Book

Programme de recherche Biodiversité et gestion forestière : bilan 1996-2018

Authors:
  • GIP Ecofor
  • GIP Ecofor
ResearchGate has not been able to resolve any citations for this publication.
Article
Full-text available
Dans cette mise au point sémantique, nous proposons de formaliser une série de définitions des termes les plus fréquemment utilisés pour qualifier une forêt selon son degré d’anthropisation. La forêt est appréhendée ici sous sa dimension écosystémique, incluant biotope et biocœnose. Dans un souci de robustesse conceptuelle, nous nous appuyons sur quatre théories scientifiques : la théorie des communautés végétales, la théorie des successions écologiques, la théorie des perturbations et la théorie de la hiérarchie, dont les contributions sont brièvement analysées. Sur cette base, nous reprenons un certain nombre de définitions et en proposons de nouvelles, de manière à qualifier une forêt selon quatre attributs fondamentaux : son origine et sa genèse ; son degré de naturalité ; son historicité et sa morphologie. Chaque définition est explicitée, argumentée et illustrée à l’aide d’exemples concrets. Nous concluons par une réflexion ouverte sur le concept d’état de référence pour une forêt.
Article
Full-text available
The genetic and phenotypic variability of life history traits determines the demographic attributes of tree populations and, thus, their responses to anthropogenic climate change. Growth‐ and survival‐related traits have been widely studied in forest ecology, but little is known about the determinism of reproductive traits. Using an elevation gradient experiment in the Pyrenees we assessed the degree to which variations in reproductive effort along climatic gradients are environmentally or genetically driven, by comparing oak populations (Quercus petraea) growing under field and common garden conditions. In situ monitoring revealed a decline in reproductive effort with increasing elevation and decreasing temperature. In common garden conditions, significant genetic differentiation was observed between provenances for reproduction and growth: trees from cold environments (high elevations) grew more slowly, and produced larger acorns in larger numbers. Our observations show that genetic and phenotypic clines for reproductive traits have opposite signs (counter‐gradient) along the environmental gradient as opposed to growth, for which genetic variation parallels phenotypic variation (co‐gradient). The counter‐gradient found here for reproductive effort reveals that genetic variation partly counteracts the phenotypic effect of temperature, moderating the change in reproductive effort according to temperature. We consider the possible contribution to this counter‐gradient in reproductive effort as an evolutionary trade‐off between reproduction and growth.
Article
Full-text available
Climate change modifies ecosystem processes directly through its effect on environmental conditions, but also indirectly by changing community composition. Theoretical studies and grassland experiments suggest that diversity may increase and stabilize communities’ productivity over time. Few recent studies on forest ecosystems suggested the same pattern but with a larger variability between the results. In this paper, we aimed to test stabilizing diversity effect for two kinds of mixtures (Fagus sylvatica–Quercus pubescens and F. sylvatica–Abies alba), and to assess how climate may affect the patterns. We used tree ring data from forest plots triplets distributed along a latitudinal gradient across French Alps, adapting NBE approach to study temporal stability. We found that diversity effect on stability in productivity varies with stand composition. Most beech-fir stands showed a greater stability in productivity over time than monocultures, while beech-oak stands showed a less stable productivity. Considering nonadditive effects, no significant trends were found, regardless of the type of mixed stands considered. We further highlighted that these patterns could be partially explained by asynchrony between species responses (notably to variation in temperature or precipitation), overyielding and climatic conditions. We also showed that the intensity of the diversity effect on stability varies along the ecological gradient, consistently with the stress gradient hypothesis for beech in beech-oak forests, but not for beech-fir forests. This study showed the importance of the species identity on the relationships between diversity, climate and stability of forest productivity. Better depicting diversity and composition effects on forest ecosystem functioning appears to be crucial for forest managers to promote forest adaptation and maintain timber resource in the context of ongoing climate change.
Article
Full-text available
Expansion of planted forests and intensification of their management has raised concerns among forest managers and the public over the implications of these trends for sustainable production and conservation of forest biological diversity. We review the current state of knowledge on the impacts of plantation forestry on genetic and species diversity at different spatial scales and discuss the economic and ecological implications of biodiversity management within plantation stands and landscapes. Managing plantations to produce goods such as timber while also enhancing ecological services such as biodiversity involves tradeoffs, which can be made only with a clear understanding of the ecological context of plantations in the broader landscape and agreement among stakeholders on the desired balance of goods and ecological services from plantations
Article
Full-text available
Key message In this exploratory study, we show how combining the strength of tree diversity experiment with the long-term perspective offered by forest gap models allows testing the mixture yielding behavior across a full rotation period. Our results on a SW France example illustrate how mixing maritime pine with birch may produce an overyielding (i.e., a positive net biodiversity effect). ContextUnderstanding the link between tree diversity and stand productivity is a key issue at a time when new forest management methods are investigated to improve carbon sequestration and climate change mitigation. Well-controlled tree diversity experiments have been set up over the last decades, but they are still too young to yield relevant results from a long-term perspective. Alternatively, forest gap models appear as appropriate tools to study the link between diversity and productivity as they can simulate mixed forest growth over an entire forestry cycle.AimsWe aimed at testing whether a forest gap model could first reproduce the results from a tree diversity experiment, using its plantation design as input, and then predict the species mixing effect on productivity and biomass in the long term.Methods Here, we used data from different forest experimental networks to calibrate the gap model ForCEEPS for young pine (Pinus pinaster) and birch (Betula pendula) stands. Then, we used the refined model to compare the productivity of pure and mixed pine and birch stands over a 50-year cycle. The mixing effect was tested for two plantation designs, i.e., species substitution and species addition, and at two tree densities.ResultsRegarding the comparison with the experiment ORPHEE (thus on the short term), the model well reproduced the species interactions observed in the mixed stands. Simulations showed an overyielding (i.e., a positive net biodiversity effect) in pine-birch mixtures in all cases and during the full rotation period. A transgressive overyielding was detected in mixtures resulting from birch addition to pine stands at low density. These results were mainly due to a positive mixing effect on pine growth being larger than the negative effect on birch growth.Conclusion Although this study remains explorative, calibrating gap models with data from monospecific stands and validating with data from the manipulative tree diversity experiment (ORPHEE) offers a powerful tool for further investigation of the productivity of forest mixtures. Improving our understanding of how abiotic and biotic factors, including diversity, influence the functioning of forest ecosystems should help to reconsider new forest managements optimizing ecosystem services.
Article
Full-text available
Tree health declines can be caused by interactions between pests and pathogens and many studies have shown a reduction in their damage in mixed species forests compared to monocultures. Yet few authors have considered tree diversity effects on both groups simultaneously. Moreover, it is unclear whether diversity effects on tree pests and pathogens are robust to changes in abiotic conditions, such as drought. We addressed tree diversity effects on foliar insect herbivory, oak powdery mildew and their interaction under contrasting water regimes in a large‐scale tree diversity experiment in SW France. Using an irrigation treatment that alleviated drought conditions, we were able to experimentally assess the effects of tree diversity under contrasting abiotic environments. We surveyed plots along a richness gradient from 1 – 4 tree species, in which a focal study species of oak (Q. robur) was mixed with other oak species (Q. pyrenaica and Q. ilex) and a taller, broadleaved species (Betula pendula). Increasing tree species richness lowered leaf miner abundance, leaf chewer damage and oak powdery mildew infection, consistent with a protective effect of resource dilution. However, richness effects on leaf miners were stronger in irrigated compared to non‐irrigated blocks, indicating that environmental conditions can modulate diversity effects. Separate from the effect of tree species richness, the presence of birch in a plot increased damage by leaf chewers and powdery mildew, but lowered leaf miner damage, suggesting additional tree neighbour identity effects potentially linked to modulation of microclimate. We found a negative association between leaf miner abundance and oak powdery mildew, consistent with antagonism between oak damage agents. Overall, our study illustrates the importance of considering both tree diversity and composition (neighbour identity) in designing forests more resistant to pest and pathogen damage.
Article
Full-text available
Background and aims-Plants may use various defence mechanisms to protect their tissues against deer browsing and the allocation of resources to defence may trade-off with plants' growth. In a context of increasing deer populations in European forests, understanding the resource allocation strategies of trees is critical to better assess their ability to face an increasing browsing pressure. The aim of this study was to determine how deer removal affects the resource allocation to both defensive and growth-related traits in field conditions for three tree species (Abies alba, Picea abies and Fagus sylvatica). Methods-We compared eight pairs of fenced-unfenced plots to contrast plots with and without browsing pressure. The pairs were set up in 2005 and 2014 to compare different fencing duration. We measured leaf and shoot traits related to the defence against herbivores (phenolic content, structural resistance, C:N ratio) and to the investment in plants' growth and productivity (specific leaf area and nutrient content). Key results-For the three species, the structural resistance of leaves and shoots was negatively correlated with SLA, nutrient content and phenolic content. For Abies alba, exclusion of deer decreased shoot structural resistance in favour of higher nutrient content, SLA and phenolic content. The fencing duration had no effect on the different measured traits. Conclusions-Our results support the assumption of a trade-off between structural defence and growth-related traits at the intraspecific scale for the three studied species. We also confirmed the hypothesis that exposure to deer browsing is involved in the resource allocation of woody species. For Abies alba, fencing led to a change in resource allocation from structural defence to growth-related traits and chemical defence.
Article
Full-text available
Many perennial plants display masting, i.e., fruiting with strong interannual variations, irregular and synchronized between trees within the population. Here, we tested the hypothesis that the early flower phenology in temperate oak species promotes stochasticity into their fruiting dynamics, which could play a major role in tree reproductive success. From large field monitoring network, we compared the pollen phenology between temperate and Mediterranean oak species. Then, focusing on temperate oak species, we explored the influence of the weather around the time of bud‐burst and flowering on seed production, and simulated with a mechanistic model the consequences an evolutionary shifting of flower phenology would have on fruiting dynamics. Temperate oak species release pollen earlier in the season than Mediterranean oak species. Such early flowering in temperate oak species results in pollen being often released during unfavorable weather conditions and resulting in frequent reproductive failure. If pollen release was delayed due to natural selection, fruiting dynamics would exhibit much reduced stochastic variation. We propose that early flower phenology might be adaptive by making mast‐seeding years rare and unpredictable, which would greatly help controlling the dynamics of seed consumers.
Article
Full-text available
In many perennial wind‐pollinated plants, the dynamics of seed production is commonly known to be highly fluctuating from year to year and synchronised among individuals within populations. The proximate causes of such seeding dynamics, called masting, are still poorly understood in oak species that are widespread in the northern hemisphere, and whose fruiting dynamics dramatically impacts forest regeneration and biodiversity. Combining long‐term surveys of oak airborne pollen amount and acorn production over large‐scale field networks in temperate areas, and a mechanistic modelling approach, we found that the pollen dynamics is the key driver of oak masting. Mechanisms at play involved both internal resource allocation to pollen production synchronised among trees and spring weather conditions affecting the amount of airborne pollen available for reproduction. The sensitivity of airborne pollen to weather conditions might make oak masting and its ecological consequences highly sensitive to climate change.
Article
Full-text available
Both plant neighbourhood composition and drought have well-known independent effects on insect herbivore performance, but their interactive effects remain elusive. In this study we performed a laboratory experiment to investigate the independent and combined effects of plant neighbourhood composition and drought on the performance of Gypsy moth larvae (Lymantria dispar) feeding on silver birch (Betula pendula) leaves. For this, we collected leaf samples from birch trees growing in a field experiment where we manipulated both host-tree species diversity (three levels: birch monocultures, two-species mixtures associating birch with the pedunculate oak Quercus robur or maritime pine Pinus pinaster, and three-species mixture with pedunculate oak, the maritime pine and birch) and water availability (two levels: irrigated vs. non-irrigated). In most cases, plant neighbourhood composition and irrigation treatments independently and interactively affected herbivore performance traits, especially those related to growth and food (i.e. birch leaves) processing. By addressing the interactive effects of tree species diversity and drought on insect herbivory from the herbivore's point of view, our study builds toward a better understanding of the multiple ecological drivers of plant-insect interactions.
Article
Full-text available
Climate change affects ecosystem functioning directly through impacts on plant physiology, resulting in changes of global productivity. However, climate change has also an indirect impact on ecosystems, through changes in the composition and diversity of plant communities. The relative importance of these direct and indirect effects has not been evaluated within a same generic approach yet. Here we took advantage of a novel approach for disentangling these two effects in European temperate forests across a large climatic gradient, through a large simulation-based study using a forest succession model. We first showed that if productivity positively correlates with realized tree species richness under a changed climate, indirect effects appear pivotal to understand the magnitude of climate change impacts on forest productivity. We further detailed how warmer and drier conditions may affect the diversity-productivity relationships (DPRs) of temperate forests in the long term, mostly through effects on species recruitment, ultimately enhancing or preventing complementarity in resource use. Furthermore, losing key species reduced the strength of DPRs more severely in environments that are becoming climatically harsher. By disentangling direct and indirect effects of climate change on ecosystem functioning, these findings explain why high-diversity forests are expected to be more resilient to climate change.
Article
Full-text available
Elaborée dans le cadre du programme national de recherche "Biodiversité, gestion forestière et politiques publiques" (BGF), cette synthèse thématique vise principalement les utilisateurs de la recherche (décideurs, gestionnaires...). Elle fait le point sur les principaux résultats de la recherche qui permettent d'éclairer les relations entre la biodiversité des sols et la gestion forestière.
Article
Full-text available
Disturbance controls rainforest dynamics and, according to the Intermediate Disturbance Hypothesis (IDH), is a key driver of local diversity. Variations in disturbance regimes and their consequences for regional diversity at broad spatiotemporal scales are still poorly understood. Using multi-disciplinary large-scale inventories and LiDAR acquisitions in Guianan rainforests, we developed a robust generic indicator of disturbance regimes based on the frequency of a few early successional and widely distributed pioneer species. We demonstrate that tree-species diversity and disturbance regimes vary at the landscape scale with climate and relief categories. Significant relationships between the disturbance indicator, tree-species diversity and soil phosphorus content support the hypothesis that lowland rainforests diversity is controlled by disturbance regimes, along with long-term ecosystem stability. These effects explain the broad scale patterns of floristic diversity observed between landscapes, contrasting species rich forests on old highlands, which have benefited from long-term stability combined with a moderate and regular regime of local disturbances, and less diversified forests on recently shaped plains and hills, which have undergone more recent changes and irregular dynamics. These results suggest that taking the current disturbance regime into account and including geomorphological landscape stratifications in climate-vegetation models may be an efficient way to improve the prediction of changes in local vegetation under climate change.
Article
Full-text available
A new species of Humiriaceae, Vantanea maculicarpa, growing in French Guiana terra-firme forest is described and illustrated. This new species is distinguished from all other species of Vantanea by fruits covered by white lenticels, a character so far unknown in this genus. It also presents a pubescent intrastaminal disk, a feature encountered in two other Vantanea species only: it is further distinguished from V. parviflora, the morphologically most similar species, by more stamens and from V. ovicarpa by a much smaller rough endocarp with five valves. A key to the species of French Guiana and the IUCN status Least Concern (LC) are proposed.
Article
Full-text available
Forests are critical habitats for biodiversity and they are also essential for the provision of a wide range of ecosystem services that are important to human well-being. There is increasing evidence that biodiversity contributes to forest ecosystem functioning and the provision of ecosystem services. Here we provide a review of forest ecosystem services including biomass production, habitat provisioning services, pollination, seed dispersal, resistance to wind storms, fire regulation and mitigation, pest regulation of native and invading insects, carbon sequestration, and cultural ecosystem services, in relation to forest type, structure and diversity. We also consider relationships between forest biodiversity and multifunctionality, and trade-offs among ecosystem services. We compare the concepts of ecosystem processes, functions and services to clarify their definitions. Our review of published studies indicates a lack of empirical studies that establish quantitative and causal relationships between forest biodiversity and many important ecosystem services. The literature is highly skewed; studies on provisioning of nutrition and energy, and on cultural services, delivered by mixed-species forests are under-represented. Planted forests offer ample opportunity for optimising their composition and diversity because replanting after harvesting is a recurring process. Planting mixed-species forests should be given more consideration as they are likely to provide a wider range of ecosystem services within the forest and for adjacent land uses. This review also serves as the introduction to this special issue of Biodiversity and Conservation on various aspects of forest biodiversity and ecosystem services.
Article
Full-text available
Plant competition and deer browsing are two main factors which limit tree recruitment. We examined natural tree-recruitment processes under continuous- tree-cover management. Changes in plant communities and tree regeneration were monitored over an eight-year period at two different sites in a temperate hardwood forest in the North-East of France. We used paired control plot (unfenced areas, free access to deer) and exclosures (fenced areas, excluding deer) at both sites. Shade-tolerant browsing-tolerant opportunistic species (beech, Fagus sylvatica at site 1 and bramble, Rubus spp. at site 2) were present in low numbers at the beginning of the study. We found that these species used a sit-and-wait strategy, waiting for opportunities to proliferate (thinning and deer exclusion). In the exclosure at site 1, beech proliferate slowly. In the exclosure at site 2, bramble proliferated enough during the first two growing seasons to prevent tree recruitment. Thus, fencing encouraged beech sapling or bramble growth, and this growth in turn was detrimental to the richness and diversity of the plant community. The two study cases presented show that both plant competition and deer browsing can be problematic for tree recruitment. Our results further suggest that excluding deer is not sufficient to enhance the growth of browse-sensitive and moderately shade-tolerant tree species such as oaks (Quercus petraea and Q. robur).
Article
Full-text available
The changes in reproductive phenology (i.e. timing of flowering and fruiting) observed in recent decades demonstrate that tree reproduction has already been altered by climate change. However, understanding the impact of these changes in reproductive success and fitness remains a major challenge for ecologists. We describe here a previously unreported phenomenon: a significant increase in the reproductive effort (seed production) of temperate oaks with increasing spring temperature, observed over the last decade. In contrast, no relationship was found between seed production and precipitation. This sensitivity of seed production to temperature was confirmed by a "space-for-time" substitution based on elevation gradients. Our findings suggest that global warming may enhance oak reproductive effort in temperate ecosystems. Nevertheless, while fitness can be enhanced by higher levels of seed production, it also depends on the frequency and synchronization of mast seeding production, which may also be influenced by climate change.
Article
Full-text available
Forests are frequently exposed to natural disturbances, which are likely to increase with global change, and may jeopardize the delivery of ecosystem services. Mixed-species forests have often been shown to be more productive than monocultures, but it is unclear whether this results from mixed stands being in part more resistant to various biotic and abiotic disturbance factors. This review investigates the relationships between tree diversity and stand resistance to natural disturbances and explores the ecological mechanisms behind the observed relationships. Download full article here: http://www.springer.com/home?SGWID=0-0-1003-0-0&aqId=3315777&download=1&checkval=3718a7a79c09f728241d31ff367d3f0e
Article
Full-text available
The diversity of plant neighbors commonly results in direct, bottom-up effects on herbivore ability to locate their host, and in indirect effects on herbivores involving changes in plant traits and a top-down control by their enemies. Yet, the relative contribution of bottom-up and top-down forces remains poorly understood. We also lack knowledge on the effect of abiotic constraints such as summer drought on the strength and direction of these effects. We measured leaf damage on pedunculate oak (Quercus robur), alone or associated with birch, pine or both in a long-term tree diversity experiment (ORPHEE), where half of the plots were irrigated while the other half remained without irrigation and received only rainfall. We tested three mechanisms likely to explain the effects of oak neighbors on herbivory: (1) Direct bottom-up effects of heterospecific neighbors on oak accessibility to herbivores, (2) indirect bottom-up effects of neighbors on the expression of leaf traits, and (3) top-down control of herbivores by predators. Insect herbivory increased during the growth season but was independent of neighbor identity and irrigation. Specific leaf area, leaf toughness, and thickness varied with neighbor identity while leaf dry matter content or C:N ratio did not. When summarized in a principal component analysis (PCA), neighbor identity explained 87% of variability in leaf traits. PCA axes partially predicted herbivory. Despite greater rates of attack on dummy caterpillars in irrigated plots, avian predation, and insect herbivory remained unrelated. Our study suggests that neighbor identity can indirectly influence insect herbivory in mixed forests by modifying leaf traits. However, we found only partial evidence for these trait-mediated effects and suggest that more attention should be paid to some un-measured plant traits such as secondary metabolites, including volatile organic compounds , to better anticipate the effects of climate change on plant-insect interactions in the future. K E Y W O R D S associational effects, biodiversity, drought, dummy caterpillars, leaf traits, predation, Quercus robur
Article
Full-text available
The importance of plant litter traits and decomposability for nutrient cycling processes and plant community dynamics through plant-litter-soil feedbacks has been largely emphasized. However, the role of biotic interactions as drivers of intraspecific variability in litter traits remains surprisingly little studied. In this study, we used a large-scale, multi-site network of long-term tree removal experiments manipulating the abundance of a foundation tree species, i.e. Quercus petraea, to assess how plant interactions control intraspecific variation in oak leaf litter traits and decomposability. We studied 19 plots across eight experimental sites covering a large gradient of oak abundance, stand age and local abiotic context. Oak leaf litter quality strongly declined with tree removal in early forest successional stage. Litter became poorer in nutrients such as N and Mg and richer in secondary metabolites such as lignin and condensed tannins. This in turn slowed its decomposition. Importantly, litter N loss switched from N release to N immobilization. Variance partitioning indicated that oak abundance explained as much variation in oak leaf litter traits as oak age and twice as much as soil inherent fertility. Confirmatory path analysis revealed that the decline of oak leaf litter quality induced by tree removal was most likely driven by a shift in understory plant species composition. Plasticity of oak leaf litter traits to the shortage of nutrient supply related to the development of understory plants competitors with higher nutrient capture and retention ability could potentially explain this response pattern. Our data also give consistent but weaker support that the decline of oak leaf litter quality could be driven by alleviated competition for light among canopy trees and subsequent enhanced crown exposure to light. Overall, our study provides evidence that biotic factors such as plant interactions are major drivers of plasticity in leaf litter traits and decomposability. This finding contributes to the emerging view that phenotypic plasticity is fundamentally related to biotic interactions for sessile organisms, especially for long-lived and large plant species such as trees. Taking this source of functional diversity into account could help us to better understand plant community dynamics and ecological processes in terrestrial ecosystems. This article is protected by copyright. All rights reserved.
Article
Full-text available
Pulsed resources influence the demography and evolution of consumer populations and, by cascading effect, the dynamics of the entire community. Mast seeding provides a case study for exploring the evolution of life history traits of consumers in fluctuating environments. Wild boar (Sus scrofa) population dynamics is related to seed availability (acorns/beechnuts). From a long-term monitoring of two populations subjected to markedly different environmental contexts (i.e., both low vs. high frequency of pulsed resources and low vs. high hunting pressure in Italy and in France, respectively), we assessed how pulsed resources shape the reproductive output of females. Using path analyses, we showed that in both populations, abundant seed availability increases body mass and both the absolute and the relative (to body mass) allocation to reproduction through higher fertility. In the Italian population, females equally relied on past and current resources for reproduction and ranked at an intermediate position along the capital-income continuum of breeding tactics. In contrast, in the French population, females relied on current more than past resources and ranked closer to the income end of the continuum. In the French population, one-year old females born in acorn-mast years were heavier and had larger litter size than females born in beechnut-mast years. In addition to the quantity, the type of resources (acorns/beechnuts) has to be accounted for to assess reliably how females allocate resources to reproduction. Our findings highlight a high plasticity in breeding tactics in wild boar females and provide new insight on allocation strategies in fluctuating environments.
Article
Full-text available
Uneven-aged mountain forests are considered favourable for the continuous provisioning of multiple ecosystem services (ES). These ES may however exhibit trade-offs or synergies that can be modulated by forest management. Yet, our knowledge remains poor on both the relationships between ES and the way management practices can optimise and reconcile them. In this study, we aimed at (1) characterising trade-offs and synergies between timber production, biodiversity conservation and protection against natural hazards; (2) identifying efficient (i.e. Pareto-optimal) management scenarios for the joint provisioning of these ES; and (3) comparing them to “reference” management scenarios. Using a simulation framework that couples a forest dynamics model, a silviculture algorithm and linker functions relating ES indicators to stand structure, we predicted the response of different ES indicators to various uneven-aged management practices in the Western Alps. With a metamodeling approach and Pareto front techniques, we intensively explored and analysed relationships between ES indicators and found trade-offs between timber production and other ES, but synergies between protection and biodiversity. “Pareto-optimal” management scenarios were characterised by low thinning and harvesting intensities but exhibited gradients of total removals and deadwood and large tree retention along the Pareto front. They greatly differed from our set of production and biodiversity oriented reference scenarios, thus emphasising the strong impact of considering additional ES in scenario optimisation processes. This study highlighted the strengths and weaknesses of Pareto front techniques for both the analysis of trade-offs and synergies between ES and the identification of efficient management practices.
Preprint
Mixture effect on stand productivity is usually apprehended through a substitutive approach, whereby productivity in mixed stands is compared to productivity in monocultures, at equivalent stand density. This approach has proved that in many cases mixed stands perform better than monospecific forests, however, we do not yet have a solid theory about species behaviour in the mixture or even guidelines for combining species. The addition of a second tree species to an existing mono-specific stand has received much less consideration. Yet, this approach has the potential to separate the facilitation effect from the complementarity effect. We compared the effect of tree species substitution vs. addition on the productivity of maritime pine and silver birch in a young tree diversity experiment implemented in 2008 in SW France. Substituting pines with birches to create two-species mixtures resulted in an increase of tree productivity at stand level beyond what was expected from monocultures (i.e., overyielding). In contrast, creating mixture through the addition of birches to pine stands had no effect on the maritime pine stand productivity (transgressive mixture effect not significant). This absence of effect is produced by two distinct density-dependence responses at an individual level. Our results allow clarifying the cases in which a mixed stand can be considered as an alternative to a monoculture of a productive species. In particular, the addition of a pioneer and soil low-demanding species during young developmental stages is a possibility to diversify the stand and potentially to increase ecosystem services without altering the productivity of the target species.
Article
Cette première synthèse présente les résultats de divers projets du programme de recherche « Biodiversité, gestion forestière et politiques publiques » (BGF).
Book
Le projet étudie la biodiversité associée aux peupleraies cultivées, en comparaison avec celle des milieux ouverts (prairies subnaturelles et/ou jachères) et des forêts subnaturelles (récentes et/ou anciennes), pour trois groupes taxonomiques : la flore (414 relevés), les Coléoptères carabiques (63 placettes de piégeage) et l'avifaune (124 points d'écoute). La zone d'étude est constituée par les grandes vallées de Champagne (Seine, Aube, Marne) des départements de l'Aube (10) et de la Marne (51). Elle couvre une superficie approchant 100 000 ha où la populiculture couvre 8,4 % du territoire et la forêt seulement 7,4 %. En plus de la comparaison avec les milieux ouverts et les forêts, l'étude prend en compte divers facteurs de variation de la peupleraie : l'âge (pour les 3 groupes taxonomiques), la présence de sous-étage (flore et avifaune), l'antécédent cultural (flore), l'environnement paysager (carabiques et flore). Les principaux résultats sont : la biodiversité des peupleraies présente des caractères intermédiaires entre celle des milieux ouverts et celle des forêts, mais la peupleraie abrite aussi préférentiellement certaines espèces généralistes (sauf pour l'avifaune) ou eutrophiles, tandis que d'autres espèces restent préférentielles ou exclusives des habitats de référence (prairies, jachères, forêts), les communautés évoluent très rapidement avec l'âge de la peupleraie, tendant vers un état forestier (succession emboîtée pour la flore, décalée pour les 2 autres groupes), les peupleraies à sous-étage favorisent les communautés forestières (flore) et augmentent la densité des oiseaux nicheurs, les peupleraies favorisent la flore typique des mégaphorbiaies (habitat Natura 2000), l'antécédent cultural de la peupleraie modifie faiblement les patrons de succession végétale, l'effet de la composition du paysage autour des peupleraies semble assez faible pour les carabiques et nul pour la flore, tandis que la plupart des oiseaux réagissent à l'échelle locale (100 m). Les communautés de carabiques répondent essentiellement à la proportion de surface forestière dans le paysage (à 500 m). Au final, si la peupleraie ne remplit qu'un rôle très limité de refuge pour la flore prairiale, la populiculture classique majoritairement pratiquée sur la zone d'étude ne porte pas une atteinte irrémédiable à la biodiversité floristique forestière. Toutefois, les résultats sont plus mitigés pour les oiseaux et les carabiques. Une populiculture avec sous-étage serait en mesure de jouer un rôle important, dans le cadre de la mise en ½uvre de la trame verte, pour reconnecter les forêts anciennes en fort déclin sur la zone d'étude. Ces résultats, conjugués aux avis d'experts recueillis lors des réunions du comité de pilotage mis en place dans le cadre d'un volet technico-économique, ont conduit à initier trois groupes de recommandations techniques pour favoriser la biodiversité, qui seront vulgarisés sous forme d'une plaquette auprès des propriétaires : recommandations générales, destinées à l'ensemble des boisements alluviaux, recommandations spécifiques aux peupleraies, transformation de la peupleraie en forêt.
Article
Le bois mort, reconnu comme un des indicateurs de gestion durable, héberge près de 25 % de la biodiversité forestière ; de plus, on estime que deux tiers des espèces associées aux arbres dans les forêts à dynamique naturelle ne sont présentes qu'après l'âge d'exploitabilité économique ou technologique, notamment dans les micro-habitats liés à la sénescence des arbres. La compétition entre le forestier et les organismes saproxyliques pour la ressource bois se traduit aujourd'hui par un déficit généralisé du bois mort dans les forêts exploitées. Face à ces enjeux, des pistes de gestion réalistes et favorables à la biodiversité peuvent être définies.
Article
Dans le cadre de projets de recherche sur l'intérêt du bois mort pour la biodiversité forestière, des pièges d'interception aériens nous ont permis de localiser dans le massif de Rambouillet (Yvelines), deux Mycetophagus (Coleoptera, Mycetophagidae) peu communs en France. En compagnie de Mycetophagus fulvicollis F. ou Berginus tamarisci Woll., 13 exemplaires de Mycetophagus (Mycetophagus) ater (Reitter 1879) et 4 exemplaires de Mycetophagus (Philomyces) populi Fabricius 1798 ont été observés dans l'ouest et le nord-ouest d'un massif dont ils confirment l'intérêt faunistique. La distribution et l'écologie de ces 2 Mycetophagidae est discutée.
Article
Les pâturages du Massif Central sont assez fréquemment soumis à l'abandon et à la colonisation par le genêt à balai (Cytisus scoparius L.). L'étude présentée cherche à évaluer l'impact de cet abandon et de cette colonisation arbustive sur les sols et la végétation d'une pâture de la Chaîne des Puys. Différents stades d'abandon d'une pâture et de sa colonisation par le genêt ont été échantillonnés: 50 placettes ont été installées dans une pâture gérée, dans une pâture abandonnée faiblement colonisée et dans des peuplements de genêts jeunes et âgés. Sur chaque placette, après avoir mesuré le peuplement de genêts, des relevés de flore ont été effectués et les valeurs Ellenberg indicatrices des conditions de sol et de milieu ont été calculées. Les sols ont été analysés pour déterminer leurs principales caractéristiques physico-chimiques notamment leur teneur en C et N, et leur potentiel de minéralisation en N par incubation au laboratoire. L'abondance isotopique en 15N (delta 15N) des sols a aussi été mesurée. Les résultats montrent que le nombre d'espèces diminue fortement lors de l'abandon de la pâture puis avec la fermeture du milieu par le genêt. L'évolution de la composition de la végétation suggère une augmentation de l'acidité, de l'humidité et de la disponibilité en azote au cours de la colonisation. L'évolution des principales propriétés des sols pour les différents stades confirme ces résultats, les changements étant nettement plus marqués dans le premier que dans le second horizon. Le passage de la pâture gérée à la pâture abandonnée non colonisée s'accompagne: d'une forte baisse de la densité apparente, d'une augmentation relative des teneurs en C et N, d'une diminution du delta 15N, d'une hausse de la nitrification potentielle alors que les stocks en C et N du sol restent stables entre raison de l'évolution opposée entre les teneurs et la densité apparente. La fermeture par le genêt dans les stades suivants accentue l'augmentation de la teneur en C et N et de la nitrification alors que les stocks augmentent modérément et que le delta15N reste stable. Cette étude souligne l'impact fort de l'abandon du pâturage puis du rôle plus modéré de la colonisation par le genêt sur le taux de matière organique et la dynamique de l'azote dans les sols.
Article
La Chaîne des Puys, a connu une déprise agricole importante et rapide au cours des 5 dernières décennies. L'abandon des anciennes cultures et terrain de parcours a permis la formation de boisements spontanés monospécifiques de bouleau (Betula pendula Roth) au Nord de la Chaîne et de pin sylvestre (Pinus sylvestris L.) au Sud. Dans le cadre de l'étude de cette dynamique forestière, des sols ont été prélevés et analysés sous bouleau et sous pin en fonction d'usages passés contrastés (lande, pâture et culture) ; des relevés de végétation ont été effectués et les coefficients d'Ellenberg indicateurs des conditions environnementales ont été calculés.Les sols des deux zones de prélèvement diffèrent par leur substratum, composé de scories basaltiques foncées au Sud, alors qu'au Nord, les scories trachytiques de couleur claires sont plus abondantes. Au Nord les sols ont un pH plus bas et montrent une forte accumulation de complexes organométalliques typiques des andosols non allophaniques, alors qu'au Sud leur pH plus elevé, leur taux de matière organique plus faible et leur teneur en allophanes plus forte les classent parmi les andosols à allophanes. Pour chaque zone, les sols sur anciennes cultures se distinguent des sols sur anciennes landes ou pâtures par un rapport C/N plus bas, un d15N plus élevé et par une minéralisation potentielle d'azote et une production potentielle de nitrate plus fortes. La végétation est plus nitrophile sur les anciennes cultures et les coefficients d'Ellenberg pour l'humidité, l'azote et le pH permettent de différencier très clairement les usages passés.La composition chimique des projections volcaniques et l'intensité d'utilisation des anciennes terres agricoles apparaissent comme des facteurs clés pour comprendre la fertilité actuelle des sols et la composition de la végétation dans les boisements spontanés des zones volcaniques.
Article
Questions Tree diversity is key to the functioning of forest ecosystems. However, which components of tree diversity are responsible for tree diversity effects on associated organisms, and in which context, is poorly understood. Location ORPHEE Experimental site, Cestas – Pierroton in the South‐West of France. Methods We used a large scale tree diversity experiment in which we controlled water availability by an irrigation treatment to address tree diversity and water stress effects on the diversity and height of forest understorey vegetation. We assessed the species richness and height of understorey vegetation in irrigated and non‐irrigated 20 x 20 m plots, either being monocultures of Pinus pinaster, Betula pendula or Quercus robur, or either mixtures of two to five species among P. pinaster, B. pendula, Q. robur, Q. ilex and Q. pyrenaica. Results Tree species composition, i.e. the proportion of birch or pine had a significant effect on understorey plant assemblage, species richness and diversity. The proportion of the fast‐growing deciduous angiosperm B. pendula was negatively correlated to understorey plant richness and diversity, and positively correlated with understorey vegetation height. Understorey vegetation was higher in irrigated plots than in non‐irrigated plots, but irrigation had no clear effect on the species richness, diversity or composition of undestorey plant assemblages. Conclusions Forest tree species composition and in particular the relative proportions of different tree species had stronger effects on understorey plants than tree species richness per se. These effects were consistent across irrigation treatments. Even in young forest plantations, effects of tree mixture on understorey vegetation may be observed and seem mainly driven by the functional type of tree in the canopy and initial dynamics of plant regeneration in planted forests.
Article
As climate change should lead to an increase in the vulnerability and the sensitivity of forests to extreme climatic events, quantifying and predicting their response to more severe droughts remains a key task for foresters. Furthermore, recent works have suggested that tree diversity may affect forest ecosystem functioning, including their response to extreme events. In this study we aimed at testing whether the growth response of forest stands to stressful climatic events varied between mixed and monospecific stands, under various environmental conditions. We focused on beech-fir forests (Fagus sylvatica [L.] and Abies albs [L.]) and beech-oak forests (F. sylvatica [L.] and Quercus pubescent [L.]) in the French Alps. We used a dendrochronological dataset sampled in forest plots organized by triplets (one mixture and two monospecific stands) distributed in six sites along a latitudinal gradient. We tested (1) whether stand diversity (two-species stands vs monospecific stands) modulates the stands' response to drought events in terms of productivity, (2) whether species identity may drive the diversity effect on resistance and recovery, and (3) whether this can be explained by interspecific interactions. We found that (1) interspecific differences in response to extreme drought events (possibly due to interspecific differences in hydraulic characteristics) can induce a mixture effect on stand growth, although it appeared (2) to be strongly depending on species identity (positive effect only found for beech-fir mixed stands), while (3) there were no significant non-additive effects of diversity on stand resistance and recovery, except for some specific cases. Overall, our study shows that promoting selected mixed stands management may buffer extreme drought effect on stand productivity.
Article
1.Over the coming decades, the predicted increase in frequency and intensity of extreme events such as droughts is likely to have a strong effect on forest functioning. Recent studies have shown that species mixing may buffer the temporal variability of productivity. However, most studies have focused on temporal stability of productivity, while species mixing may also affect forest resilience to extreme events. Our understanding of mechanisms underlying species mixing effects on forest stability and resilience remains limited because we ignore how changes from intraspecific to interspecific interactions in the neighbourhood of a given tree might affect its stability and resilience to extreme drought (i.e. response during and after this drought). This is crucial to better understand forests' response to climate change and how diversity may help maintain forest functioning. 2.Here we analyzed how local intra‐ or interspecific interactions may affect the temporal stability and resilience to drought of individual trees in French mountain forests, using basal area increment data over the previous 20 years for Fagus sylvatica, Abies alba, and Quercus pubescens. We analyzed the effect of interspecific competition on i) the temporal stability and ii) the resilience to drought (resistance and recovery) of individual tree radial growth. 3.We found no significant interspecific competition effect on temporal stability, but species‐specific effects on tree growth resilience to drought. There was a positive effect of heterospecific proportion on the drought resilience of Q. pubescens, a negative effect for A. alba, and no effect for F. sylvatica. These differences may be related to interspecific differences in water use or rooting depth. 4.Synthesis: In this study, we showed that stand composition influences individual tree growth resilience to drought, but this effect varied depending on the species and its physiological responses. Our study also highlighted that a lack of biodiversity effect on long‐term stability might hide important effects on short‐term resilience to extreme climatic events. This may have important implications in the face of climate change.
Article
Size inequality has been considered a key feature of plant population structure with impacts on ecosystem functions. In forest ecosystems, studies examining the relationship between tree size inequality and stand productivity have produced mixed outcomes. These studies found positive, neutral or negative relationships and discussed how this could be influenced by competition for light between trees (e.g. light interception efficiency), but far less attention has been paid to the role played by tree ontogenetic growth. In this article, we present a simple mathematical model that predicts the basal area growth of a two-strata stand as a function of tree basal areas and asymmetric competition. Comparing the growth of this stand to the growth of a spatially homogeneous one-stratum stand and a spatially heterogeneous one-stratum stand, we show that higher growth of the two-strata stand is achieved for concave shape, increasing functions of ontogenetic growth and for low intensities of absolute size-asymmetric competition. We also demonstrate that the difference in growth between the two-strata stand and the one-stratum stands depends on tree size inequality, mean tree basal area and total basal area in the two-strata stand. We finally found that the relationships between tree size inequality and productivity can vary from positive to negative and even non-monotonous. However, we highlight that negative relationships may be more frequent. As a conclusion, our results indicate that ontogenetic growth can have a major impact on the form and the magnitude of the size inequality-productivity relationship.
Article
Key message In tree communities, tree size inequality reduces productivity and interacts with tree shade tolerance to modulate stand productivity, with a higher productivity in stands where shade-intolerant species dominate shade-tolerant species in size. Context Positive diversity–productivity relationships have been reported in different plant communities, including tree communities. These effects may be strongly related to both structural diversity and functional diversity, but also to their interactions if there is a non-random distribution of species functional characteristics among canopy layers. Aims We explore the relative effects on forest productivity of tree species diversity, tree size inequality, and species shade tolerance diversity, as well as the effect of the distribution of tree shade tolerance in the canopy. Methods We used 11,054 mixed-species forest plots from the French Forest Inventory (IGN) distributed throughout France (2006–2011). We analyzed the effects of species richness, shade tolerance diversity, and height inequality on forest plot productivity, represented by basal area annual increment over a period of 5 years, while controlling for first-order structure characteristics (basal area and quadratic mean diameter) and environmental factors (soil water budget and sum of growing degree days). Using the covariance between tree height and shade tolerance in mixed species canopies, we also explored the effect of the distribution of species’ shade tolerance among canopy layers. Results The results showed a positive effect of species richness (effect size, 0.02) and a negative effect of height inequality (− 0.05) on mixed-forest productivity. We also showed that a negative covariance between shade tolerance and height (e.g., higher proportion of shade-tolerant species in lower height classes) increased productivity (0.01). Shade tolerance diversity did not affect productivity. Conclusion In tree communities, as shown previously in monospecific forest stands, tree size inequality reduces productivity. This effect is modulated by the distribution of shade tolerance among canopy layers. Previous studies on species diversity effect have generally overlooked the importance of the size structure and the size hierarchy of functional characteristics. These effects are, however, crucial and deserve to be explored in greater detail.
Article
Masting, or mast-seeding, defined as a synchronized and highly variable seed production from year-to-year within a population of plants, is one of the most common example of pulsed resources in terrestrial ecosystems. In oaks, the dramatic fluctuations of acorn production impact its reproductive success and regeneration, the dynamics of a large diversity of seed consumers that rely on it, and, by cascade effects, the dynamics of the entire forest community. However, reproductive effort is difficult to quantify and there is therefore an urgent need of a reliable assessment of the dynamic of acorn production based on a low-cost, unbiased, and robust tool. One of the most commonly used method, the "visual on-tree" method, is very easy and quick to carry out, but is biased under high seed production or when branches are difficult to see. We here assessed the robustness of an alternative method, the "ground plot" (GP), based on a unique annual ground survey after peak of acorn fall, which has not been tested so far. We compared this method at tree and site levels (10 forests throughout France) with the costly and time-consuming trap acorn collection (TNR) method (used here as a reference method). We show that results from the GP method closely matched with those obtained using the TNR method, which demonstrates the efficiency and robustness of the GP method at both tree and forest site levels. Despite some limitations in specific environmental contexts we review, this GP method offers a powerful tool to quantify acorn production and should be deployed to understand mechanisms underlying oak masting and/or to assess its ecological or economic consequences.
Article
TreeDivNet is the largest network of biodiversity experiments worldwide, but needs to expand. We encourage colleagues to establish new experiments on the relation between tree species diversity and forest ecosystem functioning, and to make use of the platform for collaborative research.
Article
How much a plant is attacked by insect herbivores likely depends on its apparency and ability to produce defensive traits, which may be modified by neighbouring plants and abiotic conditions. Yet, how much the direct and trait-mediated effects of neighbours on herbivory is modified by abiotic factors is still unknown. 2.By using a tree diversity experiment in SW France, we measured leaf insect herbivory (chewers and miners), nutritional quality (water content, C/N ratio, sugar and starch content) and chemical defences (total polyphenolics and condensed tannins) on birch (Betula pendula) trees growing in monocultures and mixtures with oak, pine or both species. We alleviated water stress by irrigating trees in half of the plots while trees remained unwatered (i.e., drought-stressed) in the other half. 3.Overall, insect herbivory was higher among heterospecific neighbours, which corresponds to associational susceptibility. Consistent with this finding, leaves had lower amount of anti-herbivore defences among heterospecific neighbours. In turn, insects caused more damage in drought-stressed conditions, but such effect was independent of leaf chemistry. We also found that the effect of tree species diversity on herbivory was contingent of drought conditions as associational susceptibility only occurred in drought-stressed trees. The independent and interactive effects of neighbour diversity and irrigation on leaf herbivory remained significant after accounting for birch apparency and leaf chemistry, suggesting that unmeasured plant traits or some other mechanisms not associated with plant trait variation and apparency might be involved in the observed herbivory patterns. 4.Synthesis. By demonstrating that associational effects are contingent upon abiotic constraints, we bring new insights into our understanding of the mechanisms driving diversity - resistance relationships across climatic gradients. This article is protected by copyright. All rights reserved.
Article
Cross-taxon surrogacy (between-taxon similarities in species patterns) can help conservation biologists to design simplified, standardized and efficient tools for biodiversity monitoring. Our study aims to identify potential sets of indicator taxa to be recommended in temperate forests. We focused on nine forest taxa: vascular plants, bryophytes, saproxylic beetles, polypores, lichens, ground beetles, hoverflies, birds and bats. We assessed crosstaxon congruence patterns, in terms of both alpha and beta-diversity, using empirical biodiversity data from 206 plots in ten French forested areas. We evaluated the cost-efficiency of potential surrogate taxa using both strictly encoded expert knowledge and results of this study. The most congruent taxa in alpha-diversity were bryophytes (with bats and polypores), and ground beetles (with bats and saproxylic beetles), though levels of covariation were mostly weak. The most congruent taxon in beta-diversity was vascular plants (with bryophytes, ground beetles, lichens and forest birds). Contrary to our expectations, the subsets of forest species within a given taxon exhibited a lower surrogacy than the taxon as a whole. Four categories of taxa were delineated based on costefficiency scores – from costless but ineffective (bats and ground beetles) to costly but effective (saproxylic beetles and polypores). No single taxon was firmly identified as a relevant surrogate for other taxa; using a set of two or three taxa drastically increased surrogacy, compared with single-taxon approaches. Saproxylic beetles associated with vascular plants, or with both vascular plants and birds, seemed to be the most cost-efficient associations. Further research is required to up-scale our results from the short-term, local scale to the long-term, landscape scale in European temperate forests.
Article
Despite considerable research demonstrating that biodiversity increases productivity in forests and regulates herbivory and pathogen damage, there remain gaps in our understanding of the shape, magnitude, and generality of these biodiversity-ecosystem functioning (BEF) relationships. Here, we review findings from TreeDivNet, a global network of 25 tree diversity experiments, on relationships between levels of biodiversity and (a) tree growth and survival and (b) damage to trees from pests and pathogens. Tree diversity often improved the survival and above- and belowground growth of young trees. The mechanistic bases of the diversity effects on tree growth and survival include both selection effects (i.e., an increasing impact of particular species in more species-rich communities) and complementary effects (e.g. related to resource differentiation and facilitation). Plant traits and abiotic stressors may mediate these relationships. Studies of the responses of invertebrate and vertebrate herbivory and pathogen damage have demonstrated that trees in more diverse experimental plots may experience more, less, or similar damage compared to conspecific trees in less diverse plots. Documented mechanisms producing these patterns include changes in concentration, frequency, and apparency of hosts; herbivore and pathogen diet breadth; the spatial scale of interactions; and herbivore and pathogen regulation by natural enemies. Our review of findings from TreeDivNet indicates that tree diversity experiments are extending BEF research across systems and scales, complementing previous BEF work in grasslands by providing opportunities to use remote sensing and spectral approaches to study BEF dynamics, integrate belowground and aboveground approaches, and trace the consequences of tree physiology for ecosystem functioning. This extension of BEF research into tree-dominated systems is improving ecologists’ capacity to understand the mechanistic bases behind BEF relationships. Tree diversity experiments also present opportunities for novel research. Since experimental tree diversity plantations enable measurements at tree, neighbourhood and plot level, they allow for explicit consideration of temporal and spatial scales in BEF dynamics. Presently, most TreeDivNet experiments have run for less than ten years. Given the longevity of trees, exciting results on BEF relationships are expected in the future.
Article
Previous analyses of the regional distribution of forest plants have revealed that some species have a biased distribution towards either ancient or recent forest patches. It has been therefore proposed to classify forest plant species according to their affinity for ancient or recent patches. In this contribution, we aimed at providing a dynamical perspective on this static concept of ancient/recent forest species. We developed an inference method to estimate the metapopulation dynamics of forest plants based on landscape history and static (and incomplete) biodiversity data accounting for false absence records. We assessed the power of this novel inference method using simulated metapopulation and landscape dynamics. We finally applied this method to occupancy data of 174 and 121 forest species in two networks of 9208 and 9201 forest patches respectively. These patch networks are located in two French regions, with corresponding landscape historical data based on two forest maps conceived in 1840 and 2000. Our analyses revealed that i) the inference method enables to satisfactorily infer three parameters of the metapopulation model: the rates of colonization, extinction and decay of colonization with distance; ii) this three parameter metapopulation model is sufficient to reproduce the occurrence spatial structure of 72% and 61% of the investigated species in the two regions; iii) forest plant species are distributed along a spectrum of turn-over speed, in which small (large) colonization capacity are associated with small (large) propensity to extinction; iv) species position along this spectrum can be partially predicted from plant functional traits; and v) species metapopulation dynamics are driven by the interaction between landscape and species intrinsic properties, suggesting that ancient/recent forest species lists are unlikely to be easily extrapolated to novel landscapes.
Book
La forêt fait face à des modifications rapides du climat et des pratiques sylvicoles. Pour maintenir la biodiversité forestière et garantir les capacités d'adaptations face à ces évolutions, nous devons mieux comprendre son fonctionnement.Ce guide pratique présente de manière simple les éléments fondamentaux pour mieux intégrer la biodiversité à la gestion forestière : évaluer les enjeux de biodiversité propres à sa forêt : quelles questions faut-il se poser ? Où trouver les sources d'informations ? en fonction de ces enjeux, adapter la gestion dans les documents d'objectifs et les interventions sylvicoles. Adapté au contexte de la forêt française métropolitaine, il promeut une stratégie équilibrée entre actions individuelles et collectives, qui tient compte des connaissances scientifiques actuelles sur la biodiversité forestière.Cet ouvrage s'adresse aux professionnels de la forêt et des espaces naturels qui pourront y trouver les informations utiles pour alimenter leurs documents de communication à destination des propriétaires publics et privés. Les propriétaires y trouveront également des éclairages utiles sur la manière de mieux prendre en compte l'écologie dans la gestion de leur forêt.
Article
This study compared the total carbon (C), mineral nitrogen (N) contents and N mineralization potentials of the rhizospheric and bulk soils, collected at two depths in three forest sites in France. The site at Breuil is a comparative plantation of different species with or without fertilization, the Fougères site is a time sequence of four Fagus sylvatica L. stands including a limed plot, and the Aubure site is a comparison between adjacent young and old Picea abies. (L.) Karst stands with different nitrifying activity. Mineral N was extracted from fresh soil with K2SO4 and after laboratory incubation at 15°C for 2 days or 1 week. The moisture, C and N contents of the rhizospheric soil were higher than in the bulk soil in the A, horizon, but only slightly higher or similar in A1B horizons. Soil-extractable NH4 and net mineralization were much larger in the rhizospheric soil than in the bulk soil. Soil-extractable NO3 and net nitrification were not significantly different. Soil-extractable NH4 and net N mineralization were linearly and positively related to the soil C (or N) contents, but the relationship was stronger and the amount of mineral N per gram of carbon was higher for rhizospheric soil. This suggests that the quality of rhizospheric carbon should be taken into account. Net N mineralization was negatively related to the soil C/N ratio. In summary, tree roots appear to have a strong influence on N transformation in soils.
Article
The establishment of Natura 2000, the European Union’s network of protected areas, has been a challenging process and has caused a variety of conflicts. These conflicts are related to contradictory stakeholder interests and perceptions, as well as to procedural issues and feelings of exclusion, especially by concerned local land user groups. To prevent further conflict, local participation has been stressed as an important tool to increase the inclusiveness of Natura 2000 and its acceptance among land users. In this paper, we present an analysis of participation practices related to the Natura 2000 implementation processes in six EU member states. Based on material collected from semi-structured interviews and document analysis, we describe the organisational settings of the participatory processes, focusing, among other things, on the type of participants involved, the level and intensity of their involvement, and the goal of participation. In addition, we also describe the local context in which the participation processes have been embedded. Finally, we assess the outcomes of the participatory processes in terms of their impact on forest and nature conservation management practices. Our results show that local participation practices were shaped not just by the Natura 2000 policy, but also by the history of the area, including, for example, earlier conflicts among the local actors. We also show that although the participation process leads to a greater acceptance of the Natura 2000 policy, this does not relate to significant changes in management practices among local actors. These findings, however, do not suggest that participation is irrelevant. Rather, we conclude that participation involves context-dependent, localised learning processes that can only be understood by taking the historical socio-economic and institutional context in which they are situated into account.
Article
Species richness estimation is one of the most widely used analyses carried out by ecologists, and nonparametric estimators are probably the most used techniques to carry out such estimations. We tested the assumptions and results of nonparametric estimators and those of a logseries approach to species richness estimation for simulated tropical forests and five datasets from the field. We conclude that nonparametric estimators are not suitable to estimate species richness in tropical forests, where sampling intensity is usually low and richness is high, because the assumptions of the methods do not meet the sampling strategy used in most studies. The logseries, while also requiring substantial sampling, is much more effective in estimating species richness than commonly used nonparametric estimators, and its assumptions better match the way field data is being collected. This article is protected by copyright. All rights reserved.
Article
Tree microhabitats (cavities, conks of fungi, bark features) play an important role for both rare and specialized species biodiversity; their preservation should therefore be targeted by biodiversity-friendly forest practices. However, when compared to other old-growth characteristics like deadwood or large trees, tree microhabitats have only recently been studied so related scientific knowledge is still relatively limited. Defining target values for microhabitat densities in managed forests is mostly based on expert knowledge rather than quantitative empirical data.
Article
Since economic incentives are typically fairly low for many non-industrial private forest owners, it is of interest for public policy to examine whether other motives might play a role on adoption of Biodiversity-related Protection Programs. In a survey of non-industrial private forest owners, a number of current programs, that include biodiversity protection to some degree, are investigated: Prosilva, environmental associations, other programs of forest management. Across the survey, adoption amounts to 22% for all the programs jointly, and is shown to depend on economic, social and intrinsic motives, with significant crowding-out only between the economic and intrinsic motives, that is, intrinsic motives likely lessen the effectiveness of economic incentives. That does not occur with social motives; these results constitute a test of the "reputational crowding-out" theory of Bénabou and Tirole, (2006). Adoption of any program is strongly negatively correlated to the others. Nearly no respondent adopted the Natura 2000 program.