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Larrieu L.,French National Institute for Agricultural Research | Larrieu L.,Center Regional Of La Propriete Forestiere Of Midi Pyrenees | Cabanettes A.,French National Institute for Agricultural Research | Delarue A.,Center Regional Of La Propriete Forestiere Of Midi Pyrenees
European Journal of Forest Research | Year: 2012

In forest ecosystems, the level of biodiversity is strongly linked to dead wood and tree microhabitats. To evaluate the influence of current forest management on the availability of dead wood and on the abundance and distribution of microhabitats, we studied the volume and diversity of dead wood objects and the distribution and frequency of cavities, dendrothelms, cracks, bark losses and sporophores of saproxylic fungi in montane beech-fir stands. We compared stands unmanaged for 50 or 100 years with continuously managed stands. A total of 1,204 live trees and 460 dead wood objects were observed. Total dead wood volume, snag volume and microhabitat diversity were lower in the managed stands, but the total number of microhabitats per ha was not significantly different between managed and unmanaged stands. Cavities were always the most frequent microhabitat and cracks the least frequent. Dendrothelm and bark loss were favored by management. Beech (Fagus sylvatica) carried many more microhabitats than silver fir (Abies alba), especially cavities, dendrothelms and bark losses. Fir very scarcely formed dendrothelms. Secondary tree species played an important role by providing cracks and bark losses. The proportion of microhabitat-bearing trees increased dramatically above circumference thresholds of 225 cm for beech and 215 cm for fir. Firs with a circumference of less than 135 cm did not carry microhabitats. In order to conserve microhabitat-providing trees and to increase the volume of dead wood in managed stands, we recommend conserving trees that finish their natural cycle over 10-20% of the surface area. © 2011 Springer-Verlag.

Bouget C.,IRSTEA | Larrieu L.,French National Institute for Agricultural Research | Larrieu L.,Center Regional Of La Propriete Forestiere Of Midi Pyrenees | Nusillard B.,IRSTEA | And 2 more authors.
Biodiversity and Conservation | Year: 2013

Deadwood-associated species are increasingly targeted in forest biodiversity conservation. In order to improve structural biodiversity indicators and sustainable management guidelines, we need to elucidate ecological and anthropogenic drivers of saproxylic diversity. Herein we aim to disentangle the effects of local habitat attributes which presumably drive saproxylic beetle communities in temperate lowland deciduous forests. We collected data on saproxylic beetles in 104 oak and 49 beech stands in seven French lowland forests and used deadwood, microhabitat and stand features (large trees, openness) as predictor variables to describe local forest conditions. Deadwood diversity and stand openness were consistent key habitat features for species richness and composition in deciduous forests. Large downed deadwood volume was a significant predictor of beetle species richness in oak forests only. In addition, the density of cavity- and fungus-bearing trees had weak but significant effects. We recommend that forest managers favor the local diversification of deadwood types, especially the number of combinations of deadwood positions and tree species, the retention of large downed deadwood and microhabitat-bearing trees in order to maximize the saproxylic beetle diversity at the stand scale in deciduous forests. To improve our understanding of deadwood-biodiversity relationships, further research should be based on targeted surveys on species-microhabitat relationships and should investigate the role of landscape-scale deadwood resources and of historical gaps in continuity of key features availability at the local scale. © 2013 Springer Science+Business Media Dordrecht.

Lassauce A.,IRSTEA | Lassauce A.,French Environment and Energy Management Agency | Larrieu L.,French National Institute for Agricultural Research | Larrieu L.,Center Regional Of La Propriete Forestiere Of Midi Pyrenees | And 3 more authors.
Insect Conservation and Diversity | Year: 2013

In French oak high forests, current silvicultural trends include two seemingly opposed practices: shortening the forestry cycle, which contributes to forestry intensification, and lengthening rotations in temporary set-aside stands, called 'ageing islands', to favour biodiversity and high-quality large-diameter tree production. To derive the potential effects of these two trends, we studied habitat structure and saproxylic beetles biodiversity along an age gradient in a French oak high forest. Four age classes were surveyed: premature (i) 160/180 years and (ii) 180/200 years, (iii) mature 200/220 years, and (iv) overmature 300-year-old stands. Structural features were noted: deadwood volumes, density of large trees with or without microhabitats, number of cavities, presence of dead large canopy branches, sap droppings and sporophores of saproxylic fungi. Results showed that beetle species richness was positively related to stand age. Globally, overmature stands differed significantly from younger premature and mature forests in species composition and structure. Younger stands tended to show both fewer structural features and lower levels of saproxylic biodiversity. As the forest aged, the overall structural complexity and saproxylic biodiversity increased. However, no individual stand characteristic influenced preferentially biodiversity, and stand age was the best explaining factor. In conclusion, we discuss how (i) shorter rotations in the high forest production cycle and (ii) temporary set-aside forest islands affect forest structure and deadwood-associated assemblages. Shortening rotation length in oak high forests may negatively impact saproxylic biodiversity, whereas temporary set-asides may play a key role for biodiversity conservation in a managed forest matrix. © 2012 The Royal Entomological Society.

Bouget C.,IRSTEA | Larrieu L.,French National Institute for Agricultural Research | Larrieu L.,Center Regional Of La Propriete Forestiere Of Midi Pyrenees | Brin A.,Purpan Engineering School
Ecological Indicators | Year: 2014

Managing and monitoring forest biodiversity is challenging and rapid habitat assessment protocols should be developed to provide us with general key features based on field data. A rapid habitat assessment protocol was implemented over a wide forest gradient in France to analyze surrogacy patterns and performance consistency of presumed key attributes for saproxylic beetle diversity (large trees, microhabitat-bearing trees with trunk cavities, fruiting bodies of saproxylic fungi, tree crown deadwood and sap runs, large logs and snags) and of stand openness. Data compiled in this study include standardized deadwood and window-flight trapped beetle data from 313 plots in oak, lowland and highland beech, lowland pine, highland spruce-fir and mixed temperate forests throughout France. The most structuring factors for species richness and composition of saproxylic beetles were the density of cavity- or fungus-bearing trees and of snags, as well as the degree of openness in the 1-ha surrounding the stand. These key habitat features were nevertheless inconsistent over the different types of temperate forests, and for rare species vs. all species combined. No one variable robustly explained variations in species richness in the deciduous or conifer forest types. The influence of deadwood and "habitat trees" was affected by meso- and micro-climatic features. A significant effect of stand openness on saproxylic beetles was observed both in deciduous and in conifer forests, but only in lowlands. Effects on species richness due to an interaction between substrate availability and openness were observed in montane forests only. Our results point toward the relevance of ecological attributes in tracking changes in saproxylic beetle biodiversity in specific forest contexts, but our study failed to identify any universal structural biodiversity indicators which could be surveyed in part with data from national forest inventories and used to track progress in sustainable forest management or in the protection of sensitive areas. © 2013 Elsevier Ltd. All rights reserved.

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