Comparison of pollinators and natural enemies: a meta‐analysis of landscape and local effects on abundance and richness in crops

To manage agroecosystems for multiple ecosystem services, we need to know whether the management of one service has positive, negative, or no effects on other services. We do not yet have data on the interactions between pollination and pest‐control services. However, we do have data on the distributions of pollinators and natural enemies in agroecosystems. Therefore, we compared these two groups of ecosystem service providers, to see if the management of farms and agricultural landscapes might have similar effects on the abundance and richness of both. In a meta‐analysis, we compared 46 studies that sampled bees, predatory beetles, parasitic wasps, and spiders in fields, orchards, or vineyards of food crops. These studies used the proximity or proportion of non‐crop or natural habitats in the landscapes surrounding these crops (a measure of landscape complexity), or the proximity or diversity of non‐crop plants in the margins of these crops (a measure of local complexity), to explain the abundance or richness of these beneficial arthropods. Compositional complexity at both landscape and local scales had positive effects on both pollinators and natural enemies, but different effects on different taxa. Effects on bees and spiders were significantly positive, but effects on parasitoids and predatory beetles (mostly Carabidae and Staphylinidae) were inconclusive. Landscape complexity had significantly stronger effects on bees than it did on predatory beetles and significantly stronger effects in non‐woody rather than in woody crops. Effects on richness were significantly stronger than effects on abundance, but possibly only for spiders. This abundance‐richness difference might be caused by differences between generalists and specialists, or between arthropods that depend on non‐crop habitats (ecotone species and dispersers) and those that do not (cultural species). We call this the ‘specialist‐generalist’ or ‘cultural difference’ mechanism. If complexity has stronger effects on richness than abundance, it might have stronger effects on the stability than the magnitude of these arthropod‐mediated ecosystem services. We conclude that some pollinators and natural enemies seem to have compatible responses to complexity, and it might be possible to manage agroecosystems for the benefit of both. However, too few studies have compared the two, and so we cannot yet conclude that there are no negative interactions between pollinators and natural enemies, and no trade‐offs between pollination and pest‐control services. Therefore, we suggest a framework for future research to bridge these gaps in our knowledge.     

The challenge of accurately documenting bee species richness in agroecosystems: bee diversity in eastern apple orchards

Bees are important pollinators of agricultural crops, and bee diversity has been shown to be closely associated with pollination, a valuable ecosystem service. Higher functional diversity and species richness of bees have been shown to lead to higher crop yield. Bees simultaneously represent a mega‐diverse taxon that is extremely challenging to sample thoroughly and an important group to understand because of pollination services. We sampled bees visiting apple blossoms in 28 orchards over 6 years. We used species rarefaction analyses to test for the completeness of sampling and the relationship between species richness and sampling effort, orchard size, and percent agriculture in the surrounding landscape. We performed more than 190 h of sampling, collecting 11,219 specimens representing 104 species. Despite the sampling intensity, we captured <75% of expected species richness at more than half of the sites. For most of these, the variation in bee community composition between years was greater than among sites. Species richness was influenced by percent agriculture, orchard size, and sampling effort, but we found no factors explaining the difference between observed and expected species richness. Competition between honeybees and wild bees did not appear to be a factor, as we found no correlation between honeybee and wild bee abundance. Our study shows that the pollinator fauna of agroecosystems can be diverse and challenging to thoroughly sample. We demonstrate that there is high temporal variation in community composition and that sites vary widely in the sampling effort required to fully describe their diversity. In order to maximize pollination services provided by wild bee species, we must first accurately estimate species richness. For researchers interested in providing this estimate, we recommend multiyear studies and rarefaction analyses to quantify the gap between observed and expected species richness.     

Relationships between biological soil crusts,bacterial diversity and abundance,and ecosystem functioning: Insights from a semi‐arid Mediterranean environment

Questions: To what degree do biological soil crusts (BSCs), which are regulators of the soil surface boundary, influence associated microbial communities? Are these associations important to ecosystem functioning in a Mediterranean semi‐arid environment? Location: Gypsum outcrops near Belmonte del Tajo, Central Spain. Methods: We sampled a total of 45 (50 cm × 50 cm) plots, where we estimated the cover of every lichen and BSC‐forming lichen species. We also collected soil samples to estimate bacterial species richness and abundance, and to assess different surrogates of ecosystem functioning. We used path analysis to evaluate the relationships between the richness/abundance of above‐ and below‐ground species and ecosystem functioning. Results: We found that the greatest direct effect upon the ecosystem function matrix was that of the biological soil crust (BSC) richness matrix. A few bacterial species were sensitive to the lichen community, with a disproportionate effect of Collema crispum and Toninia sedifolia compared to their low abundance and frequency. The lichens Fulgensia subbracteata and Toninia spp. also had negative effects on bacteria, while Diploschistes diacapsis consistently affected sensitive bacteria, sometimes positively. Despite these results, very few of the BSC effects on ecosystem function could be ascribed to changes within the bacterial community. Conclusion: Our results suggest the primary importance of the richness of BSC‐forming lichens as drivers of small‐scale changes in ecosystem functioning. This study provides valuable insights on semi‐arid ecosystems where plant cover is spatially discontinuous and ecosystem function in plant interspaces is regulated largely by BSCs.     

生态恢复中生态系统服务的演变:趋势、过程与评估

经过10余年的发展,生态系统服务已经成为生态恢复研究关注的前沿和热点。生态恢复改变了生态系统格局与过程,对生态系统服务的产生和提供具有重要影响。但是目前对于生态系统服务在生态恢复过程中的演化仍缺少系统性研究。对国内外相关研究的最新成果进行综述,总结了生态系统服务评估中框架的构建和方法的选择(参数转移法、系统模型法和定量指标法),介绍了生态恢复对生态系统服务的促进作用、生态系统服务的演变过程以及不同生态系统服务间的协同与权衡关系,分析了社会经济因素对生态恢复和生态系统服务维持的影响。最后结合我国生态恢复实践,提出未来生态恢复和生态系统服务研究可以从深化作用机制研究、推动服务评估创新、增强研究成果应用3方面深化和拓展。     

Differential roles of species richness versus species asynchrony in regulating community stability along a precipitation gradient

Plant community may provide products and services to humans. However, patterns and drivers of community stability along a precipitation gradient remain unclear. A regional‐scale transect survey was conducted over a 3‐year period from 2013 to 2015, along a precipitation gradient from 275 to 555 mm and spanning 440 km in length from west to east in a temperate semiarid grassland of northern China, a central part of the Eurasian steppe. Our study provided regional‐scale evidence that the community stability increased with increasing precipitation in the semiarid ecosystem. The patterns of community stability along a precipitation gradient were ascribed to community composition and community dynamics, such as species richness and species asynchrony, rather than the abiotic effect of precipitation. Species richness regulated the temporal mean (μ) of aboveground net primary productivity (ANPP), while species asynchrony regulated the temporal standard deviation (σ) of ANPP, which in turn contributed to community stability. Our findings highlight the crucial role of community composition and community dynamics in regulating community stability under climate change.     

Food web complexity and higher-level ecosystem services

Studies mostly focused on communities of primary producers have shown that species richness provides and promotes fundamental ecosystem services. However, we know very little about the factors influencing ecosystem services provided by higher trophic levels in natural food webs. Here we present evidence that differences in food web structure and the richness of herbivores in 19 plant‐herbivore‐parasitoid food webs influence the service supplied by natural enemies, namely, the parasitism rates on hosts. Specifically, we find that parasitoids function better in simple food webs than in complex ones, a result relevant to biological control practice. More generally, we show that species richness per se only contributes partially to the understanding of higher‐level ecosystem services in multitrophic communities, and that changes in food web complexity should also be taken into account when predicting the effects of human‐driven disturbances in natural communities.     

Forest edges have high conservation value for bird communities in mosaic landscapes

A major conservation challenge in mosaic landscapes is to understand how trait‐specific responses to habitat edges affect bird communities, including potential cascading effects on bird functions providing ecosystem services to forests, such as pest control. Here, we examined how bird species richness, abundance and community composition varied from interior forest habitats and their edges into adjacent open habitats, within a multi‐regional sampling scheme. We further analyzed variations in Conservation Value Index (CVI), Community Specialization Index (CSI) and functional traits across the forest‐edge‐open habitat gradient. Bird species richness, total abundance and CVI were significantly higher at forest edges while CSI peaked at interior open habitats, i.e., furthest from forest edge. In addition, there were important variations in trait‐ and species‐specific responses to forest edges among bird communities. Positive responses to forest edges were found for several forest bird species with unfavorable conservation status. These species were in general insectivores, understorey gleaners, cavity nesters and long‐distance migrants, all traits that displayed higher abundance at forest edges than in forest interiors or adjacent open habitats. Furthermore, consistently with predictions, negative edge effects were recorded in some forest specialist birds and in most open‐habitat birds, showing increasing densities from edges to interior habitats. We thus suggest that increasing landscape‐scale habitat complexity would be beneficial to declining species living in mosaic landscapes combining small woodlands and open habitats. Edge effects between forests and adjacent open habitats may also favor bird functional guilds providing valuable ecosystem services to forests in longstanding fragmented landscapes.     

The Effects of Cropping Systems on Avian Communities in Cacao and Banana Agro‐Forestry Systems of Talamanca,Costa Rica

Multispecies agro‐forestry is generally lauded for providing ecosystem services, especially in tropical environments. Avian communities contribute to services such as biodiversity and pest management. Characterizing and evaluating avian community composition in similar cropping systems will help optimize management for ecosystem services. We examined the relationship between cropping system vegetation and avian communities in four shaded agro‐forestry systems common to the Limón province of Costa Rica: abandoned and managed systems of cacao, cacao with banana, and banana. During two field seasons, we detected 2605 birds from 106 species and identified 2791 trees and shrubs from 62 morphospecies. We compared vegetation and avian species richness across systems with mixed‐effects linear models. Canopy, understory, and groundcover vegetation differed among agro‐forestry systems. More ground‐ and understory‐foraging forest species were detected in agro‐forestry systems lacking banana, whereas richness of agricultural generalist species was highest in systems with banana. Richness of understory‐ and ground‐foraging species correlated with understory tree species richness and leaf litter. Our results indicate that shaded cacao and banana systems can have similar canopy‐foraging species richness that includes both agricultural and woodland generalist species, but that interspersing banana with cacao can adversely influence understory forest bird community composition. Agro‐forests with diverse understory vegetation support more understory‐foraging bird species that have proven valuable in pest management. Abstract in Spanish is available at http://www.blackwell‐synergy.com/loi/btp .     

Local and landscape effects on bee communities of Hungarian winter cereal fields

• 1 Pollination is a key ecosystem service. Although bees are the most important pollinators, they are endangered by intensive agricultural practices. The present study investigated the effects of farmland management and environmental factors at local and landscape scales on bees in Central Hungary.
• 2 Bees were sampled in winter cereal fields that varied in the amount of applied fertilizer and insecticide use. Measurements included total, small and large bee species richness and abundance; stability of total species richness and abundance (coefficient of variation, CV); the nitrogen content of fertilizers; the number of insecticide applications; within‐field location; species richness and abundance of insect‐pollinated plants; and the percentage of semi‐natural areas in a 500‐m radius circle around the fields under study.
• 3 Increasing the amount of fertilizer decreased total and small bee abundance and increased the CV of total bee abundance. Insecticide use had a significant negative effect on total and small bee species richness and on large bee abundance. The percentage of semi‐natural habitats in a 500‐m radius did not influence bee species richness and abundance.
• 4 The results obtained confirms that the intensification of farmland management poses a threat to bee diversity, and thus may reduce pollination services. Recently‐introduced agri‐environment schemes are one potential approach for managing agricultural land use: reduced amounts of fertilizer and a cessation of insecticide application might lead to high bee species richness and abundance and ensure the pollination of wild plants and flowering crops.

     

Global effects of non‐native tree species on multiple ecosystem services

Non‐native tree (NNT) species have been transported worldwide to create or enhance services that are fundamental for human well‐being, such as timber provision, erosion control or ornamental value; yet NNTs can also produce undesired effects, such as fire proneness or pollen allergenicity. Despite the variety of effects that NNTs have on multiple ecosystem services, a global quantitative assessment of their costs and benefits is still lacking. Such information is critical for decision‐making, management and sustainable exploitation of NNTs. We present here a global assessment of NNT effects on the three main categories of ecosystem services, including regulating (RES), provisioning (PES) and cultural services (CES), and on an ecosystem disservice (EDS), i.e. pollen allergenicity. By searching the scientific literature, country forestry reports, and social media, we compiled a global data set of 1683 case studies from over 125 NNT species, covering 44 countries, all continents but Antarctica, and seven biomes. Using different meta‐analysis techniques, we found that, while NNTs increase most RES (e.g. climate regulation, soil erosion control, fertility and formation), they decrease PES (e.g. NNTs contribute less than native trees to global timber provision). Also, they have different effects on CES (e.g. increase aesthetic values but decrease scientific interest), and no effect on the EDS considered. NNT effects on each ecosystem (dis)service showed a strong context dependency, varying across NNT types, biomes and socio‐economic conditions. For instance, some RES are increased more by NNTs able to fix atmospheric nitrogen, and when the ecosystem is located in low‐latitude biomes; some CES are increased more by NNTs in less‐wealthy countries or in countries with higher gross domestic products. The effects of NNTs on several ecosystem (dis)services exhibited some synergies (e.g. among soil fertility, soil formation and climate regulation or between aesthetic values and pollen allergenicity), but also trade‐offs (e.g. between fire regulation and soil erosion control). Our analyses provide a quantitative understanding of the complex synergies, trade‐offs and context dependencies involved for the effects of NNTs that is essential for attaining a sustained provision of ecosystem services.     

Integrating trait‐based empirical and modeling research to improve ecological restoration

A global ecological restoration agenda has led to ambitious programs in environmental policy to mitigate declines in biodiversity and ecosystem services. Current restoration programs can incompletely return desired ecosystem service levels, while resilience of restored ecosystems to future threats is unknown. It is therefore essential to advance understanding and better utilize knowledge from ecological literature in restoration approaches. We identified an incomplete linkage between global change ecology, ecosystem function research, and restoration ecology. This gap impedes a full understanding of the interactive effects of changing environmental factors on the long‐term provision of ecosystem functions and a quantification of trade‐offs and synergies among multiple services. Approaches that account for the effects of multiple changing factors on the composition of plant traits and their direct and indirect impact on the provision of ecosystem functions and services can close this gap. However, studies on this multilayered relationship are currently missing. We therefore propose an integrated restoration agenda complementing trait‐based empirical studies with simulation modeling. We introduce an ongoing case study to demonstrate how this framework could allow systematic assessment of the impacts of interacting environmental factors on long‐term service provisioning. Our proposed agenda will benefit restoration programs by suggesting plant species compositions with specific traits that maximize the supply of multiple ecosystem services in the long term. Once the suggested compositions have been implemented in actual restoration projects, these assemblages should be monitored to assess whether they are resilient as well as to improve model parameterization. Additionally, the integration of empirical and simulation modeling research can improve global outcomes by raising the awareness of which restoration goals can be achieved, due to the quantification of trade‐offs and synergies among ecosystem services under a wide range of environmental conditions.     

Experimental evidence for the effects of dung beetle functional group richness and composition on ecosystem function in a tropical forest

Much of the literature on the relationship between species richness or functional group richness and measures of ecosystem function focuses on a restricted set of ecosystem function measures and taxonomic groups. Few such studies have been carried out under realistic levels of diversity in the field, particularly in high diversity ecosystems such as tropical forests. We used exclusion experiments to study the effects of dung beetle functional group richness and composition on two interlinked and functionally important ecological processes, dung removal and secondary seed dispersal, in evergreen tropical forest in Sabah, Malaysian Borneo. Overall, both dung and seed removal increased with dung beetle functional group richness. However, levels of ecosystem functioning were idiosyncratic depending on the identity of the functional groups present, indicating an important role for functional group composition. There was no evidence for interference or competition among functional groups. We found strong evidence for overyielding and transgressive overyielding, suggesting complementarity or facilitation among functional groups. Not all mixtures showed transgressive overyielding, so that complementarity was restricted to particular functional group combinations. Beetles in a single functional group (large nocturnal tunnellers) had a disproportionate influence on measures of ecosystem function: in their absence dung removal is reduced by approximately 75%. However, a full complement of functional groups is required to maximize ecosystem functioning. This study highlights the importance of both functional group identity and species composition in determining the ecosystem consequences of extinctions or altered patterns in the relative abundance of species.     

A global synthesis of the effects of diversified farming systems on arthropod diversity within fields and across agricultural landscapes

Agricultural intensification is a leading cause of global biodiversity loss, which can reduce the provisioning of ecosystem services in managed ecosystems. Organic farming and plant diversification are farm management schemes that may mitigate potential ecological harm by increasing species richness and boosting related ecosystem services to agroecosystems. What remains unclear is the extent to which farm management schemes affect biodiversity components other than species richness, and whether impacts differ across spatial scales and landscape contexts. Using a global metadataset, we quantified the effects of organic farming and plant diversification on abundance, local diversity (communities within fields), and regional diversity (communities across fields) of arthropod pollinators, predators, herbivores, and detritivores. Both organic farming and higher in‐field plant diversity enhanced arthropod abundance, particularly for rare taxa. This resulted in increased richness but decreased evenness. While these responses were stronger at local relative to regional scales, richness and abundance increased at both scales, and richness on farms embedded in complex relative to simple landscapes. Overall, both organic farming and in‐field plant diversification exerted the strongest effects on pollinators and predators, suggesting these management schemes can facilitate ecosystem service providers without augmenting herbivore (pest) populations. Our results suggest that organic farming and plant diversification promote diverse arthropod metacommunities that may provide temporal and spatial stability of ecosystem service provisioning. Conserving diverse plant and arthropod communities in farming systems therefore requires sustainable practices that operate both within fields and across landscapes.     

Protecting a single endangered species and meeting multiple conservation goals: an approach with Guaiacum sanctum in Yucatan Peninsula,Mexico

Aim New protected areas should consider safeguarding high conservation value sites based on multiple criteria and not just the presence of a single endangered or charismatic species. However, the extent to which complementary criteria coincide is usually unknown. We use the case of Guaiacum sanctum (Zygopyllaceae), an endangered timber tree species, to explore whether the protection of forests where this species is most abundant would meet other complementary conservation goals, such as capturing regional plant biodiversity, protecting other threatened/endemic species or safeguarding ecosystem services. Location Yucatan Peninsula, southern Mexico. Methods We conducted an analysis of the structure, composition and diversity of tree communities (including stems ≥5 cm dbh) at eight G. sanctum forest sites. We identified endemic and threatened tree species and quantified above‐ground tree biomass and carbon storage in these G. sanctum forests. Results Guaiacum sanctum forests contain 35–59 tree species on plots as small as 1000 m². The species composition of tree communities changed rapidly (high β‐diversity) across soil boundaries and rainfall regimes. Twenty‐one endemic and eight threatened tree species were recorded in our inventories. Individuals of G. sanctum represented up to 55% of the above‐ground carbon for trees ≥5 cm dbh. The high basal area of G. sanctum forests plus the high wood density, abundance, large size and longevity (more than 500 years) of G. sanctum and other tree species enhance the potential importance of these forests for carbon storage. Main conclusions A conservation strategy focused on protecting important populations of G. sanctum in the Yucatan Peninsula would have significant co‐benefits for conservation of regional tree species biodiversity and provision of critical ecosystem services. Our study illustrates a multiple criteria approach useful for the selection of areas with high conservation value on the basis of endemic, threatened species, species richness and ecosystem services.     

Effects of Urbanization on Tree Species Functional Diversity in Eastern North America

Urban forests provide ecosystem services for millions of people. Numerous introductions have elevated tree species richness in cities, which may enhance functional diversity. However, few studies have examined changes in tree community composition or functional diversity with urbanization, even though functional diversity, and not species number per se, is directly linked with ecosystem function and associated services. We combined tree abundance data from both urban and extra-urban forest inventory plots for seven metropolitan areas in eastern North America to analyze changes in species composition, Shannon’s diversity, and functional diversity with urbanization. As expected, urban tree diversity was reduced at local scales, and the effect varied with land use. Rarefaction analysis indicated that at large scales, urban tree species pools were equal with respect to species or functional diversity compared to extra-urban forests, but in urban areas at small scales this diversity is not realized because of low tree density. Ordination revealed that with urbanization, introduced species increased in importance, and regional variation in species composition became more homogenous. Increasing tree density and/or tree cover through changes in management practices and urban design could facilitate local scale urban tree diversity using existing species pools, which are functionally diverse. Monitoring of forests at large spatial scales that include urban areas, and the use of methods that account for abundance and functional trait variation can provide insights into the effects of urbanization on tree diversity at multiple scales.     

Dominant species maintain ecosystem function with non-random species loss

Loss of species caused by widespread stressors, such as drought and fragmentation, is likely to be non‐random depending on species abundance in the community. We experimentally reduced the number of rare and uncommon plant species while independently reducing only the abundance of dominant grass species in intact, native grassland. This allowed us to simulate a non‐random pattern of species loss, based on species abundances, from communities shaped by natural ecological interactions and characterized by uneven species abundance distributions. Over two growing seasons, total above‐ground net primary productivity (ANPP) declined with reductions in abundance of the dominant species but was unaffected by a threefold decline in richness of less common species. In contrast, productivity of the remaining rare and uncommon species decreased with declining richness, in part due to loss of complementary interactions among these species. However, increased production of the dominant grasses offset the negative effects of species loss. We conclude that the dominant species, as controllers of ecosystem function, can provide short‐term resistance to reductions in ecosystem function when species loss is nonrandom. However, the concurrent loss of complementary interactions among rare and uncommon species, the most diverse component of communities, may contribute to additional species loss and portends erosion of ecosystem function in the long term.     

Regional zooplankton dispersal provides spatial insurance for ecosystem function

Changing environmental conditions are affecting diversity and ecosystem function globally. Theory suggests that dispersal from a regional species pool may buffer against changes in local community diversity and ecosystem function after a disturbance through the establishment of functionally redundant tolerant species. The spatial insurance provided by dispersal may decrease through time after environmental change as the local community monopolizes resources and reduces community invasibility. To test for evidence of the spatial insurance hypothesis and to determine the role dispersal timing plays in this response we conducted a field experiment using crustacean zooplankton communities in a subarctic region that is expected to be highly impacted by climate change – Churchill, Canada. Three experiments were conducted where nutrients, salt, and dispersal were manipulated. The three experiments differed in time‐since‐disturbance that the dispersers were added. We found that coarse measures of diversity (i.e. species richness, evenness, and Shannon–Weiner diversity) were generally resistant to large magnitude disturbances, and that dispersal had the most impact on diversity when dispersers were added shortly after disturbance. Ecosystem functioning (chl‐a) was degraded in disturbed communities, but dispersal recovered ecosystem function to undisturbed levels. This spatial insurance for ecosystem function was mediated through changes in community composition and the relative abundance of functional groups. Results suggest that regional diversity and habitat connectivity will be important in the future to maintain ecosystem function by introducing functionally redundant species to promote compensatory dynamics.     

Butterfly community ecology: the influences of habitat type,weather patterns,and dominant species in a temperate ecosystem

We compared variation in butterfly communities across 3 years at six different habitats in a temperate ecosystem near Boulder, Colorado, USA. These habitats were classified by the local Open Space consortium as Grasslands, Tallgrass, Foothills Grasslands, Foothills Riparian, Plains Riparian, and Montane Woodland. Rainfall and temperature varied considerably during these years. We surveyed butterflies using the Pollard‐Yates method of invertebrate sampling and compared abundance, species richness, and diversity across habitats and years. Communities were most influenced by habitat, with all three quantitative measures varying significantly across habitats but only two measures showing variation across years. Among habitats, butterfly abundance was higher in Plains Riparian sites than in Montane Woodland or Grassland sites, though diversity was lowest in Plains Riparian areas. Butterfly species richness was higher in Foothills Riparian sites than it was in all but one other habitat (Tallgrass). Among years, butterfly abundance and species richness were lower during the year of least rainfall and highest temperatures, suggesting a substantial impact of the hot, dry conditions. Across habitats and years, butterfly abundance was consistently high at Plains Riparian and Foothills Riparian sites, and richness and diversity were consistently high in Foothills Riparian areas. These two habitats may be highly suitable for butterflies in this ecosystem, regardless of weather conditions. Generally low abundance and species richness in Montane Woodlands sites, particularly in 2002, suggested low suitability of the habitat to butterflies in this ecosystem, and this may be especially important during drought‐like conditions. Finally, to examine the effect that the presence of the very abundant non‐native species Pieris rapae L. (Lepidoptera: Pieridae) has on these communities, we re‐analyzed the data in the absence of this species. Excluding P. rapae dramatically reduced variation of both butterfly abundance and diversity across habitats, highlighting the importance of considering community membership in analyses like ours.     

Greater than the sum of the parts: how the species composition in different forest strata influence ecosystem function

The mechanisms underpinning forest biodiversity‐ecosystem function relationships remain unresolved. Yet, in heterogeneous forests, ecosystem function of different strata could be associated with traits or evolutionary relationships differently. Here, we integrate phylogenies and traits to evaluate the effects of elevational diversity on above‐ground biomass across forest strata and spatial scales. Community‐weighted means of height and leaf phosphorous concentration and functional diversity in specific leaf area exhibited positive correlations with tree biomass, suggesting that both positive selection effects and complementarity occur. However, high shrub biomass is associated with greater dissimilarity in seed mass and multidimensional trait space, while species richness or phylogenetic diversity is the most important predictor for herbaceous biomass, indicating that species complementarity is especially important for understory function. The strength of diversity‐biomass relationships increases at larger spatial scales. We conclude that strata‐ and scale‐ dependent assessments of community structure and function are needed to fully understand how biodiversity influences ecosystem function.     

Does Tree Species Composition Affect Productivity in a Tropical Planted Forest?

With growing pressure on primary forests from destructive land uses, increasing the diversity of native species plantations can increase ecosystem service provision, such as timber production or carbon sequestration, thus better supporting sustainable livelihoods. Understanding the effects of tree species composition on productivity can inform plantation design and ecological restoration strategies. However, tree species composition effects have been neglected in experimental biodiversity‐ecosystem function (BEF) research. This study uses a 10‐yr data set from one of the first tropical planted forest experiments established with native species and designed for BEF research at scales relevant to forest management. At our site in Sardinilla, Panama, we established plots containing 6 species from a pool of 18, in four combinations, to investigate how composition affects species and plot productivity. We used basal area as a proxy for productivity through time, measured annually, and summed this at species and plot levels for analysis. We found that plots that differed in species composition appeared to differ in temporal rate of basal area increase, but did not differ in BA after 10 yr. Species were generally consistent in size between compositions, and composition performance was correlated with the size of component species, suggesting that species identities were most important in determining plot productivity. Our results suggest that species choice can be based on preferences for individual species, as species performance was consistent across composition contexts. We make recommendations for the use of particularly productive species that also provide multiple services such as Guazuma ulmifolia, Spondias mombin, and Anacardium excelsum.