Showing papers by "Andy Hector published in 2016"
United States Geological Survey1, Wake Forest University2, University of Minnesota3, Utah State University4, Martin Luther University of Halle-Wittenberg5, Utrecht University6, University of Oldenburg7, University of Tartu8, University of Washington9, Trinity College, Dublin10, Imperial College London11, University of Wisconsin-Madison12, University of Colorado Boulder13, United States Department of Agriculture14, Queensland University of Technology15, University of Maryland, College Park16, University of Oxford17, University of Nebraska–Lincoln18, University of Guelph19, La Trobe University20, Commonwealth Scientific and Industrial Research Organisation21, Colorado State University22
TL;DR: It is found that an integrative model has substantially higher explanatory power than traditional bivariate analyses and several surprising findings that conflict with classical models are revealed.
Abstract: How ecosystem productivity and species richness are interrelated is one of the most debated subjects in the history of ecology. Decades of intensive study have yet to discern the actual mechanisms behind observed global patterns. Here, by integrating the predictions from multiple theories into a single model and using data from 1,126 grassland plots spanning five continents, we detect the clear signals of numerous underlying mechanisms linking productivity and richness. We find that an integrative model has substantially higher explanatory power than traditional bivariate analyses. In addition, the specific results unveil several surprising findings that conflict with classical models. These include the isolation of a strong and consistent enhancement of productivity by richness, an effect in striking contrast with superficial data patterns. Also revealed is a consistent importance of competition across the full range of productivity values, in direct conflict with some (but not all) proposed models. The promotion of local richness by macroecological gradients in climatic favourability, generally seen as a competing hypothesis, is also found to be important in our analysis. The results demonstrate that an integrative modelling approach leads to a major advance in our ability to discern the underlying processes operating in ecological systems.
494 citations
Journal Article•
TL;DR: In this paper, by integrating the predictions from multiple theories into a single model and using data from 1,126 grassland plots spanning five continents, the authors detect the clear signals of numerous underlying mechanisms linking productivity and richness.
Abstract: How ecosystem productivity and species richness are interrelated is one of the most debated subjects in the history of ecology1. Decades of intensive study have yet to discern the actual mechanisms behind observed global patterns2, 3. Here, by integrating the predictions from multiple theories into a single model and using data from 1,126 grassland plots spanning five continents, we detect the clear signals of numerous underlying mechanisms linking productivity and richness. We find that an integrative model has substantially higher explanatory power than traditional bivariate analyses. In addition, the specific results unveil several surprising findings that conflict with classical models4, 5, 6, 7. These include the isolation of a strong and consistent enhancement of productivity by richness, an effect in striking contrast with superficial data patterns. Also revealed is a consistent importance of competition across the full range of productivity values, in direct conflict with some (but not all) proposed models. The promotion of local richness by macroecological gradients in climatic favourability, generally seen as a competing hypothesis8, is also found to be important in our analysis. The results demonstrate that an integrative modelling approach leads to a major advance in our ability to discern the underlying processes operating in ecological systems.
453 citations
Ghent University1, Helmholtz Centre for Environmental Research - UFZ2, Institut national de la recherche agronomique3, National Institute of Amazonian Research4, Florida International University5, Université du Québec à Montréal6, Martin Luther University of Halle-Wittenberg7, University of Bordeaux8, University of Zurich9, University of Freiburg10, ETH Zurich11, University of Oxford12, Royal Holloway, University of London13, Centre national de la recherche scientifique14, University of Sassari15, Université du Québec en Outaouais16, Katholieke Universiteit Leuven17, Smithsonian Environmental Research Center18, University of Western Australia19, Université catholique de Louvain20, Smithsonian Tropical Research Institute21, McGill University22, University of Minnesota23, University of Western Sydney24, Bangor University25, Swedish University of Agricultural Sciences26
TL;DR: Early results on the carbon sequestration and pest resistance potential of more diverse plantations are highlighted and suggestions are made for new, innovative experiments in understudied regions to complement the existing network.
Abstract: The area of forest plantations is increasing worldwide helping to meet timber demand and protect natural forests. However, with global change, monospecific plantations are increasingly vulnerable to abiotic and biotic disturbances. As an adaption measure we need to move to plantations that are more diverse in genotypes, species, and structure, with a design underpinned by science. TreeDivNet, a global network of tree diversity experiments, responds to this need by assessing the advantages and disadvantages of mixed species plantations. The network currently consists of 18 experiments, distributed over 36 sites and five ecoregions. With plantations 1-15 years old, TreeDivNet can already provide relevant data for forest policy and management. In this paper, we highlight some early results on the carbon sequestration and pest resistance potential of more diverse plantations. Finally, suggestions are made for new, innovative experiments in understudied regions to complement the existing network.
205 citations
University of Bern1, University of Freiburg2, Ghent University3, Leipzig University4, University of Alcalá5, University of Oxford6, Institut national de la recherche agronomique7, Martin Luther University of Halle-Wittenberg8, Ştefan cel Mare University of Suceava9, University of Florence10, University of Liège11, University of Cambridge12, Spanish National Research Council13, University of Copenhagen14, Katholieke Universiteit Leuven15, Los Alamos National Laboratory16, University of Montpellier17, University of Warsaw18, Royal Holloway, University of London19, Swedish University of Agricultural Sciences20, King Juan Carlos University21
TL;DR: Simulations demonstrate that jack-of-all-trades effects occur whenever species effects on different functions are not perfectly correlated, meaning they may contribute to diversity–multifunctionality relationships in many of the world's ecosystems.
Abstract: There is considerable evidence that biodiversity promotes multiple ecosystem functions (multifunctionality), thus ensuring the delivery of ecosystem services important for human well-being. However, the mechanisms underlying this relationship are poorly understood, especially in natural ecosystems. We develop a novel approach to partition biodiversity effects on multifunctionality into three mechanisms and apply this to European forest data. We show that throughout Europe, tree diversity is positively related with multifunctionality when moderate levels of functioning are required, but negatively when very high function levels are desired. For two well-known mechanisms, ‘complementarity’ and ‘selection’, we detect only minor effects on multifunctionality. Instead a third, so far overlooked mechanism, the ‘jack-of-all-trades’ effect, caused by the averaging of individual species effects on function, drives observed patterns. Simulations demonstrate that jack-of-all-trades effects occur whenever species effects on different functions are not perfectly correlated, meaning they may contribute to diversity–multifunctionality relationships in many of the world’s ecosystems.
187 citations
Leipzig University1, University of Minnesota2, University College Dublin3, Martin Luther University of Halle-Wittenberg4, University of Jena5, Wageningen University and Research Centre6, Iowa State University7, University of Bayreuth8, University of Zurich9, Swansea University10, Utrecht University11, University of Oxford12, University of Greifswald13, Sewanee: The University of the South14, Centre national de la recherche scientifique15, Technische Universität München16, Yokohama National University17, Columbia University18, Swedish University of Agricultural Sciences19, Agricultural Research Service20, Helmholtz Centre for Environmental Research - UFZ21
TL;DR: It is found that diversity and the complementarity of species are important regulators of grassland ecosystem productivity, regardless of changes in other drivers of ecosystem function.
Abstract: Global change drivers are rapidly altering resource availability and biodiversity. While there is consensus that greater biodiversity increases the functioning of ecosystems, the extent to which biodiversity buffers ecosystem productivity in response to changes in resource availability remains unclear. We use data from 16 grassland experiments across North America and Europe that manipulated plant species richness and one of two essential resources—soil nutrients or water—to assess the direction and strength of the interaction between plant diversity and resource alteration on above-ground productivity and net biodiversity, complementarity, and selection effects. Despite strong increases in productivity with nutrient addition and decreases in productivity with drought, we found that resource alterations did not alter biodiversity–ecosystem functioning relationships. Our results suggest that these relationships are largely determined by increases in complementarity effects along plant species richness gradients. Although nutrient addition reduced complementarity effects at high diversity, this appears to be due to high biomass in monocultures under nutrient enrichment. Our results indicate that diversity and the complementarity of species are important regulators of grassland ecosystem productivity, regardless of changes in other drivers of ecosystem function.
167 citations
TL;DR: It is argued that niche theory predicts that diversity–functioning relationships are likely to be stronger (and require more species) in the field than in simplified experimental settings, but that while many of the biological processes that promote coexistence can also generate diversity– function relationships, there is no simple mapping between the two.
Abstract: Biodiversity experiments have generated robust empirical results supporting the hypothesis that ecosystems function better when they contain more species. Given that ecosystems provide services that are valued by humans, this inevitably suggests that the loss of species from natural ecosystems could diminish their value. This raises two important questions. First, will experimental results translate into the real world, where species are being lost at an alarming rate? And second, what are the benefits and pitfalls of such valuation exercises? We argue that the empirical results obtained in experiments are entirely consistent with well-established theories of species coexistence. We then examine the current body of work through the lens of niche theory and highlight where closer links with theory could open up opportunities for future research. We argue that niche theory predicts that diversity–functioning relationships are likely to be stronger (and require more species) in the field than in simplified experimental settings. However, we caution that while many of the biological processes that promote coexistence can also generate diversity–function relationships, there is no simple mapping between the two. This implies that valuation exercises need to proceed with care.
99 citations
TL;DR: The results reveal the species differences required for potential insurance effects including a trade-off in which species with denser wood have lower growth rates but higher survival, and average survival rates were extreme in monocultures than mixtures.
Abstract: One of the main environmental threats in the tropics is selective logging, which has degraded large areas of forest. In southeast Asia, enrichment planting with seedlings of the dominant group of dipterocarp tree species aims to accelerate restoration of forest structure and functioning. The role of tree diversity in forest restoration is still unclear, but the ‘insurance hypothesis’ predicts that in temporally and spatially varying environments planting mixtures may stabilize functioning owing to differences in species traits and ecologies. To test for potential insurance effects, we analyse the patterns of seedling mortality and growth in monoculture and mixture plots over the first decade of the Sabah biodiversity experiment. Our results reveal the species differences required for potential insurance effects including a trade-off in which species with denser wood have lower growth rates but higher survival. This trade-off was consistent over time during the first decade, but growth and mortality varied spatially across our 500 ha experiment with species responding to changing conditions in different ways. Overall, average survival rates were extreme in monocultures than mixtures consistent with a potential insurance effect in which monocultures of poorly surviving species risk recruitment failure, whereas monocultures of species with high survival have rates of self-thinning that are potentially wasteful when seedling stocks are limited. Longer-term monitoring as species interactions strengthen will be needed to more comprehensively test to what degree mixtures of species spread risk and use limited seedling stocks more efficiently to increase diversity and restore ecosystem structure and functioning.
38 citations
TL;DR: The results suggest that tree species richness in the litter layer can indirectly promote decomposition and nutrient cycling via positive non-additive mixture effects.
Abstract: Tree diversity is considered to influence decomposition either by changing environmental conditions or by non-additive litter mixture effects. Thus, we examined the influence of tree species richness, forest age and environmental factors on single-species decomposition, and tested the hypothesis that high litter species diversity induces predominantly positive non-additive mixture effects on decomposition processes. Decomposition trials using litter bags were performed in subtropical forests in China. Plot-specific decompositions rates of the abundant species Schima superba were related to environmental factors across 27 forest stands differing in age and tree species richness. Effects of litter species diversity on decomposition and N loss was assessed based on 27 plot-specific litter mixtures comprising 7 to 17 species. Decomposition rate of Schima superba leaf litter was mainly affected by stand characteristics and microclimate but not tree diversity. Two thirds of plot-specific litter mixtures showed a positive non-additive mixture effect whose strength was marginally positively influenced by litter species richness. Tree diversity at stand level does not directly influence decomposition of a common litter substrate. However, our results suggest that tree species richness in the litter layer can indirectly promote decomposition and nutrient cycling via positive non-additive mixture effects.
38 citations
TL;DR: The results suggest that changes in forest management will disproportionately affect certain understory taxa and that maintaining high diversity in temperate forests can promote the diversity of multiple taxa in the understory.
Abstract: Understory herbs and soil invertebrates play key roles in soil formation and nutrient cycling in forests. Studies suggest that diversity in the canopy and in the understory are positively associated, but these studies often confound the effects of tree species diversity with those of tree species identity and abiotic conditions. We combined extensive field sampling with structural equation modeling to evaluate the simultaneous effects of tree diversity on the species diversity of understory herbs, beetles, and earthworms. The diversity of earthworms and saproxylic beetles was directly and positively associated with tree diversity, presumably because species of both these taxa specialize on certain species of trees. Tree identity also strongly affected diversity in the understory, especially for herbs, likely as a result of interspecific differences in canopy light transmittance or litter decomposition rates. Our results suggest that changes in forest management will disproportionately affect certain understory taxa. For instance, changes in canopy diversity will affect the diversity of earthworms and saproxylic beetles more than changes in tree species composition, whereas the converse would be expected for understory herbs and detritivorous beetles. We conclude that the effects of tree diversity on understory taxa can vary from positive to negative and may affect biogeochemical cycling in temperate forests. Thus, maintaining high diversity in temperate forests can promote the diversity of multiple taxa in the understory.
23 citations
TL;DR: There was no reduction of genetic variation in naturally regenerating dipterocarp seedlings in areas of selective logging, which suggests that enrichment-planting strategies should adopt diverse mixtures that should promote levels of both species richness and genetic diversity within species.
Abstract: Background: The impact of logging and restoration on species diversity has been well studied in tropical forests. However, little is known about their effects on genetic diversity within species.Aims: We assess the degree of genetic diversity among dipterocarp seedlings used for enrichment planting of selectively logged forests in Sabah, Malaysia, and compare it with diversity in naturally regenerating seedlings.Methods: We sampled young leaf tissues from seedlings of Shorea leprosula and Parashorea malaanonan for DNA genotyping, using microsatellite markers.Results: The levels of genetic diversity (expected heterozygosity and rarefied allelic richness) of naturally regenerating seedlings were statistically indistinguishable among unlogged, once logged and repeatedly logged forest areas. Enrichment-planted seedlings of P. malaanonan exhibited similar levels of genetic diversity to naturally regenerating seedlings whereas those of S. leprosula had significantly lower genetic diversity than natural seedling...
19 citations
University of Reading1, Joint Nature Conservation Committee2, University of Southampton3, University of Sheffield4, University of Oxford5, Imperial College London6, University of Zurich7, Instituto Superior Técnico8, University of York9, University of California, Berkeley10, University College London11, Lüneburg University12
TL;DR: Mori's argument is somewhat surprising given the number of recent biodiversity–ecosystem functioning studies that incorporate aspects of both resistance and recovery (e.g., see references in [2,3]).
Abstract: A recent paper by Mori [1] states the need for a unification of studies of ‘engineering’ and ‘ecological’ frameworks of resilience. Engineering resilience focuses on the capacity of a system to recover to equilibrium following some kind of perturbation, while ecological resilience (ER) explicitly recognizes multiple stable states and the capacity for systems to resist ‘regime shifts’ between alternative states. We find Mori's argument somewhat surprising given the number of recent biodiversity–ecosystem functioning (B-EF) studies that incorporate aspects of both resistance and recovery (e.g., see references in [2,3]).
TL;DR: The results give little support to the hypothesis that dipterocarp seedlings growing in the shaded forest understorey benefit from being connected, through a common EcM network, to surrounding trees.
Abstract: Background: Connections between mature trees and seedlings via ectomycorrhizal (EcM) hyphal networks existing in dipterocarp-dominated tropical rain forests of South-east Asia could have strong implications for seedling growth and survival and the maintenance of high diversity in such forests.Aim: To test whether EcM hyphal network connections are important for the growth and survival of dipterocarp seedlings.Methods: We conducted four independent experiments that prevented contact of experimental seedlings with an EcM network by using a series of fine meshes and/or plastic barriers. We measured the growth and survival (and foliar δ13C in one experiment) of seedlings of six dipterocarp species over intervals ranging from 11 to 29 months.Results: Seedling growth (diameter, height or leaf number) was unaffected by exclusion from the EcM network in three experiments and there were no differences in foliar δ13C values in the fourth. Seedling survival was reduced following exclusion from the EcM network in one...
TL;DR: According to the results, soil water uptake complementarity could only occur through inherent (fundamental) specific differences in water uptake niches based on sapling specialization, while phenotypic adjustments to interspecific interaction or neighbor diversity are less important.
TL;DR: The results show that a generalist species is unique based on its response of NSC concentration to a gap opening, and emphasise that the ecology of these species needs to be further studied in the context of their physiology to support their effective use in large-scale forest restoration efforts.
Abstract: Background: Acclimation to light is a driver of tropical forest dynamics and key to understanding the coexistence of dipterocarps, and how their demographic rates and traits trade-off.Aims: We examined light niche divergence in six dipterocarp species and hypothesised that seedlings can be functionally grouped, and allocate resources to either growth or storage in response to light changes.Methods: A pot experiment was performed to measure size-specific growth rate, wood density and total non-structural carbohydrate (NSC) concentrations of dipterocarp seedlings exposed to a simulated gap opening.Results: Light-demanding species responded to a gap opening with increased growth and decreased wood density, whereas shade-tolerant species showed a greater relative increase in NSC concentration. Iditol – an alditol – was identified, and Dryobalanops lanceolata responded to a gap opening with a significantly smaller increase in alditol concentration compared to other species.Conclusions: We group light-demanding...