Biology subjects

Jactel, H.

Publications and source records attributed to Jactel, H..

12 recordsLinked to original sources

bioRxiv2026

Broadleaved hedgerows as complementary habitats for small mammals in pine plantation landscapes

O_LIThe global decline of natural forests is accompanied by a rapid expansion of commercial tree plantations, which are expected to further increase to meet growing demand for wood products. However, planted forests generally support lower biodiversity than natural forests, particularly when monospecific and intensively managed. In this context, broadleaved hedgerows have been proposed as a nature-based solution to enhance biodiversity within conifer-dominated plantation landscapes. Such features may be especially beneficial for small mammals, including rodents and shrews, which are key contributors to forest ecosystem functioning. However, their effects on small mammal communities remain largely unquantified. C_LIO_LIHere, we assessed variation in small mammal communities among habitat types within a native pine plantation-dominated landscape in southwestern France. Using a multi-year, multi-season survey, we compared species richness and abundance among plantation edges, broadleaved hedgerows embedded within plantations and natural broadleaved forests. We further tested whether environmental descriptors of hedgerow sites influenced dominant species and whether seasonal and interannual demographic dynamics modified habitat-related patterns. C_LIO_LIPine plantation edges and broadleaved hedgerows supported lower small mammal species richness than natural broadleaved forests and were dominated by two habitat generalists, Apodemus sylvaticus and Crocidura russula. This pattern was driven by the near absence of the forest specialist Clethrionomys glareolus. Hedgerows did not increase species richness relative to plantations, but provided favourable habitat for A. sylvaticus, which was scarce in pine plantation, while supporting fewer C. russula. Variation in hedgerow structure and composition further influenced A. sylvaticus abundance, while seasonal and interannual rodent population dynamics modulated habitat-related differences. C_LIO_LIOur results indicate that intensively managed pine plantations act as environmental filters, excluding forest-associated small mammals. While broadleaved hedgerows benefited one species, their capacity to restore forest-specialist communities was limited without broader landscape-scale interventions. These findings highlight both the ecological benefits and constraints of edge-based habitat interventions and provide guidance for designing and evaluating biodiversity-oriented management in plantation landscapes. C_LI

ecology↗

bioRxiv2025

Worldwide spread of Hylurgus ligniperda (Coleoptera: Scolytinae), and the potential role of bridgehead invasions

Hylurgus ligniperda (F.) is a highly successful invader among bark beetles (Scolytinae) and forest insects in general. Native to the western Palearctic region, it has become established in every continent where its host plants (Pinus spp.) occur. Especially in southern hemisphere regions with large pine plantations, it is often highly abundant. As a repeat invader with a wealth of information on various aspects relevant for biological invasions, it is highly suitable as a model organism for studying the role of international trade, the planting of non-native trees, and the potential occurrence of bridgehead invasions (where abundant non-native populations precipitate further invasions). In the present study, our specific objectives were to reconstruct the worldwide invasions of H. ligniperda and the pathways involved by using a multi-pronged approach including population genetics, analysis of historic interception data generated from inspections of imports, and records of establishments in the literature. Our review of the native and non-native ranges of H. ligniperda and the chronology of establishments revealed at least 13 separate invasions of non-native regions, beginning with Madeira (Portugal) before 1850, and, most recently, eastern China in 2019. We compared the population genetics of 464 specimens from eight countries in the native range and eight countries in the non-native range. Sequencing of the mitochondrial COI gene revealed the presence of 29 haplotypes in six well-supported clades, based on a Bayesian analysis. Non-native populations had significantly lower haplotype diversity (mean h = 0.219) than populations in the native range (mean h = 0.691). Countries in the non-native range had an average of about two haplotypes compared with about four haplotypes in native countries. In the non-native range, only one or two haplotypes were dominant, and these differed among invaded regions except for haplotype HL-H3 which occurred in Australia, New Zealand and China as well as in four countries in southern Europe, and HL-H4 which was dominant in New Zealand, California, New York State, and eastern China as well as two countries in southern Europe. Analyses of interceptions of H. ligniperda with imports arriving in five countries revealed that between 74% and 99% of interceptions originated from other non-native regions while in the USA, most interceptions were linked to imports from the native range beginning in the 1970s. Based on the combined evidence of the chronology of invasions, interception data, and analysis of haplotype distribution, we conclude that the early invasions (before 1950) probably all originated from the native range, while several of the more recent invasions probably originated from parts of the non-native range (suggestive of a bridgehead effect). However, it cannot be determined with certainty what the original sources of each of the invading populations were.

ecology↗

bioRxiv2024

Multi-year drought strengthens positive and negative functional diversity effects on tree growth response

O_LIMixed-species forests are proposed as strategy to increase the resistance and resilience of forests to drought stress. However, evidence suggest that increasing tree species richness does not consistently enhance tree growth responses to drought. Moreover, tree diversity effects under unprecedented multiyear droughts remain uncertain, calling for a better understanding of the underlying processes. C_LIO_LIHere, we used a network of planted tree diversity experiments to investigate how drought-induced growth responses of individual trees are influenced by neighborhood tree diversity and the functional traits of the focal tree species. We analyzed tree cores (948 trees across 16 species) from nine experiments across Europe featuring gradients of tree species richness (1-6 species), which experienced severe droughts in recent years. Radial growth response to drought was quantified as tree-ring biomass increment using X-ray computed tomography. We applied hydraulic trait-based growth models to analyze single-year drought responses across all sites and site-specific responses during consecutive drought years for six sites as a function of neighborhood tree diversity. C_LIO_LIThe large variability in tree growth responses to a single-year drought was partially explained by the focal species hydraulic safety margin (representing species drought tolerance) and drought intensity, but independent of neighborhood species richness or functional trait diversity. However, tree diversity effects on growth responses strengthened during consecutive drought years and were site-specific, with contrasting direction (both positive and negative). This indicated opposing pathways of diversity effects under consecutive drought events, possibly resulting from competitive release or greater water consumption in diverse mixtures. C_LIO_LIWe conclude that tree diversity effects on growth responses to single-year droughts may differ considerably from responses to consecutive drought years. Our study highlights the need to consider trait-based approaches (specifically, hydraulic traits) and tree neighborhood scale processes to understand the multifaceted growth responses of tree mixtures under prolonged drought stress. C_LI

ecology↗

bioRxiv2022

Cosmopolitan Scolytinae: strong common drivers but too many singularities for accurate prediction

AimMany scolytine beetle species have been expanding their range in new territories across geographic barriers, traveling with wood, wood products and plants for planting, sometimes with a high impact on plant health. Here we attempt to quantify the mobility of these cosmopolitan species and to identify the biological drivers of mobility and impact. LocationWorld Major taxa studiedColeoptera; Curculionidae; Scolytinae MethodsMobility was estimated by counting the numbers of landmasses (contiguous pieces of land, surrounded by ocean or sea) colonized by each species. A series of potential drivers (taxonomic tribes; feeding habits; polyphagy; reproductive strategy; host taxa; pheromones and primary attractants) as well as impact on host health were recorded. Results163 species were identified, out of 5546 counted in the whole subfamily. Four tribes (Xyleborini; Ipini; Crypturgini; Hylastini) were significantly over-represented, and two others (Corthylini; Hexacolini) were under-represented. 53% of the 163 species are inbreeding, a very significant excess as compared to the whole subfamily (29%). The inbreeders colonized more landmasses than the outbreeders. There is a significant relationship between the number of host families attacked by a species and the number of colonized landmasses. Species restricted to conifers colonized fewer landmasses than hardwood generalists. Species attacking both types of hosts are the most mobile. Most of the invasive species respond to host primary attractants, only one quarter respond to pheromones. All very mobile species respond to primary attractants, and none responds to pheromones. Very mobile species are all associated with a high or moderate impact. Main conclusionsThe most mobile species belong for a large part to a limited number of subtribes. They are often inbreeding, polyphagous and respond to primary attractants but do not produce pheromones. However, many species that do not, or only partly, belong to these categories, have established in several landmasses, sometimes with a high impact. For example, the outbreeding Scolytus multistriatus, that attacks only 3 host families and produces aggregation pheromones, has established in thirteen landmasses, with a high impact. Therefore, risk prediction needs to assess diversity of species-specific biological traits beyond the few routinely analyzed in literature.

ecology↗

bioRxiv2022

Tree diversity and density affect damage caused by the invasive pest Cameraria ohridella in urban areas

Invasive, non-native invasive pests pose a growing threat to urban trees and the services they provide to urban residents. With the reluctance to use chemical insecticides in cities, environmentally friendly methods of pest management are needed. Tree diversity is known to affect insect herbivory in forest, with higher tree species diversity leading to lower level of damage. However, the validity of those findings for a non-native insect in an urban environment remains to be demonstrated. We monitored 54 horse chestnut trees attacked by the invasive horse chestnut leafminer Cameraria ohridella in the city of Bordeaux, France. We analyzed the effects of neighboring tree diversity and density on the abundance, damage and parasitism rate of these leafminers. We showed that the abundance and damage of C. ohridella significantly increased with higher local tree canopy cover. We found that the parasitism rate of C. ohridella increased with the species diversity of neighboring trees. However, this increase in parasitism rate was not associated with a decrease in leaf area damaged. Our results pave the way for the management of exotic insect pests in cities based on the manipulation of spatial distribution and species diversity of urban trees.

ecology↗

bioRxiv2022

Higher aboveground carbon stocks in mixed-species planted forests than monocultures - a meta-analysis

Natural forest is declining globally as the area of planted forest increases. Planted forests are often monocultures, despite results suggesting that higher species richness improves ecosystem functioning and stability. To test if this is generally the case, we performed a meta-analysis of available results. We assessed aboveground carbon stocks in mixed-species planted forests vs (a) the average of constituent species monocultures, (b) the best constituent species monoculture, and (c) commercial species monocultures. We investigated whether any advantage of mixtures over monocultures was positively related to species richness, as well as potential mechanisms driving differences in carbon stocks between mixtures and monocultures. The meta-analysis dataset included 79 comparisons from 21 sites. Carbon stocks in mixed planted forests were higher than the average of stocks in monocultures of their constituent species, containing on average 70% more carbon. Mixed planted forests also out-performed commercial monocultures, containing on average 77% more carbon. There was c.25% more carbon in mixed planted forests relative to the best performing monocultures, although this difference was not statistically significant. Overyielding was highest in four-species mixtures (richness range 2-6 species). More data providing better coverage of richness and age gradients (study sites aged 3.5-28 years) is needed to increase confidence in these results. None of the potential mechanisms we examined (nitrogen-fixer present vs absent; native vs non-native/mixed origin; tree diversity experiment vs forestry plantation) consistently explained variation in the diversity effects. This suggests that our findings are driven by a combination of small (statistically insignificant) effects from these sources or further unidentified mechanisms or some combination of the two. We conclude that increasing tree species richness in planted forests can increase carbon stocks while bringing other potential benefits associated with diversification. However, implementation will depend on the balance of these benefits relative to the operational challenges and costs of diversification.

ecology↗

bioRxiv2021

Meta-analysis of tree diversity effects on the abundance, diversity and activity of herbivores' enemies

O_LIThe natural enemies hypothesis predicts that the abundance and diversity of antagonists such as predators and parasitoids of herbivores increases with the diversity of plants, which can lead to more effective top-down control of insect herbivores. However, although the hypothesis has received large support in agricultural systems, fewer studies have been conducted in forest ecosystems and a comprehensive synthesis of previous research is still lacking. C_LIO_LIWe conducted a meta-analysis of 65 publications comparing the diversity, abundance or activity of various groups of natural enemies (including birds, bats, spiders and insect parasitoids) in pure vs. mixed forest stands. We tested the effects of forest biome, natural enemy taxon and type of study (managed vs experimental forest). C_LIO_LIWe found a significant positive effect of forest tree diversity on natural enemy abundance and diversity but not on their activity. The effect of tree diversity on natural enemies was stronger towards lower latitudes but was not contingent on the natural enemy taxon level. C_LIO_LIOverall, our study contributes toward a better understanding of the "natural enemies hypothesis" in forest systems and provides new insights about the mechanisms involved. Furthermore, we outline potential avenues for strengthening forest resistance to the growing threat of herbivorous insects. C_LI

ecology↗

bioRxiv2021

Tree diversity effects on forest productivity: disentangling the effects of tree species addition vs. substitution

O_LIMixture effect on stand productivity is usually apprehended through a substitutive approach, whereby productivity in mixed stands is compared to productivity in monocultures, at equivalent stand density. This approach has proved that in many cases mixed stands perform better than monospecific forests, however, we do not yet have a solid theory about species behaviour in the mixture or even guidelines for combining species. The addition of a second tree species to an existing mono-specific stand has received much less consideration. Yet, this approach has the potential to separate the facilitation effect from the complementarity effect. C_LIO_LIWe compared the effect of tree species substitution vs. addition on the productivity of maritime pine and silver birch in a young tree diversity experiment implemented in 2008 in SW France. C_LIO_LISubstituting pines with birches to create two-species mixtures resulted in an increase of tree productivity at stand level beyond what was expected from monocultures (i.e., overyielding). In contrast, creating mixture through the addition of birches to pine stands had no effect on the maritime pine stand productivity (transgressive mixture effect not significant). This absence of effect is produced by two distinct density-dependence responses at an individual level. C_LIO_LIOur results allow clarifying the cases in which a mixed stand can be considered as an alternative to a monoculture of a productive species. In particular, the addition of a pioneer and soil low-demanding species during young developmental stages is a possibility to diversify the stand and potentially to increase ecosystem services without altering the productivity of the target species. C_LI

ecology↗

bioRxiv2020

Host-mediated, cross-generational intraspecific competition in a multivoltine herbivore species

AO_SCPLOWBSTRACTC_SCPLOWConspecific insect herbivores co-occurring on the same host plant interact both directly through interference competition and indirectly through exploitative competition, plant-mediated interactions and enemy-mediated interactions. However, the situation is less clear when the interactions between conspecific insect herbivores are separated in time within the same growing season, as it is the case for multivoltine species. We hypothesized that early season herbivory would result in reduced egg laying and reduced performance of the next generation of herbivores on previously attacked plants. We tested this hypothesis in a choice experiment with box tree moth females (Cydalima perspectalis Walker, Lepidoptera: Crambidae). These females were exposed to box trees (Buxus sempervirens L., Buxaceae) that were either undamaged or attacked by conspecific larvae earlier in the season. We then compared the performance of the next generation larvae on previously damaged vs undamaged plants. Previous herbivory had no effect on oviposition behaviour, but the weight of next generation larvae was significantly lower in previously damaged plants. There was a negative correlation between the number of egg clutches laid on plants by the first generation and the performance of the next generation larvae. Overall, our findings reveal that early season herbivory reduces the performance of conspecific individuals on the same host plant later in the growing season, and that this time-lagged intraspecific competition results from a mismatch between the oviposition preference of females and the performance of its offspring.

ecology↗

bioRxiv2020

Insect herbivory on urban trees: Complementary effects of tree neighbours and predation

O_LIInsect herbivory is an important component of forest ecosystems functioning and can affect tree growth and survival. Tree diversity is known to influence insect herbivory in natural forest, with most studies reporting a decrease in herbivory with increasing tree diversity. Urban ecosystems, on the other hand, differ in many ways from the forest ecosystem and the drivers of insect herbivory in cities are still debated. C_LIO_LIWe monitored 48 urban trees from five species - three native and two exotic - in three parks of Montreal (Canada) for leaf insect herbivory and predator activity on artificial larvae, and linked herbivory with both predation and tree diversity in the vicinity of focal trees. C_LIO_LILeaf insect herbivory decreased with increasing tree diversity and with increasing predator attack rate. C_LIO_LIOur findings indicate that tree diversity is a key determinant of multitrophic interactions between trees, herbivores and predators in urban environments and that managing tree diversity could contribute to pest control in cities. C_LI This article has been peer-reviewed and recommended by Peer Community in Ecology https://doi.org/10.24072/pci.ecology.100061

ecology↗

bioRxiv2020

Biotic and abiotic drivers of soil microbial functions across tree diversity experiments

AimSoil microorganisms are essential for the functioning of terrestrial ecosystems. Although soil microbial communities and functions may be linked to the tree species composition and diversity of forests, there has been no comprehensive study of how general potential relationships are and if these are context-dependent. A global network of tree diversity experiments (TreeDivNet) allows for a first examination of tree diversity-soil microbial function relationships across environmental gradients. LocationGlobal Major Taxa StudiedSoil microorganisms MethodsSoil samples collected from eleven tree diversity experiments in four biomes across four continents were used to measure soil basal respiration, microbial biomass, and carbon use efficiency using the substrate-induced respiration method. All samples were measured using the same analytical device in the same laboratory to prevent measurement bias. We used linear mixed-effects models to examine the effects of tree species diversity, environmental conditions, and their interactions on soil microbial functions. ResultsAcross biodiversity experiments, abiotic drivers, mainly soil water content, significantly increased soil microbial functions. Potential evapotranspiration (PET) increased, whereas soil C-to-N ratio (CN) decreased soil microbial functions under dry soil conditions, but high soil water content reduced the importance of other abiotic drivers. Tree species richness and phylogenetic diversity had overall similar, but weak and context-dependent (climate, soil abiotic variables) effects on soil microbial respiration. Positive tree diversity effects on soil microbial respiration were most pronounced at low PET, low soil CN, and high tree density. Soil microbial functions increased with the age of the experiment. Main conclusionsOur results point at the importance of soil water content for maintaining high levels of soil microbial functions and modulating effects of other environmental drivers. Moreover, overall tree diversity effects on soil microbial functions seem to be negligible in the short term (experiments were 1-18 years old). However, context-dependent tree diversity effects (climate, soil abiotic variables) have greater importance at high tree density, and significant effects of experimental age call for longer-term studies. Such systematic insights are key to better integrate soil carbon dynamics into the management of afforestation projects across environmental contexts, as todays reforestation efforts remain focused largely on aboveground carbon storage and are still dominated by less diverse forests stands of commercial species.

ecology↗

bioRxiv2019

Growth and mortality of the oak processionary moth, Thaumetopoea processionea L., on two oak species: direct and trait-mediated effects of host and neighbour species identity

The presence of heterospecific neighbours can affect damage caused by pest insects on focal plants. However, how plant neighbours influence herbivore performance is poorly understood. We tested the independent and interactive effects of tree species identity and tree neighbour type (conspecific vs. heterospecific) on the performance of a major oak pest, the oak processionary moth larvae (OPM, Thaumetopoea processionea) fed on Quercus robur and Q. petraea. We performed a factorial greenhouse experiment in which we grew two oak saplings per pot, either from the same species or from both species. We quantified growth and mortality of OPM larvae, leaf phenolic compounds, C:N ratio and bud phenology. OPM larvae performed significantly better on Q. petraea than on Q. robur, regardless of plant neighbour type. Phenolic compounds and C:N, but not phenology, differed between oak species and neighbour species identity. Only bud phenology had a significant effect on OPM performance, which was better when young larvae had access to recently unfolded leaves, regardless of oak species and neighbour identity. Although oak neighbour identity altered the expression of leaf traits, this effect had no measurable consequences on OPM performance. However, further studies should consider the effect of oak species neighbour on OPM preferences for either Q. robur or Q. petraea, in pure and mixed stands, before translating current results into recommendations for forest management. Author ContributionTD and BC conceived the study and acquired the data. TD performed experiment and analysed the data. EV, TD and XM performed the chemical analyses. TD and BC drafted the first version of the manuscript and all authors wrote the final version of the manuscript. TD, BC conceived and designed research. TD performed experiment and analysed data. EV, TD, XM performed the chemical analyses. TD, BC wrote the manuscript. All authors read and approved the manuscript. AM and DB conceived and designed research. AM and BB conducted experiments. GR contributed new reagents or analytical tools. AM, BB and GR analysed data. AM wrote the manuscript. All authors read and approved the manuscript.

ecology↗