Influence of leaf traits on the spatial distribution of arboreal arthropods within an overstorey rainforest tree

Abstract.

• 1 Several attributes of foliage were measured from the Australian rainforest tree Argyrodendron actinophyllum Edlin (Sterculiaceae). These were related to estimates of abundance per leaf area of the most common arthropod guilds and families sampled with restricted canopy fogging.
• 2 When all these arthropod groups were considered, much of the overall variance in arthropod spatial distribution could be attributed to leaf age characteristics, arthropod aggregation patterns, arthropod activity and distance to tree trunk.
• 3 The fraction of variance which could be specifically explained by foliage attributes such as nitrogen-, water- and fibre-content, specific leaf weight, and epiphyll load was small for most arthropod groups (usually <30%). However, an index of food quality explained a higher proportion of variance (50%) in the abundance of phloem-feeders. Leaf size and foliage compactness did not influence significantly the abundance of any arthropod group.
• 4 Most herbivores were more abundant on young foliage than on mature leaves. With the exception of Corylophidae and Chrysomelidae, which were more abundant in the lower and upper canopy respectively, arthropod stratification was not conspicuous within the inner core of tree crowns.
• 5 The results firstly emphasize the distribution of young foliage as a key factor affecting the abundance of many herbivores and, secondly, the importance of the local illumination regime for host leaf production and its indirect effects on the spatial distribution of arboreal arthropods.

     

Phytophagous insect communities in the canopies of three Eucalyptus forest types in south-eastern Australia

Intensive sampling of tree canopies for phytophagous insects was carried out in three contrasting eucalypt forest types comprised of species widely distributed in sub-alpine forests in Victoria and New South Wales (Eucalyptus delegatensis, E. dives, and E. pauciflora). The number of phytophagous insects present in the canopies of these forest types was low, with a seasonal average of 20 individuals per kg of foliage (dry weight). Numbers were much lower than expected from past literature reporting‘chronically high’levels of defoliation in eucalypt forests. Microlepidoptera, Geometridae, Chrysomelidae, and Curculionidae were the major leaf-chewing groups recorded. Most sap-feeders were either leafhoppers (Cercopidae and Cicadellidae) or in the superfamily Fulgoroidea. Psyllidae and gall-making species were rare. Leafhoppers made up a very large portion of the phytophagous insect communities in each forest type, particularly in the E. dives forest. Microlepidoptera was the most commonly encountered defoliator group in all three forest types making up 33-44% of the total count. Non-phytophagous arthropods accounted for 44-48% of all individuals encountered. The density of insect defoliators was greater in the lower crown than upper crown. The E. dives canopy supported many more phytophagous insects per unit weight of foliage, as well as more per hectare, than the other two forest types. The greatest number of phytophagous species was also encountered in E. dives canopy. The E. delegatensis canopy supported the lowest number of phytophagous insects per unit weight of foliage as Well as numbers per hectare. Abundance of insect defoliators in the eucalypt forest types in this study was similar to published figures of insect defoliators in northern temperate forests.     

Comparing the precision,accuracy, and efficiency of branch clipping and sweep netting for sampling arthropods in two Jamaican forest types

ABSTRACT Devising methods for sampling arthropods presents many challenges, including understanding possible differences in results obtained by different individuals (precision), investigating differences between estimates and the actual variable of interest (accuracy), and assessing the effort and cost of a given method (efficiency). We assessed the precision, accuracy, and efficiency of sweep netting and branch clipping, two common methods of sampling arthropods, in mangrove and second‐growth scrub forests in Jamaica, West Indies, in 2009. Three individuals used both methods sequentially to sample arthropods in the territories of American Redstarts (Setophaga ruticilla). We found that both branch clipping and sweep netting lacked precision because different individuals produced different estimates of either arthropod abundance (number of individuals per sample) or biomass. In both forests, more arthropods were sampled with sweep netting, in terms of biomass and abundance, and several orders of arthropods were collected that were missed by branch clipping. We also detected the absence of a predictable habitat‐based difference in arthropod biomass with sweep netting, but not with branch clipping. Sweep netting took longer overall (field and processing time combined) and was therefore less efficient. Despite problems with precision and efficiency, our results suggest that sweep netting may be a more accurate method than branch clipping for sampling foliage arthropods in some forest habitats. Our study also reveals the importance of recognizing and controlling for individual bias and of choosing arthropod sampling methods most appropriate to each study species and habitat type.     

Convergence in Arthropod Assemblages with Various Restoration Approaches for Canadian Deciduous Forests

Silvicultural practices are traditionally aimed at increasing forest profits; however, recent approaches to forest conservation have broadened to include nature-based silviculture for regenerating forests. In southern Ontario (Canada), originally dominated by deciduous forests, conifer plantations were established on abandoned agricultural sites. Currently, there is an increasing interest to convert these conifer stands to a state that mimics the original deciduous forest. We investigated arthropod abundance, species richness of carabid beetles, and abundance of arthropod assemblages (trophic and prey groups) under five silvicultural treatments conducted to regenerate deciduous forests (the natural forest type) from the old conifer plantations. The treatments included: (1) uniform canopy removal; (2) uniform canopy removal and understory removal; (3) group canopy removal; (4) group canopy removal and understory removal; and (5) untreated control plots (relatively pure red pine). Insects were sampled annually using sweepnets and pitfall traps. Results revealed treatment effects on the abundance of Coleoptera, Heteroptera, herbivores, and small arthropods (<3 mm) caught in sweepnet samples, where plots subjected to group shelterwood removal and understory removal supported higher abundances than the control plots. There was no treatment effect on the abundance of other arthropod groups or on the species richness and abundance of carabid beetles. The silvicultural treatments used to encourage natural regeneration did not seem to affect arthropod food availability for insectivorous vertebrates. Thus, the type of silvicultural strategy used to convert pine plantations to a stage that mimics the natural deciduous forests had little overall impact on arthropods.     

Leaf litter arthropod responses to tropical forest restoration

Soil and litter arthropods represent a large proportion of tropical biodiversity and perform important ecosystem functions, but little is known about the efficacy of different tropical forest restoration strategies in facilitating their recovery in degraded habitats. We sampled arthropods in four 7‐ to 8‐year‐old restoration treatments and in nearby reference forests. Sampling was conducted during the wet and dry seasons using extractions from litter and pitfall samples. Restoration treatments were replicated in 50 × 50‐m plots in four former pasture sites in southern Costa Rica: plantation – trees planted throughout the plot; applied nucleation/islands – trees planted in patches of different sizes; and natural regeneration – no tree planting. Arthropod abundance, measures of richness and diversity, and a number of functional groups were greater in the island treatment than in natural regeneration or plantation treatments and, in many cases, were similar to reference forest. Litter and pitfall morphospecies and functional group composition in all three restoration treatments were significantly different than reference sites, but island and plantation treatments showed more recovery than natural regeneration. Abundance and functional group diversity showed a much greater degree of recovery than community composition. Synthesis and applications: The less resource‐intensive restoration strategy of planting tree islands was more effective than tree plantations in restoring arthropod abundance, richness, and functional diversity. None of the restoration strategies, however, resulted in similar community composition as reference forest after 8 years of recovery, highlighting the slow rate of recovery of arthropod communities after disturbance, and underscoring the importance of conservation of remnant forests in fragmented landscapes.     

Communities of insect herbivores foraging on saplings versus mature trees of Pourouma bicolor (Cecropiaceae) in Panama

The arthropod fauna of 25 saplings and of three conspecific mature trees of Pourouma bicolor (Cecropiaceae) was surveyed for 12 months in a tropical wet forest in Panama, with particular reference to insect herbivores. A construction crane erected at the study site provided access to tree foliage in the upper canopy. A similar area of foliage (ca. 370 m²) was surveyed from both saplings and trees, but samples obtained from the latter included 3 times as much young foliage as from the former. Arthropods, including herbivores and leaf-chewing insects with a proven ability to feed on the foliage of P. bicolor were 1.6, 2.5 and 2.9 times as abundant on the foliage of trees as on that of saplings. The species richness of herbivores and proven chewers were 1.5 (n=145 species) and 3.5 (n=21) times higher on trees than on saplings, respectively. Many herbivore species preferred or were restricted to one or other of the host stages. Host stage and young foliage area in the samples explained 52% of the explained variance in the spatial distribution of herbivore species. Pseudo-replication in the two sampling universes, the saplings and trees studied, most likely decreased the magnitude of differences apparent between host stages in this forest. The higher availability of food resources, such as young foliage, in the canopy than in the understorey, perhaps combined with other factors such as resource quality and enemy-free space, may generate complex gradients of abundance and species richness of insect herbivores in wet closed tropical forests.     

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.     

Does Argentine ant invasion affect prey availability for foliage-gleaning birds?

Food availability during the breeding season plays a critical role in reproductive success of insectivorous birds. Given that the invasive Argentine ant (Linepithema humile) is known to alter arthropod communities, we predicted that its invasion may affect the availability of food resources for coexisting foliage-gleaning birds. With this aim we studied, for 3 years, foliage arthropods occurring on cork oaks (Quercus suber) and tree heaths (Erica arborea) in invaded and non-invaded secondary forests of the northeastern Iberian Peninsula. Our results show that Argentine ants interact with arboreal foliage arthropods in a different manner than the native ants they displace do. The invasive ant impacted the arthropod community by reducing order diversity and ant species richness and by causing extirpation of most native ant species. Arthropod availability for foliage gleaners’ nestlings diminished in invaded cork oaks, mainly responding to the abundance and biomass depletion of caterpillars. Results suggest that the reproduction of canopy-foraging foliage-gleaning species that mostly rely on caterpillars to feed their young could be compromised by the Argentine ant invasion. Thus, the Argentine ant could be promoting bottom-up effects in the trophic web through its effects on the availability of arthropod preys for insectivorous birds.     

Comparing four simple,inexpensive methods for sampling forest arthropod communities

Terrestrial arthropods are diverse, and quantifying their availability to consumers is important for understanding both consumer and insect distribution, abundance, and communities. However, characterizing arthropod communities in complex forest ecosystems is challenging. We compared arthropod communities in a wet‐limestone forest in Jamaica during the dry season sampled by four methods: branch clips, sweep netting, and sticky traps applied to tree trunks and hanging free of vegetation. We found no effect of relative height in the canopy for the two methods that could be used at different heights, i.e., hanging sticky traps and branch clips. In addition, the arthropod community sampled changed over time (season) for sweep nets and branch clips. We also found that branch clips and sweep nets sampled more arthropod taxa than the two sticky‐trap methods. In addition, branch clips and sweep nets sampled more ants and spiders than the two sticky‐trap methods, whereas collar sticky traps on tree trunks sampled more bark lice (Psocoptera), and hanging sticky traps more flies (Diptera) than the other methods. Percentages of flying insects and strong‐flying insects sampled did not differ between sweep netting and branch clipping, but a higher percentage of both groups were captured with collar and hanging sticky traps. Because we found that the different methods sampled different subsets of the arthropod community, both taxonomically and in terms of aerial versus non‐aerial taxa, investigators should choose the arthropod sampling methods that most closely align with their focal species and study questions. For example, investigators might use collar traps for studies of bark gleaners, hanging sticky traps for aerial foragers, and branch clips or sweep nets for foliage gleaners. Alternatively, if a focal species is known to prefer certain prey items, investigators may instead select a method that effectively samples those prey taxa. Finally, for some studies, using multiple sampling methods may be the best option.     

The Amazonas‐trap: a new method for sampling plant‐inhabiting arthropod communities in tropical forest understory

Methods to quantify plant‐insect interactions in tropical forests may miss many important arthropods and can be time consuming and uneven in capture efficiency. We describe the Amazonas‐trap, a new method that rapidly envelops the target plant for sampling arthropods. We evaluated the efficiency of the Amazonas‐trap by comparing it with two commonly used sampling methods to collect arthropods from plants: the beating tray and manual collection. Samples were collected in 10 permanent plots, in the Ducke forest reserve, Manaus (Amazonas, Brazil). In each plot we sampled 18 plant individuals of Protium sp. (Burseraceae): six by a beating tray, six by manual collection, and six using the Amazonas‐trap. All insects were identified to the family level and those belonging to the order Hymenoptera were identified to the species and morphospecies level. The new method sampled more insect families and more Hymenoptera species than tree beating and manual collection. Of the 75 total families collected, 20 were sampled exclusively by the Amazonas‐trap, seven were only collected with a beating tray, and seven were sampled exclusively with manual collecting. A similar pattern was found for abundance: Amazonas‐trap sampled more individuals, followed by the beating tray and manual collection. Small and winged arthropods were more abundant in Amazonas‐trap, explaining the highest richness of Hymenoptera and insect families sampled with this method. The new method sampled more spiders, wood‐fungi feeders, sap suckers, omnivorous, parasitoids, and insect predators than the other methods, but was equally effective in sampling leaf‐feeders and ants. Amazonas‐trap was more time consuming in the field, but for all diversity parameters evaluated, the new method showed better performance for collecting invertebrates on plants.     

Effects of Tree Genotypic Diversity and Species Diversity on the Arthropod Community Associated with Big‐leaf Mahogany

Despite potential interactive effects of plant species and genotypic diversity (SD and GD, respectively) on consumers, studies have usually examined these effects separately. We evaluated the individual and combined effects of tree SD and mahogany (Swietenia macrophylla) GD on the arthropod community associated with mahogany. We conducted this study within the context of a tree diversity experiment consisting of 74 plots with 64 saplings/plot. We sampled 24 of these plots, classified as monocultures of mahogany or polycultures of four species (including mahogany). Within each plot type, mahogany was represented by either one or four maternal families. We surveyed arthropods on mahogany and estimated total arthropod abundance and species richness, as well as abundance and richness separately for herbivorous and predatory arthropods. Overall tree SD and mahogany GD had positive effects on total arthropod species richness and abundance on mahogany, and also exerted interactive effects on total species richness (but not abundance). Analyses conducted by trophic level group showed contrasting patterns; SD positively influenced herbivore species richness but not abundance, and did not affect either predator richness or abundance. GD influenced predator species richness but not abundance, and did not influence herbivore abundance or richness. There were interactive effects of GD and SD only for predator species richness. These results provide evidence that intra‐ and inter‐specific plant diversity exert interactive controls on associated consumer communities, and that the relative importance of SD and GD may vary among higher trophic levels, presumably due to differences in the underlying mechanisms or consumer traits.     

North—South Patterns within Arboreal Ant Assemblages from Rain Forests in Eastern Australia1

This paper describes the ant assemblages sampled from rain forest canopies ranging from southern Victoria through to Cape York Peninsula, Australia, and also in Brunei. Specifically, it examines the influence of decreasing latitude and variations in elevation on the character, richness, and abundance of the arboreal rain forest ant fauna, and also the relative contribution of ants to the total arthropod community. The sites that were examined included: cool temperate Nothofagus cunninghamii forest from a range of locations in Victoria; cool temperate N. moorei forest at both Werrikimbe and Styx River, New South Wales; notophyll vine forest in Lamington National Park, southeast Queensland; high elevation notophyll vine forest in Eungella National Park, central Queensland; complex notophyll vine forest at Robson Creek, Atherton Tablelands, north Queensland; complex mesophyll vine forest at Cape Tribulation, north Queensland; and mixed dipterocarp forest in Brunei. Although these sites represent a gradient increasingly tropical in character, botanically speaking, Eungella is less tropical than Lamington because of its high elevation. All samples were obtained by fogging the canopy with a rapid‐knockdown pyrethrin pesticide. In all cases, circular funnels were suspended beneath the foliage of individual trees or small plots of mixed canopy. Arthropods were collected four hours after fogging. Following ordinal sorting, ants were identified and counted to morphospecies level. The resulting catch were then standardized across sites as numbers caught per 0.5 m² sampling funnel. Generic and species richness were higher at the lowland tropical Cape Tribulation sites than at the sites to the south and was comparable with values in the Brunei site. Species richness was negatively correlated with latitude and elevation. Within the Australian rain forest, the lowland/highland break appears to be the strongest predictor of ant relative abundance, with a weaker latitudinal relationship superimposed.     

The effects of land-use change on arthropod richness and abundance on Santa Maria Island (Azores): unmanaged plantations favour endemic beetles

We study how endemic, native and introduced arthropod species richness, abundance, diversity and community composition vary between four different habitat types (native forest, exotic forest of Cryptomeria japonica, semi-natural pasture and intensive pasture) and how arthropod richness and abundance change with increasing distance from the native forest in adjacent habitat types in Santa Maria Island, the Azores. Arthropods were sampled in four 150 m long transects in each habitat type. Arthropods were identified to species level and classified as Azorean endemic, single-island endemic (SIE), native, or introduced. The native forest had the highest values for species richness of Azorean endemics, SIEs and natives; and also had highest values of Azorean endemic diversity (Fisher’s alpha). In contrast, the intensive pasture had the lowest values for endemic and native species richness and diversity, but the highest values of total arthropod abundance and introduced species richness and diversity. Arthropod community composition was significantly different between the four habitat types. In the semi-natural pasture, the number of SIE species decreased with increasing distance from the native forest, and in the exotic forest the abundance of both Azorean endemics and SIEs decreased with increasing distance from the native forest. There is a gradient of decreasing arthropod richness and abundance from the native forest to the intensive pasture. Although this study demonstrates the important role of the native forest in arthropod conservation in the Azores, it also shows that unmanaged exotic forests have provided alternative habitat suitable for some native species of forest specialist arthropods, particularly saproxylic beetles.     

Complexity of leaf miner–parasitoid food webs declines with canopy height in Patagonian beech forests

1. Consumer–resource species interactions form complex, dynamic networks, which may exhibit structural heterogeneity at various scales. This study set out to address whether host–parasitoid food web size and topology vary across forest canopy strata, and to what extent foliar resources and species abundances account for vertical patterns in network structure. 2. The vertical stratification of leaf miner–parasitoid food webs was examined in two monotypic beech (Nothofagus pumilio) forests in northern Patagonia, Argentina. Quantitative food webs were constructed for separate canopy layers by sampling foliage from three tree‐height classes at 0.5–1, 2–3 and 5–6 m above ground. 3. Leaf miner abundance per unit leaf mass and foliar damage (%) did not differ across strata, although foliage quality and quantity increased from the understorey to the upper canopy. Parasitism rates and food web complexity decreased with canopy height, as reflected by reduced linkage richness, linkage density, mean interaction strength, and host vulnerability. 4. Null model analyses revealed that food web metrics, especially in the upper canopy, were often lower than expected when compared with randomly structured networks. Overall, these patterns held for two forests differing in vertical structure and in dominant miner morphotype and parasitoid species. 5. These results suggest that vertical declines in network complexity may be driven by the parasitoids' limited functional response to host abundance and dispersal from pupation sites in the forest floor. A broader constraint on food web structure seemed to be imposed by host–parasitoid trait matching, a reflection of large‐scale assembly processes.     

Leaf-Litter Arthropods in Restored Forests in the Colombian Andes: A Comparison Between Secondary Forest and Tree Plantations

Tree monocultures of native and exotic species are frequently used as tools to catalyze forest recovery throughout the tropics. Although plantations may rapidly develop a canopy cover, they need to be evaluated as habitat for other organisms. We compared samples of leaf‐litter arthropods from two elevations in restored forest in the Colombian Andes. At the upper elevation (2,430 m), we compared native Andean alder (Alnus acuminata) plantation and secondary forest, and at the lower elevation (1,900 m) exotic Chinese ash (Fraxinus chinensis) plantation and secondary forest. Samples were obtained in two periods, March–April and September 1995. Species richness and abundance of arthropods were highest in secondary forest at the lower elevation. There were no differences in richness between both plantations and high‐elevation forest. Arthropod richness and abundance increased in the second sampling period in both secondary forest types and the ash plantation but not in the alder plantation, reflecting population recovery after the dry season. Alder leaf litter apparently buffered seasonal variations in arthropod richness and abundance. Composition of morphospecies was different among forest types. Although arthropod richness was lower in ash plantations compared to secondary forest, plantations still provided habitat for these organisms. On the other hand, the alder plantation was not different from secondary forest at the same elevation. At our site, plantations are embedded in a forested landscape. Whether our results apply to different landscape configurations and at different spatial scales needs to be established. The use of plantations as a restoration tool depends on the objectives of the project and on local conditions of forest cover and soils.     

Long‐term directional changes in upland Quercus forests throughout Oklahoma,USA

Questions: (1) How have the composition and structure of undisturbed upland Quercus forests changed over 50 years across a large region and moisture gradient; (2) What factors are associated with long‐term and broad‐scale changes in these forests? Location: Oklahoma, USA. Methods: We re‐sampled 30 forest stands originally sampled in the 1950s across a large geographical area and compared basal area, tree density, and sapling density between the sampling periods using paired t‐tests, CCA, and DCA. We examined vegetation dynamics in the context of drought indices compiled for the sample period. Results: Total and Quercus stellata basal area and tree density increased, but Q. stellata and Q. marilandica sapling density decreased. Juniperus virginiana and woody species richness increased for all measures. DCA indicated that re‐sampled stands generally changed from Q. stellata–Q. marilandica‐dominated forests to forests with greater woody species richness and more J. virginiana. Q. stellata remained a dominant tree species; otherwise, composition shifted towards mesophytic and invasive woody species. Measurements taken in the 1950s immediately followed a major drought; whereas subsequent decades were significantly moister. Conclusions: Fire exclusion and drought may have played an important role in driving changes towards lower dominance by Quercus, increased importance of mesophytic and invasive species, and greater woody species richness. These phenomena are similar to those found in Quercus‐dominated forests throughout the northern hemisphere.     

Short-term Effects of Harvest Technique and Mechanical Site Preparation on Arthropod Communities in Jack Pine Plantations

Arthropods play a key role in the functioning of forest ecosystems and contribute to biological diversity. However, the influence of current silvicultural practices on arthropod communities is little known in jack pine (Pinus banksiana) forests, a forest type comprising a major portion of the Canadian boreal forest. In this study, the effects of silvicultural treatments on arthropod communities were compared to identify those treatments that minimize ecological impacts on arthropods. The influence of harvesting techniques and mechanical site preparations on insect family richness and abundance of arthropods (total, by orders and by trophic groups) was examined in young (three-year-old) jack pine plantations of northern Ontario. Each of the following treatments were conducted in three plots: (1) tree length harvest and trenching; (2) full tree harvest and trenching; (3) full tree harvest and blading; and (4) full tree harvest and no site preparation. Arthropods were collected using sweepnets and pitfall traps over two years. Blading significantly reduced insect family richness, the total abundance of arthropods, abundance of Orthoptera, Heteroptera, Hymenoptera, Diptera, insect larvae, and plant feeders when compared to the other treatments. The use of either full tree or tree length harvesting had similar short-term effects on family richness and the abundance of arthropods. Arthropod diversity declined with increasing post-harvest site disturbance. These results suggest that arthropod communities in the understory and on the ground are reduced most on sites mechanically prepared by blading, but are similar under conditions immediately following either full tree or tree length harvesting. The implications for regenerating jack pine in the boreal forest are discussed.     

Forest plant community as a driver of soil biodiversity: experimental evidence from collembolan assemblages through large‐scale and long‐term removal of oak canopy trees Quercus petraea

Plant–soil interactions are increasingly recognized to play a major role in terrestrial ecosystems functioning. However, few studies to date have focused on slow dynamic ecosystems such as forests. As they are vertically stratified by multiple vegetation strata, canopy tree removal by thinning operations could alter forest plant community through tree canopy opening. Very little is known about cascading effects on soil biodiversity. We conducted a large‐scale, multi‐site assessment of collembolan assemblage response to long‐term canopy tree removal in sessile oak Quercus petraea temperate forests. A total of 33 experimental plots were studied covering a large gradient of canopy tree basal area, stand age and local abiotic contexts. Collembolan abundance strongly declined with canopy tree removal in early forest successional stage and this was mediated by negative effect of understory plant community composition changes, i.e. shift from moss and forb to tree seedling, fern, shrub and grass species. Negative effect of this composition shift on collembolan species richness was largely offset by positive effect of the increase in understory plant species richness. This gives support to both the plant mass‐ratio and functional diversity hypotheses. Collembolan functional groups had contrasting response patterns, which were mediated by different ecological factors. Epedaphic (r‐strategist) abundance and species richness increased with canopy tree removal in relation with the increase in understory plant species richness. In contrast, euedaphic (K‐strategist) abundance and species richness declined with canopy tree removal in early forest successional stage in relation with changes in understory plant community composition and species richness, as well as microclimatic conditions. Overall, our study provides experimental evidence that forest plant community can be a strong driver of collembolan assemblages. It also emphasizes the role of trees as foundation species of forest ecosystems that can shape soil biodiversity through their regulation of understory plant community and ecosystem abiotic conditions.     

You'd better walk alone: Changes in forest composition affect pollination efficiency and pre‐dispersal cone damage in Iberian Juniperus thurifera forests

• Changes in land‐use patterns are a major driver of global environmental change. Cessation of traditional land‐use practices has led to forest expansion and shifts in forest composition. Consequently, former monospecific forests maintained by traditional management are progressing towards mixed forests. However, knowledge is scarce on how the presence of other tree species will affect reproduction of formerly dominant species. We explored this question in the wind‐pollinated tree Juniperus thurifera. We hypothesised that the presence of heterospecific trees would have a negative effect on cone production and on the proportion of cones attacked by specialised predators.
• We assessed the relative importance of forest composition on cone production, seed development and pre‐dispersal cone damage on nine paired pure and mixed J. thurifera forests in three regions across the Iberian Peninsula. The effects of forest composition on crop size, cone and seed characteristics, as well as damage by pre‐dispersal arthropods were tested using mixed models.
• Cone production was lower and seed abortion higher in mixed forests, suggesting higher pollination failure. In contrast, cone damage by arthropods was higher in pure forests, supporting the hypothesis that presence of non‐host plants reduces damage rates. However, the response of each arthropod to forest composition was species‐specific and the relative rates of cone damage varied depending on individual tree crops.
• Larger crop sizes in pure forests compensated for the higher cone damage rates, leading to a higher net production of sound seeds compared to mixed forests. This study indicates that ongoing changes in forest composition after land abandonment may impact tree reproduction.

     

Effect of prey availability on the abundance of White‐breasted Wood‐Wrens,insectivorous birds of tropical lowland forests

Some understory insectivorous birds manage to persist in tropical forest fragments despite significant habitat loss and forest fragmentation. Their persistence has been related to arthropod biomass. In addition, forest structure has been used as a proxy to estimate prey availability for understory birds and for calculating prey abundance. We used arthropod biomass and forest structural variables (leaf area index [LAI] and aerial leaf litter biomass) to explain the abundance of White‐breasted Wood‐Wrens (Henicorhina leucosticta), tropical understory insectivorous birds, in six forests in the Caribbean lowlands of Costa Rica. To estimate bird abundance, we performed point counts (100‐m radius) in two old‐growth forests, two second‐growth forests, and two selectively logged forests. Arthropod abundance was the best predictor of wood‐wren abundance (wi = 0.75). Wood‐wren abundance increased as the number of arthropods increased, and the estimated range of bird abundance obtained from the model varied from 0.51 (0.28 – 0.93 [95%CI]) to 3.70 (1.68 – 5.20 [95%CI]) within sites. LAI was positively correlated to prey abundance (P = 0.01), and explained part of the variation in wood‐wren abundance. In forests with high LAI, arthropods have more aerial leaf litter as potential habitat so more potential prey are available for wood‐wrens. Forests with a greater abundance of aerial leaf litter arthropods were more likely to sustain higher densities of wood‐wrens in a fragmented tropical landscape.