In recent years, budburst, the timing of leaf emergence, has advanced less than expected despite continued spring warming, suggesting counteracting ecological forces. One of these forces might be increased and earlier herbivory on young leaves under climate warming. Here using 5 years of satellite radar data from 27,500 pixels (10 ×10 m2) across 60 temperate oak forest sites under experimental manipulation of insect herbivore loads in Central Europe, we show that prior-year leaf herbivory delayed budburst by 3 days, cancelling the phenological advance observed during a decade of warming. This delay reduced subsequent herbivory by 55%, exceeding the effects of parasitoids or pathogens, and persisted even during pest outbreaks. Across landscapes, the delay was strongest where it probably provided the highest benefit, that is, where a given amount of delay most effectively reduced following herbivory, which suggests an adaptive tree defence. Ultimately, trees may be trapped between responding to two opposing consequences of global change: warming selects for earlier budburst, whereas herbivory selects for delay. Our results underscore the need to consider not only climate, but also plant-herbivore interactions and adaptive evolution to predict tree responses to a changing world.

Background:For several regions, ecologists and taxonomists have assembled information on phenotypes for almost all species of the megadiverse angiosperms. However, testing hypotheses on regional evolutionary and biogeographic history requires highly resolved and dated phylogenies covering the same taxa, which are often lacking at regional scales. Here, we filled this knowledge gap for one of the best-studied regional floras: the native angiosperms of the Netherlands. New information:We provide a molecular phylogenetic dataset and two time-calibrated trees (based on BEAST and MrBayes approaches) of the native angiosperm flora of the Netherlands, reconstructed from publicly available DNA sequences. The resulting phylogenies include 1178 species from the 2017 species list on SynBioSys NL, a national database that provides a curated checklist of native vascular plant species occurring in the Netherlands (also core to the flora of adjacent countries), and are provided in multiple formats (Newick, Nexus), along with alignments, BEAST and MrBayes input files, and metadata linking taxa to GenBank accession numbers. This dataset offers a phylogenetic framework that is based on molecular data covering more than 95% of the native species included in the checklist, reproducible and extremely well-resolved phylogeny (99.92% of nodes resolved in the maximum clade credibility tree; reflecting the absence of polytomies; 67.9% of nodes with posterior probability above 0.95 and 92.3% above 0.50) for researchers. These data will permit the signal of evolutionary history in patterns of biodiversity across the Netherlands, such as the age structure of habitat species pools or functional groups, where a focus on native species is essential. All resources are openly available via IDiv (https://doi.org/10.25829/idiv.3600-myr3t3) under a CC-BY license.

1. Koinobiont parasitoids have been shown to both reduce and increase the growth rate of caterpillars. However, no comprehensive study has been conducted on all caterpillar hosts of a given plant species. Moreover, most of the existing case studies are on large caterpillars attacking crop plants. This may not be representative of the effect of parasitoids on caterpillar growth on trees. 2. We measured the growth rate of parasitised and non-parasitised spring caterpillars collected from oak trees ( Quercus robur & Q. petraea ) in France and Poland. 3. Across six species of Lepidoptera, parasitoids reduced caterpillar growth rate on average. 4. Further studies should determine if the reduced growth rate is accompanied by lower consumption rates, so that the plant directly benefits from attracting parasitoids when they are attacked by caterpillars. ### Competing Interest Statement The authors have declared no competing interest. NCN, 2018/29/B/NZ8/00112

ABSTRACT Across the planet, angiosperm diversification has been shaped by palaeoclimates and biotic interactions, particularly with pollinators, leaving signatures in the angiosperm age structure. Regional floras represent biased samples of this global diversification shaped by dispersal, extinction and environmental filtering, yet it remains unclear whether floristic age structure reflects pollination strategies or their interaction with palaeoclimates. We constructed a 93% resolved phylogeny of all native 1178 angiosperms in the Netherlands and characterized age structure of eight pollination syndromes by standardized epoch‐specific lineage diversities (stELDs) quantifying the proportional increase in lineages per 10‐Myr interval. Overall, stELDs peaked under the coldest intervals and were lowest for intermediate‐temperature intervals (geological age alone had no effect). This age structure was strongest in wind‐pollinated species. Resolving insect pollination into six syndromes revealed strong heterogeneity: lepidoptera‐pollination was most strongly associated with warmest palaeotemperatures, bumblebee and wasp‐pollination under intermediate temperatures, and fly, lepidoptera and beetle‐pollination under coldest temperatures. Paleotemperature signatures correlated positively with contemporary seasonal flowering temperatures, indicating conserved thermal niches across ecological and macroevolutionary timescales. We suggest that temperate floras reflect both recent cold‐house diversification of wind‐ and certain insect‐pollinated lineages and earlier warm‐house radiations of lineages pollinated by older insect clades. Phylogenetic age structures permit detecting such patterns.

Phylogenetic divergence between species may weaken both negative and positive biotic interactions. Whether, as a result, divergent species aggregate or segregate remains unclear. These interactions differ among lineages, and without immigration, the effects of interactions might be overridden by dispersal limitation. We studied changes in co-occurrence across 5 years for 1770 pairs of grassland species drawn primarily from four major lineages (families), reducing dispersal limitation by seed addition. Across all lineages, changes in co-occurrence were almost unrelated to phylogenetic divergence, partly reflecting opposing relationships within two groups of families: Fabaceae/Poaceae, where more divergent species segregated, versus Asteraceae/Apiaceae, where they aggregated. Dispersal limitation through lack of immigration existed, without eliminating divergence effects. We conclude that species assembly differed between major lineages, with spatial aggregation in Asteraceae/Apiaceae possibly reflecting limiting similarity, whereas segregation in Fabaceae/Poaceae may reflect mutualist incompatibility or asymmetric competition. These processes could feedback on within-lineage diversification.

For half a century, biologists considered trees as particularly apparent to their enemies. But why then do some trees escape herbivorous enemies by bursting buds either too early or too late, leading to phenological mismatch? We hypothesize that such mismatches occur on trees that are unapparent in time – those that burst buds ‘discreetly' (slowly) and unpredictably (inconsistently across years), and are difficult to access (host trees among non‐hosts). We studied herbivores on oaks in western France. We for the first‐time characterized phenology matching of an entire guild of herbivores, early spring ectophagous caterpillars (45 species). We examined whether, on a given date, caterpillars have a large body size and impact (herbivory), and whether this size or impact are largest on trees that burst buds earliest. Furthermore, we distinguished the contributions of within‐guild sorting of species and within‐population selection of individuals to phenology matching, we investigated whether present phenology matching was determined during past generations by testing if caterpillars from trees with early‐maturing foliage pupate early, even when transferred into a common garden. We found that caterpillar size and herbivory impact in the field and pupation date in the lab generally matched leaf phenology in the field. Such phenology matching was consistently observed at the intraspecific level but was less evident at the interspecific level. Together this indicates that phenology matching is mainly driven by past within‐population selection rather than present, within‐guild sorting. Furthermore, herbivores size and impact were most constrained by late bursting of host trees if these trees burst buds slowly and unpredictably and are difficult to access. We suggest that, during the assembly of early‐spring herbivore guilds, trees can best constrain development of herbivore populations by late budburst and remaining unapparent in time – bursting buds discreetly, unpredictably across years, or in inaccessible neighbourhoods.

Aim: Species richness of local communities is often considered to be disconnected from the macroevolutionary diversification of lineages operating at much larger spatiotemporal scales. However, local communities occupy patches of habitat types, many of which persist across large spatiotemporal scales. We hypothesise that high local species richness of specific habitat types could result from ongoing local assembly in which both very closely related and very distantly related species can locally co-occur. Alternatively, such local richness of specific habitat types could result from historical assembly in which historical colonisation by many lineages and diversification within habitat-type increased richness of the habitat species-pool and thereby the local communities sampled from it. Location: The Netherlands. Time Period: 1932-2012. Major Taxa Studied: Angiosperms. Methods: We analysed 6851 small-scale local plots (median 54 m2) belonging to all major habitat types in the Netherlands. We quantified mean pairwise phylogenetic distances across all species and between phylogenetically nearest species, standardised for 0-expectations for a given species richness. We quantified these measures for local communities, averaged within habitat types and for the species-pools of the habitat types. Results: Local richness varied 21-fold among habitat types. Local richness increased with mean pairwise distances and decreased with mean nearest-taxon distances of local communities (but not of habitat species-pools). These patterns were independent of the size of the regional habitat species-pool, the presence of exotic species and the environmental conditions. Main Conclusions: Local species richness varies massively among habitat types within a region. We suggest that some habitat types are locally species rich because today they permit the most distantly related and the most closely related species to coexist, likely through stabilising and equalising mechanisms, respectively. These mechanisms should be tested in the future.

High herbivore abundances on trees surrounded by distantly related neighbors (phylogenetic isolation) might in part be due to local adaptation of herbivores to host trees, but this has not been tested. We studied if free-feeding and semi-concealed (shelter-building) Lepidoptera can be adapted to leaf traits of individual trees, and if this is affected by phylogenetic isolation. We performed a reciprocal transplant experiment on free-feeding and semi-concealed lepidopteran caterpillars collected from oak trees (Quercus petraea) in a mixed forest in Poland. Within a set of trees with early and a set with late budburst, we selected oak trees that varied from being surrounded by other oak trees (low phylogenetic isolation) to oaks surrounded by pine trees (high phylogenetic isolation), and collected canopy branches to obtain caterpillars. We then fed half of the caterpillars leaves from the tree they were collected from (home tree) and others on the leaves of another tree in the set (away trees) in the laboratory. We measured caterpillar mass over a five-day interval to calculate growth rate and determined aspects of leaf chemistry of each tree. Five species of Lepidoptera (Acrobasis repandana, Eudemis profundana, Operopthera brumata, Phycita roborella, Zeiraphera isertana) yielded sufficient sample sizes for statistical analyses. Overall, we found faster growth on home trees, which could be attributed to one species, E. profundana. There was no effect of phylogenetic isolation. Our results indicate that local adaptation to leaf traits of individual trees is rare in these lepidopterans, and we found no evidence that local adaptation would be more pronounced on trees that are more phylogenetically isolated from their neighbors. Therefore, the effects phylogenetic isolation on herbivory are not likely to be mediated by local adaptation to individual trees.

Background and Aims There is ongoing debate about whether offspring perform best next to phylogenetically distantly related adult neighbours (due to the scarcity of enemies and competitors) or next to closely related adults (due to the abundance of mutualists). Here we hypothesize that relatedness of adult neighbours affects which traits confer performance rather than performance itself. Methods We studied seed removal, seed germination and sapling growth in sessile oaks (Quercus petraea and hybrids) and how they depend on size, shape and other traits, under both closely and distantly related canopies, manipulating offspring density, presence of insects and fungi, and spatial proximity to oaks. Key Results We found that phylogenetic distance of adult neighbours affects only little the performance of offspring but strongly affects which traits confer performance on offspring, in particular the size and shape of seeds and saplings. Differences in trait-performance relationships mostly disappear once insects or conspecific competitors are excluded (albeit exclusion of fungi reinforced these differences). Effects of phylogenetic distance of neighbours were not replaceable by the percentage of gymnosperms among neighbours or by the environmental conditions considered. Conclusions We suggest that, by responding to a biotic micro-mosaic of selection pressures, sessile oak flexibly succeeds in diverse neighbourhoods. Sessile oak might maintain the potential for both convergence with and divergence from phylogenetically distantly related species, thereby reinforcing or eroding phylogenetic signal of niches.

Timing of seed germination is critical for survival of annual plants in seasonal climates. We tested the hypothesis that seeds of the winter annual species Cardamine impatiens (Brassicaceae) “track” their thermal environment and synchronize germination with favorable growth conditions. We predicted that seeds buried in the field from maturity to autumn germinate best at autumn temperatures, while those buried from maturity to spring germinate best in early spring. We monitored seasonal changes in germinability by exhuming field-buried seeds monthly for 30 months and incubating them under laboratory conditions. The effects of temperature on the transition of dormancy status also were investigated. Seeds of C. impatiens were dormant at dispersal in May, and during summer dormancy transitioned to conditional dormancy and then to non-dormancy. By early autumn, seeds germinated in a wide range of temperature regimes in light. Nongerminated seeds re-entered conditional dormancy during winter, losing the ability to germinate at high, but not low, temperatures in light. The light requirement for germination was reduced during prolonged seed burial. Overall, our hypothesis is supported. Buried seeds of C. impatiens exhibited a seasonally synchronized conditional dormancy/non-dormancy cycle, enabling germination in both autumn and early spring; this information will facilitate management efforts of this weedy species. We conclude that dormancy cycling in C. impatiens is an adaptive functional trait that controls the timing of germination, thereby optimizing seedling emergence under favorable conditions while avoiding summer heat.

Closely related species often conserve similar niches despite interacting negatively. We suggest that close relatives may interact positively via ecosystem feedbacks: leaf litter produced or exposed in a closely related neighbourhood (low phylogenetic isolation) may decompose more quickly, leading to more rapid nutrient recycling. We studied decomposition of leaf litter of oaks Quercus petraea across 8 and 14 months, reciprocally transplanting leaf litters between low and high phylogenetic isolation to distinguish between effects mediated by leaf litter quality and by decomposition environment. We found that, by affecting litter quality, phylogenetic isolation reduced decomposition across 14 months (loss of litter mass and C). Moreover, by affecting litter quality and decomposition environment, phylogenetic isolation reduced microbial biomass and extensively altered relationships between C and N losses and abundances/diversities of different soil organisms across 8 and 14 months. Phylogenetic isolation was to a large extant driven by percentage of gymnosperms, explaining the decomposition‐environment mediated effects. Such environment‐mediated effects reflected decreasing soil humidity and pH with phylogenetic isolation, while litter‐quality mediated effects reflected decreasing leaf phytophagy or increasing leaf phenolics. Tree‐species richness, in contrast, did not explain effects of phylogenetic isolation, and had little effect overall. To conclude, coexistence of oaks with distant relatives partly impedes recycling of leaf litter and re‐organizes the trajectories of this recycling. In contrast, oaks coexisting with close relatives may profit from a positive ecosystem feedback through increased nutrient recycling, possibly contributing to the conservation of the oak's niches. We suggest that such a positive ecosystem feedback among close relatives might exist in other late successional tree species.

We know little about how parasitoids of herbivorous insects use herbivore-induced volatile organic compounds (VOCs) to locate potential hosts on saplings in forests, and how this depends on tree composition. Therefore, we performed an experiment in a forest in Poland where we placed pairs of oak saplings (Quercus robur or Q. petraea) in neighborhoods dominated by oak, beech, or pine trees. We treated one sapling in each pair with the phytohormone methyl jasmonate, which triggers induced responses in plants. We measured the VOC emissions of thirty-six saplings and placed Malaise traps with five of the pairs. We counted the parasitoids in the ten Malaise samples and identified them using DNA metabarcoding. We used parasitoids reared from oak-feeding caterpillars to estimate which species are associated with oaks. The two species of oak differed in both the proportions of VOCs and the specific VOCs that were elevated following the application of methyl jasmonate. We did not detect any overall effects of treatment on parasitoid abundance or community composition. However, some parasitoid species that were associated with oaks appeared to be attracted to elevated emissions of specific induced VOCs. The parasitoid communities differed significantly between sites and showed marginally significant differences between neighborhoods. Overall, our results suggest that parasitoids in the understory are affected by tree composition of the canopy, but the effects of VOC emissions are limited.

While there is long-standing interest in the role of inter- and transgenerational plasticity via the maternal line, it rarely has been studied via the paternal line. Thus, consequences of the paternal environment for parental fitness and for performance of offspring in the environments experienced by either fathers or mothers are not known. We studied the intergenerational plasticity (IGP) of the plant species Paeonia ostii (Paeoniaceae) and tested the hypothesis that exposure of fathers to environmental stress (i) reduces parental fitness and performance of offspring grown under non-stressful conditions, but (ii) mitigates the negative effects of environmental stress on fitness of parents and performance of offspring. Crosses were made in a greenhouse within six families of P. ostii between parents grown under drought and in a mesic environment, and the offspring of each cross were grown under both dry and mesic conditions. Production and germination of seeds and morphological and physiological traits of offspring were measured as indicators of parental fitness and offspring performance, respectively. Paternal drought decreased seed number per fruit, except when maternal plants also were grown in drought conditions. Offspring drought decreased seedling performance. However, when fathers experienced drought this negative effect on the offspring was partly mitigated, in particular when mothers also had experienced drought. In contrast, offspring grown in mesic conditions had improved seedling performance, especially when either parent (or both) also were grown in mesic conditions. Such statistical differences remained when seed mass was included as a covariate. Overall, paternal pollen of P. ostii mediated IGP to drought almost as well as it did for maternal ovules. IGP was adaptive if environments remained constantly dry across generations but maladaptive if environments changed. Hence, under future climate changes, paternal IGP might be both a blessing and a curse, with the blessing occurring when the focal habitat becomes drier and pollen comes from already-dry places, while the curse may dominate in predictably moist habitats surrounded by drier habitats.

To what extent particular plant defences against herbivorous insects are constitutive or inducible will depend on the costs and benefits in their neighbourhood. Some defensive chemicals in leaves are thought to be costly and hard to produce rapidly, while others, including volatile organic compounds that attract natural enemies, might be cheaper and can be released rapidly. When surrounding tree species are more closely related, trees can face an increased abundance of both specialist herbivores and their parasitoids, potentially increasing the benefits of constitutive and inducible defences. To test if oaks ( Quercus robur ) respond more to herbivore attacks with volatile emission than with changes in leaf phenolic chemistry and carbon to nitrogen ratio (C: N), and whether oaks respond to the neighbouring tree species, we performed an experiment in a forest in Poland. Oak saplings were placed in neighbourhoods dominated by oak, beech, or pine trees, and half of them were treated with the phytohormone methyl jasmonate (elicitor of anti-herbivore responses). Oaks responded to the treatment by emitting a different volatile blend within 24 h, while leaf phenolic chemistry and C: N remained largely unaffected after 16 days and multiple treatments. Leaf phenolics were subtly affected by the neighbouring trees with elevated flavan-3-ols concentrations in pine-dominated plots. Our results suggest that these oaks rely on phenols as a constitutive defence and when attacked emit volatiles to attract natural enemies. Further studies might determine if the small effect of the neighbourhood on leaf phenolics is a response to different levels of shading, or if oaks use volatile cues to assess the composition of their neighbourhood.

Aim: Climate is a major driver of large-scale variability in biodiversity, as a likely result of more intense biotic interactions under warmer conditions. This idea fuelled decades of research on plant-herbivore interactions, but much less is known about higher-level trophic interactions. We addressed this research gap by characterizing both bird diversity and avian predation along a climatic gradient at the European scale. Location: Europe. Taxon: Insectivorous birds and pedunculate oaks. Methods: We deployed plasticine caterpillars in 138 oak trees in 47 sites along a 19 degrees latitudinal gradient in Europe to quantify bird insectivory through predation attempts. In addition, we used passive acoustic monitoring to (i) characterize the acoustic diversity of surrounding soundscapes; (ii) approximate bird abundance and activity through passive acoustic recordings; and (iii) infer both taxonomic and functional diversity of insectivorous birds from recordings. Results: The functional diversity of insectivorous birds increased with warmer climates. Bird predation increased with forest cover and bird acoustic activity but decreased with mean annual temperature and functional richness of insectivorous birds. Contrary to our predictions, climatic clines in bird predation attempts were not directly mediated by changes in insectivorous bird diversity or acoustic activity, but climate and habitat still had independent effects on predation attempts. Main Conclusions: Our study supports the hypothesis of an increase in the diversity of insectivorous birds towards warmer climates but refutes the idea that an increase in diversity would lead to more predation and advocates for better accounting for activity and abundance of insectivorous birds when studying the large-scale variation in insect-tree interactions.

Background and Aims One response of plants to climate warming is plasticity of traits, but plasticity might come at a cost and might be limited by the integration among traits or by simultaneous shift of another environmental condition such as shading. Empirical studies treating simultaneously such costs and limitations of plasticity across populations or maternal lineages within species, and how they depend on the environmental context remain few. Methods We studied three plant species from the sub-Antarctic, a region currently facing one of the fastest warming worldwide. For multiple populations or maternal lineages we identified (i) plasticity by exposing seeds from a given source population to different temperature and light treatments, (ii) performance (photosynthesis or morphological performance) and (iii) morphological integration of traits in young plants. Key Results We found that plants from more plastic source populations performed poorly. Plants from more integrated source populations were more plastic. Exposure to shade rendered plants less plastic to a warming trend. Moreover, simultaneous shading and warming, rather than sole shading or sole warming, reduced plant performance. Conclusions Our results suggest that phenotypic integration of intraspecific lineages surprisingly might favour rather than limit plasticity. However, our results also suggest that plasticity in response to climate warming may be limited by parallel increase in shading from other plants including competitors, and itself does not ensure success due to induced performance costs.

Phylogenetically closely related plant species often share similar trait states (phylogenetic signal), but local assembly may favor dissimilar relatives and thereby decouple the diversity of a trait from the diversity of phylogenetic lineages. Associated fauna might either benefit from plant trait diversity, because it provides them complementary resources, or suffer from it due to dilution of preferred resources. We hence hypothesize that decoupling of trait and phylogenetic diversity weakens the relationship between the plant-trait diversity and the abundance and diversity of associated fauna. Studying permanent meadows, we tested for combined effects of plant phylogenetic diversity and diversity of two functional traits (specific leaf area, leaf dry matter content) on major groups of soil fauna (earthworms, mites, springtails, nematodes). We found that only in phylogenetically uniform plant communities, was uniformity in the functional traits associated with (i) high abundance in springtails, and (ii) high abundance of the sub-group that feeds more directly on plant material (in springtails and mites) or those that are more prone to disturbance (in nematodes), and (iii) high diversity in all three groups tested (springtails, earthworms, nematodes). Our results suggest that soil fauna profits from the resource concentration in local plant communities that are uniform in both functional traits and phylogenetic lineages. Soil fauna would hence benefit from co-occurrence of closely related plants that have conserved the same trait values, rather than of distantly related plants that have converged in traits. This might result in faster decomposition and a positive feedback between trait conservatism and ecosystem functioning.

Plant lineages differ markedly in species richness globally, regionally, and locally. Differences in whole-genome characteristics (WGCs) such as monoploid chromosome number, genome size, and ploidy level may explain differences in global species richness through speciation or global extinction. However, it is unknown whether WGCs drive species richness within lineages also in a recent, postglacial regional flora or in local plant communities through local extinction or colonization and regional species turnover. We tested for relationships between WGCs and richness of angiosperm families across the Netherlands/Germany/Czechia as a region, and within 193,449 local vegetation plots. Families that are species-rich across the region have lower ploidy levels and small monoploid chromosomes numbers or both (interaction terms), but the relationships disappear after accounting for continental and local richness of families. Families that are species-rich within occupied localities have small numbers of polyploidy and monoploid chromosome numbers or both, independent of their own regional richness and the local richness of all other locally co-occurring species in the plots. Relationships between WGCs and family species-richness persisted after accounting for niche characteristics and life histories. Families that have few chromosomes, either monoploid or holoploid, succeed in maintaining many species in local communities and across a continent and, as indirect consequence of both, across a region. We suggest evolutionary mechanisms to explain how small chromosome numbers and ploidy levels might decrease rates of local extinction and increase rates of colonization. The genome of a macroevolutionary lineage may ultimately control whether its species can ecologically coexist.