CREAF

Reports on forest decline, changes in species composition and the distribution of forests in response to changes in climate and land use are increasing worldwide. Temperate forests are largely dominated by two tree families: Pinaceae and Fagaceae. These two families have distinct functional properties and different responses to environmental factors. Several local and regional assessments, particularly in Europe, have found that species of Fagaceae are invading areas previously dominated by Pinaceae. The main aim of this synthesis study is to analyze the relative dynamics of Pinaceae and Fagaceae species in temperate forests around the world, with the following specific objectives: (1) establish if there is a consistent directional substitution of Pinaceae by Fagaceae worldwide; and (2) determine whether these directional changes are associated with specific climatic conditions or certain geographic regions, reflecting differences in historical forest management and land use. A bibliographic review was performed and 51 papers were found that met the search criteria, including a total of 121 case studies in which the relative dynamics of Pinaceae and Fagaceae were evaluated. Our results show that the relative abundance of Fagaceae increased in 71% of cases (P → F dynamics), whereas Pinaceae relative abundance increased in 17% of cases (F → P) and 12% of cases did not show clear changes. Increases of Fagaceae relative to Pinaceae were less clear in areas where vegetation dynamics were driven by natural disturbances. Our results indicate a widespread increase in dominance of Fagaceae species at the expense of Pinaceae across northern temperate forests, with the exception of Eastern North America. The potential implications for ecosystem function and forest resilience under ongoing climate change are large and clearly deserve further study. © 2018 Elsevier B.V.

Long-term climate change experiments are extremely valuable for studying ecosystem responses to environmental change. Examination of the vegetation and the soil should be non-destructive to guarantee long-term research. In this paper, we review field methods using isotope techniques for assessing carbon dynamics in the plant–soil–air continuum, based on recent field experience and examples from a European climate change manipulation network. Eight European semi-natural shrubland ecosystems were exposed to warming and drought manipulations. One field site was additionally exposed to elevated atmospheric CO2. We discuss the isotope methods that were used across the network to evaluate carbon fluxes and ecosystem responses, including: (1) analysis of the naturally rare isotopes of carbon (13C and 14C) and nitrogen (15N); (2) use of in situ pulse labelling with 13CO2, soil injections of 13C- and 15N-enriched substrates, or continuous labelling by free air carbon dioxide enrichment (FACE) and (3) manipulation of isotopic composition of soil substrates (14C) in laboratory-based studies. The natural 14C signature of soil respiration gave insight into a possible long-term shift in the partitioning between the decomposition of young and old soil carbon sources. Contrastingly, the stable isotopes 13C and 15N were used for shorter-term processes, as the residence time in a certain compartment of the stable isotope label signal is limited. The use of labelled carbon-compounds to study carbon mineralisation by soil micro-organisms enabled to determine the long-term effect of climate change on microbial carbon uptake kinetics and turnover. Based on the experience with the experimental work, we provide recommendations for the application of the reviewed methods to study carbon fluxes in the plant–soil–air continuum in climate change experiments. 13C-labelling techniques exert minimal physical disturbances, however, the dilution of the applied isotopic signal can be challenging. In addition, the contamination of the field site with excess 13C or 14C can be a problem for subsequent natural abundance (14C and 13C) or label studies. The use of slight changes in carbon and nitrogen natural abundance does not present problems related to potential dilution or contamination risks, but the usefulness depends on the fractionation rate of the studied processes. © 2018 The Authors. Methods in Ecology and Evolution © 2018 British Ecological Society

Synchrony between seed growth and oogenesis is suggested to largely shape trophic breadth of seed-feeding insects and ultimately to contribute to their co-existence by means of resource partitioning or in the time when infestation occurs. Here we investigated: (i) the role of seed phenology and sexual maturation of females in the host specificity of seed-feeding weevils (Curculio spp.) predating in hazel and oak mixed forests; and (ii) the consequences that trophic breadth and host distribution have in the genetic structure of the weevil populations. DNA analyses were used to establish unequivocally host specificity and to determine the population genetic structure. We identified 4 species with different specificity, namely Curculio nucum females matured earlier and infested a unique host (hazelnuts, Corylus avellana) while 3 species (Curculio venosus, Curculio glandium and Curculio elephas) predated upon the acorns of the 2 oaks (Quercus ilex and Quercus pubescens). The high specificity of C. nucum coupled with a more discontinuous distribution of hazel trees resulted in a significant genetic structure among sites. In addition, the presence of an excess of local rare haplotypes indicated that C. nucum populations went through genetic expansion after recent bottlenecks. Conversely, these effects were not observed in the more generalist Curculio glandium predating upon oaks. Ultimately, co-existence of weevil species in this multi-host-parasite system is influenced by both resource and time partitioning. To what extent the restriction in gene flow among C. nucum populations may have negative consequences for their persistence in a time of increasing disturbances (e.g. drought in Mediterranean areas) deserves further research. © 2017 The Authors. Integrative Zoology published by International Society of Zoological Sciences, Institute of Zoology/Chinese Academy of Sciences and John Wiley & Sons Australia, Ltd