Temporal coexistence mechanisms contribute to the latitudinal gradient in forest diversity.

The tropical forests of Borneo and Amazonia may each contain more tree species diversity in half a square kilometre than do all the temperate forests of Europe, North America, and Asia combined. Biologists have long been fascinated by this disparity, using it to investigate potential drivers of biodiversity. Latitudinal variation in many of these drivers is expected to create geographic differences in ecological and evolutionary processes, and evidence increasingly shows that tropical ecosystems have higher rates of diversification, clade origination, and clade dispersal. However, there is currently no evidence to link gradients in ecological processes within communities at a local scale directly to the geographic gradient in biodiversity. Here, we show geographic variation in the storage effect, an ecological mechanism that reduces the potential for competitive exclusion more strongly in the tropics than it does in temperate and boreal zones, decreasing the ratio of interspecific-to-intraspecific competition by 0.25% for each degree of latitude that an ecosystem is located closer to the Equator. Additionally, we find evidence that latitudinal variation in climate underpins these differences; longer growing seasons in the tropics reduce constraints on the seasonal timing of reproduction, permitting lower recruitment synchrony between species and thereby enhancing niche partitioning through the storage effect. Our results demonstrate that the strength of the storage effect, and therefore its impact on diversity within communities, varies latitudinally in association with climate. This finding highlights the importance of biotic interactions in shaping geographic diversity patterns, and emphasizes the need to understand the mechanisms underpinning ecological processes in greater detail than has previously been appreciated.

Effects of information provision on willingness to pay for conservation of alpine plants in Japan.

Information provision is essential for obtaining the cooperation of the general public for the conservation of unfamiliar ecosystems towards a sustainable (e.g. carbon-neutral and nature-positive) society. The purpose of this study is to identify effective ways of raising public awareness for ecosystem conservation. We explored the interaction between the manner of information provision (i.e. the medium through which and how much information is provided) and the personal attributes (e.g. environmental attitude) of the recipients on their willingness to pay (WTP) for conservation using Japanese alpine plants as the subject. Discrete choice experiments using an online survey were conducted with public citizens aged 20-69 years across Japan, and data from 8457 respondents were analysed. The data analysis was performed in two steps: 1) estimating individual WTP and 2) exploring factors affecting WTP. The results demonstrated that individual WTP was 135,798 ± 82,840 (mean ± standard deviation) JPY per person for a lifetime. The WTP increased when information was provided in the form of short texts and graphics for those proactive about nature conservation, but increased more when video information was provided to those reactive about nature conservation. The study shows that ecosystem conservation groups need to adapt the amount and format of information for target audiences (e.g. Generation Z youth, who are more sustainability-oriented and prefer to accomplish more in less time).

Limited stomatal regulation of the largest-size class of Dryobalanops aromatica in a Bornean tropical rainforest in response to artificial soil moisture reduction.

The physiological response of trees to drought is crucial for understanding the risk of mortality and its feedbacks to climate under the increase in droughts due to climate change, especially for the largest trees in tropical rainforests because of their large contribution to total carbon storage and water use. We determined the response of the mean canopy stomatal conductance per unit leaf area (gs) and whole-tree hydraulic conductance (Gp) of the largest individuals (38-53 m in height) of a typical canopy tree species in a Bornean tropical rainforest, Dryobalanops aromatica C.F.Gaertn., to soil moisture reduction by a 4-month rainfall exclusion experiment (REE) based on the measurements of sap flux and leaf water potentials at midday and dawn. In the mesic condition, the gs at vapor pressure deficit (D) = 1 kPa (gsref) was small compared with the reported values in various biomes. The sensitivity of gs to D (m) at a given gsref (m/gsref) was ≥ 0.6 irrespective of soil moisture conditions, indicating intrinsically sensitive stomatal control with increasing D. The REE caused greater soil drought and decreased the mean leaf water potentials at midday and dawn to the more negative values than the control under the relatively dry conditions due to natural reduction in rainfall. However, the REE did not cause a greater decrease in gs nor any clear alteration in the sensitivity of gs to D compared with the control, and induced greater decreases in Gp during REE than the control. Thus, though the small gs and the sensitive stomatal response to D indicate the water saving characteristics of the studied trees under usual mesic conditions, their limited stomatal regulation in response to soil drought by REE and the resulting decline in Gp might suggest a poor resistance to the unusually severe drought expected in the future.

When and why do trees begin to decrease their resource allocation to apical growth? The importance of the reproductive onset.

Trees reduce their allocation to apical growth compared with that to radial growth during later life stages. This has often been attributed to hydraulic and mechanical limitations; however, a growth-reproduction tradeoff might also play an important role. To test whether the height-diameter (H-D) relationship in trees changes with the timing of the onset of reproduction, we analyzed the H-D relationship of 13 deciduous broad-leaved tree species in a Japanese old-growth temperate forest using linear and segmented-linear regression models. These models showed a better fit than common continuous models (simple allometry and saturating curve). For 11 out of 13 species having break points on the H-D lines, we assessed whether the height at the breakpoint (BPH) was related to the height at the onset of reproduction determined by multiyear observatory records on several trees. Although BPH estimates for these 11 species were highly variable, most were within 3.1 m of the stable flowering height (staFLH), or the height at which trees achieve the ability to flower regardless of their growth conditions. The interspecies mean value of the difference between staFLH and BPH was only 45 cm, which suggested a causal relationship between these parameters. BPHs of nine out of 11 species were within the canopy layer and, for the two remaining species, were within the subcanopy layer. These results suggest that several species in this forest begin to reduce their allocation to apical growth around the canopy layer at the onset of stable reproduction.

A global meta-analysis of the relative extent of intraspecific trait variation in plant communities.

Recent studies have shown that accounting for intraspecific trait variation (ITV) may better address major questions in community ecology. However, a general picture of the relative extent of ITV compared to interspecific trait variation in plant communities is still missing. Here, we conducted a meta-analysis of the relative extent of ITV within and among plant communities worldwide, using a data set encompassing 629 communities (plots) and 36 functional traits. Overall, ITV accounted for 25% of the total trait variation within communities and 32% of the total trait variation among communities on average. The relative extent of ITV tended to be greater for whole-plant (e.g. plant height) vs. organ-level traits and for leaf chemical (e.g. leaf N and P concentration) vs. leaf morphological (e.g. leaf area and thickness) traits. The relative amount of ITV decreased with increasing species richness and spatial extent, but did not vary with plant growth form or climate. These results highlight global patterns in the relative importance of ITV in plant communities, providing practical guidelines for when researchers should include ITV in trait-based community and ecosystem studies.

Estimating bee distributions and their functional range to map important areas for protecting bee species and their functions.

The decline of wild bee populations causes the decline of bee-pollinated plant populations through the deterioration of pollination services. Since high bee species richness generally involves high functional group diversity, protecting areas of high bee species richness will help to maintain pollination services for plants. However, those areas do not always include the habitats of bee species with specialized functions that expand the range of plants being pollinated. To map important areas for protecting native bee species and their functions, we estimated the distributions and functional range of 13 bumble bee species and 1 honey bee species in Japan. The distributions were estimated from an ensemble of six species distribution models using bee occurrence data and environmental data. The functional range of bee species was estimated by combining the estimated distributions and proboscis length, which frequently corresponds to the floral shape of the plant species they pollinate. The estimated species richness was high in western Hokkaido and the estimated functional range was wide in central Honshu. Our method is useful to see whether areas important for high species richness of pollinators differ from those for rare species or their functions.

Variable effects of vegetation characteristics on a recreation service depending on natural and social environment.

In this study, we examined roles of three vegetation characteristics in provisioning of a recreation service by applying a machine-learning method to 4,708,229 spatially-explicit records of hiking activity in Japan. Then, expected impacts of land-use changes assessed and mapped based on the model. Associations between a recreation service and three vegetation characteristics were considerably variable depending on the social and natural environment such as accessibility and altitude. As a consequence, expected impacts of unit changes in vegetation characteristics on the service flow were considerably heterogeneous throughout the study area. The signs (positive or negative) of the impact can be reversed depending on the contexts even among nearby sites. Such notable but variable contributions of vegetation on a recreation service should be carefully reflected in landscape management. Even moderate changes in either the quantity or quality of vegetation can have a considerable impact on the frequency of hiking activity. Landscape management for promotion of the recreation service should be carefully designed for each locality on the grounds of the context-dependent effects of vegetation.

Deep learning increases the availability of organism photographs taken by citizens in citizen science programs.

Citizen science programs using organism photographs have become popular, but there are two problems related to photographs. One problem is the low quality of photographs. It is laborious to identify species in photographs taken outdoors because they are out of focus, partially invisible, or under different lighting conditions. The other is difficulty for non-experts to identify species. Organisms usually have interspecific similarity and intraspecific variation, which hinder species identification by non-experts. Deep learning solves these problems and increases the availability of organism photographs. We trained a deep convolutional neural network, Xception, to identify bee species using various quality of bee photographs that were taken by citizens. These bees belonged to two honey bee species and 10 bumble bee species with interspecific similarity and intraspecific variation. We investigated the accuracy of species identification by biologists and deep learning. The accuracy of species identification by Xception (83.4%) was much higher than that of biologists (53.7%). When we grouped bee photographs by different colors resulting from intraspecific variation in addition to species, the accuracy of species identification by Xception increased to 84.7%. The collaboration with deep learning and experts will increase the reliability of species identification and their use for scientific researches.

Assessing the Cooling and Air Pollution Tolerance among Urban Tree Species in a Tropical Climate.

We present the results of classifying plants at species level that can tolerate air pollution, provide cooling, and simultaneously survive and thrive in urban environments. For this purpose, we estimated the air pollution tolerance index (APTI) and anticipated performance index (API) of several species growing in a park located in central Bangkok, Thailand. The cooling effect was quantified by calculating the reduction in soil and air temperatures. Melaleuca quinquenervia (Cav.) S.T. Blake, Albizia saman (Jacq.) Merr., Chukrasia tabularis A. Juss. had the highest API score and were able to substantially reduce the temperature and were in a group of highly recommended species which also included other species like A. saman, C. tabularis, Tabebuia rosea (Bertol.) Bertero ex A. DC., Dalbergia cochinchinensis Pierre etc. Species from both evergreen and deciduous habitat were able to provide ambient cooling but were vulnerable to air pollution and included Elaeocarpus grandifloras Sm. and Bauhinia purpurea L. However, there were other species which had a high air pollution tolerance but failed to provide adequate cooling, such as Hopea odorata Roxb. and Millingtonia hortensis L.f. The results would be of interest to urban greenspace landscapers in such climates while selecting suitable species that can provide multiple ecosystem services ranging from air pollution tolerance to temperature reduction without reducing plant vitality.

Interspecific variation in mortality and growth and changes in their relationship with size class in an old-growth temperate forest.

Understanding trade-offs between demographic parameters is crucial when investigating community assembly rules in high-diversity forests. To this end, we estimated mortality and growth parameters, and correlations among them, across entire size classes for 17 tree species (Betula, Carpinus, Fagus, Quercus, Castanea, Acer, Cerasus, Swida, Kalopanax, and Styrax) using a dataset over 18 years obtained from an old-growth forest in Japan.Size classes were represented by 12 categories determined by age, height, and diameter at breast height (DBH) from new seedlings to stems of DBH >85 cm. We derived the annual mortality and growth for each species and class using estimates of transition probabilities between classes. Trade-offs or synergies in growth and survival among species per size class were analyzed with and without the inclusion of phylogenetic relationships.Annual mortality showed U-shaped patterns across size classes for species that could potentially reach a DBH ≥55 cm: 0.2-0.98 for seedlings, 0.002-0.01 at DBH 35-45 cm, and ca. 0.01 at DBH ≥55 cm. Other species demonstrated monotonically decreasing mortality toward specific maximum size classes. When phylogenetic information was included in analyses, the correlations between survival and growth changed across size classes were significant for some classes: As an overall tendency, synergy was observed in growth and survival for seedling to sapling classes, trade-offs for juvenile to DBH 15-25 cm classes, and synergy again for larger classes. When phylogenetic information was not included, a significant trade-off was observed only at DBH 5-15 cm. Synthesis. Trade-offs at intermediate classes imply differentiation in demographic characteristics related to life history strategies. However, evolutionarily obtained demographic characteristics are not substantial drivers of niche differentiation in the study area. The polylemma of mortality, growth, and other parameters such as the onset of reproduction may also be important factors driving species-specific demographic traits.

Neighborhood aggregation effect and its effective scale on reproductive success in Shorea laxa (Dipterocarpaceae).

This study investigated whether reproductive success is affected by the intensity of neighborhood aggregation of adults in the tropical tree Shorea laxa. We focused on three processes in the early reproductive stages: seed maturation; seed survival (categorizing sound seed, predation by insects and predation by vertebrates) in pre-seed dispersal; and seedling survival in the post-seed dispersal stage. We used a model selection procedure to examine the aggregation effect on reproductive success. The intensity of neighborhood aggregation was represented by the neighborhood aggregation index, which contains the adult number within a specific radius and the distances to neighboring adults (weight of proximity). Then, we evaluated the models exhaustively with the aggregation index having different scales (radius and weight of proximity) to assess the scale on which aggregation had significant effects. In particular, the best effective neighborhood scale, which is defined as the scale of the index in the model with minimum Akaike information criterion, was examined to compare those scales among processes. We found that the probability of seed maturation, seed survival and seedling survival decreased with the aggregation index at specific scales. This suggests that aggregation influenced reproductive success negatively in both the pre- and post-seed dispersal stages. However, the selected radii differed among processes: >200 and 130 m in pre- and post-seed dispersal stages, respectively. The selected weight of proximity also seemed to have a weak effect on all processes and was not different among processes.

Estimating possible bumblebee range shifts in response to climate and land cover changes.

Wild bee decline has been reported worldwide. Some bumblebee species (Bombus spp.) have declined in Europe and North America, and their ranges have shrunk due to climate and land cover changes. In countries with limited historical and current occurrence data, it is often difficult to investigate bumblebee range shifts. Here we estimated the past/present distributions of six major bumblebee species in Japan with species distribution modeling using current occurrence data and past/present climate and land cover data. The differences identified between estimated past and present distributions indicate possible range shifts. The estimated ranges of B. diversus, B. hypocrita, B. ignitus, B. honshuensis, and B. beaticola shrank over the past 26 years, but that of B. ardens expanded. The lower altitudinal limits of the estimated ranges became higher as temperature increased. When focusing on the effects of land cover change, the estimated range of B. diversus slightly shrank due to an increase in forest area. Such increase in forest area may result from the abandonment of agricultural lands and the extension of the rotation time of planted coniferous forests and secondary forests. Managing old planted coniferous forests and secondary forests will be key to bumblebee conservation for adaptation to climate change.

Spatial distribution of the basidiocarps of aphyllophoraceous fungi in a tropical rainforest on Borneo Island, Malaysia.

The spatial distribution of basidiocarps provides much information on the dispersal abilities, habitat preferences, and inter- and intraspecific interactions of aphyllophoraceous fungi. To reveal the spatial distribution and resource utilization patterns of aphyllophoraceous fungi in Malaysia, we conducted field observations in a primary forest in 2006 and analyzed the relationships between the abundance of eight dominant fungal species and various environmental factors. The topographical characteristics were significantly patchily distributed at the 100-m scale, whereas woody debris and most fungal species were distributed randomly. Although the dominant fungal species differed among the decay classes and diameters of the woody debris, the abundance of a few dominant species was significantly correlated with environmental factors. Although the latter factors might affect the spatial distribution of these fungi, the effects appear to be so small that they would not create an aggregated distribution at a few 100-m scales.

Leaf herbivory and decomposability in a Malaysian tropical rain forest.

There is accumulating evidence that similar suites of plant traits may affect leaf palatability and leaf litter decomposability. However, the possible association between leaf herbivory and litter decomposition rates across species in species-diverse natural ecosystems such as tropical rain forests remains unexplored, despite its importance in estimating the herbivory effects on carbon and nutrient cycling of ecosystems. We found no strong association between leaf herbivory and litter decomposition rates across 40 tree species in a Malaysian tropical rain forest, even though the leaf and litter traits were tightly correlated. This is because the leaf and litter traits related to herbivory and decomposition rates in the field were inconsistent. Leaf toughness accounted for only a small part of the variation in the herbivory rate, whereas a number of litter traits (the leaf mass per area, lignin to nitrogen ratio, and condensed tannin concentration) accurately predicted the decomposition rate across species. These results suggest that herbivory rate across species may not be strongly related to single leaf traits, probably because plant-herbivore interactions in tropical rain forests are highly diverse; on the other hand, plant-decomposer interactions are less specific and can be governed by litter chemicals. We also investigated two factors, phylogeny and tree functional types, that could affect the relationship between herbivory and decomposition across species. Phylogenetic relatedness among the species did not affect the relationship between herbivory and decomposition. In contrast, when the plants were segregated according to their leaf emergence pattern, we found a significant positive relationship between herbivory and decomposition rates for continuous-leafing species. In these species, the condensed tannin to N ratios in leaves and litter were related to herbivory and decomposition rates, respectively. However, we did not observe a similar trend for synchronous-leafing species. These results suggest that the relationship between herbivory and decomposition may be more greatly affected by functional types than by phylogenetic relatedness among species. In conclusion, our results suggest that well-defended leaves are not necessarily less decomposable litter in a tropical rain forest community, implying that herbivory may not generate positive feedback for carbon and nutrient cycling in this type of ecosystem.

Population maintenance of the short-lived shrub Sambucus in a deciduous forest.

This study quantitatively clarifies the life history of a shrub, Sambucus racemosa ssp. sieboldiana, in an old-growth forest, the Ogawa Forest Reserve, Japan, by a demographic approach using a projection matrix model that incorporates interactions between demographic parameters and canopy height dynamics. S. racemosa is a common deciduous shrub in central Japan and is known to grow predominantly at forest edges or roadsides. This indicates that it is a highly light-demanding species, and occurrence in gaps in old-growth stands suggests its "fugitive," gap-dependent life history in old-growth forests. We found that one distinctive feature of this species was that its seedlings can survive well in shaded conditions by alternating stems every year like perennial herb species. Matrix model analyses demonstrated that S. racemosa can continuously regenerate under the present disturbance regime of this forest and is highly adaptable to the structural dynamics of the old-growth forest. The maturity of S. racemosa shrubs depends on their size, and nearly all (>90%) of the mature (reproducing) individuals were found in gaps or near gaps. But wide seed dispersal by birds and the ability to form both seed banks and seedling banks, the latter of which has been regarded as a common characteristic of shade-tolerant climax species, probably increase the species' chances to encounter canopy gaps. Dynamic-canopied matrix models showed that the greatest elasticity is with shaded seedling survival. The frequent stem alternation of shaded seedlings often makes the growth rate negative, but the survival rate of seedlings in low light awaiting new gap creation is remarkably high (0.93 yr(-1)). The lower survival rate of the larger individuals and smaller minimum size to start reproduction than other canopy or subcanopy shade-tolerant species indicate that S. racemosa has the potential to reproduce before the closure of the encountered gaps and to complete its life history rapidly.

Utilization of photographs taken by citizens for estimating bumblebee distributions.

Citizen science is a powerful tool for collecting large volumes of observational data on various species. These data are used to estimate distributions using environmental factors with Species Distribution Models (SDM). However, if citizens are inexperienced in recognizing organisms, they may report different species as the subject species. Here we show nation-wide bumblebee distributions using photographs taken by citizens in our project, and estimated distributions for six bumblebee species using land use, climate, and altitude data with SDM. We identified species from photographic images, and took their locations from GPS data of photographs or the text in e-mails. When we compared our data with conventional data for specimens in the Global Biodiversity Information Facility (GBIF), we found that the volume and the number of species were larger, and the bias of spatial range was lower, than those of GBIF. Our estimated distributions were more consistent with bumblebee distributions reported in previous studies than with those of GBIF. Our method was effective for collecting distribution data, and estimating distributions with SDM. The estimated SDM allows us to predict the previous and future species distributions, and to develop conservation policies taking account of future city planning and/or global climate changes.

Effects of rainfall exclusion on leaf gas exchange traits and osmotic adjustment in mature canopy trees of Dryobalanops aromatica (Dipterocarpaceae) in a Malaysian tropical rain forest.

Climate change exposes vegetation to unusual levels of drought, risking a decline in productivity and an increase in mortality. It still remains unclear how trees and forests respond to such unusual drought, particularly Southeast Asian tropical rain forests. To understand leaf ecophysiological responses of tropical rain forest trees to soil drying, a rainfall exclusion experiment was conducted on mature canopy trees of Dryobalanops aromatica Gaertn.f. (Dipterocarpaceae) for 4 months in an aseasonal tropical rain forest in Sarawak, Malaysia. The rainfall was intercepted by using a soft vinyl chloride sheet. We compared the three control and three treatment trees with respect to leaf water use at the top of the crown, including stomatal conductance (gsmax), photosynthesis (Amax), leaf water potential (predawn: Ψpre; midday: Ψmid), leaf water potential at turgor loss point (πtlp), osmotic potential at full turgor (π100) and a bulk modulus of elasticity (ε). Measurements were taken using tree-tower and canopy-crane systems. During the experiment, the treatment trees suffered drought stress without evidence of canopy dieback in comparison with the control trees; e.g., Ψpre and Ψmid decreased with soil drying. Minimum values of Ψmid in the treatment trees decreased during the experiment, and were lower than πtlp in the control trees. However, the treatment trees also decreased their πtlp by osmotic adjustment, and the values were lower than the minimum values of their Ψmid. In addition, the treatment trees maintained gs and Amax especially in the morning, though at midday, values decreased to half those of the control trees. Decreasing leaf water potential by osmotic adjustment to maintain gs and Amax under soil drying in treatment trees was considered to represent anisohydric behavior. These results suggest that D. aromatica may have high leaf adaptability to drought by regulating leaf water consumption and maintaining turgor pressure to improve its leaf water relations.

Detecting latitudinal and altitudinal expansion of invasive bamboo Phyllostachys edulis and Phyllostachys bambusoides (Poaceae) in Japan to project potential habitats under 1.5°C-4.0°C global warming.

Rapid expansion of exotic bamboos has lowered species diversity in Japan's ecosystems by hampering native plant growth. The invasive potential of bamboo, facilitated by global warming, may also affect other countries with developing bamboo industries. We examined past (1975-1980) and recent (2012) distributions of major exotic bamboos (Phyllostachys edulis and P. bambusoides) in areas adjacent to 145 weather stations in central and northern Japan. Bamboo stands have been established at 17 sites along the latitudinal and altitudinal distributional limit during the last three decades. Ecological niche modeling indicated that temperature had a strong influence on bamboo distribution. Using mean annual temperature and sun radiation data, we reproduced bamboo distribution (accuracy = 0.93 and AUC (area under the receiver operating characteristic curve) = 0.92). These results infer that exotic bamboo distribution has shifted northward and upslope, in association with recent climate warming. Then, we simulated future climate data and projected the climate change impact on the potential habitat distribution of invasive bamboos under different temperature increases (i.e., 1.5°C, 2.0°C, 3.0°C, and 4.0°C) relative to the preindustrial period. Potential habitats in central and northern Japan were estimated to increase from 35% under the current climate (1980-2000) to 46%-48%, 51%-54%, 61%-67%, and 77%-83% under 1.5°C, 2.0°C, 3.0°C, and 4.0°C warming levels, respectively. These infer that the risk areas can increase by 1.3 times even under a 1.5°C scenario and expand by 2.3 times under a 4.0°C scenario. For sustainable ecosystem management, both mitigation and adaptation are necessary: bamboo planting must be carefully monitored in predicted potential habitats, which covers most of Japan.

Biodiversity conservation values of fragmented communally reserved forests, managed by indigenous people, in a human-modified landscape in Borneo.

This study explored the conservation values of communally reserved forests (CRFs), which local indigenous communities deliberately preserve within their area of shifting cultivation. In the current landscape of rural Borneo, CRFs are the only option for conservation because other forested areas have already been logged or transformed into plantations. By analyzing their alpha and beta diversity, we investigated how these forests can contribute to restore regional biodiversity. Although CRFs were fragmented and some had been disturbed in the past, their tree species diversity was high and equivalent to that of primary forests. The species composition of intact forests and forests disturbed in the past did not differ clearly, which indicates that past logging was not intensive. All CRFs contained unique and endangered species, which are on the IUCN Red List, Sarawak protected plants, or both. On the other hand, the forest size structure differed between disturbed and intact CRFs, with the disturbed CRFs consisting of relatively smaller trees. Although the beta diversity among CRFs was also high, we found a high contribution of species replacement (turnover), but not of richness difference, in the total beta diversity. This suggests that all CRFs have a conservation value for restoring the overall regional biodiversity. Therefore, for maintaining the regional species diversity and endangered species, it would be suitable to design a conservation target into all CRFs.

Quantifying the evidence for biodiversity effects on ecosystem functioning and services.

Concern is growing about the consequences of biodiversity loss for ecosystem functioning, for the provision of ecosystem services, and for human well being. Experimental evidence for a relationship between biodiversity and ecosystem process rates is compelling, but the issue remains contentious. Here, we present the first rigorous quantitative assessment of this relationship through meta-analysis of experimental work spanning 50 years to June 2004. We analysed 446 measures of biodiversity effects (252 in grasslands), 319 of which involved primary producer manipulations or measurements. Our analyses show that: biodiversity effects are weaker if biodiversity manipulations are less well controlled; effects of biodiversity change on processes are weaker at the ecosystem compared with the community level and are negative at the population level; productivity-related effects decline with increasing number of trophic links between those elements manipulated and those measured; biodiversity effects on stability measures ('insurance' effects) are not stronger than biodiversity effects on performance measures. For those ecosystem services which could be assessed here, there is clear evidence that biodiversity has positive effects on most. Whilst such patterns should be further confirmed, a precautionary approach to biodiversity management would seem prudent in the meantime.