Hoverfly (diptera: syrphidae) richness and abundance vary with forest stand heterogeneity: preliminary evidence from a case study in a montane beech fir forest

Hoverflies (Diptera: Syrphidae) provide crucial ecological services and are increasingly used as bioindicators in environ- mental assessment studies. Information is available for a wide range of life history traits at the species level for most Syrphidae but little is recorded about the environmental requirements of forest hoverflies at the stand scale. The aim of this study was to explore whether the structural heterogeneity of a stand influences species richness or abundance of hoverflies in a montane beech-fir forest. We used the catches of Malaise traps set in 2004 and 2007 in three stands in the French Pyrenees, selected to represent a wide range of structural heterogeneity in terms of their vertical structure, tree diversity, deadwood and tree-microhabitats. We assessed hoverfly assemblages by recording species richness, abundance and functional diversity. Malaise traps caught 2,374 hoverflies belonging to 104 species. The catches of hoverflies fluctuated both in species richness and abundance between 2004 and 2007. Strictly forest species were only caught in the most heterogeneous stand. Species strictly associated with fir were not recorded in the least heterogeneous stand although fir was present. Although most of the functional groups were recorded in the three stands, species richness, abundance and functional diversity decreased dramatically from the most heterogeneous to the least heterogeneous stand. However, the species assemblages in the less heterogeneous stands were not perfect subsets of that in the most heterogeneous stand, as some additional species not found in the most heterogeneous stand were also present

Les accrus de frêne dans les Pyrénées Centrales : un avenir énergétique local ?

Alors que l’économie agricole de la montagne pyrénéenne centrale régresse, des peuplements forestiers naturels ont progressé sur des terres agricoles abandonnées, plus précisément sur d’anciennes prairies d’altitude. Nous définissons les conditions d’un usage énergétique de peuplements d’accrus de frênes installés sur ces terres. Un agriculteur propriétaire forestier d’accrus peut prendre en charge lui-même leur exploitation, y compris le transport jusqu’à sa ferme et la fente de ses bois, afin de satisfaire ses propres besoins de bûches de chauffage. Le propriétaire pourrait ainsi récupérer une valeur résiduelle unitaire maximale variant de 11,2 à 22,3 €/st (euros par stère), soit une valeur moyenne d’environ 16,8 €/st, tous coûts déduits. L’exploitation des accrus en bois bûche pour le chauffage est donc financièrement possible. Une politique de développement d’une telle filière serait alors envisageable. Elle stimulerait les initiatives des agriculteurs propriétaires d’accrus forestiers

Tree-related microhabitats (TreMs) as key elements for forest biodiversity

Tree-related microhabitats (TreMs) are specific above-ground morphological singularities borne by standing living or dead trees. They are regularly observed and are crucial issues for forest management in such a way that standards are currently negotiated (e.g. PEFC, FSC, N2000). TreMs depend on tree characteristics. The largest trees play a pivotal role in TreM supply and only the largest trees bear all the TreM types. Living and dead trees are complementary in their supply of TreM types. For instance, cracks and fungus sporocarps are rather borne by snags than by living trees. TreMs distribution patterns are very different in old-growth forests or in managed stands. As «ephemeral resource patches », TreMs host a wide diversity of taxa and play a wide range of pivotal biological roles. Certain Trems, like dendrothelms, host poor but very specific species assemblages. Other TreMs are composite habitats and host several communities. TReMs participate in a complex functional habitat network in species life cycles. How TReMs contribute to local biodiversity depends both on forest type and taxon conservation status. Positive relationships between TReMs density and local species richness are sometimes thresholded. Practical considerations for forest management integrating TreMs include the search for quantitative thresholds. Set-aside areas more than 20 ha in area are needed in mixed forest to conserve TreMs diversity. After a drastic harvesting, the recovery of TreMs needs decades and TreM-associated taxa may have a delayed response. A hierarchical typology is now available as a reference for TreM recording in temperate and Mediterranean European forests. The modelling of TreM ontogenesis is at work, as well as simulation models evaluating long-term effects of management scenarii

Diversity of woody plant seedling banks under closed canopy in fragmented coppice forests

Seedling banks of woody species established under closed canopy have received little consideration in coppice forests despite their potential importance for natural regeneration. This study aimed to evaluate the influences of canopy composition and of distance from the nearest forest edge on the abundance and species richness of the seedling bank, for different ecological groups of seedlings (age, successional status and dispersal vector) in 68 fragmented coppice stands. Seedlings were found in 67 stands, with 19 species identified. Eight species present as older seedlings were lacking as first-year old seedlings, suggesting temporal variability of species recruitment. Seedling abundances of species with low-dispersal ability were positively correlated with the abundances of their conspecific adults. Seedling abundance of mid-successional species was negatively correlated with the distance from the nearest forest edge, while mid-to-late successional species seedling abundance presented the opposite pattern. Our results showed that woody species were able to establish frequently under closed canopy in these fragmented coppices and form a seedling bank which may be used for natural regeneration

Spontaneous ash tree reforestation in the Central Pyrenees: a future local energy source?

With the agricultural economy of the Central Pyrenees in steady decline, natural forest stands are colonising abandoned agricultural meadows. The present study seeks to define the economic conditions for a new fuel-wood local economy based on these extensions of the forest cover. Farmer/forest owners are capable of exploiting this resource, involving logging, hauling and cutting the wood to size, to meet their own heating needs. In this way, owners could thus recuperate a maximum unit value estimated at 11.2 to 22.3 € per stere (1 cubic metre), or an average value of 16.8 € per stere after deduction of all costs. An economy based on wood energy, using wood from spontaneously generated forest growth on private land, is therefore possible. A development policy for such an activity could be envisaged with appropriate initiatives to stimulate the owners of land where spontaneous ash reforestation has occurred to harvest this potential resource

Why are there so many small woodlots in southwestern France landscapes?

Despite a trend during the last century towards a disconnection between agriculture and forestry, small woodlots strongly associated to farming activities are still very common in south western France. To explain the origin of this particularity and its consequences, we engaged ethnological, biotechnical and ecological studies. The ethnological study showed that the ‘house-centred’ social system - which is characteristic in this region - has shaped landscapes and reinforced the need for scattered small woodlots. Due to a principle of self-sufficiency, each farm had to have a direct access on its property or in its vicinity to all the resources needed. Woodlots had been maintained on lands that might have been cultivated and they contain a large diversity of woody species - even in the dominant tree layer - corresponding to the species needed for the family uses. Even if they are less able to apply all the usual practices, small woodlots are still seen by farmers as important components of their resources and landscapes. Their management lead to a particularly fine-grained mosaic of stands with different historical trajectories. Ecological studies revealed that these woodlots, and especially their edges, are key components of processes impacting agricultural activities, such as pest regulation. We argue that the small woodlots maintained in rural landscapes in south western France are beneficial for agriculture, forestry and rural activities, especially in a global change perspective. The question is how to keep their characteristics when their managers are leaving because of the lack of support from policy makers

Why are there so many small woodlots in southwestern France landscapes?

Despite a trend during the last century towards a disconnection between agriculture and forestry, small woodlots strongly associated to farming activities are still very common in south western France. To explain the origin of this particularity and its consequences, we engaged ethnological, biotechnical and ecological studies. The ethnological study showed that the ‘house-centred’ social system - which is characteristic in this region - has shaped landscapes and reinforced the need for scattered small woodlots. Due to a principle of self-sufficiency, each farm had to have a direct access on its property or in its vicinity to all the resources needed. Woodlots had been maintained on lands that might have been cultivated and they contain a large diversity of woody species - even in the dominant tree layer - corresponding to the species needed for the family uses. Even if they are less able to apply all the usual practices, small woodlots are still seen by farmers as important components of their resources and landscapes. Their management lead to a particularly fine-grained mosaic of stands with different historical trajectories. Ecological studies revealed that these woodlots, and especially their edges, are key components of processes impacting agricultural activities, such as pest regulation. We argue that the small woodlots maintained in rural landscapes in south western France are beneficial for agriculture, forestry and rural activities, especially in a global change perspective. The question is how to keep their characteristics when their managers are leaving because of the lack of support from policy makers

Sylviculture et nutrition des accrus de frêne dans les Hautes-Pyrénées

Le projet CHAPAY a contribué à produire des connaissances, des méthodes et des outils pour prendre en compte les relations entre le changement des activités agricoles et des paysages dans l’action publique et la gouvernance des territoires. Le frêne trouve dans de nombreux sites des Hautes-Pyrénées des conditions favorables à son installation, mais sa croissance est très variable selon les stations. L’exploitation forestière de ces accrus nécessite, au préalable, une connaissance du potentiel de croissance auquel on peut s’attendre selon la fertilité de la station concernée. Nos résultats sont fondés sur une étude de terrain portant sur des accrus représentatifs des Hautes-Pyrénées. Nous les avons classés en niveaux de potentiel de croissance actuels et futurs et nous avons interprété ces niveaux par rapport aux données de fertilité chimique des stations. Cette méthodologie peut être étendue à d’autres régions et à d’autres types d’accrus. Elle peut servir de base à une catégorisation des accrus selon leur intérêt écologique ou économique

Edge contrast does not modulate edge effect on plants and pollinators

Edge contrast, is one of the main determinants of edge effects. This study examines the response of plant and pollinator diversity (bees and butterflies) to forest edge contrast, i.e. the difference between forests and adjacent open habitats with different disturbance regimes. We also investigated a potential cascading effect from plants to pollinators and whether edge structure and landscape composition mediate the relationship between edge contrast and beta diversity of pollinators. We sampled 51 lowcontrast edges where forests were adjacent to habitats showing low levels of disturbance (i.e. grey dunes, mowed fire-breaks, orchards, grasslands) and 29 high-contrast edges where forests were adjacent to more intensively disturbed habitats (i.e. tilled firebreaks, oilseed rape) in three regions of France. We showed that plant diversities were higher in edges than in adjacent open habitat, whatever the edge contrast. However, plant beta diversity did not differ significantly between low and highcontrast edges. While we observed higher pollinator diversities in adjacent habitats than in low-contrast edges, there were no significant differences in pollinator beta diversity depending on edge contrast. We did not observe a cascading effect from plants to pollinators. Plant and bee beta diversities were mainly explained by local factors (edge structure and flower cover) while butterfly beta diversity was explained by surrounding landscape characteristics (proportion of land cover in grassland)

Optimization of chestnut production within a sustainable development frame.

International audienceDiversilication of agro-ecosystenis can play a role in developing sustainable agriculture insofar as they allow for the diversification of products and goods on the same farm. The present study deals with the possibilities of 'fruit and wood' orchard management in the case of chestnut trees. The main objective of this work is to determine, for two clones of hybrid trees Castanea sativa x Castanea crenata, the technical methods for getting (from the same tree)nuts in the short term and quality timber in the long term. Four varying lengths of pruned stems were tested on trees between three and eight years of age in a trial located in southwest France. After five years of pruning, growth was reduced by 3 to 4 % in height and by 13 to 23 % in diameter, according to fruit pruning literature, but for the two lengthiest pruning types of the more vigorous clone, the pruning effect is positive, indicating fast top growth reaction to pruning of branches, assesse to be about + 6%. For fruit production, the reduction due to pruning is only in terms of bur number and varies from 30 to 70% between fruit pruning and forest pruning. The maximum lenght prunable in chestnut is limited by the amountt of natural defects, but it can reach a maximum of 7 m