Early Tree Diversity and Composition Effects on Topsoil Chemistry in Young Forest Plantations Depend on Site Context

Ecosystems - Trees have a strong influence on the chemical properties of the soil in which they grow. Establishing plantations with different tree species combinations thus potentially leads to...     

Low habitat specificity in one of Europe’s most invasive spiders – Mermessus trilobatus

Most spiders are mobile and easily transported across the world via human activity, making them ideal candidates for biological invasions. Mermessus trilobatus (Emerton, 1882) is one of Europe’s most invasive spider species and one of the few invasive spider species that successfully invade (semi-) natural ecosystems. Yet, its invasion success is not well understood. We investigated the Niche Breadth-Invasion Success Hypothesis in an old sand quarry with high habitat diversity in northern Belgium. We captured spiders using pitfall traps at 25 locations over 14 months. The activity-density of M. trilobatus could be linked to soil pH and temperature. Mermessus trilobatus showed the highest habitat diversity of all 150 species captured and was one of the few species found in each pitfall trap. The low habitat specificity of M. trilobatus could be key in population establishment, fast spread and invasion success.

     

Driving Factors Behind Litter Decomposition and Nutrient Release at Temperate Forest Edges

Forest edges have become important features in landscapes worldwide. Edges are exposed to a different microclimate and higher atmospheric nitrogen (N) deposition compared to forest interiors. It is, however, unclear how microclimate and elevated N deposition affect nutrient cycling at forest edges. We studied litter decomposition and release of N, phosphorus (P), total cations (TC) and C/N ratios during 18 months via the litterbag technique along edge-to-interior transects in two oak (Quercus robur L.) and two pine (Pinus nigra ssp. laricio Maire and ssp. nigra Arnold) stands in Belgium. Furthermore, the roles of edge conditions (microclimate, atmospheric deposition, soil fauna and soil physicochemical conditions), litter quality and edge decomposer community were investigated as underlying driving factors for litter decomposition. Litter of edge and interior was interchanged (focusing on the influence of edge conditions and litter quality) and placed in open-top chamber (OTC), which create an edge (warmer) microclimate. As the decomposer macrofauna was more abundant at the edge than in the interior, the OTCs were used to isolate the effects of warming versus soil fauna. Oak litter at the edge lost 87 and 37% more mass than litter in the interior. We demonstrated an edge effect on litter decomposition and nutrient release, caused by an interplay of edge conditions (atmospheric deposition of N and TC, soil pH and C/N ratio), litter quality and soil fauna. Consequently, edge effects must be accounted for when quantifying ecosystem processes, such as litter decomposition and nutrient cycling in fragmented landscapes.     

Tree diversity is key for promoting the diversity and abundance of forest-associated taxa in Europe

Plant diversity is an important driver of diversity at other trophic levels, suggesting that cascading extinctions could reduce overall biodiversity. Most evidence for positive effects of plant diversity comes from grasslands. Despite the fact that forests are hotspots of biodiversity, the importance of tree diversity, in particular its relative importance compared to other management related factors, in affecting forest-associated taxa is not well known. To address this, we used data from 183 plots, located in different forest types, from Mediterranean to Boreal, and established along a climatic gradient across six European countries (FunDivEUROPE project). We tested the influence of tree diversity, tree functional composition (i.e. functional trait values), forest structure, climate and soil on the diversity and abundance/activity of nine taxa (bats, birds, spiders, microorganisms, earthworms, ungulates, foliar fungal pathogens, defoliating insects and understorey plants) and on their overall diversity and abundance/activity (multidiversity, multiabundance/activity). Tree diversity was a key driver of taxon-level and overall forest-associated biodiversity, along with tree functional composition, forest structure, climate and soil. Both tree species richness and functional diversity (variation in functional trait values) were important. The effects of tree diversity on the abundance/activity of forest-associated taxa were less consistent. Nonetheless, spiders, ungulates and foliar fungal pathogens were all more abundant/active in diverse forests. Tree functional composition and structure were also important drivers of abundance/activity: conifer stands had lower overall multidiversity (although the effect was driven by defoliating insects), while stands with potentially tall trees had lower overall multiabundance/activity. We found more synergies than tradeoffs between diversity and abundance/activity of different taxa, suggesting that forest management can promote high diversity across taxa. Our results clearly show the high value of mixed forest stands for multiple forest-associated taxa and indicate that multiple dimensions of tree diversity (taxonomic and functional) are important.     

A Red List of terrestrial isopods (Isopoda: Oniscidea) in Flanders (northern Belgium) and its implications for conservation

Journal of Insect Conservation - Although diversity and abundance of arthropods have been shown to decline globally, they are underrepresented in nature conservation efforts and policies....