) in retrieving Landsat-8 surface reflectance. Atmospheric correction of Sentinel-2 data is vastly improved by SIAC when compared against the use of in situ AErosol RObotic NETwork (AERONET) data. Based on this, we can trace the uncertainty of tower-measured albedo during its propagation through high-resolution EO measurements up to coarse satellite scales. These upscaled albedo products can then be compared with space-based albedo products over heterogeneous land surfaces. In this study, both tower-measured albedo and upscaled albedo products are examined at Ground Based Observation for Validation (GbOV) stations (https://land.copernicus.eu/global/gbov/), and used to compare with satellite observations, including Copernicus Global Land Service (CGLS) based on ProbaV and VEGETATION 2 data, MODIS and multi-angle imaging spectroradiometer (MISR).
ano.nymous@ccsd.cnrs.fr.invalid (Rui Song) 25 Oct 2023
https://hal.inrae.fr/hal-02948750
