Thibault Lachat

Arthropod diversity in Lama forest reserve (South Benin), a mosaic of natural, degraded and plantation forests

Arthropod assemblages were examined in Lama forest reserve, a protected area situated in the Dahomey gap, southern Benin, composed of plantations, degraded forest and remnants of natural forest. The objectives were to compare assemblages in relation to forest type and use, to elucidate the value of forest plantations for biodiversity conservation and to identify indicator species for specific forest habitats. Arthropods were collected over an 11-month period, using standardized sets of traps (pitfall, emergence, Malaise and flight intercept traps). Nine different habitats were studied, including natural and degraded forest, forest plantations (Tectona grandis and Senna siamea) of different age, and isolated forest fragments. Our analysis focused on detritivorous and xylophagous arthropods but also included ground beetles and heteropterans, totalling 393 species. We found no differences in species richness among natural and degraded forest habitats in the centre of the reserve (Noyau central). Outside of the Noyau central, species richness was highest in old teak plantations and isolated forest fragments and lowest in young teak and fuelwood plantations. Detrended correspondence analysis (DCA) separated three main groups: (1) natural forest, (2) degraded forest and young plantations, and (3) old plantations and isolated forest fragments. Multiple regression of DCA scores of the first two axes on environmental variables identified one natural and three disturbance-related predictors of arthropod assemblages in Lama forest: soil type (texture), canopy height, naturalness (proportion of Guineo-Congolian plant species) and understorey vegetation cover. We identified 15 indicator species for six different forest habitats. The highest numbers were found in abandoned settlements and old teak plantations. β-diversity was similar among the three DCA ordination groups (degraded forest excluded). Values for β-diversity were relatively high, suggesting that all major forest habitats contribute significantly to regional species pools and should therefore be protected. To enhance arthropod diversity, we propose that management practices in Lama forest should aim to encourage the development of species-rich understorey vegetation of the Guineo-Congolian phytogeographical region.

Saproxylic beetle assemblages on native and exotic snags in a West African tropical forest

The management of dead wood is crucial to the conservation of saproxylic beetles, species dependent on dead wood. This holds for both natural forest and tree plantations. However, the importance of dead wood in tropical forest ecosystems is not yet well understood. The present study investigates saproxylic beetle assemblages of native and exotic standing dead trees (snags). The study was conducted in semi-deciduous protected forest and tree plantations of the Lama Forest Reserve in Benin, West Africa. The snag beetle fauna was sampled for a total of 12 weeks during one year, using trunk window traps. As a control an equal number of live trees was sampled to distinguish saproxylic and non-saproxylic beetles. Mean snag beetle species richness, relative abundance and the number of singletons, species sampled only once, per snag were similar among native and exotic snags. The total number of snag beetle species and beta-diversity of snag beetle assemblages were higher for native than for exotic snags, reflecting high heterogeneity in habitat quality among snags in natural forest. It is concluded that snag beetle assemblages were influenced mainly by the forest system, semi-deciduous forest vs plantations. With regard to dead wood management, retention or creation of snags in semi-deciduous forest, as well as in plantations, can enhance and preserve the diversity of the saproxylic beetle fauna.

Influence of canopy gaps on saproxylic beetles in primeval beech forests: a case study from the Uholka-Shyrokyi Luh forest, Ukraine

The distribution of canopy gaps has been studied intensively in primeval forest, but their role as keystone structure for biodiversity under natural conditions is still poorly understood. We investigated the effect of habitat properties on saproxylic beetles in the centre, at the edge of gaps and in closed stands in one of the last and largest primeval beech forest of Europe (Uholka‐Shyrokyi Luh forest, Ukraine). The abundance of saproxylic beetles was significantly higher in canopy gaps compared to the closed forest. The number of species did not differ significantly between gap centres and closed forest, but was higher in gap centres than at gap edges. Species composition in gap centres was clearly distinct from that in closed forests. The effects of biotic resources, such as the amount of dead wood or the density of big trees (DBH>70 cm), on diversity measures were weak, which might be caused by the abundance of these resources under natural conditions. Since our study site is embedded in a landscape dominated by primeval forest, the effects of habitat properties on saproxylic beetle fauna might differ from that in managed forests of Central Europe. Nevertheless, species assemblages in primeval beech forests play an important role as a reference for conservation efforts in managed beech forests of Europe.

Importance of Primary Forests for the Conservation of Saproxylic Insects

Primary forests represent the ultimate intact habitat for saproxylic insects. However, their extent has been considerably reduced over the past centuries, and those remaining are very heterogeneously distributed. Primary forests are still locally abundant in tropical and boreal zones but are rare in temperate zones. Consequently, many saproxylic insects that were adapted to typical characteristics of primary forests, such as large amounts of dead wood or overmature and senescent trees, might have become extinct regionally due to habitat loss. The remaining primary forests therefore function as refuges for those saproxylic species that cannot survive in managed forests because of their high ecological requirements. Here we identify six characteristics of primary forests important for saproxylic insects that differentiate these forests greatly from managed forests, namely, absence of habitat fragmentation, continuity, natural disturbance regimes, dead-wood amount and quality, tree species composition and habitat trees. These six characteristics highlight the importance of primary forests for the conservation of saproxylic insects in all three main climatic domains (tropical, boreal and temperate). As primary forests are rare in northern temperate zones and are being dramatically lost in boreal and tropical zones, we propose that they should be strictly conserved independently of their climatic zone. Furthermore, we recommend that studies in primary forests intensify to provide reference data for integrating primary forest characteristics into managed forests to improve the conservation of saproxylic species.