187 research outputs found
Faibles variations microclimatiques dans les lisiĂšres de petits bois du sud-ouest de la France
Faibles variations microclimatiques dans les lisiĂšres de petits bois du sud-ouest de la Franc
Distribution des communautés végétales sous l'influence des lisiÚres forestiÚres dans des bois fragmentés
Les lisiĂšres forestiĂšres constituent un enjeu pour la gestion des territoires, par la biodiversitĂ© quâelles abritent, les processus Ă©cologiques quâelles rĂ©gulent et les services environnementaux quâelles rendent Ă lâagriculture et Ă la foresterie. Câest pourquoi il est nĂ©cessaire de connaitre et quantifier prĂ©cisĂ©ment leurs influences sur la vĂ©gĂ©tation pour proposer des mesures de gestion adaptĂ©es Ă la variabilitĂ© des situations de lisiĂšre. En rĂ©fĂ©rence aux hypothĂšses de la littĂ©rature, ce travail vise Ă comprendre comment varie la rĂ©partition des communautĂ©s vĂ©gĂ©tales forestiĂšres en rĂ©ponse Ă la diversitĂ© des types de lisiĂšres, dans un paysage agriforestier. Les espĂšces vasculaires de la strate basse de la vĂ©gĂ©tation forestiĂšre ont Ă©tĂ© recensĂ©es le long de 28 transects, reprĂ©sentatifs de sept types de lisiĂšres des coteaux de Gascogne. Ces transects, perpendiculaires Ă la bordure et dirigĂ©s vers lâintĂ©rieur du bois, comportent 20 quadrats contigus de 2 m Ă 2 m. Jâai cherchĂ© Ă mesurer la profondeur dâinfluence des effets de lisiĂšres sur la vĂ©gĂ©tation par la mĂ©thode de rĂ©gression Ă deux phases. Face Ă lâhĂ©tĂ©rogĂ©nĂ©itĂ© observĂ©e, jâai caractĂ©risĂ© les patrons de distribution des communautĂ©s vĂ©gĂ©tales par cinq modĂšles continus pour les comparer. Les lisiĂšres structurent la rĂ©partition des communautĂ©s vĂ©gĂ©tales suivant un gradient, de la bordure vers lâintĂ©rieur du bois, mais les patrons sont plus variables quâattendus et remettent en cause la gĂ©nĂ©ricitĂ© du modĂšle thĂ©orique Ă deux phases largement admis dans la littĂ©rature. NĂ©anmoins, un patron de distribution de la vĂ©gĂ©tation commun Ă lâensemble des lisiĂšres a Ă©tĂ© identifiĂ© au moyen de la mĂ©thode STATIS dâanalyse Ă k-tableaux. Lâanalyse des effets de lisiĂšre sur un sous-Ă©chantillon dâespĂšces a Ă©tĂ© affinĂ©e par la prise en compte des caractĂ©ristiques biologiques et Ă©cologiques des espĂšces dâune part, et des variables environnementales, Ă diffĂ©rentes Ă©chelles spatio-temporelles dâautre part. Les traits biologiques et Ă©cologiques des espĂšces rĂ©pondent davantage Ă lâĂąge et lâhistoire des lisiĂšres quâĂ la distance Ă la bordure. La hiĂ©rarchie des facteurs environnementaux, paysagers et historiques confirment le rĂŽle prĂ©pondĂ©rant de la qualitĂ© locale de lâhabitat dans la structure des communautĂ©s. La variabilitĂ© temporelle des effets de lisiĂšre a Ă©tĂ© abordĂ©e par un suivi horaire des variations microclimatiques au cours dâune annĂ©e. Les faibles Ă©carts microclimatiques entre la lisiĂšre et lâintĂ©rieur du bois au cours des saisons suggĂšrent un rĂŽle faible du microclimat sur la structure des assemblages dâespĂšces. Enfin, la variabilitĂ© spatiale des lisiĂšres dans un paysage de large Ă©tendue a Ă©tĂ© Ă©valuĂ©e par la mise au point dâune mĂ©thode originale afin de caractĂ©riser et cartographier la diversitĂ© des segments de lisiĂšres. Les rĂ©sultats remettent en cause les modĂšles thĂ©oriques antĂ©rieurs et ouvrent des perspectives pour une meilleure comprĂ©hension des principes dâorganisation des communautĂ©s vĂ©gĂ©tales en lisiĂšres de forĂȘt. La complexitĂ© des patrons de rĂ©ponse aux effets de lisiĂšre justifie de porter une attention plus soutenue Ă la diversitĂ© des lisiĂšres dans la perspective de mieux les gĂ©rer. ABSTRACT : Forest edges are a challenge for land management. They contain high biodiversity, regulate ecological processes and provide environmental services to agriculture and forestry. Therefore, it is necessary to evaluate and quantify precisely edge influence on vegetation to propose management measures adapted to edge diversity. Referring to the literature asusmptions, this paper focuses on understanding the variation in the distribution patterns of forest plant communities in response to contrasted edge types in rural landscape. All vascular plant species of the understorey forest vegetation have been identified along 28 transects, pertaining to seven edge types of âcoteaux de Gascogneâ. Transects were perpendicular to the forest border and included 20 contiguous quadrats of 2 m Ă 2 m, towards forest interior. I tried to measure the depth of edge influence on vegetation using the two-phase linear regression method. Facing to high heterogeneity, I characterized the distribution patterns of plant communities by five continuous models for comparison. Edge effect structure the distribution of plant communities along a gradient from the border toward the forest interior. Response patterns to edge influence were more variable than expected and challenge the hypothetical response model pattern widely accepted in the literature. However, a common pattern of vegetation for all transects was identified using the k-tables STATIS method. Analysis of edge effects on a sub-sample of species was refined using on the one hand biological and ecological species traits and environmental variables at different spatio-temporal scales, on the other. The functional response of plant species better suited to the age and history of the edges than the distance from the border. Nevertheless, the hierarchy of environmental, landscape and historical context confirm the role of habitat quality on distribution patterns of forest vegetation. Temporal variability of edge effects has been addressed by monitoring hourly microclimatic variations over one year. The small differences in microclimate between edge and forest interior over seasons suggest a weak role of microclimate on the structure of plant species assemblages. Finally, the spatial variability of edges at the landscape level has been evaluated. An original method, Cartolis, has been developed to characterize and map the diversity of forest edge segments. Our results, calling into question the earlier theoretical models, provide opportunities for a better understanding of plant distribution patterns in forest edges. The complexity of responses obtained warrants to bring more attention to edge diversity for better management and conservation of plant species
High variability of edge effects on forest vegetation diversity
The influence of edges on vegetation diversity in forest fragments is an important issue for biodiversity conservation because of the large part of temperate woodlands concerned. In numerous empirical studies, a general pattern has been identified; it is described as two zones: the edge where plant distribution is linked to the distance from the forest border, the core area where the variability of vegetation is not linked to this distance. We present results of a study aiming at measuring the edge effects on vegetation in forest fragments in south-western France and at identifying potential factors of their variability. Vegetation was sampled in 28 transects constituted by 20 contiguous quadrats (2x2m). Environmental conditions (soil, light) of each quadrat was measured and each transect was assigned to a type of forest border based on its orientation and adjacent land cover. Historical records on each border were also available. Multivariate ordination methods were used to analyse data to identify patterns in species distribution. Our results showed a larger variability of vegetation response to edge influence than what was expected from literature. Beta diversity between transects, and in a given transect between quadrats was high and few species appeared as associated with edge conditions. However, multitable ordination of the quadrats from the 28 transects analysed together showed a common pattern of response of vegetation, but it seemed to have several parts that had not been described before in the literature. None of the factors measured was able to explain this variability. These results underlined the variability of edge effects on forest vegetation that was often underestimated by biodiversity managers
Forest edge responses present a variety of patterns in southwestern France
Forest edge responses present a variety of patterns in southwestern Franc
Patterns of forest vegetation responses to edge effect as revealed by a continuous approach
Context: Understanding the variability of vegetation distribution and its determinants is a central issue for addressing the effects of edges on ecological processes. Recent studies have revealed inconsistencies in the patterns of responses to edge effects that raise important questions about their determinants. We investigated the edge effect response patterns by adapting a recently proposed continuous approach to the case of small forest fragments in southwestern France. Methods: We surveyed forest understory vegetation (composition, species richness, and percent cover) and abiotic variables (soil temperature, moisture, pH, and canopy openness) along 28 transects across hard forest edges. We tested five statistical models to describe the response pattern of each variable (1) over all transects and (2) per transect. We then compared the response patterns as a function of the attributes of the edge (orientation, topography, and adjacent land cover) and forest patch size. Results: Over all transects, a general decreasing trend was observed for all variables as the distance from the edge increased. In the individual transects, we evidenced a large variability in the response patterns that was not related to edge attributes or to patch size. Conclusion: It is difficult to assess the depth of edge influence in highly fragmented forests and to identify the determinants of edge effects. We recommend that care should be taken with studies using pool of transects, and that further studies should be carried out including situations with neutral patterns, in order to gain a broader understanding of edge effects on vegetation
Postdispersal weed seed predation ranged between 19 to 84% per week following a species preference rank
Postdispersal weed seed predation ranged between 19 to 84% per week following a species preference ran
High variability of edge effects on forest vegetation diversity
The influence of edges on vegetation diversity in forest fragments is an important issue for biodiversity conservation because of the large part of temperate woodlands concerned. In numerous empirical studies, a general pattern has been identified; it is described as two zones: the edge where plant distribution is linked to the distance from the forest border, the core area where the variability of vegetation is not linked to this distance. We present results of a study aiming at measuring the edge effects on vegetation in forest fragments in south-western France and at identifying potential factors of their variability. Vegetation was sampled in 28 transects constituted by 20 contiguous quadrats (2x2m). Environmental conditions (soil, light) of each quadrat was measured and each transect was assigned to a type of forest border based on its orientation and adjacent land cover. Historical records on each border were also available. Multivariate ordination methods were used to analyse data to identify patterns in species distribution. Our results showed a larger variability of vegetation response to edge influence than what was expected from literature. Beta diversity between transects, and in a given transect between quadrats was high and few species appeared as associated with edge conditions. However, multitable ordination of the quadrats from the 28 transects analysed together showed a common pattern of response of vegetation, but it seemed to have several parts that had not been described before in the literature. None of the factors measured was able to explain this variability. These results underlined the variability of edge effects on forest vegetation that was often underestimated by biodiversity managers
Wild herbaceous vegetation in agroforestry systems: an asset that should not be overlooked
Thanks to agroforestry, trees and hedgerows are back in numbers in agricultural landscapes, where they provide many services. Agroforestry also gives pride of place to wild herbaceous vegetation, often perceived as a constraint or neglected by humans. Omnipresent when the soil is not tilled, herbaceous vegetation grows spontaneously at the foot of trees. From alley-cropping agroforestry to bocage landscapes, these 'little' plants are proving to be a major asset for the agroecological transition. Through the presentation of key results, this article explains how to take advantage of the wild herbaceous vegetation in agroforestry systems, in order to conserve biodiversity and promote sustainable agricultural productio
MĂ©thode dâĂ©talonnage de mini capteurs enregistreurs de tempĂ©rature et dâhumiditĂ© relative pour utilisation in situ
Une procĂ©dure simple dâĂ©talonnage dâun type de mini-capteurs enregistreurs HOBO, utilisĂ©s en milieu extĂ©rieur pour des durĂ©es longues (1 an), a Ă©tĂ© mise au point au laboratoire dâĂ©cologie de lâInra de Toulouse. Les capteurs ont Ă©tĂ© testĂ©s dans une gamme de valeurs proche de leur condition dâutilisation in situ : par palier de 5°C entre 0°C et +40°C pour la tempĂ©rature et par palier de 10 % entre 60 % et 90 % pour lâhumiditĂ© relative. LâĂ©talonnage des capteurs est validĂ© par comparaison Ă une sonde Ă©talon placĂ©e dans le mĂȘme milieu et Ă lâaide de seuils dâerreur maximale tolĂ©rĂ©e (EMT) prĂ©alablement dĂ©finis pour nos besoins sur le terrain. Les rĂ©sultats de cette Ă©tude montrent la nĂ©cessitĂ© de corriger les valeurs enregistrĂ©es par les capteurs. AprĂšs correction, lâensemble des capteurs prĂ©sente des valeurs de tempĂ©rature et dâhumiditĂ© relative fidĂšles et justes. LâĂ©talonnage des capteurs HOBO est donc une Ă©tape nĂ©cessaire avant de les mettre en service sur une expĂ©rimentatio
PrĂ©dire lâoccurrence des espĂšces adventices : quelles Ă©chelles de temps et dâespace ?
Comprendre la distribution spatiale des communautĂ©s vĂ©gĂ©tales et les processus Ă©cologiques sous-jacents constituent un enjeu majeur en particulier pour la gestion intĂ©grĂ©e de la flore adventice. Le projet europĂ©en PURE ("Pesticide Use-and-risk Reduction in European farming systems with Integrated Pest Management") vise Ă concevoir, Ă partir dâĂ©tudes empiriques identifiant les dĂ©terminants locaux et rĂ©gionaux de la distribution dâespĂšces nuisibles, des paysages qui leur soient dĂ©favorables. Les dĂ©terminants de la distribution des adventices sont gĂ©nĂ©ralement Ă©tudiĂ©s Ă lâĂ©chelle de la parcelle or, de rĂ©centes Ă©tudes suggĂšrent quâil est Ă©galement nĂ©cessaire de tenir compte du contexte paysager. Par ailleurs, les paysages agricoles constituent des systĂšmes dynamiques dans lesquels les cultures et les pratiques se succĂšdent. Nous faisons lâhypothĂšse que la flore adventice qui sâexprime dans une parcelle une annĂ©e donnĂ©e dĂ©pend Ă la fois des pratiques appliquĂ©es lâannĂ©e donnĂ©e mais Ă©galement les annĂ©es prĂ©cĂ©dentes et des pratiques sur les parcelles voisines. Notre Ă©tude vise ainsi Ă identifier quelles Ă©chelles de temps et dâespace sont les plus pertinentes pour prĂ©dire lâoccurrence des espĂšces adventices. La flore adventice a Ă©tĂ© Ă©chantillonnĂ©e dans 58 parcelles de la zone de FĂ©nay pendant 4 annĂ©es consĂ©cutives. Les pratiques de ces parcelles ont Ă©tĂ© recensĂ©es de 2004 Ă 2011 par enquĂȘtes auprĂšs des agriculteurs. Nous avons adoptĂ© une approche de sĂ©lection de modĂšles basĂ©e sur le critĂšre dâAIC, complĂ©tĂ©e par une validation croisĂ©e pour quantifier les capacitĂ©s prĂ©dictives du meilleur modĂšle. Les premiers rĂ©sultats montrent que lâintĂ©gration dâĂ©chelles de temps et dâespace larges amĂ©liore la description de la distribution des adventices
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