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Aim Plant functional groups are widely used in community ecology and earth system modelling to describe trait variation within and across plant communities. However, this approach rests on the assumption that functional groups explain a large proportion of trait variation among species. We test whether four commonly used plant functional groups represent variation in six ecologically important plant traits. Location Tundra biome. Time period Data collected between 1964 and 2016. Major taxa studied 295 tundra vascular plant species. Methods We compiled a database of six plant traits (plant height, leaf area, specific leaf area, leaf dry matter content, leaf nitrogen, seed mass) for tundra species. We examined the variation in species‐level trait expression explained by four traditional functional groups (evergreen shrubs, deciduous shrubs, graminoids, forbs), and whether variation explained was dependent upon the traits included in analysis. We further compared the explanatory power and species composition of functional groups to alternative classifications generated using post hoc clustering of species‐level traits. Results Traditional functional groups explained significant differences in trait expression, particularly amongst traits associated with resource economics, which were consistent across sites and at the biome scale. However, functional groups explained 19% of overall trait variation and poorly represented differences in traits associated with plant size. Post hoc classification of species did not correspond well with traditional functional groups, and explained twice as much variation in species‐level trait expression. Main conclusions Traditional functional groups only coarsely represent variation in well‐measured traits within tundra plant communities, and better explain resource economic traits than size‐related traits. We recommend caution when using functional group approaches to predict tundra vegetation change, or ecosystem functions relating to plant size, such as albedo or carbon storage. We argue that alternative classifications or direct use of specific plant traits could provide new insights for ecological prediction and modelling.

The majority of variation in six traits critical to the growth, survival and reproduction of plant species is thought to be organised along just two dimensions, corresponding to strategies of plant size and resource acquisition. However, it is unknown whether global plant trait relationships extend to climatic extremes, and if these interspecific relationships are confounded by trait variation within species. We test whether trait relationships extend to the cold extremes of life on Earth using the largest database of tundra plant traits yet compiled. We show that tundra plants demonstrate remarkably similar resource economic traits, but not size traits, compared to global distributions, and exhibit the same two dimensions of trait variation. Three quarters of trait variation occurs among species, mirroring global estimates of interspecific trait variation. Plant trait relationships are thus generalizable to the edge of global trait-space, informing prediction of plant community change in a warming world.

Flowering time is a trait that reflects the timing of specific resource requirements by plants. Consequently, several predictions have been made related to how species are assembled within communities according to flowering time. Strong overlap in flowering time among coexisting species may result from clustered abiotic resources, or contribute to improved pollination success. Conversely, low flowering time overlap (asynchrony) among coexisting species may reduce competition for soil, light, or pollinator resources and alleviate interspecific pollen transfer. Here, we present evidence that coexisting species in an old-field community generally overlap less in flowering time than expected under a commonly used and statistically validated null model. Flowering time asynchrony was more pronounced when abundance data were used (compared to presence-absence data), and when analyses focused on species that share bees as pollinators. Control and herbivore-exclusion plots did not differ in flowering time overlap, providing no evidence of the reduction in overlap expected to result from increased competition. Our results varied with the randomization algorithm used, emphasizing that the choice of algorithm can influence the outcome of null models. Our results varied between 2 years, with patterns being less clear in the second year, when both growing season and flowering times were contracted. Finally, we found evidence that further supports a previous finding that higher plot-level flowering time overlap was associated with higher proportions of introduced species. Reduced flowering time overlap among species in our focal community may promote coexistence via temporal niche differentiation and reduced competition for pollinators and other abiotic resources.

1 The prominently right-skewed distribution of species sizes has been the subject of a large literature in animal ecology, but has received comparatively little attention from plant ecologists. It is evident that not all explanations that have been offered for animals are directly applicable to plants. 2 We suggest three hypotheses that require further study in the interpretation of size-dependent species richness in plants. 3 These hypotheses are all based on mechanisms that have generated, for smaller plants, a greater historical opportunity for speciation: (i) large adult plant size confers significant adaptation primarily in habitat types that have been relatively uncommon in space, across evolutionary time; (ii) relatively small species are more widely differentiated from each other in the environmental qualities defining their niches, many of which are made possible by the mere presence of larger species residing in the same habitat; and (iii) compared with large species, smaller species generally have higher fecundity allocation, i.e. they can produce a greater number of offspring per unit plant size per unit time, which generally confers a higher premium under most circumstances of natural selection, thus generating a potentially greater number of descendant individuals, and derived species. 4 We discuss the implications of these hypotheses in addressing an underlying paradox in plant competition/coexistence theory, i.e. that large adult size is assumed to be the principal trait that confers competitive ability yet, even in those habitat types where competition is assumed to reach the highest levels of intensity within vegetation, the vast majority of the resident species are, nevertheless, relatively small.

Aim : Plant functional groups are widely used in community ecology and earth system modelling to describe trait variation within and across plant communities. However, this approach rests on the assumption that functional groups explain a large propor ‐ tion of trait variation among species. We test whether four commonly used plant functional groups represent variation in six ecologically important plant traits. Location : Tundra biome. Time period : Data collected between 1964 and 2016. Major taxa studied : 295 tundra vascular plant species. Methods : We compiled a database of six plant traits (plant height, leaf area, specific leaf area, leaf dry matter content, leaf nitrogen, seed mass) for tundra species. We exam ‐ ined the variation in species‐level trait expression explained by four traditional func ‐ tional groups (evergreen shrubs, deciduous shrubs, graminoids, forbs), and whether variation explained was dependent upon the traits included in analysis. We further compared the explanatory power and species composition of functional groups to al ‐ ternative classifications generated using post hoc clustering of species‐level traits. Results : Traditional functional groups explained significant differences in trait expres ‐ sion, particularly amongst traits associated with resource economics, which were con ‐ sistent across sites and at the biome scale. However, functional groups explained 19% of overall trait variation and poorly represented differences in traits associated with plant size. Post hoc classification of species did not correspond well with traditional functional groups, and explained twice as much variation in species‐level trait expression. Main conclusions : Traditional functional groups only coarsely represent variation in well‐measured traits within tundra plant communities, and better explain resource economic traits than size‐related traits. We recommend caution when using func ‐ tional group approaches to predict tundra vegetation change, or ecosystem func ‐ tions relating to plant size, such as albedo or carbon storage. We argue that alternative classifications or direct use of specific plant traits could provide new insights for ecological prediction and modelling.

Source at https://doi.org/10.1111/geb.12783 .

The majority of variation in six traits critical to the growth, survival and reproduction of plant species is thought to be organised along just two dimensions, corresponding to strategies of plant size and resource acquisition. However, it is unknown whether global plant trait relationships extend to climatic extremes, and if these interspecific relationships are confounded by trait variation within species. We test whether trait relationships extend to the cold extremes of life on Earth using the largest database of tundra plant traits yet compiled. We show that tundra plants demonstrate remarkably similar resource economic traits, but not size traits, compared to global distributions, and exhibit the same two dimensions of trait variation. Three quarters of trait variation occurs among species, mirroring global estimates of interspecific trait variation. Plant trait relationships are thus generalizable to the edge of global trait-space, informing prediction of plant community change in a warming world.

We tested the prediction that the main stems of four common deciduous tree species grow phototropically as saplings in the forest understory in response to variable canopy structure. Our predictions were confirmed forFraxinus americana,Acer saccharum, andUlmus americana, which all had stems bent in the direction of greatest canopy openness. The fourth species,Tilia americana, did not demonstrate the predicted phototropic main stem bending. Our tests also enabled us to distinguish between alternative bending strategies, confirming that for three species, bending is associated with a phototropic shade avoidance response rather than a nonphototropic shade avoidance response and is not a consequence of biomechanical constraints. Additionally, we found evidence that the four species differ in the canopy conditions under which their saplings grow, suggesting niche separation along understory light environment gradients.

The project was funded by the UK Natural Environment Research Council [ShrubTundra Project NE/M016323/1 (IMS, AB, HT, SAB, DG) & PhD Studentship NE/L002558/1 (HT)], the Synthesis Centre of the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig (DFG FZT 118; sTundra working group [postdoctoral fellowship to AB]). The study has been supported by the TRY initiative on plant traits (https://www.try-db.org). The TRY initiative and database is hosted at the Max Planck Institute for Biogeochemistry, Jena, Germany. TRY is currently supported by DIVERSITAS/Future Earth and the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig. Authors were supported by the Swedish Research Council (2015-00465) (DB) and (2015-00498) (EK), Marie Skłodowska Curie Actions (INCA 600398) (DB), the National Science Foundation (USA; RH), the Carlsberg Foundation (2013-01-0825) (SN), the Danish Council for Independent Research - Natural Sciences (DFF 4181-00565) (SN), European Research Council Synergy grant ERC-SyG-2013-610028 IMBALANCE-P (JP), University of Zurich Research Priority Program on Global Change and Biodiversity (GSS, MIG), the Office of Biological and Environmental Research in the U.S. Department of Energy's Office of Science (Next-Generation Ecosystem Experiments in the Arctic - NGEE Arctic) (CMI), NASA Arctic Boreal Vulnerability Experiment - ABoVE (LB, SG), The Swiss National Science Foundation (EF, AK, SV), NSERC Canada (EL, JJ, AP, BSPG, TZ), ArcticNet (EL, AP, GH), The US National Science Foundation Niwot Ridge LTER (DEB-1637686) (MJ), Long-Term Ecological Research (DEB-1234162) (PR) and Long-Term Research in Environmental Biology (DEB-1242531) (PR), Organismo Autónomo Parques Nacionales (JMN), the Arctic Research Centre, Denmark (JNN), RSF (#14-50-000290) (VO), the Polar Continental Shelf Program (AP, EL, GH), the Royal Canadian Mounted Police (GH), the Montagna di Torricchio Nature Reserve (Italy) (GC) the Academy of Finland Decisions no. 256991 (BF), JPI Climate no. 291581 (BF), and the BBSRC David Phillips Fellowship (BB/L02456X/1) (FTdV). Additional data and contributions were provided by L. Andreu-Hayles, P. Beck, A. Blach Overgaard, B. Bond-Lamberty, J. Craine, J. Dickie, S. Dullinger, B. Eberling, B. Enquist, J. Fang, K. Fleischer, H. Ford, G. Freschet, E. Garnier, D. Georges, R. Halfdan Jørgensen, K. Harper, S. Harrison, M. Harze, G. Henry, S. Jansen, J. Hille Ris Lambers, R. Klady, M. Kleyer, S. Kuleza, T. Lantz, A. Lavalle, F. Louault, B. Medlyn, R. Milla, J. Ordonez, C. Pladevall, H. Poorter, P. Poschlod, C. Price, N. Rueger, B. Sandel, F. Schweingruber, B. Shipley, A. Siefert, L. Street, K. Suding, J. Tremblay, M. Tremblay, M. Vellend, E. Weiher, C. Wirth, P. Wookey and I. Wright and the Royal Botanic Gardens Kew Seed Information Database (SID). We thank innumerable field technicians, logistics teams, graduate and undergraduate assistants for help with data collection, and parks, wildlife refuges, field stations, and the local and indigenous people for the opportunity to conduct research on their land. Finally, we thank the referees and editors for their constructive comments on the manuscript.

Numerous studies have reported a significant pattern of decreasing plant species richness across regional habitat gradients of increasing productivity or community biomass (Grace 1999, Waide et al. 1999). The interpretation of this pattern has been the focus of several hypotheses (see reviews by Rosenzweig and Abramsky 1993, Abrams 1995, Grace 1999, Aarssen 2001) but none that have emerged with strong supporting evidence. In this article we propose a simple method for evaluating one of these hypotheses and illustrate its application using published data.