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International audience; Many forest soils are acidic and have very low plant-available pools of magnesium. Past and present sylvicultural, nutritional and/or climatic pressures endured by forest ecosystems can result in net losses of nutrients and ecosystem function losses. Liming with a carbonate product is an alternative to counteract these degradations but the effects of liming on the biogeochemical cycling of nutrients over time and the dynamics of Mg released from liming products are still unclear. We studied the Mg isotopes composition in four paired-treatment experimental beech forest ecosystems in northern France. At the sites where dolomitic lime was applied, the variation in exchangeable and foliar δ26Mg demonstrated the direct contribution of dolomite-derived Mg to the replenishment of topsoil exchangeable pools and to tree nutrition improvement: dolomite-derived Mg was incorporated into the biological cycling which allows its retention on the mid to long term in the soil–plant system. At the sites limed with calcium carbonate, the changes in exchangeable and foliar Mg contents and δ26Mg observed on the long term suggest that the applied product contained a small amount of Mg and/or that Mg cycling changed after liming, to cope in particular with the low Mg availability. Lastly, our results highlight the high δ26Mg of the organic layer (humus): fractionation processes occurring within this layer (mineralization/ageing of organic matter, preferential retention of 26 Mg) could explain these singular signatures that could greatly influence the topsoil Mg exchangeable pools.

International audience; 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.

National audience; Dans cet article, nous proposons d’examiner « l’œil du forestier » comme un instrument et un miroir de l’activité cognitive du forestier quand il doit réaliser un diagnostic de parcelle forestière en vue de prendre des décisions d’actions sylvicoles. Comment voir et apprendre à voir dans un environnement vivant que l’ergonomie cognitive qualifie d’environnement complexe et dynamique ? Dans une perspective de didactique professionnelle, nous étudions comment le « savoir voir » des forestiers s’exerce en situation, s’enseigne et se construit en formation. Nous analysons les compétences visuelles des forestiers mobilisées dans l’activité professionnelle en situation de travail et en formation et dégageons les principaux concepts organisateurs qui structurent leur représentation de la forêt. Nous modélisons à la suite une structure conceptuelle de la situation de diagnostic d’une parcelle forestière prenant en compte différentes variables et indicateurs pour raisonner et articuler peuplement et station, production et écologie. Ces résultats peuvent constituer une ressource potentielle au développement d’une intelligence professionnelle du « savoir voir » forestier.

International audience; Our work entitled: Diversity of Rodents (Rodentia: Mammalia) in the Kandolo Forest Reserve (Maniema Province, DR Congo) aimed to assess the biodiversity of Rodents in the Kandolo Forest Reserve while comparing the specific diversity during two capture sessions and in the two prospected habitats (Mixed primary forest (FPM) and Gilbertiodendron dewevrei primary forest (FPG) Finally, assess the distribution of Rodents in the two habitats (FPG and FPM) prospected by sex. These objectives have been achieved. To achieve this, only one method was used in the field, the only in-line trapping using two types of traps including Sharmen and Pitfall. Two habitats were explored (primary mixed forest and primary forest at Gilbertiodendron dewevrei) during 2 capture sessions. After processing the data, the results presented 153 captured Rodents synthesized as follows: For a total of 153 individuals captured in the two habitats prospected during the two capture sessions, the first capture session carried out in the FPM, totaled 40 individuals of Rodents including: Praomys cf. jacksoni is the most represented with 22 individuals captured or 55 %. In contrast, Graphiurus lorraineus, Lophuromys luteogaster and Saccostomus campestris are the least represented with a score of an individual captured, 2, 5 %. On the other hand, during the second session which took place in the FPG, it emerges the following: For the 113 individuals captured, Praomys cf. jacksoni is the most represented with 69 individuals captured, or 61, 06 %. Lophuromys dudui, on the other hand, is the least represented with a score of one specimen, ie 0, 88 %. In comparison with habitats and capture sessions, the following is concluded: the FPG is the best represented quantitatively and qualitatively (113 specimens, TS = 7, 06 %, Ep = 1600 trap nights and 10 species) with Praomys cf. jacksoni which ranks first with 69 individuals out of 113 carcasses captured. Unlike the FPM which occupies the second position (40 specimens, TS = 2, 5 %, EC = 1600 trap nights,) with 9 species caught. But for the indices of specific diversity, it appears that, in the two habitats there is the probability of randomly drawing 2 individuals to have 2 different species because Simpson tends towards1 everywhere. And in the two habitats, the species are not evenly distributed (E tends towards 1). Also, the specific richness evaluated at the level of the two different habitats reveals that there is not a significant difference between the populations of Rodents (Kuskal-Walis test, H = 2, 802; p = 0, 09055). Finally, taking into account the sex distribution of the Rodents caught in the two habitats during the two sessions, it has been shown that, the Rodents sampled are marked by the dominance of the males in percentage as the females. Thus, in the FPM the dominance of the males is expressed at 70 % against 30 % of the females and in the FPG 69, 91 % of the males against 30, 09 % of the females.

We propose an innovative mathematical model for studying the dynamics of a complex network of forest ecosystems, in which two forest entities interact which each other through water exchanges. Our model reproduces a recently analyzed principle of constant precipitation quantity over densely forested areas. We perform a stability and bifurcation analysis and show that the distance separating two forest ecosystems can attract a part of the network to an extinction state. We incorporate a randomly generated perturbation modeling deforestation and investigate the effect of the level of deforestation on the equilibrium states of the network. We also exhibit a type of synchronization in the case of densely distributed forest ecosystems.

International audience; Calcium (Ca) is an essential macronutrient which plays a fundamental role in ecosystem structure and function. In temperate forest ecosystems, Ca oxalate is ubiquitous, existing in live and decomposing biomass pools. Calcium in minerals occurs principally as carbonate and silicate. Because of structural differences between its different forms, Ca speciation can influence the Ca biogeochemical cycle. In this study, we compared three beech temperate forests of contrasting soil Ca availability, i.e., dystric cambisol (DC), eutric cambisol, and rendzic leptosol (RL), but with similar climates, atmospheric depositions, species compositions and management. The pools and fluxes of total Ca (Ca-t) and Ca oxalate (Ca-ox) were assessed in plant samples (aboveground and belowground tree tissues, forest floor). Pools and fluxes of Ca-t were also quantified in the atmospheric inputs (dry and wet deposits), in the soil (total and exchangeable fractions) and in the soil solutions at different depths. The soil solutions were measured monthly for 4 years to study the seasonal dynamics of Ca fluxes. A budget of dissolved Ca was also determined for the forest floor and soil layers. Regarding the global Ca cycle at the stand scale, our study highlighted: (i) the predominant role of biological recycling in the Ca cycle in forest ecosystems for all soil types; the turnover rates of fine roots and leaves were approximately 43 and 39% of the total Ca taken up by trees each year, revealing that only 18% accumulated in the perennial tissues; (ii) the vegetation was Ca-enriched in the high Ca soil (RL) compared to the low-Ca soil (DC); (iii) the existence of an unexpected available Ca source in DC due to upwelling by the diffusion of Ca issued from the dissolution of carbonates in-depth; (iv) a higher production of dissolved Ca (from carbonate dissolution) in RL compared to DC, resulting in an important loss of Ca by drainage (280 kg ha(-1) year vs. 14 kg ha(-1) year); (v) monthly measurements demonstrated that the seasonal dynamics was mainly linked to biological activity. In addition, our study showed that the distribution of Ca-ox differs greatly between vegetation compartments, ranging from null (stem and branch wood) to up to 40% (stem and branch bark and fine roots) of the Ca-t in the biomass. Vegetation is a factory of Ca oxalate, and the return of this Ca-ox enriched vegetation to the soil influences the Ca mobility in the forest floor, as demonstrated by a Ca-ox residence time shorter than that of Ca-t in the DC.

The forest ecosystems of Central Africa in general and those of Cameroon in particular, are very rich in natural resources. They offer many opportunities for people in terms of livelihoods. However, faced with the implementation of the process of socio-economic development, this environment is confronted with many threats including deforestation, degradation, poaching, pollution, overexploitation of biotic and abiotic resources, etc. The Cameroonian legislator, spurred by the action of international cooperation, has adopted several international legal instruments and has legislated on measures to protect forest ecosystems during the implementation of socio-economic development projects. However, a careful analysis of the normative and institutional framework put in place in Cameroon shows that the legal mechanisms for protecting forest ecosystems during the implementation of socio-economic development projects, although plural, remain ineffective and inefficient. There is still much work to be done on some aspects of legislation and enforcement of existing legal mechanisms to ensure that forest ecosystem protection objectives are effective and efficient. The problems of human and financial resources, forest governance, institutional incoordination, ecological illiteracy, widespread poverty of the people, conflict between tradition and modernity have the effect of putting into perspective the effectiveness and efficiency of the protection of forest ecosystems in Cameroon. Meeting this challenge requires the implementation of several actions, the most salient of which are the reformulation of the legislative framework, the improvement of governance and the elaboration of an international convention on forests., Les écosystèmes forestiers d’Afrique centrale en général, et ceux du Cameroun en particulier, sont très riches en ressources naturelles. Ils offrent de nombreuses opportunités aux populations pour leurs moyens de subsistance. Cependant, face à la mise en place du processus de développement socio-économique, ce milieu est confronté à de nombreuses menaces, notamment, la déforestation, la dégradation, le braconnage, la pollution, la surexploitation des ressources biotiques et abiotiques, etc. Le législateur camerounais, sous l’impulsion de l’action de la coopération internationale, a adopté plusieurs instruments juridiques internationaux et nationaux prévoyant des mesures de protection des écosystèmes forestiers durant la réalisation des projets de développement socio-économique. Toutefois, l'analyse minutieuse du dispositif normatif et institutionnel mis en place au Cameroun, montre que les mécanismes juridiques de protection des écosystèmes forestiers durant la réalisation des projets de développement socio-économique, quoique pluriels, restent ineffectifs et inefficaces. Beaucoup d’efforts restent encore à fournir sur certains aspects qualitatifs de la législation. L’application des mécanismes juridiques existants ne favorise pas l’atteinte des objectifs d’une protection efficace et efficiente des écosystèmes forestiers. Les problèmes liés aux ressources humaines et financières, de gouvernance forestière, d’incoordination institutionnelle, d’analphabétisme écologique, de la pauvreté généralisée des populations, de conflit entre la tradition et la modernité ont pour conséquence de relativiser l’effectivité et l’efficacité de la protection des espaces forestiers au Cameroun. Pour relever ce défi, il faut nécessairement mettre en œuvre de nombreuses actions, dont les plus pertinentes sont la reformulation du cadre législatif, l’amélioration du système de gouvernance et l’élaboration d’une convention internationale sur les forêts.

International audience; AbstractKey messagePrecipitation mediates the dynamic of net primary productivity and precipitation use efficiency across the North-South Transect forests of China, which may result from an increase of productivity in warm temperate deciduous broad-leaved forests or a decrease of precipitation use efficiency in temperate coniferous broad-leaved mixed forests.ContextPrecipitation use efficiency (PUE), the ratio of net primary productivity (NPP) to annual precipitation, is one of the key factors that can clarify the response of forest ecosystem carbon and water cycles to ongoing climate change.AimsTo investigate large-scale patterns of NPP and PUE, and to determine how NPP and PUE would respond to climate and soil variables across the North-South Transect forests (TNSTF) of China.MethodsWe revealed the spatial pattern dynamics of NPP and PUE in the TNSTF from 2000 to 2010 employing MOD17 NPP data and further explored the responses of NPP and PUE to environment factors across the TNSTF. Additionally, the temporal dynamics of NPP and PUE in different forest types and their dependencies on climate variation were investigated.ResultsThe results indicated that NPP increased from 2000 to 2010 in most regions across the TNSTF. The spatial distribution pattern of NPP was mainly correlated with climate factors in the TNSTF rather than soil properties. Spatially, an increased trend of PUE (2000–2010) was found in the south and decreased PUE was revealed in the north of the TNSTF. In addition, the spatial distribution of PUE in the TNSTF was associated with both climate and soil factors. For different forests, only the NPP in warm temperate deciduous broad-leaved forests significantly increased (2000–2010, R2 = 0.33, P

International audience; Plant litter decomposition is an essential process of ecosystem functioning, driven by a complex soil food web. The identity and density of the predators, as well as the quality and quantity of litter, could conjointly affect the strength of trophic interactions within a soil food web. Pine and oak are dominant tree species in temperate and Mediterranean forests and, although they exhibit distinct litter characteristics, no previous study attempted to decipher how these two litters can affect a litter-based multi-trophic system with varying predator density. Using a microcosm experiment, we aimed at understanding how different densities of a predatory Acari (Stratiolaelaps scimitus) and two Mediterranean litter species (Quercuspubescens and Pinus halepensis) may impact the demographic parameters of the predatory Acari, its Collembola prey (Folsomia candida) and the fungal biomass associated with litter. We did not observe any interactive effect of litter identity and predator density on both predator and prey demographic parameters. Survival and fecundity rates of the predator and its prey decreased at high predator density. However, demographic parameters of the predator and its prey were differentially affected by litter identity, with greater prey demographic parameters in Quercus litter and, in the opposite, greater predator demographic parameters in Pinus litter, probably due to differences in physical characteristics providing more or less refuge for the prey. We also observed a higher increase in fungal biomass in Pinus compared to Quercus litter, i.e. the litter with the fungivorous Collembola abundance reduced by the predatory Acari. Litter identity could thus strongly regulate these tri-trophic interactions (Fungi – fungivorous Collembola – predatory Acari) in forest ecosystems. Finally, the implications of our findings could be important as the distribution area of oak and pine forests may be altered in response to climate change with then potentially strong cascading effects on soil organisms and the processes they drive.

International audience; Forest ecosystems can spontaneously establish themselves on former industrial sites contaminated by metals. The sustainable management of these sites by natural attenuation requires a better understanding of the relationships between soil biodiversity, metals and soil functioning in such ecosystems. In this context, a forest ecosystem growing on iron industry by-products containing potentially toxic metals as major elements was studied using a multiproxy approach including chemical soil properties, microstructure, meso-and macro-fauna. Fauna communities in the topsoil were characterized by a high abundance and taxonomic diversity, but also by an unusual predominance of epigeic and detritivorous species. Fauna community structures were partly explained by the presence not only of heavy metals (Zn, Cd), but also Fe and Mn, dominant metals in iron industry by-products. The uncommon structure of macrofauna communities could have effects on the soil functioning, such as limiting the incorporation and mixing of organic matter into the soil. Mesofauna communities contributed to the metal redistribution in the soil by integrating metals into organo-mineral associations. In terms of management, this study showed the feasibility of using natural attenuation to manage sites with high metal contents but low metal availability and favorable conditions for plant growth. However, the influence of soil biota on metal mobility and soil functioning needs to be further investigated in order to assess the sustainability of such management.

Key message More and more environmental and resource economists are taking a particular interest in research on forest ecosystem services (FES), especially in a context of climate change. Spatial and temporal issues are crucial to economic analyses and for the design of conservation policies. Interdisciplinary research involving ecological and economic disciplines is a prerequisite for the more effective management of forest ecosystems. Context Economists define non-market ecosystem services (ES) as public or common goods due to their characteristics of non-rivalry in terms of consumption and/or non-excludability. Just because they do not have a price does not mean that ES have no economic value because their social benefits are undoubtedly considerable. These features, associated with the market demand for timber and a poor climate risk assessment, may lead to the under-provision of non-market forest ES and the over-harvesting of timber. Aims In this article, we review research questions that are central to the enhancement of FES provision. Beyond the economic modelling of the joint provision of FES, we focus on issues related to the design of public policies to guide forest management. The objective is to provide crucial insights concerning the importance of a spatial and sustainable provision of FES. Results First, we provide an economic interpretation of the FES concept and a review of economic models of forest management. Second, we explain how spatial and temporal dimensions of FES can have major implications on their supply and demand. Both dimensions explain why FESs have to be taken into account in production decisions and public policies (including the design of payment for environmental services (PESs)). Conclusion A better understanding of FES provision and public policies to be enhanced is not possible without accounting for spatial and temporal dimensions. This helps to analyse the impact of intervention on FES and the cost-effectiveness of economic instruments, implying a coordinated effort to bring together ecological and economic data and models.

The role of forest vegetation in the silicon (Si) cycle has been widely examined. However, to date, little is known about the specific role of fine roots. The main objective of our study was to assess the influence of fine roots on the Si cycle in a temperate forest in north-eastern France. Silicon pools and fluxes in vegetal solid and solution phases were quantified within each ecosystem compartment, i.e. in the atmosphere, above-ground and below-ground tree tissues, forest floor and different soil layers, on three plots, each with different soil types, i.e. Dystric Cambisol (DC), Eutric Cambisol (EC) and Rendzic Leptosol (RL). In this study, we took advantage of a natural soil gradient, from shallow calcic soil to deep moderately acidic soil, with similar climates, atmospheric depositions, species compositions and management. Soil solutions were measured monthly for 4 years to study the seasonal dynamics of Si fluxes. A budget of dissolved Si (DSi) was also determined for the forest floor and soil layers. Our study highlighted the major role of fine roots in the Si cycle in forest ecosystems for all soil types. Due to the abundance of fine roots mainly in the superficial soil layers, their high Si concentration (equivalent to that of leaves and 2 orders higher than that of coarse roots) and their rapid turnover rate (approximately 1 year), the mean annual Si fluxes in fine roots in the three plots were 68 and 110 kgha-1yr-1 for the RL and the DC, respectively. The turnover rates of fine roots and leaves were approximately 71 and 28 % of the total Si taken up by trees each year, demonstrating the importance of biological recycling in the Si cycle in forests. Less than 1 % of the Si taken up by trees each year accumulated in the perennial tissues. This study also demonstrated the influence of soil type on the concentration of Si in the annual tissues and therefore on the Si fluxes in forests. The concentrations of Si in leaves and fine roots were approximately 1.5–2.0 times higher in the Si-rich DC compared to the Si-poor RL. In terms of the DSi budget, DSi production was large in the three plots in the forest floor (9.9 to 12.7 kgha-1yr-1), as well as in the superficial soil layer (5.3 to 14.5 kgha-1yr-1), and decreased with soil depth. An immobilization of DSi was even observed at 90 cm depth in plot DC (−1.7 kgha-1yr-1). The amount of Si leached from the soil profile was relatively low compared to the annual uptake by trees (13 % in plot DC to 29 % in plot RL). The monthly measurements demonstrated that the seasonal dynamics of the DSi budget were mainly linked to biological activity. Notably, the peak of dissolved Si production in the superficial soil layer occurred during winter and probably resulted from fine-root decomposition. Our study reveals that biological processes, particularly those involving fine roots, play a predominant role in the Si cycle in temperate forest ecosystems, while the geochemical processes appear to be limited.

This thesis deals with the impact of soil type on the biogeochemical functioning of a typical forest ecosystem of Central and Western Europe. For this study, a strongly instrumented experimental site was implemented in a beech stand (Fagus sylvatica) within the state forest of Montiers-sur-Saulx (Meuse, France), in order to monitor the biogeochemical cycling between the different compartments of the ecosystem (the atmosphere, the canopy, the forest floor and the soil). The particular value of the Montiers experimental site resides in the strong contrast between soil types under the same beech stand: Rendzic Leptosol, Eutric Cambisol and Dystric Cambisol. For the first time, stocks and fluxes of water and elements were measured and compared in situ and over the long term (from January 2012 to December 2015) on different forest soil types, all other site conditions being equal (climate, atmospheric inputs, stand age and structure). Total and exchangeable pools in the soil and stocks in the different compartments of the vegetation (branches, trunk, fine and coarse roots) were determined via chemical analysis and modelisation. Fluxes of elements were calculated from monthly sampling of the ecosystem’s solutions (atmospheric deposition, throughfall, stemflow, gravitational and bound soil solutions) and of litter fall. The water balance model BILJOU© was used to estimate the different components of the water budget. The results show that the soil water holding capacity, the stocks of elements in the soil, the chemical composition of soil solutions, the rooting strategy and the perennial biomass production differ strongly between soil types. Contrary to what might have been expected in regard to the marked differences between the chemical signatures of the soils solutions in the three soils, the foliar elemental composition of the beech stand and the aboveground fluxes of elements in solution (canopy exchange, stand deposition) and in solid state (litter fall) do not differ significantly between the three experimental stations for the majority of the studied elements. The biological part of the mineral cycles is overall predominant and the recycling through fine roots turnover is generally higher than litter fall. We also show that the quantity of water transpired by the forest canopy, directly linked to the soil water holding capacity, is the primary control factor of the annual stand productivity. Stand adaptation mechanisms to physico-chemical soil properties seemed to reduce, or even entirely compensate for, secondary factors controlling the stand productivity (in particular nutrient availability in the soil). Thus a significant issue for forest managers might be to further adapt forestry practices to management units based on soil physical properties, especially depth to the bedrock and rooting depth, Cette thèse porte sur l’impact du type de sol sur le fonctionnement biogéochimique d’un écosystème forestier typique d’Europe centrale et occidentale. Pour cette étude, un dispositif expérimental a été mis en place par l’INRA et l’ANDRA au sein d’une hêtraie (Fagus sylvatica) dans la forêt de Montiers-sur-Saulx (Meuse, France) afin de suivre les cycles biogéochimiques entre les différents compartiments de l’écosystème (l’atmosphère, la canopée, la litière et le sol). L’intérêt particulier du site expérimental de Montiers vient du contraste important entre les types de sols pour un même peuplement : rendisol, calci-brunisol et alocrisol/brunisol. Pour la première fois, les stocks et les flux de l’eau et des éléments ont été mesurés et comparés in situ et sur le long terme (entre janvier 2012 et décembre 2015) sur des sols forestiers différents, toutes les autres conditions du site égales par ailleurs (climat, apports atmosphériques, âge et structure du peuplement). Les stocks totaux et échangeables dans le sol et les stocks dans les différents compartiments de la biomasse végétale (branches, tronc, racines grosses et fines) ont été déterminés par le biais d’analyses chimiques et de modélisations. Les flux élémentaires ont été calculés à partir des prélèvements mensuels des solutions de l’écosystème (dépôt atmosphérique, pluviolessivat, écoulement de tronc, solutions libres et liées du sol) et des chutes de litière. Le modèle hydrique BILJOU© a été utilisé pour estimer les composantes du bilan hydrique de l’écosystème. Les résultats montrent que la réserve utile du sol, les stocks des éléments dans le sol, les compositions chimiques des solutions du sol, la stratégie de colonisation racinaire et la production de biomasse pérenne diffèrent fortement en fonction du type de sol. Contrairement à ce que l’on pouvait supposer compte tenu des différences marquées entre les signatures chimiques des solutions des trois sols, les compositions foliaires du peuplement et les flux des éléments hors sol en solution (échange de la canopée, apport au sol) et sous forme solide (chute de litière) ne diffèrent pas ou peu entre les trois stations expérimentales pour la majorité des éléments. La part biologique des cycles minéraux est globalement prédominante et le renouvellement des racines fines représente un flux de recyclage généralement supérieur à la chute de litière aérienne. Nous montrons également que la quantité d’eau transpirée par la canopée, directement liée à la taille de la réserve utile du sol, est le facteur de contrôle principal de la productivité du peuplement à l’échelle annuelle. Des processus d’adaptation du peuplement aux conditions physico-chimiques du sol semblent réduire, voire compenser entièrement, les facteurs secondaires de contrôle de la productivité du peuplement (notamment la disponibilité des nutriments dans le sol). Ainsi un enjeu significatif pour les gestionnaires forestiers pourrait être l’adaptation des pratiques sylvicoles à des parcelles de gestion davantage basées sur les propriétés physiques des sols, et en particulier les profondeurs d’apparition de la roche-mère et de colonisation racinaire

Natural attenuation of petroleum contamination in forest ecosystems. Role of pedological and biological (microorganisms, flora and fauna) characteristics – the CONPET project. 14t. International Conference on Sustainable Use and Management of Soil, Sediment and Water Resources (AquaConSoil)

For forest ecosystems, the relationship between root biomass, root growth and soil nitrification is still debated. Following repeated findings of significant differences in soil nitrification beneath comparable stands at the Breuil experimental site, a reciprocal soil exchange experiment combining high (H)- and low (L)-nitrifying stands was conducted to highlight the effect of tree root colonization on the control of nitrification. Soil percent nitrification and fine root biomass were measured in undisturbed and in transplanted soil cores after 16 and 28 months. In undisturbed soils, the fine root biomass varied by tree species and explained only 14% of the variation in percent nitrification. In transplanted soil cores, percent nitrification converged, at different rates, towards values close to those measured in the undisturbed soil at the receptor stands. On the one hand, percent nitrification increased rapidly in soil cores from L transferred to H, while soil core colonization by roots remained low during the study period. Soil cores might have been colonized by active nitrifiers from their new environment, or/and the activity of the nitrifiers originally present was less suppressed by root activity in their new environment. On the other hand, percent nitrification decreased progressively in soil cores from H transferred to L as root colonization increased. This suggests that root colonization reduced nitrifier population and activity. Our findings suggest that the often-reported influence of forest species on soil nitrification is probably multifactorial but the tree root colonization contributes.

The Formica rufa group of species is considered to be a good indicator of the state of conservation of montaneforests. The standardised protocol for tracking myrmecological populations developed by Torossian in1983 is re-examined thirty years onwards at the same site using measurements of the myrmecological populationof a montane forest in the Pyrenees. Results show that the density of domes has dropped drastically.We hypothesize that the density of ski runs, the contrasts between different-facing slopes, and the type offorest stands may explain these variations. Considering the life expectancy of Formica rufa populations, thisstudy underscores the importance of diachronic analyses like these for the purpose of long term monitoringof forest ecosystems.; Le groupe d’espèces Formica rufa est considéré comme un bon indicateur de l’état de conservation des forêtsde montagne. Le protocole standardisé pour le suivi des peuplements myrmécologiques mis au point parTorossian en 1982 a été repris trente ans après sur le même site avec des mesures sur le peuplement myrmécologique d’une forêt de montagne pyrénéenne. Les résultats indiquent que la densité des dômes a fortementchuté. Nous avançons que la densité des pistes de ski, les oppositions de versants et la nature despeuplements forestiers pourraient expliquer ces variations. Compte tenu de la durée de vie des populationsde Formica rufa, cette étude souligne l’importance de telles analyses diachroniques pour le suivi à long termedes écosystèmes forestiers.

International audience; The Formica rufa group of species is considered to be a good indicator of the state of conservation of montane forests. The standardised protocol for tracking myrmecological populations developed by Torossian in 1983 is re-examined thirty years onwards at the same site using measurements of the myrmecological population of a montane forest in the Pyrenees. Results show that the density of domes has dropped drastically. We hypothesize that the density of ski runs, the contrasts between different-facing slopes, and the type of forest stands may explain these variations. Considering the life expectancy of Formica rufa populations, this study underscores the importance of diachronic analyses like these for the purpose of long term monitoring of forest ecosystems.; Le groupe d’espèces Formica rufa est considéré comme un bon indicateur de l’état de conservation des forêts de montagne. Le protocole standardisé pour le suivi des peuplements myrmécologiques mis au point par Torossian en 1982 a été repris trente ans après sur le même site avec des mesures sur le peuplement myrmécologique d’une forêt de montagne pyrénéenne. Les résultats indiquent que la densité des dômes a fortement chuté. Nous avançons que la densité des pistes de ski, les oppositions de versants et la nature des peuplements forestiers pourraient expliquer ces variations. Compte tenu de la durée de vie des populations de Formica rufa, cette étude souligne l’importance de telles analyses diachroniques pour le suivi à long terme des écosystèmes forestiers.

Boron concentrations and isotopic compositions of atmospheric dust and dissolved depositions were monitored over a two-year period (2012-2013) in the forest ecosystem of Montiers (Northeastern France).This time series allows the determination of the boron atmospheric inputs to this forest ecosystem and contributes to refine our understanding of the sources and processes that control the boron atmospheric cycle. Mean annual dust and dissolved boron atmospheric depositions are comparable in size (13 g.ha(-1).yr(-1) and 16 g.ha(-1).yr(-1), respectively), which however show significant intra- and interannual variations.Boron isotopes in dust differ from dissolved inputs, with an annual mean value of +1 and +18 for, respectively. The notable high boron contents (190-390 mu g.g(1)) of the dust samples are interpreted as resulting from localized spreading of boron-rich fertilizers, thus indicating a significant local impact of regional agricultural activities. Boron isotopes in dissolved depositions show a clear seasonal trend.The absence of correlation with marine cyclic solutes contradicts a control of atmospheric boron by dissolution of seasalts. Instead, the boron data from this study are consistent with a Rayleigh-like evolution of the atmospheric gaseous boron reservoir with possible but limited anthropogenic and/or biogenic contributions.

In terrestrial ecosystems, plant-available pools of magnesium and calcium are assumed to be stored in the soil as exchangeable cations adsorbed on the surface of mineral and/or organic particles. The pools of exchangeable magnesium and calcium are measured by ion-exchange soil extractions. These pools are sustained in the long term by the weathering of primary minerals in the soil and atmospheric inputs. This conceptual model is the base of input-output budgets from which soil acidification and the sustainability of soil chemical fertility is inferred. However, this model has been questioned by data from long-term forest ecosystem monitoring sites, particularly for calcium. Quantifying the contribution of atmospheric inputs, ion exchange and weathering of both primary, secondary and non-crystalline phases to tree nutrition in the short term is challenging. In this study, we developed and applied a novel isotopic dilution technique using the stable isotopes of magnesium and calcium to study the contribution of the different soil phases to soil solution chemistry in a very acidic soil. The labile pools of Mg and Ca in the soil (pools in equilibrium with the soil solution) were isotopically labeled by spraying a solution enriched in 26Mg and 44Ca on the soil. Labeled soil columns were then percolated with a dilute acid solution during a 3-month period and the isotopic dilution of the tracers was monitored in the leaching solution, in the exchangeable (2 sequential 1 mol L−1 ammonium acetate extractions) and non-crystalline (2 sequential soil digestions: oxalic acid followed by nitric acid) phases. Significant amounts of Mg and Ca isotope tracer were recovered in the non-crystalline soil phases. These phases represented from 5% to 25% and from 24% to 50%, respectively, of the Mg and Ca labile pools during the experiment. Our results show that non-crystalline phases act as both a source and a sink of calcium and magnesium in the soil, and contribute directly to soil solution chemistry on very short-term time scales. These phases are very abundant in acid soils and, in the present study, represent a substantial calcium pool (equivalent in size to the Ca exchangeable pool). The gradual isotopic dilution of Mg and Ca isotope ratios in the leaching solution during the experiment evidenced an input flux of Mg and Ca originating from a pool other than the labile pool. While the Mg input flux originated primarily from the weathering of primary minerals and secondarily from the non-crystalline phases, the Ca input flux originated primarily from the non-crystalline phases. Our results also show that the net calcium release flux from these phases may represent a significant source of calcium in forest ecosystems and actively contribute to compensating the depletion of Ca exchangeable pools in the soil. Non-crystalline phases therefore should be taken into account when computing input-output nutrient budgets and soil acid neutralizing capacity. (Resume d'auteur)

Chapitre 7; In many parts of the world, forests are likely to face novel disturbance regimes as a result of global change processes, and there is concern that the capacity of forest ecosystems to withstand, recover from, or adapt to these novel disturbance regimes may decline. Creation and maintenance of species-diverse forests is seen as an important option to adapt forests to uncertain future disturbances.However, it is not known whether benefits of mixed-species forests consist mainly of risk spreading among tree species that have different susceptibility to various stressors and disturbance agents or whether they also have emergent properties resulting from interactions among species, which increase the resistance and resilience of participating species or the entire ecosystem. Here we review the evidence for the effects of tree diversity on the resistance and resilience of forests in relation to a number of abiotic (drought, wind, fire) and biotic (insect herbivores, pathogens) stress and disturbance factors. For the abiotic disturbances, damage or reduction in ecosystem function can be reduced, compared with monocultures of susceptible or less resilient species, when more resistant or resilient species are mixed with less susceptible and less resilient species. However, storm, fire, or drought damage to individual species may not be reduced in mixtures when compared to monocultures. The stress or disturbance impacts may even be aggravated for one or more species in somemixtures, as is shown for drought. There is more evidence for beneficial diversity effects in relation to biotic disturbance agents. Mixing tree species reduces the impact of insect herbivores on individual susceptible tree species in the majority of cases, where the community is dominated by specialist herbivores. However, the opposite effect may occur with generalist herbivores, which can be promoted by tree diversity. Similarly, tree diversity can reduce the impact of specialist pathogens on host tree species, whereas there is little evidence for positive influences in the case of generalist pathogens. In most cases, tree species diversity dilutes the impact of disturbance agents and, owing to different susceptibility of species to specific disturbances, insures against a complete damage or loss. In addition, mixing tree species can reduce temporal variation in growth and stabilise productivity. However, there is little evidence for true, positive diversity effects, where diversity leads to an increase in the resistance and resilience of component species in mixed-species communities. From an economic point of view, mixing might help to reduce risk for a more vulnerable and valuable species, even if there are no benefits for the admixed species. However, forest managers should be aware that mixtures do not provide universally higher resistance or resilience in relation to disturbances than monocultures. In most cases, it depends to a large extent on the attributes of the species in mixture inrelation to the specific disturbances.

Historical ecology traces the evolution of ecosystems and landscapes in time while taking into consideration the influence of human practices. To this cross-disciplinary approach, we added another convergence in associating pedoanthracology which aims acutely at reconstructing ancient forest ecosystems. However, the question of its representativeness arises to assess the real contribution of pedoanthracology in understanding past human-forest interactions in context of European temperate deciduous forest. Through this work, our goal was to develop a new sampling protocol based on a data analysis methodology taken from ecology to ensure the representativeness of taxonomic and quantitative pedoanthracological data.To be consistent with this purpose, two ancient forests of northern France were chosen: Compiègne and Saint Gobain. We explored the archives of each anthracological massif considering the pedological impact on vegetation. Three soil types have been prospected: podzols, cambisols and luvisols. An original mixed protocol was established combining a vertical methodology, soil pits (2.25 m²), with a horizontal procedure based on a 1000 m² auger grid in upper soil horizons (0-20 cm). To determine the representativeness of the sampling method, each liter was treated individually. Charcoals were extracted to measure anthracomasses from which spatial autocorrelation was tested by the Moran I Index. For Compiègne, taxonomic identifications were achieved to evaluate the specific richness. We used rarefaction curves and the additive partitioning of species diversity to analyze the representativeness of sampling efforts in liters and charcoals. Fifteen fragments were then selected and radiocarbon dated. The whole results were subsequently confronted with archeological and historical data including Lidar imagery. The results of spatial autocorrelation indicate that charcoals are randomly and heterogeneously distributed regardless of measurement scales. Soil and biological disturbances (bioturbation, distribution of burnt trees) may have caused this lack of overall spatial pattern. The taxonomic richness increases fastly with augers even though they contain less taxa than the pits. The sampling efforts are inadequate for the pits and must be specifically adapted by horizon. Only augers have reached representativeness thresholds. The minimal sampling effort is influenced by the sampling method as well as the pedological context. We observe that the combination of the two sampling techniques more efficiently reflects the anthracological diversity than either applied separately. Horizontal samplings are thus relevant to take into account the spatial variability and to supply new taxa enriching the anthracological assemblages of the pits. The pedoanthracological sampling strategy proves to be crucial since it affects the results. The synthesis of the data provided by the different disciplines enables us to establish three stages related to the Compiégnois territory: the forest recolonization during the early Middles Ages, the establishment of a large oak-birch open canopy forest shaped by the using rights until the late Middle Ages and finally a beech-oak canopy closure from the 18th century to nowadays. The historical ecology can then rely on pedoanthracology as a trustworthy source of information correlating with hypothesis and scenarii from other disciplines such as history and archeology in the reconstruction of landscapes and forest history in northern France and western Europe.; L’écologie historique retrace l’évolution des écosystèmes et paysages dans le temps tout en considérant l’influence des pratiques humaines. C’est une approche pluridisciplinaire à laquelle nous avons associé la pédoanthracologie particulièrement encline à reconstituer les écosystèmes forestiers anciens. Cependant, la question de sa représentativité écologique se pose afin d’évaluer sa contribution réelle dans la compréhension des interactions homme-forêt passées en contexte de forêt feuillue tempérée européenne. Par ce travail, notre objectif était de mettre au point un nouveau protocole d’échantillonnage doté d’une méthode d’analyse des données empruntées à l’écologie afin de s’assurer de la représentativité des données pédoanthracologiques quantitatives et taxonomiques.En adéquation avec cet objectif, ce sont deux forêts anciennes du nord de la France qui ont été choisies : Compiègne et Saint Gobain. Nous avons exploré les archives anthracologiques de chaque massif en considérant l’impact stationnel sur la végétation. Trois types de sol ont ainsi été prospectés : podzols, cambisols et luvisols. Un protocole original a été établi couplant une approche verticale, fosse pédologique (2.25 m²), à une approche horizontale s’appuyant sur un maillage tarière (1000 m²) des horizons superficiels du sol (0-20 cm). Pour mesurer la représentativité de l’échantillonnage, chaque litre prélevé a été traité individuellement. Les charbons en ont été extraits pour mesurer les anthracomasses dont l’autocorrélation spatiale a été testée par l’indice I de Moran. Pour Compiègne, les identifications taxonomiques ont été réalisées pour déterminer les richesses spécifiques. Nous avons utilisé les courbes de raréfactions et la partition additive de la diversité pour analyser la représentativité des efforts d’échantillonnages en nombre de litres et de charbons. Quinze fragments ont ensuite été sélectionnés et datés au radiocarbone et l’ensemble des résultats finalement confronté aux données archéologiques et historiques incluant les imageries Lidar.Les résultats de l’autocorrélation spatiale indiquent que la distribution des charbons est aléatoire et hétérogène à plusieurs échelles de mesure. Les perturbations pédologiques et biologiques (bioturbation, répartition des arbres brûlés) sont probablement la cause de cette absence globale de patron spatial. Concernant la richesse taxonomique, elle augmente plus rapidement avec les tarières même si elles recueillent moins de taxons que les fosses. Les efforts d’échantillonnages sont insuffisants pour les fosses et doivent être adaptés en fonction des horizons. Seules les tarières ont atteint des seuils de représentativité. L’effort minimal d’échantillonnage est influencé par la méthode de prélèvement ainsi que le contexte pédologique. Nous constatons que l’emploi combiné des deux méthodes de prélèvements rend mieux compte de la diversité anthracologique que l’une ou l’autre appliquée séparément. Les prélèvements horizontaux sont pertinents dans la prise en compte de la variabilité spatiale et l’apport de nouveaux taxons enrichissant les inventaires des fosses. La stratégie d’échantillonnage pédoanthracologique se révèle cruciale car elle détermine les résultats obtenus. La synthèse des données apportées par les différentes approches, nous permet de situer la recolonisation forestière du territoire Compiégnois durant le haut Moyen-Âge puis l’établissement d’un massif très ouvert de type chênaie-bétulaie façonné par les droits d’usages jusqu’à la fin du Moyen-Âge et enfin une forêt fermée de type hêtraie-chênaie à partir du XVIIIème siècle jusqu’à nos jours. L’écologie historique peut alors employer la pédoanthracologie comme une source fiable d’informations venant parfaitement se corréler avec les hypothèses et scénarii des autres disciplines telles que l’histoire et l’archéologie dans la reconstitution de l’histoire des paysages et des écosystèmes forestiers du Nord de la France et de l’ouest Européen.

International audience; Since the Fukushima accident, Japanese scientists have been intensively monitoring ambient radiations in the highly contaminated territories situated within 80 km of the nuclear site. The surveys that were conducted through mainly carborne, airborne and in situ gamma-ray measurement devices, enabled to efficiently characterize the spatial distribution and temporal evolution of air dose rates induced by Caesium-134 and Caesium-137 in the terrestrial systems. These measurements revealed that radiation levels decreased at rates greater than expected from physical decay in 2011-2012 (up to a factor of 2), and dependent on the type of environment (i.e. urban, agricultural or forest). Unlike carborne measurements that may have been strongly influenced by the depuration of road surfaces, no obvious reason can be invoked for airborne measurements, especially above forests that are known to efficiently retain and recycle radiocaesium.The purpose of our research project is to develop a comprehensive understanding of the data acquired by Japanese, and identify the environmental mechanisms or factors that may explain such decays. The methodology relies on the use of a process-based and spatially-distributed dynamic model that predicts radiocaesium transfer and associated air dose rates inside/above a terrestrial environment (e.g., forests, croplands, meadows, bare soils and urban areas).Despite the lack of site-specific data, our numerical study predicts decrease rates that are globally consistent with both aerial and in situ observations. The simulation at a flying altitude of 200 m indicated that ambient radiation levels decreased over the first 12 months by about 45% over dense urban areas, 15% above evergreen coniferous forests and between 2 and 12% above agricultural lands, owing to environmental processes that are identified and discussed. In particular, we demonstrate that the decrease over evergreen coniferous regions might be due the combined effects of canopy depuration (through biological and physical mechanisms) and the shielding of gamma rays emitted from the forest floor by vegetation. Our study finally suggests that airborne surveys might have not reflected dose rates at ground level in forest systems, which were predicted to slightly increase by 5 to 10% during the same period of time.

Modelling the impact of soil Carbonic Anhydrase on the net ecosystem exchange of OCS at Harvard forest using the MuSICA model. European Geosciences Union General Assembly 2016

International audience; Abstract• Key messageSimulated and observed carbon stocks in Scots pine forests varied considerably with stand age. The contribution of biomass to the total forest carbon stocks increased and that of dead organic matter decreased with increasing stand age.• Context Understanding changes in forest carbon stocks over time is important to estimate carbon inventory. Although Scots pine (Pinus sylvestris L.) is a main species in Turkey, studies on such changes are still lacking.• Aims We aimed to estimate the changes in carbon stocks, with stand age, of Scots pine stands in Turkey using field work data and a forest carbon model (FBDC model).• Methods Biomass and dead organic matter carbon stocks were investigated to adjust the forest carbon model and to verify the model estimates. Forest carbon stocks with regards to stand age were simulated.• Results The simulated carbon stocks were generally in clear agreement with the observed values on a stand scale. Changes in simulated and observed carbon stocks of biomass and dead organic matter varied with stand age. The contribution of biomass to total forest carbon stocks increased, and that of dead organic matter decreased, with increasing stand age.• Conclusion We found that the carbon stocks in each pool and their contribution to the total forest carbon stocks varied with stand age. Our results are expected to contribute to the understanding of annual changes in the carbon stocks of Turkish forests.

Due to land use history, most of the current temperate and boreal forests are developed on nutrient-poor and rocky soils, keeping fertile soils for agriculture. Consequently, the conditions occurring in forest ecosystems strongly differ from those of other terrestrial environments, giving importance to the access of nutritive elements and their recycling for the long-lasting development of forest ecosystems. In this review, we present an overview of the recent findings on the relationships between bacterial and fungal communities and their tree hosts at both the taxonomic and functional levels. We highlighted the common and different deterministic drivers of these microbial communities, focusing on the tree species effect, the different interfaces existing between the trees and their environment, the impact of tree by-products (decaying wood and litter), the impact of soil and seasonal changes, and lastly, the consequences of forestry practices. Depicting both taxonomic and functional diversity based on cultivation-dependent and -independent analyses, we highlight the distribution patterns and the functional traits characterizing bacterial and fungal communities. We also discuss the importance of bridging environmental microbiology to genomics and how to integrate the interactions between microorganisms for a better understanding of tree growth and health.

Forest evapotranspiration: measurement and modelling at multiple scales

Clay minerals and K feldspars were evaluated as sources of K in a Norway spruce stand (Picea abies (L.) Karst.) from the Skogaby experimental forest in southwest Sweden. The soil, developed in a Quaternary glacial till, has only 3-5% clay, and more than 95% of its K resides in feldspars. Ratios of K/Rb were assessed in interlayers of 2: 1 clay minerals (extracted with hot (100 degrees C) 2 M HCl), biomass and the forest floor. These compartments had similarly low K/Rb ratios, whereas K feldspars were significantly poorer in Rb. A fractionation model indicated preferential retention of Rb in the biomass and forest floor, due to stronger adsorption of Rb than K in the humus, as well as preferential uptake of K from the exchange complex in the mineral soil. Preferential uptake of K may result from weaker adsorption of K by the cation exchanger, or preference for dissolved K over Rb by the roots. A quantitative mineralogical analysis revealed that loss from micas may account for half of the Holocene loss of K from the soil, which was approximately 22 Mg ha(-1). Exceptionally low K/Rb ratios in HCl extracts of the upper 60 cm of the profile indicated extensive loss of K from mica in the parent material and re-fixation of K and Rb at lower ratios. The results indicate that fixation in and release from clay minerals may be prominent in the cycling of K, even in a soil that is poor in clay minerals.

International audience; Loblolly pine trees (Pinus taeda L.) occupy more than 20% of the forested area in the southern United States, represent more than 50% of the standing pine volume in this region, and remove from the atmosphere about 500 g C m-2 per year through net ecosystem exchange. Hence, their significance as a major regional carbon sink can hardly be disputed. What is disputed is whether the proliferation of young plantations replacing old forest in the southern United States will alter key aspects of the hydrologic cycle, including convective rainfall, which is the focus of the present work. Ecosystem fluxes of sensible (Hs) and latent heat (LE) and large-scale, slowly evolving free atmospheric temperature and water vapor content are known to be first-order controls on the formation of convective clouds in the atmospheric boundary layer. These controlling processes are here described by a zero-order analytical model aimed at assessing how plantations of different ages may regulate the persistence and transition of the atmospheric system between cloudy and cloudless conditions. Using the analytical model together with field observations, the roles of ecosystem Hs and LE on convective cloud formation are explored relative to the entrainment of heat and moisture from the free atmosphere. Our results demonstrate that cloudy-cloudless regimes at the land surface are regulated by a nonlinear relation between the Bowen ratio Bo=Hs/LE and root-zone soil water content, suggesting that young/mature pines ecosystems have the ability to recirculate available water (through rainfall predisposition mechanisms). Such nonlinearity was not detected in a much older pine stand, suggesting a higher tolerance to drought but a limited control on boundary layer dynamics. These results enable the generation of hypotheses about the impacts on convective cloud formation driven by afforestation/deforestation and groundwater depletion projected to increase following increased human population in the southeastern United States.

Harmonisation des protocoles d’observation de la phénologie des arbres forestiers. Colloque francophone PHENOLOGIE 2015

In this paper, we first present a total forest economic value framework from an anthropocentric instrumental value perspective and differentiate gross value, economic value, market value, and valuation of forest ecosystem services. We then argue that some of the demand-side-based non-market valuation approaches only provide an estimate of gross value, not economic value. Thus, strictly speaking, they are not market valuation per se as the supply side is ignored, and as many non-marketable and non-extractive forest ecosystem services are concerned, it is often the supply side – the opportunity costs of resources used to produce them that determine the economic values of these services. Finally, we identify the role of economic valuation of forest ecosystem services in the political market that often allocates resources directly to produce these services.

International audience; Many forest stands grow on acid and nutrient poor soils. To better understand how they cope with very low mineral resources, we investigated (1) Mg and Ca uptake in relation to depth, and (2) the allocation of these elements from the roots to the canopy, using a multi-isotopic (Mg-26, Ca-44) tracing experiment in a beech stand on a very poor soil. The distribution of the tracers in the soil was taken from van der Heijden et al. (Plant Soil 369:33-45, 2013a, Geoderma 195-196:12-22, 2013b, For Ecol Manag 293:65-78, 2013c). A model simulating Mg, Ca, Mg-26 and Ca-44 uptake was developed and applied to estimate the vertical distribution of Mg and Ca uptake in the soil profile. The vertical distribution of tracers in aboveground biomass was measured from four felled trees 2 years after the application of the tracers. The modeled distribution of root uptake in relation to depth shows differences between Mg and Ca: the main source of Mg uptake is the litter layer (circa. 43 % of total uptake) and the top mineral soil (0-5 cm) for Ca (circa. 42 %). The deeper soil layers (15-60 cm) also contribute to uptake. The study does not show clear evidence that uptake occurs in the very deep soil layers (> 70 cm). The distribution of tracers in the aboveground biomass shows a vertical gradient from the stump to the canopy with no or very small amounts of tracers being observed in the foliage during the 2 years after the application of tracers. This suggests that Mg and Ca transport from roots to leaves along the xylem sap flow is quite slow. As Ca and Mg supply to the trees from deep soil horizons is not evidenced, and tracer transport from roots to the leaves is slow, we suggest that the tree internal pool of Ca and Mg may be more active than previously thought. This pool may act as a buffer when nutrient availability is in shortage.

While Amazonian forests are extraordinarily diverse, the abundance of trees is skewed strongly towards relatively few ‘hyperdominant' species. In addition to their diversity, Amazonian trees are a key component of the global carbon cycle, assimilating and storing more carbon than any other ecosystem on Earth. Here we ask, using a unique data set of 530 forest plots, if the functions of storing and producing woody carbon are concentrated in a small number of tree species, whether the most abundant species also dominate carbon cycling, and whether dominant species are characterized by specific functional traits. We find that dominance of forest function is even more concentrated in a few species than is dominance of tree abundance, with only ≈1% of Amazon tree species responsible for 50% of carbon storage and productivity. Although those species that contribute most to biomass and productivity are often abundant, species maximum size is also influential, while the identity and ranking of dominant species varies by function and by region., The Amazon rainforest is dominated by relatively few tree species, yet the degree to which this hyperdominance influences carbon cycling remains unknown. Here, the authors analyse 530 forest plots and show that ∼1% of species are responsible for 50% of the aboveground carbon storage and productivity.

International audience

Comprendre le bon fonctionnement des écosystèmes forestiers pour anticiper les conséquences liées au changement climatique. Rencontre Enseignants-Chercheurs

National audience; L’équilibre entre une population d’ongulés sauvages et son habitat constitue un objectif essentiel pour les gestionnaires. Dans un contexte d’augmentation des populations de cervidés en France, cet équilibre est défini, par la loi, relativement aux impacts économiques pour la foresterie et l’agriculture. Plus largement, l’ensemble de la biodiversité est aussi sensible aux impacts des ongulés. Alors que les fortes densités peuvent compromettre la pérennité de la forêt, et donc altérer l’ensemble de la biodiversité forestière, l’absence de cervidés peut faire baisser la richesse spécifique…

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SYNERGIE [Axe_IRSTEA]TETIS-ATTOS; International audience; After a brief presentation of the interest of spatial remote sensing for broad scale forest monitoring, the potential of lidar technology to characterize and monitor forest ecosystems is presented. Then the STEM-LEAF project, developed to tackle pending issues to optimize a spaceborne vegetation lidar system is presented.

In deciduous oaks, spring reactivation modifies the capability of ectomycorrhizal fungi (EMf to mobilise carbon from soil organic matter. Plant carbon budget is also unbalanced during spring reactivation: carbon demand is high to build new tissues and carbon may be provided by reserves only as new photoassimilates are not yet available. Using a stable isotope approach with C-13-labelled litter, we have estimated that after a six months experiment, less than 1% of carbon is derived from litter during spring reactivation and is channelled from the soil to the thick roots of Quercus petraea via ectomycorrhiza, even when leaves are photosynthetically active. Our results are promising for future detailed quantification of different carbon sources (i.e. reserves, photosynthesis and litter derived) in EMf oak trees. They also support the hypothesis that oak trees of Q petraea in north-eastern France are partially mixotrophic plants. (C) 2012 Elsevier Ltd. All rights reserved.

L'évolution des écosystèmes forestiers résulte de l'interaction entre processus écologiques et actes de gestion. Le contexte du changement global et particulièrement celui l'évolution du climat remet en question l'adaptation de ces écosystèmes. Le terme d'adaptation doit être ici considéré dans toute sa polysémie : adéquation du système biologique aux conditions environnementales à un instant donné, processus évolutif et action anthropique. Face au changement, le fonctionnement des écosystèmes forestiers doit plus que jamais être considéré dans une perspective dynamique où la question du temps, célérité des changements et temps de réponse des forêts, est primordiale. De plus, compte tenu des nombreuses incertitudes (concernant le changement lui-même, les réponses biologiques à des conditions inédites, le comportement d'un écosystème complexe ou l'impact à moyen terme des mesures adaptatives), le principal enjeu est de guider la gestion à partir de ses impacts probables sur les trajectoires du système, de gérer les transitions, plutôt que de chercher à figer un idéal à moyen ou long-terme. Pour relever le défi de l'adaptation d'écosystèmes complexes comme les forêts, il faut donc comprendre les processus en jeu et les intégrer dans des modèles permettant de réaliser une pluralité de scénarios.

In nutrient-poor forest ecosystems, minerals are the main source of inorganic nutrients for the long lasting functioning of the forests. However, these nutrients are not directly accessible to the tree roots. It is the joined action of abiotic factors, such as pH and water circulation, and biotic factors such as tree roots and soil microorganisms, and notably bacteria, which leads to the solubilisation of these minerals. To date, our knowledge of the bacterial communities involved in the mineral weathering process and their distribution in forest soils is very limited and remains restricted to habitats such as the rhizosphere and mycorrhizosphere. The goals of this PhD thesis were to characterise the mineral associated bacterial communities, their ability to weather minerals and finally to identify the bacterial genes involved in the mineral weathering process. The combination of geochemical, cultivation-dependent and -independent approaches applied on minerals grounded in a forest soil during 4 years, revealed that the mineral associated bacterial communities were specific, able to weather minerals and had restricted metabolic abilities. These results suggest that minerals could be considered as a true ecological habitat: the mineralosphere. The mineral/bacteria relationship was tested in situ through a mineral amendment applied on a small-scale plantation, which has highlighted that the nutrient availability impacted the functional structure of the mineral weathering bacterial communities. At least, random mutagenesis applied on a model mineral weathering bacterial strain revealed that its mineral weathering ability resulted from several molecular mechanisms, Dans les écosystèmes forestiers pauvres en nutriments, les minéraux du sol constituent la principale source de nutriments inorganiques nécessaires à leur bon fonctionnement. Néanmoins ces nutriments ne sont pas directement accessibles aux racines des arbres. C'est l'action conjointe de facteurs abiotiques, comme le pH ou la circulation de l'eau, et biotiques comme les racines ou les microorganismes du sol dont les bactéries, qui vont conduire à l'altération de ces minéraux. A ce jour, nos connaissances sur les communautés bactériennes impliquées dans le processus d'altération et leur distribution dans des sols forestiers restent limitées, notamment à des habitats tels que la rhizosphère et la mycorhizosphère. Les objectifs de cette thèse étaient de caractériser les communautés bactériennes colonisant les minéraux du sol et leur aptitude à altérer les minéraux et enfin d'identifier les gènes bactériens impliqués. La combinaison d'approches cultivable, non cultivable et de biogéochimie sur des minéraux enterrés pendant 4 ans dans un sol forestier, a démontré que leur surface était colonisée par des communautés bactériennes spécifiques, capables d'altérer les minéraux et présentant des capacités métaboliques limitées, suggérant que ce support pourrait être considéré comme un habitat : la minéralosphère. La relation minéral/bactéries a été testée in situ via un amendement minéral sur une plantation et a mis en évidence l'impact de la disponibilité en nutriments sur la structuration des communautés bactériennes capables d'altérer les minéraux. L'étude génétique réalisée sur la souche modèle PML1(12) a révélé l'implication de plusieurs mécanismes dans la fonction altération

Climate change is known to cause a spatial redistribution of climatic conditions which is driving poleward and upward range shifts. Such shifts imply a reorganization of plant communities which is still poorly understood. Here we aimed to assess the changes in plant communities' composition induced by climate warming at a global scale and over a long time period, as well as to analyze the effects of ecological and geographical factors that contribute to these changes at the species and community levels. The response of the forest flora to the raising temperature has been studied across the French metropolitan territory (~546,000 km²) from large floristic databases, measured and modeled environmental data, and a modeling approach based on the concept of ecological niche and the bioindicator properties of plant species. First, we showed that the reshuffling of plant communities allowed to recover 0.54°C of the temperature increase between the periods 1965–1986 and 1987–2008 in highland forests (i.e. +1.07°C), while it recovered only 0.02°C in lowland forest (warming = 1.11 °C). This partial compensation demonstrates the current occurrence of a climatic debt in forest vegetation caused by climate warming. The high climatic debt observed in lowland forest compared to the highland one is likely due to extinction and migration debts caused by a wider temperature tolerance of plants in lowland communities and a plant migration capacity (i) limited by the high spatial fragmentation of the lowland forest habitat and (ii) shorter than the shift of thermal conditions in lowland areas, respectively. The ecological and geographical specificity of lowland and highland forests led us to consider two different threats induced by climate change: (i) biotic attrition in lowland areas, and (ii) loss of a specific and an historic biodiversity in highland forest (mountaintop extinction of alpine species due the surface decrease of their potential habitat) likely replaced by more common species assemblage (increase of generalist plants). Second, the effects of abiotic, biotic and geographical factors which can amplify or reduce the magnitude of both the species range shifts and the reshuffling of plant communities induced by global warming were characterized. Last and final summary in the thesis.; Le changement climatique est connu pour entraîner une redistribution spatiale des conditions climatiques et avec elle une migration des espèces vers les pôles et les sommets. De tels changements impliquent une réorganisation des communautés végétales dont la nature, l'intensité et le déterminisme sont encore peu connus. L'objectif de cette thèse est d'évaluer, à large échelle spatiale et sur de longs pas de temps, les changements de composition des communautés végétales forestières induits par le réchauffement climatique, ainsi qu'analyser les facteurs écologiques et géographiques contribuant à ces changements à l'échelle de l'espèce et des communautés. La réponse de la flore forestière vis-à-vis du réchauffement climatique a été étudiée à l'échelle du territoire français (~546000 km²) à partir de larges bases de données d'observations floristiques, de données environnementales mesurées et modélisées, et d'une approche modélisatrice basée sur le concept de niche écologique et sur le caractère bio-indicateur des espèces. Dans un premier temps, nous avons montré que le remaniement des communautés végétales a permis la compensation de 0.54°C du réchauffement climatique ayant touché les forêts de montagne entre les périodes 1965–1986 et 1987–2008 (i.e. +1.07°C) contre seulement 0.02°C pour les forêts de plaine (réchauffement = 1.11°C). Cette compensation partielle démontre l'existence d'une dette climatique de la flore induite par le réchauffement climatique. L'importance de cette dette en plaine par rapport aux montagnes provient probablement de l'effet combiné d'un déficit d'extinction et de migration des espèces en plaine conduit respectivement par une plus large tolérance thermique des plantes forestières sur cette zone et par une migration des plantes a priori (i) limitée par l'importante fragmentation des forêts de plaine et (ii) inférieure au déplacement des conditions thermiques en plaine. Les particularités écologiques et géographiques des forêts de plaine et de montagne nous ont amené à considérer deux types de menaces induites par le changement climatique : (i) l'attrition biotique en plaine, et (ii) la perte d'une biodiversité historique et spécifique en montagne (réduction de l'habitat des espèces alpines aboutissant à leur disparition) remplacée probablement par des espèces plus communes. Dans un second temps, les effets de facteurs abiotiques, biotiques et géographiques pouvant amplifier ou réduire les changements de distribution des espèces et de composition des communautés induits par le réchauffement climatique ont été caractérisés. [...] Suite et fin du résumé dans la thèse.

In the Upper Doubs Valley, at the end of the Middle Ages, man simultaneously destroys forests to extend his agricultural space and uses trees as necessary raw materials and a key source of energy. This represents a paradoxical situation for which he must find solutions. In the Middle Ages, woods are indeed both shaped by nature and by mankind. This study first describes the natural wood environment of this era and examines the effect of climate on a land that is the result of a long evolution from the Quaternary period. Then, it studies the impact of man from the Mesolithic era to the Middle Ages. It analyzes the chronology of deforestation and its link to demography in the context of wars and various crises in the lower Middle Ages. Deforestation is studied in its political, social, technical and ecological aspects and the way the newly created farmland is used is analyzed. The forests that man erases in the lower Middle Ages remain however, a vital resource for him, in particular for the growing manufacture. Therefore, man needs to solve this contradiction (i.e. to destroy and to build) for the following reasons: first, logging is a source of social and political conflicts, then it is about to destroy a fragile ecological balance. The consequences are the creation of restrictions and laws that are significant of a need for him to protect the environment. This situation is the precursor of problems and conflicts that contemporary man is now facing and which he still tries to solve, Le fonctionnement de l’écosystème forestier dans la haute vallée du Doubs, attestant le rôle déterminant du climat, permet par l’examen des conséquences des fluctuations climatiques sur une forêt climacique, de connaître la nature de la couverture forestière médiévale. Le milieu forestier que l’homme doit détruire pour s’installer résulte de la conjugaison d’une dynamique naturelle engagée depuis l’ère quaternaire et d’un impact anthropique progressif. Le lent processus de la colonisation depuis les premières traces de fréquentation mésolithique jusqu’au Moyen Âge, se confond avec l’essor des défrichements. L’histoire du peuplement du Haut-Doubs et du recul de la forêt dont le rythme épouse les vicissitudes démographiques dues aux guerres et aux crises du bas Moyen Âge, présente des singularités dans sa chronologie, les modalités des défrichements et la mise en valeur du territoire. Pourtant, cette forêt que l’homme abat reste une ressource nourricière vitale, source de matières premières et réserve énergétique indispensables aux activités quotidiennes et à un artisanat en essor. S’impose alors à l’homme confronté aux conflits d’intérêt liés à l’usage de la forêt, la nécessité de résoudre ce paradoxe qui consiste à devoir à la fois exploiter et détruire. Les mesures restrictives et les réglementations qui s’instaurent révèlent une prise de conscience relative face aux dangers qui menacent un équilibre écologique fragile, et au nouvel impératif de protection. Cette réalité présage des conflits et des problèmes ultérieurs dont l’homme contemporain est encore à chercher les solutions

Part 3: Case Studies and Case Histories. Chapter 18; A view from continental Europe: the case-study of Prunus serotina in France

International audience; The trace metal (TM: Cd, Cu, Ni, Pb and Zn) budget (stocks and annual fluxes) was evaluated in a forest stand (silver fir, Abies alba Miller) in north-eastern France. Trace metal concentrations were measured in different tree compartments in order to assess TM partitioning and dynamics in the trees. Inputs included bulk deposition, estimated dry deposition and weathering. Outputs were leaching and biomass exportation. Atmospheric deposition was the main input flux. The estimated dry deposition accounted for about 40% of the total trace metal deposition. The relative importance of leaching (estimated by a lumped parameter water balance model, BILJOU) and net biomass uptake (harvesting) for ecosystem exportation depended on the element. Trace metal distribution between tree compartments (stem wood and bark, branches and needles) indicated that Pb was mainly stored in the stem, whereas Zn and Ni, and to a lesser extent Cd and Cu, were translocated to aerial parts of the trees and cycled in the ecosystem. For Zn and Ni, leaching was the main output flux (N95% of the total output) and the plot budget (input-output) was negative, whereas for Pb the biomass net exportation represented 60% of the outputs and the budget was balanced. Cadmium and Cu had intermediate behaviours, with 18% and 30% of the total output relative to biomass exportation, respectively, and the budgets were negative. The net uptake by biomass was particularly important for Pb budgets, less so for Cd and Cu and not very important for Zn and Ni in such forest stands.

Dynamic Vegetation Models (DVMs) simulate energy, water and carbon fluxes between the ecosystem and the atmosphere, between the vegetation and the soil, and between plant organs. They also estimate the potential biomass of a forest in equilibrium having grown under a given climate and atmospheric CO2 level. In this study, we evaluate the Above Ground Woody Biomass (AGWB) and the above ground woody Net Primary Productivity (NPPAGW) simulated by the DVM ORCHIDEE across Amazonian forests, by comparing the simulation results to a large set of ground measurements (220 sites for biomass, 104 sites for NPPAGW). We found that the NPPAGW is on average overestimated by 63%. We also found that the fraction of biomass that is lost through mortality is 85% too high. These model biases nearly compensate each other to give an average simulated AGWB close to the ground measurement average. Nevertheless, the simulated AGWB spatial distribution differs significantly from the observations. Then, we analyse the discrepancies in biomass with regards to discrepancies in NPPAGW and those in the rate of mortality. When we correct for the error in NPPAGW, the errors on the spatial variations in AGWB are exacerbated, showing clearly that a large part of the misrepresentation of biomass comes from a wrong modelling of mortality processes. Previous studies showed that Amazonian forests with high productivity have a higher mortality rate than forests with lower productivity. We introduce this relationship, which results in strongly improved modelling of biomass and of its spatial variations. We discuss the possibility of modifying the mortality modelling in ORCHIDEE, and the opportunity to improve forest productivity modelling through the integration of biomass measurements, in particular from remote sensing.

International audience; The sustainability of fast-growing tropical Eucalyptus plantations is of concern in a context of rising fertilizer costs, since large amounts of nutrients are removed with biomass every 6–7 years from highly weathered soils. A better understanding of the dynamics of tree requirements is required to match fertilization regimes to the availability of each nutrient in the soil. The nutrition of Eucalyptus plantations has been intensively investigated and many studies have focused on specific fluxes in the biogeochemical cycles of nutrients. However, studies dealing with complete cycles are scarce for the Tropics. The objective of this paper was to compare these cycles for Eucalyptus plantations in Congo and Brazil, with contrasting climates, soil properties, and management practices. The main features were similar in the two situations. Most nutrient fluxes were driven by crown establishment the two first years after planting and total biomass production thereafter. These forests were characterized by huge nutrient requirements: 155, 10, 52, 55 and 23 kg ha_1 of N, P, K, Ca and Mg the first year after planting at the Brazilian study site, respectively. High growth rates the first months after planting were essential to take advantage of the large amounts of nutrients released into the soil solutions by organic matter mineralization after harvesting. This study highlighted the predominant role of biological and biochemical cycles over the geochemical cycle of nutrients in tropical Eucalyptus plantations and indicated the prime importance of carefully managing organic matter in these soils. Limited nutrient losses through deep drainage after clear-cutting in the sandy soils of the two study sites showed the remarkable efficiency of Eucalyptus trees in keeping limited nutrient pools within the ecosystem, even after major disturbances. Nutrient input–output budgets suggested that Eucalyptus plantations take advantage of soil fertility inherited from previous land uses and that long-term sustainability will require an increase in the inputs of certain nutrients.

National audience

International audience

International audience

Leaf Area Index (LAI) is a main variable controlling carbon and water fluxes. This paper estimated the effect of thinning on the spatial distribution of leaf area in French forests. While many studies have focused on average LAI, we estimated clumping and measured both average LAI and the variation around it. LAI was derived from digital hemispherical photos at three sites: an unmanaged Fagus sylvatica forest in temperate area (control site), a mixed Mediterranean forest of Quercus ilex and Pinus halepensis , and regeneration of F. sylvatica under a mature stand of Pinus nigra in mountainous area. LAI measurements were also made with LAI 2000 devices over 5 years (from 1994 to 1998) within forest stands dominated by either beech ( F. sylvatica L.), by oaks ( Quercus petraea (Matus) Liebl., Quercus robur (Matus) Liebl.), or by Scots Pine ( Pinus sylvestris L.). Thinning led to a variable decrease in LAI. The coefficient of variation of LAI (CV LAI ) provided a useful ecological index of the level and type of thinning. For undisturbed stands, CV LAI varied from 10% to 20%, corresponding to the higher average LAI values. Disturbances created by thinning increase LAI spatial variability, resulting in larger CV LAI values for all stands considered. Possible explanations of these results and use in remote sensing were discussed.