Forest Arthropods Research Articles

Arthropods in modern resins reveal if amber accurately recorded forest arthropod communities

Amber is an organic multicompound derivative from the polymerization of resin of diverse higher plants. Compared with other modes of fossil preservation, amber records the anatomy of and ecological interactions between ancient soft-bodied organisms with exceptional fidelity. However, it is currently suggested that ambers do not accurately record the composition of arthropod forest paleocommunities, due to crucial taphonomic biases. We evaluated the effects of taphonomic processes on arthropod entrapment by resin from the plant Hymenaea, one of the most important resin-producing trees and a producer of tropical Cenozoic ambers and Anthropocene (or subfossil) resins. We statistically compared natural entrapment by Hymenaea verrucosa tree resin with the ensemble of arthropods trapped by standardized entomological traps around the same tree species. Our results demonstrate that assemblages in resin are more similar to those from sticky traps than from malaise traps, providing an accurate representation of the arthropod fauna living in or near the resiniferous tree, but not of entire arthropod forest communities. Particularly, arthropod groups such as Lepidoptera, Collembola, and some Diptera are underrepresented in resins. However, resin assemblages differed slightly from sticky traps, perhaps because chemical compounds in the resins attract or repel specific insect groups. Ground-dwelling or flying arthropods that use the tree-trunk habitat for feeding or reproduction are also well represented in the resin assemblages, implying that fossil inclusions in amber can reveal fundamental information about biology of the past. These biases have implications for the paleoecological interpretation of the fossil record, principally of Cenozoic amber with angiosperm origin.

STADS

A fundamental challenge of software testing is the statistically well-grounded extrapolation from program behaviors observed during testing. For instance, a security researcher who has run the fuzzer for a week has currently no means (1) to estimate the total number of feasible program branches, given that only a fraction has been covered so far; (2) to estimate the additional time required to cover 10% more branches (or to estimate the coverage achieved in one more day, respectively); or (3) to assess the residual risk that a vulnerability exists when no vulnerability has been discovered. Failing to discover a vulnerability does not mean that none exists—even if the fuzzer was run for a week (or a year). Hence, testing provides no formal correctness guarantees . In this article, I establish an unexpected connection with the otherwise unrelated scientific field of ecology and introduce a statistical framework that models Software Testing and Analysis as Discovery of Species (STADS). For instance, in order to study the species diversity of arthropods in a tropical rain forest, ecologists would first sample a large number of individuals from that forest, determine their species, and extrapolate from the properties observed in the sample to properties of the whole forest. The estimations (1) of the total number of species, (2) of the additional sampling effort required to discover 10% more species, or (3) of the probability to discover a new species are classical problems in ecology. The STADS framework draws from over three decades of research in ecological biostatistics to address the fundamental extrapolation challenge for automated test generation. Our preliminary empirical study demonstrates a good estimator performance even for a fuzzer with adaptive sampling bias—AFL, a state-of-the-art vulnerability detection tool. The STADS framework provides statistical correctness guarantees with quantifiable accuracy.

Temporal changes in arthropod activity in tropical anthropogenic forests.

Arthropod communities in the tropics are increasingly impacted by rapid changes in land use. Because species showing distinct seasonal patterns of activity are thought to be at higher risk of climate-related extirpation, global warming is generally considered a lower threat to arthropod biodiversity in the tropics than in temperate regions. To examine changes associated with land use and weather variables in tropical arthropod communities, we deployed Malaise traps at three major anthropogenic forests (secondary reserve forest, oil palm forest, and urban ornamental forest (UOF)) in Peninsular Malaysia and collected arthropods continuously for 12 months. We used metabarcoding protocols to characterize the diversity within weekly samples. We found that changes in the composition of arthropod communities were significantly associated with maximum temperature in all the three forests, but shifts were reversed in the UOF compared with the other forests. This suggests arthropods in forests in Peninsular Malaysia face a double threat: community shifts and biodiversity loss due to exploitation and disturbance of forests which consequently put species at further risk related to global warming. We highlight the positive feedback mechanism of land use and temperature, which pose threats to the arthropod communities and further implicates ecosystem functioning and human well-being. Consequently, conservation and mitigation plans are urgently needed.

Ormyridae (Hymenoptera, Chalcidoidea) de Panamá asociados con agallas de cinípidos (Hymenoptera, Cynipidae) sobre especies de Quercus (Fagaceae)

Se estudiaron las especies de la familia Ormyridae emergidas de 15 de los 65 morfotipos de agallas inducidas por especies de la familia Cynipidae en árboles del género Quercus conocidas para Panamá. Las recolectas se realizaron entre enero de 2008 a diciembre de 2010 en los bosques nubosos de la Cordillera Central de Panamá. Se identificaron tres especies del género Ormyrus (Chalcidoidea: Ormyridae), O. hegeli, O. unifasciatipennis y O. venustus, parasitoides de las especies inductoras e inquilinas de las agallas hospedadoras. La especie más abundante fue O. venustus y, por primera vez, se reporta para el Neotrópico O. hegeli, que sólo había sido citada para Norteamérica. Los resultados amplían los registros de distribución de esta familia de avispas parasitoides y confirman la presunción de que la carencia de datos de algunos grupos de artrópodos en los bosques tropicales se debe más a la falta de muestreo y no a la ausencia de ellos en estas áreas.

Arthropod assemblages deep in natural forests show different responses to surrounding land use

Many contemporary landscapes have vast areas of production land-uses within landscape mosaics, which may impact species dispersal and occurrence. Here, we determined the extent to which commercial exotic plantation forests affect arthropod diversity associated with natural Afrotemperate forests in the southern Cape Afrotemperate landscape mosaic, South Africa. Natural forests and fynbos vegetation naturally coexist here, with the addition of exotic plantation forests to form a heterogeneous landscape. Epigaeic arthropods were collected by means of pitfall trapping at stations along transects from inside natural Afrotemperate forest, across the edge and into the surrounding land use, which included natural fynbos vegetation, mature forestry plantation blocks (Pinus radiata) and areas where plantations have been clear-felled. Stations were set at 5, 10, 20, 30 and 50 m to both sides of the forest edge with the addition of 100 m stations situated in the natural forest. Arthropod assemblages were distinct in all land-use types. Natural edge effect between forest and fynbos, as measured by arthropod compositional changes, was 20 m into natural forests, yet when bordered by plantations this edge increased up to 30 m into the forest. Once plantations were clear-felled, edge effects increased up to 50 m into natural forests. Responses in terms of assemblage composition and species richness were however taxon specific. Results show that (1) pine plantations are not alternative habitat for native Afrotemperate forest arthropods, (2) there were stark changes in arthropod assemblage composition at edges between these land-use types and (3) that the effects of timber plantation practices (re: clear-felling) also penetrate deep into surrounding natural forests and need to be considered in regional landscape planning. The need for an effective rehabilitation strategy of clear-felled areas is identified as key priority for bordering natural forests. Ongoing monitoring in both the disturbed area and the adjoining natural forest should be undertaken to ensure sufficient recovery.

Tree diversity drives diversity of arthropod herbivores, but successional stage mediates detritivores.

The high tree diversity of subtropical forests is linked to the biodiversity of other trophic levels. Disentangling the effects of tree species richness and composition, forest age, and stand structure on higher trophic levels in a forest landscape is important for understanding the factors that promote biodiversity and ecosystem functioning. Using a plot network spanning gradients of tree diversity and secondary succession in subtropical forest, we tested the effects of tree community characteristics (species richness and composition) and forest succession (stand age) on arthropod community characteristics (morphotype diversity, abundance and composition) of four arthropod functional groups. We posit that these gradients differentially affect the arthropod functional groups, which mediates the diversity, composition, and abundance of arthropods in subtropical forests. We found that herbivore richness was positively related to tree species richness. Furthermore, the composition of herbivore communities was associated with tree species composition. In contrast, detritivore richness and composition was associated with stand age instead of tree diversity. Predator and pollinator richness and abundance were not strongly related to either gradient, although positive trends with tree species richness were found for predators. The weaker effect of tree diversity on predators suggests a cascading diversity effect from trees to herbivores to predators. Our results suggest that arthropod diversity in a subtropical forest reflects the net outcome of complex interactions among variables associated with tree diversity and stand age. Despite this complexity, there are clear linkages between the overall richness and composition of tree and arthropod communities, in particular herbivores, demonstrating that these trophic levels directly impact each other.

Relationships among site characteristics, taxonomical structure and functional trait distribution of arthropods in forest, urban and agricultural soils of Southern Italy

AbstractUrbanization and agriculture cause alterations in soil biodiversity. As arthropods quickly respond to soil changes, they have been recognized as good indicators of soil quality. This study aimed to evaluate if (1) soil physico‐chemical properties act as environmental filters of the functional trait distribution of soil arthropod community; (2) the abundance of certain functional traits is linked to different land uses; (3) the taxonomical and functional approaches provide complementary information about the evaluation of biological soil quality. The study was performed at forest, agricultural and urban sites in downtown and surroundings of Naples. The soils were characterized for texture, pH, organic matter content, water content, total Cd, Cr, Cu, Ni, Pb and Zn concentrations. The forest soils showed the highest organic matter and water contents, and the lowest metal concentrations; the agricultural soils showed the lowest organic matter and water contents and high Cd and Cu concentrations, whereas the urban soils showed high Pb and Zn concentrations. The forest soils showed the highest arthropod density, taxa richness and diversity. The distribution of the functional traits in the arthropod communities of the different land uses highlighted similarity only for the preference to occupy soil and for the percentage contribution of detritivores. The abundance of arthropods living above litter and omnivores were positively correlated to Pb and Zn concentrations, whereas predators were positively correlated to Cu concentrations. The findings suggest that the arthropod identification at order level could be enough to detect differences in functional traits among forest, urban, and agricultural soils.

Impact of windthrow and salvage-logging on taxonomic and functional diversity of forest arthropods

Windthrow is recognized as the most important driver in European forest dynamics and its importance is likely to increase with climate change. Typically, windthrown timber is salvaged for economic and phytosanitary reasons. This markedly affects the natural development of the disturbed areas, in particular by removing important dead wood resources. For a sustainable and ecologically sound management of disturbance effects, more knowledge is needed on the impact of windthrow and salvage logging on animal species communities.We monitored various arthropod taxa (spiders and insects) two and five years after the storm Lothar in 1999 in salvaged and unsalvaged windthrows as well as in adjacent intact forests. Basing on a comprehensive data set with 1276 species and 228,718 individuals, species diversity, abundance and community composition were compared. Species richness and abundance of most taxonomic and functional groups (pollinators, saproxylics and predators) in the windthrow habitats clearly differed from those in the intact forests. On average, twice as many species were present in windthrows as in the forest. Windthrows also supported more red-listed beetles (mainly saproxylics) than the intact forest and more habitat indicator species (mainly Heteroptera and Aculeata) were found in windthrow areas.No difference in species diversity was found between salvaged and unsalvaged windthrows. However, similarity analyses showed that the communities of certain taxonomic and functional groups differed between the two salvaging treatments. A combination of unsalvaged and salvaged windthrows in intact forests increased local species richness approximately 2.5times relative to that in the forests alone. Therefore after large-scale windthrows, a mosaic of salvaged and unsalvaged windthrow patches fosters high forest biodiversity levels.

Effects of Clear-cutting on Forest Arthropod Communities at Two Different Vertical Levels (Crown and Ground Surface

Effects of Clear-cutting on Forest Arthropod Communities at Two Different Vertical Levels (Crown and Ground Surface

A combined field survey and molecular identification protocol for comparing forest arthropod biodiversity across spatial scales.

Obtaining fundamental biodiversity metrics such as alpha, beta and gamma diversity for arthropods is often complicated by a lack of prior taxonomic information and/or taxonomic expertise, which can result in unreliable morphologically based estimates. We provide a set of standardized ecological and molecular sampling protocols that can be employed by researchers whose taxonomic skills may be limited, and where there may be a lack of robust a priori information regarding the regional pool of species. These protocols combine mass sampling of arthropods, classification of samples into parataxonomic units (PUs) and selective sampling of individuals for mtDNA sequencing to infer biological species. We sampled ten lowland rainforest plots located on the volcanic oceanic island of Réunion (Mascarene archipelago) for spiders, a group with limited taxonomic and distributional data for this region. We classified adults and juveniles into PUs and then demonstrated the reconciliation of these units with presumed biological species using mtDNA sequence data, ecological data and distributional data. Because our species assignment protocol is not reliant upon prior taxonomic information, or taxonomic expertise, it minimizes the problem of the Linnean shortfall to yield diversity estimates that can be directly compared across independent studies. Field sampling can be extended to other arthropod groups and habitats by adapting our field sampling protocol accordingly.

Group selection harvesting supports the diversity of epigaeic arthropod assemblages (Coleoptera: Carabidae; Araneidae: Araneae; Isopoda: Oniscidae)

Background and purpose Timber-oriented forest management alters the environmental conditions, threatening the survival of many native and rare arthropod species. Recognition of the scale and effects of the forest loss has resulted in a considerable degree of interest in the reforestation. Nowadays, the uneven-aged management is recommended during the reforestation procedure, because this is less intensive and could be less harmful than even-aged practices. Our aim was to test the effects of clear-cutting (as even-aged method) and group selection harvesting (as uneven-aged method) on forest specialist epigaeic arthropods. Material and methods Epigaeic arthropod assemblages (ground beetles, spiders and woodlice) in gaps harvested by group selection and clear-cuts were compared to those assemblages in windthrow gaps and mature forest stands. Ground beetles, spiders and woodlice were collected by litter sifting. Results The total number of epigaeic arthropod species was significantly higher in the gaps harvested by group selection than in the clear-cuts and the mature forests. The species richness of forest specialist species was significantly lower in the clear-cuts than in the other habitats. Conclusion Our findings demonstrated that the conventional clear-cutting caused a decrease in the number of forest specialist species. Therefore, group selection method should be favoured during forest management to maintain forest arthropods’s diversity. Keywords: clear-felling, diversity, forest practices, litter sifter, reforestation

Open-grown trees as key habitats for arthropods in temperate woodlands: The diversity, composition, and conservation value of associated communities

Temperate open woodlands are recognized as biodiversity hotspots. They are characterised by the presence of scattered, open-grown, often old and large trees (hereafter referred to as “solitary trees”). Such trees are considered keystone ecological features for biodiversity. However, the ecological role of solitary trees and their importance for woodland communities are still not fully understood. Communities of arthropods in temperate forests are often structured not only by the horizontal openness of the stand, but also by vertical stratification. Thus there is a need for comparisons among communities associated with solitary trees and different forest strata. In this study, we analysed the diversity, conservation value, and nestedness of four taxonomic groups (beetles (Coleoptera), bees and wasps (aculeate Hymenoptera), ants (Formicidae), and spiders (Araneae)) on (i) solitary trees in open woodlands, and four habitat types in adjacent closed-canopy forests: (ii) edge-canopy, (iii) edge-understorey, (iv) interior-canopy, and (v) interior-understorey.Across the focal insect groups, solitary trees harboured the greatest number of species, whilst spider communities were also equally rich in forest edge canopies. The conservation value of communities was highest in solitary trees for beetles, and in solitary trees and edge-canopy habitats for bees and wasps. For spiders, the conservation value was similar across all habitat types, but ordination analysis revealed general preferences for solitary trees among threatened species. We also found that communities from the forest interior were mostly only nested subsets of the communities found on solitary trees. Our results show an important and irreplaceable role that open-grown trees have in maintaining temperate woodland biodiversity. Therefore, preservation and maintenance of open-grown trees should be a primary concern in biological conservation.

Can mixed stands of native and non-native tree species enhance diversity of epigaeic arthropods in plantation forests?

In regions with low cover of natural forests and high cover of plantations predominately comprised of non-native species, inclusion of a native tree species with a more productive non-native species has the potential to enhance biodiversity and meet production goals. In this context, we tested the alternative hypotheses that: (i) equitable mixes of a non-native and a native tree species support greater diversity of ground-dwelling arthropods than single species stands; or, (ii) native ash stands support greater diversity of ground-dwelling arthropods than mixed or single species stands that include a non-native conifer species. Active epigaeic spiders (Araneae) and beetles (Coleoptera: Carabidae, Staphylinidae) were sampled using pitfall traps in three forest types in Ireland: single species stands of non-native Norway spruce (Picea abies) or native ash (Fraxinus excelsior), and mixed stands of these species.Stands of Norway spruce did not negatively influence spider and staphylinid diversity, suggesting that they maintain a similar range of biodiversity to mixed plantations or stands of native ash. However, carabid beetle richness (but not abundance) was negatively affected by the presence of spruce suggesting caution when drawing conclusions about biodiversity impacts from single taxon studies. We found that equitable mixes of spruce and ash supported many species associated with native ash stands. Thus, we recommend that mixes with an equitable species ratio (e.g. 50:50) and containing a native species will enhance epigaeic arthropod diversity and heterogeneity in plantations. Furthermore, our finding that ash stands supported greater beta diversity than spruce stands supports current guidelines that recommend a range of stand types, including native species, to enhance diversity within and between stands.

Carbon and nitrogen isotopes reveal feeding habits of arthropods in tropical rain forests

Carbon and nitrogen isotopes reveal feeding habits of arthropods in tropical rain forests

Microbial pesticide application during defoliator outbreaks may reduce loss of regional forest beetle richness

To date, research on the effects of forest defoliator outbreaks and pesticide applications to suppress these outbreaks on non‐target forest arthropods has generally focused on non‐target Lepidoptera and has not examined effects on regional diversity. In this study, we assessed the effects of forest defoliation by gypsy moths and application of the microbial pesticide Bacillus thuringiensis var. kurstaki (Btk) to suppress gypsy moth populations on the species richness and (Shannon index) diversity of beetles in Shenandoah National Park, Virginia. In addition, we examined how these disturbances affected overall beetle abundance and abundances within different feeding guilds (herbivore, predator, fungivore, or xylophage). Three years after a gypsy moth outbreak, beetles were sampled four times throughout spring and summer at 15 sites belonging to one of three disturbance histories: undisturbed, defoliated, or sprayed with Btk. Beetles were captured using blacklight traps and then sorted to family and morphospecies. We did not detect significant effects of defoliation or Btk on local species richness (α richness) or local diversity (α diversity) of beetles. However, defoliated sites had lower β richness, i.e., lower heterogeneity in beetle species composition among sites, in early summer than sites that were undisturbed or sprayed with Btk. Overall beetle abundance was lower in spring at sites sprayed with Btk, but not significantly different among disturbance histories in other seasons. Further, effects of disturbance history on abundance were not significantly different among feeding guilds. Though the local (α) richness and diversity of beetles were not significantly influenced by gypsy moth defoliation or Btk, the reduced spatial heterogeneity of species composition (lower β richness) in defoliated areas suggests gypsy moth outbreaks could adversely affect regional species richness (γ richness). Our findings additionally suggest that Btk may protect against negative effects of gypsy moth defoliation on the regional species richness of beetles.

Entrapment bias of arthropods in Miocene amber revealed by trapping experiments in a tropical forest in Chiapas, Mexico.

All entomological traps have a capturing bias, and amber, viewed as a trap, is no exception. Thus the fauna trapped in amber does not represent the total existing fauna of the former amber forest, rather the fauna living in and around the resin producing tree. In this paper we compare arthropods from a forest very similar to the reconstruction of the Miocene Mexican amber forest, and determine the bias of different trapping methods, including amber. We also show, using cluster analyses, measurements of the trapped arthropods, and guild distribution, that the amber trap is a complex entomological trap not comparable with a single artificial trap. At the order level, the most similar trap to amber is the sticky trap. However, in the case of Diptera, at the family level, the Malaise trap is also very similar to amber. Amber captured a higher diversity of arthropods than each of the artificial traps, based on our study of Mexican amber from the Middle Miocene, a time of climate optimum, where temperature and humidity were probably higher than in modern Central America. We conclude that the size bias is qualitatively independent of the kind of trap for non–extreme values. We suggest that frequent specimens in amber were not necessarily the most frequent arthropods in the former amber forest. Selected taxa with higher numbers of specimens appear in amber because of their ecology and behavior, usually closely related with a tree–inhabiting life. Finally, changes of diversity from the Middle Miocene to Recent time in Central and South America can be analyzed by comparing the rich amber faunas from Mexico and the Dominican Republic with the fauna trapped using sticky and Malaise traps in Central America.

Stand maturity affects positively ground-dwelling arthropods in a protected beech forest

Forest maturity benefits biodiversity by providing positive effects on key arthropod assemblages such as spider and ground beetles, which play a fundamental role in the ecosystem. Sustainable forest management is a widely held international goal, and more knowledge is needed on invertebrate assemblages, essential to the ecological functioning of forest ecosystems. We aim at evaluating the effects of microsite conditions on spider, centipede, and ground beetle assemblages living in an unmanaged protected beech forest within the Natural Park of Alpi Marittime (SW Alps, Italy). In view of our results, we provide insights on the successional pathways of the focal assemblages in relation to future management of the forest, recommended by the local authorities for conservation purposes. We placed 50 pitfall traps along four transects crossing the forest and emptied them monthly, from July to October 2011. We characterized the four arthropod assemblages in terms of abundance, species richness, diversity, and biomass and related them to leaf cover, rock cover, wood debris cover, litter depth, number of trees, mean tree size, and light conditions at ground level using generalized linear mixed models (GLMM) and canonical correspondence analysis (CCA). Thirty-one species of spiders (1,212 individuals), 12 of centipedes (262 individuals), and 11 of ground beetles (2,177 individuals) were collected. In all groups, mature-forest species highly dominated the samples. Tree size proved to be one of the most important parameters conditioning the assemblages, in particular spiders and ground beetles. A minor effect of light conditions and ground cover (presence of wood debris) was also detected. In view of our results, the recent guidelines for the management of the forest seem in accordance with an effective conservation of the forest arthropod assemblages. Interventions aimed at stabilizing and renovating critical areas within the forest go along with a progressive amelioration of the forest arthropod community. With respect to the maintenance of a large degree of arthropod diversity, stand thinning may not be the most effective management, and reaching a more mature stage might be of interest.

Tree diversity promotes predator but not omnivore ants in a subtropical Chinese forest

1. Epigeic ants are functionally important arthropods in tropical and subtropical forests, particularly by acting as predators. High predation pressure has been hypothesised to be a mechanism facilitating high diversity across trophic levels.2. In this study, standardised pitfall traps were used in a highly diverse subtropical forest to test if and how ant species richness is related to tree species richness and a comprehensive set of other environmental variables such as successional age, soil properties or elevation.3. A total of 13 441 ant individuals belonging to 3839 species occurrences and 71 species were collected, of which 26 species were exclusive predators and 45 species were omnivores.4. Occurrence and species richness of total and omnivore ants were positively related to soil pH. Predator ant occurrence was unrelated to all environmental variables tested.5. The species richness of predator ants increased with tree species richness but decreased with leaf functional diversity and shrub cover. Elevation negatively influenced only total ant species richness.6. The evenness of predators increased with tree species richness, while the evenness of all ants decreased with shrub cover. Omnivore ant evenness decreased with tree evenness, but increased with successional age.7. The results highlight the value of diverse forests in maintaining species richness and community evenness of a functionally important predator group. Moreover, the results stress the importance of analysing trophic groups separately when investigating biodiversity effects.

Impact of invasive earthworms on Ixodes scapularis and other litter-dwelling arthropods in hardwood forests, central New York state, USA

Invasive earthworms alter the structure of soils in northern hardwood forests, but the quantitative impacts on litter-dwelling invertebrates are unclear. Litter loss should reduce the habitat space, but nutrient-rich earthworm burrows might provide food resources. We investigated the impact of invasive earthworms on populations of Ixodes scapularis (black-legged ticks) and other litter-dwelling arthropods to determine the impact of a reduced litter environment. We used five pairs of one-hectare sites (earthworm invaded versus reference) within four separate contiguous forests in New York state. The presence of earthworms decreased the density of nymphal I. scapularis by 46.1% and larval I. scapularis by 29.3%. We also observed a dramatic decline in the total abundance of litter-dwelling arthropods with 69.9% of the arthropod population disappearing in the presence of earthworms. Additionally, litter arthropod populations declined disproportionately to leaf litter mass reduction indicating that the quality of the remaining litter material in the earthworm sites was poor. The impact of earthworm invasion on the litter environment and implications for the position of an important disease vector (I. scapularis) within the litter ecosystem are explored.

Woody plant phylogenetic diversity mediates bottom-up control of arthropod biomass in species-rich forests.

Global change is predicted to cause non-random species loss in plant communities, with consequences for ecosystem functioning. However, beyond the simple effects of plant species richness, little is known about how plant diversity and its loss influence higher trophic levels, which are crucial to the functioning of many species-rich ecosystems. We analyzed to what extent woody plant phylogenetic diversity and species richness contribute to explaining the biomass and abundance of herbivorous and predatory arthropods in a species-rich forest in subtropical China. The biomass and abundance of leaf-chewing herbivores, and the biomass dispersion of herbivores within plots, increased with woody plant phylogenetic diversity. Woody plant species richness had much weaker effects on arthropods, but interacted with plant phylogenetic diversity to negatively affect the ratio of predator to herbivore biomass. Overall, our results point to a strong bottom-up control of functionally important herbivores mediated particularly by plant phylogenetic diversity, but do not support the general expectation that top-down predator effects increase with plant diversity. The observed effects appear to be driven primarily by increasing resource diversity rather than diversity-dependent primary productivity, as the latter did not affect arthropods. The strong effects of plant phylogenetic diversity and the overall weaker effects of plant species richness show that the diversity-dependence of ecosystem processes and interactions across trophic levels can depend fundamentally on non-random species associations. This has important implications for the regulation of ecosystem functions via trophic interaction pathways and for the way species loss may impact these pathways in species-rich forests.