David A. Wardle

Swedish University of Agricultural Sciences, Uppsala, Uppsala, Sweden

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Publications (263)1581.96 Total impact

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    ABSTRACT: Relative to vascular plants, little is known about what factors control bryophyte communities or how they respond to successional and environmental changes. Bryophytes are abundant in boreal forests, thus changes in moss community composition and functional traits (for example, moisture and nutrient content; rates of photosynthesis and respiration) may have important consequences for ecosystem processes and microfaunal communities. Through synthesis of previous work and new analyses integrating new and published data from a long term successional gradient in the boreal forest of northern Sweden, we provide a comprehensive view of the biotic factors (for example, vascular plant productivity, species composition, and diversity) and abiotic factors (for example, soil fertility and light transmission) that impact the moss community. Our results show that different aspects of the moss community (that is, composition, functional traits, moss-driven processes, and associated invertebrate fauna) respond to different sets of environmental variables, and that these are not always the same variables as those that influence the vascular plant community. Measures of moss community composition and functional traits were primarily influenced by vascular plant community composition and productivity. This suggests that successional shifts in abiotic variables, such as soil nutrient levels, indirectly affect the moss community via their influence on vascular plant community characteristics, whereas direct abiotic effects are less important. Among the moss-driven processes, moss litter decomposition and moss productivity were mainly influenced by biotic variables (notably the community characteristics of both vascular plants and mosses), whereas moss functional traits (primarily specific leaf area and tissue nutrient concentrations) also were important in explaining moss di-nitrogen-fixation rates. In contrast, both abiotic and biotic variables were important drivers of moss microfaunal community structure. Taken together, our results show which abiotic and biotic factors impact mosses and their associated organisms, and thus highlight that multiple interacting factors need to be considered to understand how moss communities, associated food webs, and the ecosystem processes they influence will respond to environmental change.
    Ecosystems 03/2015; · 3.17 Impact Factor
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    ABSTRACT: Some communities are susceptible to invasions and some are not. Why? Elton suggested in 1958 that the ability of the community to withstand invading species – its biotic resistance – depends on the number of resident species. Later contributors have emphasized the habitat's ability to support species, as well as the contribution of individual species to the resistance. In this study we use information from 184 introductions of Arctic char into Swedish lakes to study both abiotic and biotic aspects of the resident community's ability to resist introductions. We find that the best model included the proportion of forest cover and the proportion of agricultural land cover in the watershed in combination with the presence versus absence of northern pike. Thus, the most important biotic factor to explain the outcome of introductions of Arctic char is the presence of northern pike, a large piscivore. This means that one single species explains the outcome of the introductions better than does the species richness or the saturation level of the community.
    Oikos 12/2014; · 3.33 Impact Factor
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    ABSTRACT: Boreal forest soils store a major proportion of the global terrestrial carbon (C) and below-ground inputs contribute as much as above-ground plant litter to the total C stored in the soil. A better understanding of the dynamics and drivers of root-associated fungal communities is essential to predict long-term soil C storage and climate feedbacks in northern ecosystems.We used 454-pyrosequencing to identify fungal communities across fine-scaled soil profiles in a 5000 yr fire-driven boreal forest chronosequence, with the aim of pinpointing shifts in fungal community composition that may underlie variation in below-ground C sequestration.In early successional-stage forests, higher abundance of cord-forming ectomycorrhizal fungi (such as Cortinarius and Suillus species) was linked to rapid turnover of mycelial biomass and necromass, efficient nitrogen (N) mobilization and low C sequestration. In late successional-stage forests, cord formers declined, while ericoid mycorrhizal ascomycetes continued to dominate, potentially facilitating long-term humus build-up through production of melanized hyphae that resist decomposition.Our results suggest that cord-forming ectomycorrhizal fungi and ericoid mycorrhizal fungi play opposing roles in below-ground C storage. We postulate that, by affecting turnover and decomposition of fungal tissues, mycorrhizal fungal identity and growth form are critical determinants of C and N sequestration in boreal forests.
    New Phytologist 12/2014; · 6.74 Impact Factor
  • David A Wardle, Björn D Lindahl
    Science (New York, N.Y.). 11/2014; 346(6213):1052-3.
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    ABSTRACT: Aims This study explores soil nutrient cycling processes and microbial properties for two contrasting vegetation types along an elevational gradient in subarctic tundra to improve our understanding of how temperature influences nutrient availability in an ecosystem predicted to be sensitive to global warming. Methods We measured total amino acid (Amino-N), mineral nitrogen (N) and phosphorus (P) concentrations, in situ net N and P mineralization, net Amino-N consumption, and microbial biomass C, N and P in both heath and meadow soils across an elevational gradient near Abisko, Sweden. Results For the meadow, NH4+ concentrations and net N mineralization were highest at high elevations and microbial properties showed variable responses; these variables were largely unresponsive to elevation for the heath. Amino-N concentrations sometimes showed a tendency to increase with elevation and net Amino-N consumption was often unresponsive to elevation. Overall, PO4-P concentrations decreased with elevation and net P immobilization mostly occurred at lower elevations; these effects were strongest for the heath. Conclusions Our results reveal that elevation-associated changes in temperature can have contrasting effects on the cycling of N and P in subarctic soils, and that the strength and direction of these effects depend strongly on dominant vegetation type.
    Plant and Soil 10/2014; 383(1-2). · 3.24 Impact Factor
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    ABSTRACT: Background/Question/Methods Arctic and Alpine tree line expansions induced by climate warming are dependent on tree seedling establishment above the tree line. This involves interactions between tree seedlings and bryophytes, because bryophytes dominate the tundra above the tree line. Bryophytes control a range of abiotic factors important for seedling establishment including soil moisture and nutrients. However, bryophyte species are diverse in their ecological attributes and their response to climate change and could therefore potentially have contrasting effects on tree seedlings. We grew tree seedlings of Betula pubescens and Pinus sylvestris (species that form the tree line or that occur at the sub tree line level in Fennoscandia, respectively) in cores containing one of eight bryophytes species or bryophyte-free control soil. The bryophyte cores were collected above the tree line close to Abisko National Park in subarctic Sweden. The experiment was run in climate-controlled chambers at tree line temperature (~7°C) and five degrees warmer than that temperature to represent projected climate warming. Seedling establishment was expressed as biomass upon harvest after 4 months (one growing season). We hypothesized that tree seedling biomass would differ between bryophyte species but that these differences would be influenced by warming treatment. We also hypothesized that these differences between moss species could be explained by bryophyte traits that relate to moisture. Results/Conclusions Seedling biomass depended on bryophyte species (p<0.0001) and was generally higher in bryophytes than in control soil. Warming increased seedling biomass (p<0.0001) but the total increase depended on bryophyte species (i.e., bryophyte species x warming interaction; p=0. 02117). Seedlings of both tree species responded most to warming when grown in the pan boreal and subarctic bryophyte species Hylocomium splendens. Seedling biomass was positively correlated to the bryophytes water loosing rates (a trait describing bryophytes ability to hold water). Our results suggest that the impact of individual bryophyte species on seedling establishment might change under a warmer climate and that bryophyte traits related to soil moisture are important for seedling success. To understand interactive effects between climate and mosses is important for understanding mechanisms explaining tree line dynamics and to make accurate predictions of future tree line expansions.
    99th ESA Annual Convention 2014; 08/2014
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    ABSTRACT: QuestionNiche differentiation results in functionally diverse communities that are often composed of dominant species with contrasting trait values. However, many predictive trait-based models that emphasize environmental filtering have implicitly assumed that traits exhibit unimodal distributions among individuals within communities centred on an optimal trait value. Does accounting for more complex, multimodal trait distributions among individuals in a community improve predictions of species abundances and functional diversity along environmental gradients?LocationFranz Josef soil chronosequence, central Westland, New Zealand.Methods Leaf nitrogen (N) and phosphorus (P) concentrations from 23 woody plant species were modelled as functions of soil total N and P from eight sites of declining soil P. We compared predictions to observations of species abundances and functional diversity along the soil chronosequence using two modelling approaches: (i) the standard application of the hierarchical Bayesian Traitspace model that assumes unimodally distributed traits at each point along the gradient, and (ii) a modified application of the model that accounts for multimodal trait distributions within each community.ResultsSoil P was the strongest predictor of traits and species abundances. The strength of the environmental filter of leaf traits changed along this gradient, as evidenced by highly constrained variances and low modality of the trait distribution at low soil P, and high variance and multimodality at high soil P. Both modelling approaches predicted species abundances that were significantly correlated with observations, but the multimodal approach significantly improved predictions of species abundances and functional diversity.Conclusions Our results indicate that predictive models that emphasize environmental filtering over niche differentiation by assuming unimodal trait distributions can be more parsimonious than more complex approaches, especially when predicting species abundances along strong environmental gradients. However, models need to account for trait multimodality if they are to accurately replicate spatial patterns in functional diversity. This is important since functional diversity may be a key predictor of ecosystem function and resilience to global change.
    Journal of Vegetation Science 08/2014; · 2.82 Impact Factor
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    ABSTRACT: QuestionsWe investigated some commonly held assumptions of community assembly theory needed to provide accurate predictions of changes in plant species assemblages across environmental gradients or following environmental change. Do (1) dominant and subordinate species respond in the same way to changes in environmental variables; (2) plant species assemblages show higher interspecific than intraspecific trait responses; and (3) co-existing dominant species differ in their responses to the same environmental variables?LocationIslands in Lakes Uddjaure and Hornavan, northern Sweden.Methods We explored the responses of forest understorey vegetation assemblages to variation in environmental resources across a chronosequence of 30 lake islands that differ in fire history, above-ground and below-ground resource availability and species diversity. For one plot on each island, we measured specific leaf area, leaf dry matter content and foliar N and P of all dominant and subordinate understorey plant species to assess species-specific and weighted and non-weighted community-level trait responses to variation across islands in all major local environmental drivers.ResultsConsistent with our expectations, we found that species responses to environmental conditions were not homogenous within assemblages, and that responses of dominant and subordinate species differed. Further, intraspecific variation was often an important component of local-scale plant community-level responses. Responses were often relatively consistent across species, but dominant species sometimes showed contrasting responses of the same trait to the same environmental factor. Finally, environmental factors that influenced community average trait values also affected functional diversity.Conclusions This study has shown that several common assumptions that underpin community assembly theory do not necessarily hold, and this can cause inaccuracies in predicting plant functional composition responses to changes in environmental variables. Because these assumptions are central to current models that predict vegetation responses to environmental change, it is crucial to further test in which particular environmental context and to what extent these assumptions are critical for model accuracy.
    Journal of Vegetation Science 08/2014; · 2.82 Impact Factor
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    ABSTRACT: There is growing interest in understanding how declining soil fertility in the prolonged absence of major disturbance drives ecological processes, or ‘ecosystem retrogression’. However, there are few well characterized study systems for exploring this phenomenon in the tropics, despite tropics occupying over 40% of the Earth's terrestrial surface. We studied two types of montane rain forest in the Blue Mountains of Jamaica that represent distinct stages in ecosystem development, i.e. an earlier stage with shallow organic matter and a late stage with deep organic matter (hereafter ‘mull’ and ‘mor’ stages). We characterized responses of soil fertility and plant, soil microbial and nematode communities to the transition from mull to mor and whether these responses were coupled. For soil abiotic properties, we found this transition led to lower amounts of both nitrogen (N) and phosphorus (P) and an enhanced N to P ratio. This led to shorter-statured and less diverse forest, and convergence of tree species composition among plots. At the whole community (but not individual species) level foliar and litter N and P diminished from mull to mor, while foliar N to P and resorption efficiency of P relative to N increased, indicating increasing P relative to N limitation. We also found impairment of soil microbes (but not nematodes) and an increasing role of fungi relative to bacteria during the transition. Our results show that retrogression phenomena involving increasing nutrient (notably P) limitation can be important drivers in tropical systems, and are likely to involve aboveground–belowground feedbacks whereby plants produce litter of diminishing quality, impairing soil microbial processes and thus reducing the supply of nutrients from the soil for plant growth. Such feedbacks between plants and the soil, mediated by plant litter and organic matter quality, may serve as major though often overlooked drivers of long term environmental change.
    Oikos 08/2014; · 3.33 Impact Factor
  • David A. Wardle, Micael Jonsson
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    ABSTRACT: While several studies have explored how short-term ecological responses to disturbance vary among ecosystems, experimental studies of how contrasting ecosystems recover from disturbance in the longer term are few. We performed a simple long-term experiment on each of 30 contrasting forested islands in northern Sweden that vary in size; as size decreases, time since fire increases, soil fertility and ecosystem productivity declines, and plant species diversity increases. We predicted that resilience of understory plant community properties would be greatest on the larger, more productive islands, and that this would be paralleled by greater resilience of soil biotic and abiotic properties. For each island, we applied three disturbance treatments of increasing intensity to the forest understory once in 1998, i.e., light trimming, heavy trimming, and burning; a fourth treatment was an undisturbed control. We measured recovery of the understory vascular plant community annually over the following 14 years, and at that time also assessed recovery of mosses and several belowground variables. Consistent with our predictions, vascular plant whole-community variables (total cover, species richness, diversity [Shannon's H′], and community composition) recovered significantly more slowly on the smaller (least fertile) than the larger islands, but this difference was not substantial, and only noticeable in the most severely disturbed treatment. When an index of resilience was used, we were unable to detect effects of island size on the recovery of any property. We found that mosses and one shrub species (Empetrum hermaphroditum) recovered particularly slowly, and the higher abundance of this shrub on small islands was sufficient to explain any slower recovery of whole-ecosystem variables on those islands. Further, several belowground variables had not fully recovered from the most intense disturbance after 14 yr, and counter to our predictions, the degree of their recovery was never influenced by island size. While several studies have shown large variation among plant communities in their short-term response (notably resistance) to environmental perturbations, our results reveal that when perturbations are applied equally to highly contrasting ecosystems, differences in resilience among them in the longer term can be relatively minor, regardless of the severity of disturbance.
    Ecology 07/2014; 95(7):1836-1849. · 5.18 Impact Factor
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    ABSTRACT: Temperature and nutrients are major limiting factors in subarctic tundra. Experimental manipulation of nutrient availability along elevational gradients (and thus temperature) can improve our understanding of ecological responses to climate change. However, no study to date has explored impacts of nutrient addition along a tundra elevational gradient, or across contrasting vegetation types along any elevational gradient. We set up a full factorial nitrogen (N) and phosphorus (P) fertilization experiment in each of two vegetation types (heath and meadow) at 500 m, 800 m and 1000 m elevation in northern Swedish tundra. We predicted that plant and microbial communities in heath or at lower elevations would be more responsive to N addition while communities in meadow or at higher elevations would be more responsive to P addition, and that fertilizer effects would vary more with elevation for the heath than for the meadow. Although our results provided little support for these predictions, the relationship between nutrient limitation and elevation differed between vegetation types; most plant and microbial properties were responsive to N and/or P fertilization but responses often varied with elevation and/or vegetation type. For instance, vegetation density significantly increased with N + P fertilization relative to the other fertilizer treatments, and this increase was greatest at the lowest elevation for the heath but at the highest elevation for the meadow. Arbuscular mycorrhizae decreased with P fertilization at 500 m for the meadow, but with all fertilizer treatments at in both vegetation types at 800 m. Fungal to bacterial ratios were enhanced by N + P fertilization for the two highest elevations in the meadow only. Additionally, microbial responses to fertilization were primarily direct rather than indirect via plant responses, pointing to a decoupled response of plant and microbial communities to nutrient addition and elevation. Because our study shows how two community types differ in their responses to fertilization and elevation, and because the temperature range across this gradient is ~3°C, our study informs on how nutrient limitation in tundra may be influenced by temperature shifts that are comparable to those expected under climate change during this century.
    Ecology 07/2014; 95(7):1819-1835. · 5.18 Impact Factor
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    ABSTRACT: The ‘home-field advantage (HFA) hypothesis’ predicts that plant litter is decomposed faster than expected in the vicinity of the plant where it originates from (i.e., its ‘home’) relative to some other location (i.e., ‘away’) because of the presence of specialized decomposers. Despite growing evidence for the widespread occurrence HFA effects, what drives HFA is not understood as its strength appears highly variable and context-dependent. Our work advances current knowledge about HFA effects by testing under what conditions HFA is most important. Using published data on mass loss from 125 reciprocal litter transplants from 35 studies, we evaluated if HFA effects were modulated by macroclimate, litter quality traits, and the dissimilarity between ‘home’ and ‘away’ of both the quality of reciprocally exchanged litters and plant community type. Our results confirmed the occurrence of an overall, worldwide, HFA effect on decomposition with on average 7.5% faster decomposition at home. However, there was considerable variation in the strength and direction (sometimes opposite to expectations) of these effects. While macroclimate and average litter quality had weak or no impact on HFA effects, home-field effects became stronger (regardless of the direction) when the quality of ‘home’ and ‘away’ litters became more dissimilar (e.g. had a greater dissimilarity in N:P ratio; F1,42 = 6.39, P = 0.015). Further, home-field effects were determined by the degree of difference between the types of dominant plant species in the ‘home’ versus ‘away’ communities (F2,105 = 4.03, P = 0.021). We conclude that home-field advantage is not restricted to particular litter types or climate zones, and that the dissimilarity in plant communities and litter quality between the ‘home’ and ‘away’ locations, are the most significant drivers of home-field effects.
    Oikos 05/2014; in press. · 3.33 Impact Factor
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    ABSTRACT: AimRecent meta-analyses have revealed that plant traits and their phylogenetic history influence decay rates of dead wood and leaf litter, but it remains unknown if decay rates of wood and litter covary over a wide range of tree species and across ecosystems. We evaluated the relationships between species-specific wood and leaf litter decomposability, as well as between wood and leaf traits that control their respective decomposability.LocationGlobal.Methods We compiled data on rates of wood and leaf litter decomposition for 324 and 635 tree species, respectively, and data on six functional traits for both organs. We used hierarchical Bayesian meta-analysis to estimate, for the first time, species-specific values for wood and leaf litter decomposability standardized to reference conditions (k*wood and k*leaf) across the globe. With these data, we evaluated the relationships: (1) between wood and leaf traits, (2) between each k* and the selected traits within and across organs, and (3) between wood and leaf k*.ResultsAcross all species k*wood and k*leaf were positively correlated, phylogenetically clustered and correlated with plant functional traits within and across organs. k* of both organs was usually better described as a function of within- and cross-organ traits, than of within-organ traits alone. When analysed for angiosperms and gymnosperms separately, wood and leaf k* were no longer significantly correlated, but each k* was still significantly correlated to the functional traits.Main conclusionsWe demonstrate important relationships among wood and leaf litter decomposability as after-life effects of traits from the living plants. These functional traits influence the decomposability of senesced tissue which could potentially lead to alterations in the rates of biogeochemical cycling, depending on the phylogenetic structure of the species pool. These results provide crucial information for a better representation of decomposition rates in dynamic global vegetation models.
    Global Ecology and Biogeography 05/2014; · 7.22 Impact Factor
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    ABSTRACT: There is growing recognition of the need to incorporate intraspecific trait variability (ITV) into trait-based studies to improve understanding of community assembly and how plant communities drive ecosystem processes. However, most studies have focused on ITV across plant communities, with few quantifying it at local scales. Further, little is known about how ITV at local scales differs among communities or across environmental gradients. Here, we studied a well characterized 5000-year-old chronosequence involving 30 islands that differed greatly in size, soil fertility, spatial heterogeneity, and species diversity. On each island we measured foliar and litter (including nutrient resorption) traits for ten individuals for each of three species that occur on all islands, i.e., Betula pubescens, Vaccinum myrtillus and Vaccinium vitis-idaea. For each trait for each species we estimated its within-island mean, and coefficient of variation as a measure of local scale ITV. We predicted within-island ITV should be highest for larger islands that have the greatest spatial heterogeneity of soil resources but lowest species diversity. Further, we predicted that the species most dominant in the most resource heterogeneous environment (V. myrtillus) should have the greatest within-island ITV. First, we found that within-island ITV of foliar traits was generally unresponsive to island size, while for litter traits it was responsive to island size only for V. myrtillus in a direction consistent with our prediction. The within-island ITV of resorption efficiency of C, N and P for the three species was often responsive to island size, but not in a consistent direction. Second, against our prediction, V. myrtillus had the lowest within-island ITV for most traits, but its within-island ITV was generally more responsive than that of the other species to island size. While plant traits are well known to vary among and within species at broad spatial scales across environmental gradients, our results show that at local scales, ITV can also be highly responsive to fine scale environmental gradients, particularly for litter and nutrient resorptive traits. Understanding how local scale ITV varies across communities offers opportunities for improving our understanding of what drives community assembly, functional diversity and ecosystem processes.
    Ecosphere 03/2014; 5(3):26. · 2.50 Impact Factor
  • Johan Asplund, David A. Wardle
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    ABSTRACT: 1.There has been growing recent interest in the relative importance of within- versus across-species trait variation of vascular plants in determining total community level trait variation across communities and environmental gradients. Recent studies on plant communities have generally found across-species variation to be more important than within-species variation, but comparable studies involving other functionally important biota, such as lichens, are largely lacking.2.We used a fire-driven chronosequence involving 30 lake islands in northern Sweden to study how declining soil fertility during retrogression affects the functional traits of each of the dominant epiphytic lichen species growing on the trunks of the tree Betula pubescens. We measured several functional traits for the commonest lichen species on each island, and used community-weighted measures to study the community level responses of lichens to the gradient.3.We found that as retrogression proceeds and soil fertility declines thallus N and P concentrations and specific thallus mass (STM) increase, both within species and at the community level. Lichen secondary compounds showed contrasting within species responses and were non-responsive at the whole community level.4.By decomposing community-level measures of these traits across the gradient, we showed that for the three most responsive traits (N, P and STM), within-species variation was substantially more important than across-species variation. This emerges in part because lichen species composition was not very responsive to ecosystem retrogression, and because unlike vascular plants, lichens easily absorb elements over their entire surface, meaning that nutrient concentrations within lichen species are likely to more closely reflect nutrient availability.5.We found that within-species variability drove the changes in community-weighted measures of lichen traits across a strong environmental gradient, which contrasts strongly with what we know from studies of vascular plants where across-species variation and species turnover is much more important. To understand how lichen functional traits at the community level respond to environmental factors it is therefore essential to consider the responses of individual species, and the application of traits-based approaches to lichen communities needs to account for their considerable intraspecific variability.This article is protected by copyright. All rights reserved.
    Functional Ecology 03/2014; · 4.86 Impact Factor
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    ABSTRACT: 1. Invasive browsing ungulates can have strong impacts on the structure and composition of forest ecosystems, particularly where ungulates are not native ecosystem components as in New Zealand. Ungulate impacts on plant communities have been considered mostly from an above-ground perspective. However, understanding below-ground effects of these invasive herbivores is critical as they may drive feedbacks to above-ground ecosystem components. 2. We measured growth responses of seedlings of five common tree species in a greenhouse experiment in soils collected from 26 plots fenced to exclude invasive ungulates for at least 17 years and from paired, unfenced-control plots. We then further investigated soil-mediated effects of ungulates on one tree species, Melicytus ramiflorus, by partitioning these effects into soil abiotic and biotic components, as well as measuring arbuscular mycorrhizal fungal (AMF) root infection. 3. Biomass of seedlings of all five species was greater in soils from within exclosures, although this was only significant for two species. These soil-mediated effects were partially driven by changes in soil physical and chemical properties; soil bulk densities were lower inside exclosures than in controls. 4. Effects of invasive ungulates on seedling biomass of M. ramiflorus were positively related to effects on percent AMF root infection. The biomass of M. ramiflorus seedlings was positively related to the AMF infection of its roots, which in turn was related to greater organic matter content and lower bulk density of soils from within exclosures. Results for M. ramiflorus indicated that soil-mediated effects of ungulates on seedling biomass were of abiotic origin, but were mediated by the biotic soil component, i.e., through effects on AMF. 5. Synthesis Invasive herbivores may potentially impact on plant performance and community structure not only directly but also indirectly through influencing soil abiotic and biotic properties. Our results show that shifts in plant–soil interactions and feedbacks represent important but understudied pathways by which invasive ungulates can have wide-ranging impacts on forest ecosystems. Future studies should consider the importance of soil-mediated effects of invasive ungulates relative to direct effects of herbivory. This article is protected by copyright. All rights reserved.
    Journal of Ecology 02/2014; · 5.69 Impact Factor
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    ABSTRACT: Studies evaluating plant-soil biota interactions in both native and introduced plant ranges are rare, and thus far have lacked robust experimental designs to account for several potential confounding factors. Here, we investigated the effects of soil biota on growth of Pinus contorta, which has been introduced from Canada to Sweden. Using Swedish and Canadian soils, we conducted two glasshouse experiments. The first experiment utilized unsterilized soil from each country, with a full-factorial cross of soil origin, tree provenance, and fertilizer addition. The second experiment utilized gamma-irradiated sterile soil from each country, with a full-factorial cross of soil origin, soil biota inoculation treatments, tree provenance, and fertilizer addition. The first experiment showed higher seedling growth on Swedish soil relative to Canadian soil. The second experiment showed this effect was due to differences in soil biotic communities between the two countries, and occurred independently of all other experimental factors. Our results provide strong evidence that plant interactions with soil biota can shift from negative to positive following introduction to a new region, and are relevant for understanding the success of some exotic forest plantations, and invasive and range-expanding native species.
    New Phytologist 01/2014; · 6.74 Impact Factor
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    ABSTRACT: Phosphorus (P) is an important macronutrient in arctic and subarctic tundra and its bioavailability is regulated by the mineralization of organic P. Temperature is likely to be an important control on P bioavailability, although effects may differ across contrasting plant communities with different soil properties. We used an elevational gradient in northern Sweden that included both heath and meadow vegetation types at all elevations to study the effects of temperature, soil P sorption capacity and oxalate-extractable aluminium (Alox) and iron (Feox) on the concentration of different soil P fractions. We hypothesized that the concentration of labile P fractions would decrease with increasing elevation (and thus declining temperature), but would be lower in meadow than in heath, given that N to P ratios in meadow foliage are higher. As expected, labile P in the form of Resin-P declined sharply with elevation for both vegetation types. Meadow soils did not have lower concentrations of Resin-P than heath soils, but they did have 2-fold and 1.5-fold higher concentrations of NaOH-extractable organic P and Residual P, respectively. Further, meadow soils had 3-fold higher concentrations of Alox + Feox and a 20% higher P sorption index than did heath soils. Additionally, Resin-P expressed as a proportion of total soil P for the meadow was on average half that in the heath. Declining Resin-P concentrations with elevation were best explained by an associated 2.5-3.0°C decline in temperature. In contrast, the lower P availability in meadow relative to heath soils may be associated with impaired organic P mineralization, as indicated by a higher accumulation of organic P and P sorption capacity. Our results indicate that predicted temperature increases in the arctic over the next century may influence P availability and biogeochemistry, with consequences for key ecosystem processes limited by P, such as primary productivity.
    PLoS ONE 01/2014; 9(3):e92942. · 3.53 Impact Factor
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    Biological Invasions 01/2014; · 2.51 Impact Factor

Publication Stats

13k Citations
1,581.96 Total Impact Points


  • 1998–2014
    • Swedish University of Agricultural Sciences
      • • Department of Forest Ecology and Management
      • • Fakulteten för skogsvetenskap
      Uppsala, Uppsala, Sweden
    • The University of Manchester
      Manchester, England, United Kingdom
  • 2013
    • University of Western Australia
      • School of Plant Biology
      Perth, Western Australia, Australia
  • 2011
    • University of California, Santa Cruz
      • Department of Ecology & Evolutionary Biology
      Santa Cruz, CA, United States
    • Stockholm University
      • Department of Ecology, Environment and Plant Sciences
      Tukholma, Stockholm, Sweden
  • 2009
    • Stanford University
      Palo Alto, California, United States
    • University of Canterbury
      • School of Biological Sciences
      Christchurch, Canterbury, New Zealand
    • New Zealand Department of Conservation
      Wellington, Wellington, New Zealand
    • University of Zurich
      Zürich, Zurich, Switzerland
  • 2007–2009
    • Netherlands Institute of Ecology (NIOO-KNAW)
      Wageningen, Gelderland, Netherlands
  • 2008
    • University of Granada
      Granata, Andalusia, Spain
  • 2005
    • Landcare Research
      Christchurch, Canterbury Region, New Zealand
    • University of Cambridge
      • Department of Plant Sciences
      Cambridge, ENG, United Kingdom
  • 2002–2005
    • University of Auckland
      • Department of Physics
      Auckland, Auckland, New Zealand
    • Wageningen University
      Wageningen, Gelderland, Netherlands
    • University of Nevada, Las Vegas
      • School of Life Sciences
      Las Vegas, Nevada, United States
  • 2001–2002
    • The University of Sheffield
      • Department of Animal and Plant Sciences
      Sheffield, ENG, United Kingdom
    • Ecole Normale Supérieure de Paris
      • Laboratoire de Géologie
      Paris, Ile-de-France, France
  • 1990–1993
    • The University of Calgary
      • Department of Biological Sciences
      Calgary, Alberta, Canada