bluuebunny/crossref_metadata_2025 huggingface dataset:
Combined impact of multiple exotic herbivores on different life stages of an endangered plant endemism, Medicago citrina
Authors: Latorre Lucía , Larrinaga Asier R. , Santamaría Luis
Published: May 2013

Herbivores and granivores represent one of the most influential drivers of plant abundance and population dynamics. Their effect can be, in turn, modulated by biotic or abiotic factors such as community composition, habitat characteristics or space heterogeneity.

Recent approaches to the study of herbivore and granivore impacts on plants have considered the combined action of multiple herbivore species, the effect of herbivores on several plant life stages or the effect of environmental gradients on these interactions. However, studies addressing the effect of multiple herbivore species on different plant life stages are still lacking.

We estimated the combined effect of multiple exotic herbivores (European rabbits, Oryctolagus cuniculus; black rats, Rattus rattus; and house mouse, Mus musculus) on four different life stages of an endangered plant species (Medicago citrina, Fabaceae). Mortality for seed, seedling and sapling was estimated at three types of plots (open, rat exclusion and rat + rabbit exclusion) replicated at four sites (N = 3 per site and treatment) within Cabrera Island (Balearic Islands, western Mediterranean). Browsing of reproductive adults was simulated under common‐garden conditions (Sóller Botanic Garden, Mallorca Island) and its effect on reproductive effort and success measured.

European rabbits and black rats had complementary impacts on the different life stages of M. citrina. These included independent effects on different life stages (seed predation by rats, seedling predation by rabbits), which resulted in multiplicative increases in plant mortality, and concurrent effects on the same life stage (sapling predation). In addition, the simulated‐herbivory experiment showed that a low rate of canopy removal (25% of initial biomass) already causes a strong decrease in fruit set (from 54% to 30%), but increasing rates of canopy removal do not increase this effect.

Synthesis. Our results stress the importance of considering the combined effects of different herbivores on several life stages of the plant's life cycle and their consecutive effects on population dynamics. From an applied point of view, future reintroduction attempts of M. citrina in Cabrera Island should consider measures to either control the populations of both exotic herbivores or mitigate their impacts on the earlier recruitment stages of the plant (seeds, seedlings and saplings).
Fuel composition influences fire characteristics and understorey hardwoods in pine savanna
Authors: Ellair Darin P. , Platt William J.
Published: May 2013

Fuels in the groundcover of frequently burned south‐eastern pine savannas include shed leaves of trees. Flammable needles of longleaf pine (Pinus palustris) potentially increase maximum fire temperatures and durations of heating, negatively affecting other trees within the groundcover. Less flammable leaves that accumulate around the bases of understorey stems of hardwood trees such as mockernut hickories (Carya alba) in the fall potentially depress maximum fire temperatures and durations of heating, enhancing post‐fire recovery.

We experimentally manipulated amounts of pine and hickory leaves beneath understorey hickory stems in a pine savanna, measured temperatures during prescribed fires and assessed combustion of fuels and survival and regrowth of hickory stems.

Pine needles increased fire temperatures and durations of heating relative to herbaceous fuels and increased combustion of hickory leaves. Hickory leaves, however, neither increased nor decreased fire characteristics relative to herbaceous fuels.

All hickories survived fire by resprouting. When pine needles were absent, most hickories resprouted from buds located above‐ground along the stem at heights inversely related to temperature increase. In contrast, resprouting occurred only from underground root crowns when pine needles were present. Such differences in locations of resprouts influenced sizes of stems at the end of the growing season.

Synthesis. Groundcover fuels containing flammable leaves shed by pyrogenic species of savanna trees affect local fire characteristics and resprouting of non‐pyrogenic understorey trees. Thus, local variation in flammable fuels produced by pyrogenic species can engineer landscape dynamics of other trees in savannas.
Tree effects on grass growth in savannas: competition, facilitation and the stress‐gradient hypothesis
Authors: Dohn Justin , Dembélé Fadiala , Karembé Moussa , Moustakas Aristides , Amévor Kosiwa A. , Hanan Niall P.
Published: May 2013

The stress‐gradient hypothesis (SGH) predicts an increasing importance of facilitative mechanisms relative to competition along gradients of increasing environmental stress. Although developed across a variety of ecosystems, the SGH's relevance to the dynamic tree–grass systems of global savannas remains unclear. Here, we present a meta‐analysis of empirical studies to explore emergent patterns of tree–grass relationships in global savannas in the context of the SGH.

We quantified the net effect of trees on understorey grass production relative to production away from tree canopies along a rainfall gradient in tropical and temperate savannas and compared these findings to the predictions of the SGH. We also analysed soil and plant nutrient concentrations in subcanopy and open‐grassland areas to investigate the potential role of nutrients in determining grass production in the presence and absence of trees.

Our meta‐analysis revealed a shift from net competitive to net facilitative effects of trees on subcanopy grass production with decreasing annual precipitation, consistent with the SGH. We also found a significant difference between sites from Africa and North America, suggesting differences in tree–grass interactions in the savannas of tropical and temperate regions.

Nutrient analyses indicate no change in nutrient ratios along the rainfall gradient, but consistent nutrient enrichment under tree canopies.

Synthesis. Our results help to resolve questions about the SGH in semi‐arid systems, demonstrating that in mixed tree–grass systems, trees facilitate grass growth in drier regions and suppress grass growth in wetter regions. Relationships differ, however, between African and North American sites representing tropical and temperate bioclimates, respectively. The results of this meta‐analysis advance our understanding of tree–grass interactions in savannas and contribute a valuable data set to the developing theory behind the SGH.
Plant functional diversity and carbon storage – an empirical test in semi‐arid forest ecosystems
Authors: Conti Georgina , Díaz Sandra
Published: May 2013

Carbon storage in vegetation and soil underpins climate regulation through carbon sequestration. Because plant species differ in their ability to capture, store and release carbon, the collective functional characteristics of plant communities (functional diversity) should be a major driver of carbon accumulation in terrestrial ecosystems.

Three major components of plant functional diversity could be put forward as drivers of carbon storage in ecosystems: the most abundant functional trait values, the variety of functional trait values and the abundance of particular species that could have additional effects not incorporated in the first two components.

We tested for associations between these components and carbon storage across 16 sites in the Chaco forest of Argentina under the same climate and on highly similar parental material. The sites differed in their plant functional diversity caused by different long‐term land‐use regimes.

We measured six plant functional traits in 27 species and weighted them by the species abundance at each site to calculate the community‐weighted mean (CWM) and the functional divergence (FDvar) of each single trait and of multiple traits (FDiv). We also measured plant and soil carbon storage. Using a stepwise multiple regression analysis, we assessed which of the functional diversity components best explained carbon storage.

Both CWM and FDvar of plant height and wood‐specific gravity, but no leaf traits, were retained as predictors of carbon storage in multiple models. Relationships of FDvar of stem traits and FDiv with carbon storage were all negative. The abundance of five species improved the predictive power of some of the carbon storage models.

Synthesis. All three major components of plant functional diversity contributed to explain carbon storage. What matters the most to carbon storage in these ecosystems is the relative abundance of plants with tall, and to a lesser extent dense, stems with a narrow range of variation around these values. No consistent link was found between carbon storage and the leaf traits usually associated with plant resource use strategy. The negative association of trait divergence with carbon storage provided no evidence in support to niche complementarity promoting carbon storage in these forest ecosystems.
Many ways to die – partitioning tree mortality dynamics in a near‐natural mixed deciduous forest
Authors: Holzwarth Frederic , Kahl Anja , Bauhus Jürgen , Wirth Christian
Published: May 2013

Partitioning of tree mortality into different modes of death allows the tracing and mechanistic modelling of individual key processes of forest dynamics each varying depending on site, species and individual risk factors. This, in turn, may improve long‐term predictions of the development of old‐growth forests.

Six different individual tree mortality modes (uprooted and snapped (both with or without rot as a predisposing factor), standing dead and crushed by other trees) were analysed, and statistical models were derived for three tree species (European beechFagus sylvatica, hornbeamCarpinus betulusand common ashFraxinus excelsior) based on a repeated inventory of more than 13 000 trees in a 28 ha near‐natural deciduous forest in CentralGermany.

The frequently describedU‐shaped curve of size‐dependent mortality was observed in beech and hornbeam (but not ash) and could be explained by the joint operation of processes related to the six distinct mortality modes. The results for beech, the most abundant species, suggest that each mortality mode is prevalent in different life‐history stages: small trees died mostly standing or being crushed, medium‐sized trees had the highest chance of survival, and very large trees experienced increased rates of mortality, mainly by uprooting or snapping. Reduced growth as a predictor also played a role but only for standing dead, all other mortality modes showed no relationship to tree growth.

Synthesis. Tree mortality can be partitioned into distinct processes, and species tend to differ in their susceptibility to one or more of them. This forms a fundamental basis for the understanding of forest dynamics in natural forests, and any mechanistic modelling of mortality in vegetation models could be improved by correctly addressing and formulating the various mortality processes.
Plant functional group identity and diversity determine biotic resistance to invasion by an exotic grass
Authors: Byun Chaeho , de Blois Sylvie , Brisson Jacques
Published: May 2013

Biotic resistance, the ability of species in a community to limit invasion, is central to our understanding of how communities at risk of invasion assemble after disturbances, but it has yet to translate into guiding principles for the restoration of invasion‐resistant plant communities. We combined experimental, functional, and modelling approaches to investigate processes of community assembly contributing to biotic resistance to an introduced lineage of Phragmites australis, a model invasive species in North America. We hypothesized that (i) functional group identity would be a good predictor of biotic resistance to P. australis, while species identity effect would be redundant within functional group (ii) mixtures of species would be more invasion resistant than monocultures.

We classified 36 resident wetland plants into four functional groups based on eight functional traits. We conducted two competition experiments based on the additive competition design with P. australis and monocultures or mixtures of wetland plants. As an indicator of biotic resistance, we calculated a relative competition index (RCIavg) based on the average performance of P. australis in competition treatment compared with control. To explain diversity effect further, we partitioned it into selection effect and complementarity effect and tested several diversity–interaction models.

In monoculture treatments, RCIavg of wetland plants was significantly different among functional groups, but not within each functional group. We found the highest RCIavg for fast‐growing annuals, suggesting priority effect.

RCIavg of wetland plants was significantly greater in mixture than in monoculture mainly due to complementarity–diversity effect among functional groups. In diversity–interaction models, species interaction patterns in mixtures were described best by interactions between functional groups when fitted to RCIavg or biomass, implying niche partitioning.

Synthesis. Functional group identity and diversity of resident plant communities are good indicators of biotic resistance to invasion by introduced Phragmites australis, suggesting niche pre‐emption (priority effect) and niche partitioning (diversity effect) as underlying mechanisms. Guiding principles to understand and/or manage biological invasion could emerge from advances in community theory and the use of a functional framework. Targeting widely distributed invasive plants in different contexts and scaling up to field situations will facilitate generalization.
Shrubs and herbaceous seed flow in a semi‐arid landscape: dual functioning of shrubs as trap and barrier
Authors: Giladi Itamar , Segoli Moran , Ungar Eugene D.
Published: May 2013

Shrubs in arid and semi‐arid ecosystems are often associated with three distinct patch types: the shrub core, the shrub periphery and surrounding open patches. The distribution of herbaceous seeds in such a patchy system exhibits a well‐documented spatial heterogeneity. However, the mechanisms that generate this heterogeneity are poorly understood, not least because of the difficulty of separating possible effects of the shrub on seed production (via the shrub's modification of resource distribution), seed dispersal and post‐dispersal processes.

We used a well‐studied system dominated by a common east Mediterranean shrub (Sarcopoterium spinosum) to directly test the effect of shrubs on herbaceous community seed dispersal. We clipped all potential herbaceous seed sources from plots with or without a shrub at their centre, designated ‘shrub’ or ‘open’, respectively. Seed rain was then sampled over a 7‐month period, along four directions within a fine‐scale radial sampling pattern from the shrub core to its periphery and in corresponding positions in the open plots. Seed predation was monitored likewise.

The overall abundance and species richness of herbaceous seeds were similar at all distances from the core in the open plots and at the shrub periphery, but lower under the shrub canopy. However, the observed patterns were clearly directional, with the highest seed abundance and species richness found on the upslope periphery of the shrub patch.

These patterns were observed after the elimination of all within‐patch herbaceous seed sources, which suggests that the movement of seeds was mainly driven by gravity‐related mechanisms whose effect was modified by the shrubs.

Synthesis. A shrub can function simultaneously as both a seed trap and a barrier to herbaceous seed flow, with the exact balance determined by location within the patch. Furthermore, whether the effect of the shrub on herbaceous seeds is regarded as facilitatory or competitive is scale‐dependent. A mechanistic dissociation of seed dispersal from other processes modulated by the shrub in shaping the herbaceous community, as done in this study, is important for understanding the resilience of semi‐arid and arid ecosystems to environmental changes, especially to the increasingly observed drought‐induced mortality of shrubs associated with climate change.
Biological Flora of theBritishIsles:Gunnera tinctoria
Authors: Gioria Margherita , Osborne Bruce A.
Published: May 2013

This account presents information on all aspects of the biology ofGunnera tinctoria(Molina) Mirb. (G. chilensisLam.;G. scabraRuix & Pav.;G. pilosaKunth) that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of theBiological Flora of theBritish Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, history and conservation.

Gunnera tinctoriais a gynomonoecious, clonal, perennial herb that is naturalized in parts ofBritain, becoming invasive in parts of Ireland and, more recently, Scotland. It occurs where winter temperatures are mild, and precipitation and humidity are high.Gunnera tinctoriais native to SouthAmerica, predominantly in theAndean region ofChile andColombia, and probably in parts ofArgentina, ranging from sea level toc. 2000 m a.s.l.

Typical habitats inBritain andIreland include stream and river banks, lake and pond margins, coastal cliffs, as well as disturbed areas, such as roadsides, quarries and ditches. In its native range it occurs predominantly on the banks of rivers and streams, on coastal cliffs and within canopy gaps or at the margins of temperate‐humid rain forests.

Gunnera tinctoriaoccurs on a variety of substrates, mainly on alluvial or colluvial soils derived from volcanic material or on thin gley soils of marine origin. InIreland, it occurs naturally on soils with apHranging from 4.6 to 6.2 and has been cultivated in soils with a pHup to 7. Soil moisture content and soil organic matter vary greatly, although it rarely colonizes highly organic soils such as peat. It is susceptible to even mild water deficits at all stages of development, and its seedlings are also sensitive to waterlogged conditions.

Gunnera tinctoriaproduces large numbers of seeds and also spreads clonally, by a horizontal rhizome system. It is wind pollinated, although insect pollination has been reported inNewZealand. Seeds are likely to be predominantly water and/or bird dispersed. In its invasive range, it can form a large and persistent soil seed bank. Recruitment from seeds seems to be important for its initial establishment, while vegetative propagation is the main means of expansion, leading to dense clonal stands. Long‐distance seed dispersal seems to be central to the colonization of new areas, although the transport of vegetative propagules may also be important.

Gunnera tinctoriais a strong competitor in its invasive range, particularly in wet, humid environments. Its competitive ability arises from its large stature, the persistence of its seeds and rhizomes and a capacity for fixing nitrogen through a unique intracellular symbiosis with cyanobacteria (Nostoc) that may be particularly important for supporting the rapid growth of established plants early in the spring.
Biogeographic comparisons of herbivore attack, growth and impact of Japanese knotweed between Japan and France
Authors: Maurel Noëlie , Fujiyoshi Masaaki , Muratet Audrey , Porcher Emmanuelle , Motard Eric , Gargominy Olivier , Machon Nathalie
Published: May 2013

To shed light on the process of how exotic species become invasive, it is necessary to study them both in their native and non‐native ranges. Our intent was to measure differences in herbivory, plant growth and the impact on other species in Fallopia japonica in its native and non‐native ranges.

We performed a cross‐range full descriptive, field study in Japan (native range) and France (non‐native range). We assessed DNA ploidy levels, the presence of phytophagous enemies, the amount of leaf damage, several growth parameters and the co‐occurrence of Fallopia japonica with other plant species of herbaceous communities.

Invasive Fallopia japonica plants were all octoploid, a ploidy level we did not encounter in the native range, where plants were all tetraploid. Octoploids in France harboured far less phytophagous enemies, suffered much lower levels of herbivory, grew larger and had a much stronger impact on plant communities than tetraploid conspecifics in the native range in Japan.

Our data confirm that Fallopia japonica performs better – plant vigour and dominance in the herbaceous community – in its non‐native than its native range. Because we could not find octoploids in the native range, we cannot separate the effects of differences in ploidy from other biogeographic factors. To go further, common garden experiments would now be needed to disentangle the proper role of each factor, taking into account the ploidy levels of plants in their native and non‐native ranges.

Synthesis. As the process by which invasive plants successfully invade ecosystems in their non‐native range is probably multifactorial in most cases, examining several components – plant growth, herbivory load, impact on recipient systems – of plant invasions through biogeographic comparisons is important. Our study contributes towards filling this gap in the research, and it is hoped that this method will spread in invasion ecology, making such an approach more common.
Life‐history trade‐offs during the seed‐to‐seedling transition in a subtropical wet forest community
Authors: Muscarella Robert , Uriarte María , Forero‐Montaña Jimena , Comita Liza S. , Swenson Nathan G. , Thompson Jill , Nytch Christopher J. , Jonckheere Inge , Zimmerman Jess K.
Published: May 2013

The transition from seed to established seedling (STS) represents a major bottleneck in plant demography with implications for community dynamics and the maintenance of species diversity. The relative strength of seed limitation versus seedling establishment limitation can reveal life‐history trade‐offs that contribute to the maintenance of community diversity. If seed limitation dominates, chance arrival to open sites may play a key role in maintaining diversity. If seedling establishment limitation dominates, however, species relative abundances may depend more on tolerance to environmental and biotic conditions during seedling establishment (i.e. species‐specific regeneration niche).

We used three years of seed rain and seedling recruitment data for 19 species of tropical woody plants collected in the Luquillo Forest Dynamics Plot in Puerto Rico to (i) examine a trade‐off between seed and seedling establishment limitation and (ii) quantify the biotic and abiotic factors that mediate the STS transition.

We did not find evidence of a life‐history trade‐off in the form of a negative correlation between seed and seedling establishment limitation. However, species varied considerably in the relative levels of seed and seedling establishment limitation they displayed. Seed mass correlated negatively with seedling establishment limitation but not with seed limitation. We found striking differences in STS transition between life‐forms categorized as trees (including two palms) and lianas; lianas exhibited significantly higher STS transition rates than trees.

The biotic and abiotic variables most strongly associated with successful STS transition differed between life‐forms. For trees, conspecific seed density and temporal fruiting concentration had negative effects on seedling establishment, while seed mass had a positive effect. A significant interaction between leaf litter input at a plot and seed size suggested that large‐seeded species had higher STS transition probability in plots with more leaf litter biomass. This effect was reversed for small‐seeded species. For lianas, leaf litter had a negative effect on STS transition and temporal fruiting concentration had a positive effect.

Synthesis. Our analyses demonstrate the multidimensional axes of regeneration niches and how they can be related to seed size. Long‐term data sets are critical for understanding these relationships because the relevant factors vary along large spatial and temporal scales.
Independent variations of plant and soil mixtures reveal soil feedback effects on plant community overyielding
Authors: Hendriks Marloes , Mommer Liesje , de Caluwe Hannie , Smit‐Tiekstra Annemiek E. , van der Putten Wim H. , de Kroon Hans
Published: May 2013

Recent studies have shown that the positive relationship between plant diversity and plant biomass (‘overyielding’) can be explained by soil pathogens depressing productivity more in low than in high diverse plant communities. However, tests of such soil effects in field studies were constrained by experimental limitations to manipulate soil community composition independent of plant community composition. Here, we report of an experiment where feedback effects to plants were tested for both plant and soil monocultures and mixtures.

Our results demonstrate that overyielding is the result of plant species in mixture being more growth‐limited by ‘own’ soil biota than by soil biota of other plant species. This effect disappeared when the soils had been sterilized by gamma‐irradiation. Mixing plants themselves did not result in overyielding except when grown in the soil of one of the species (Leucanthemum vulgare), where growth of one species disproportionally increased in mixture compared to monoculture.

Soil nutrient availability could not explain differences in growth between the non‐sterilized soils. Therefore, our results suggest that plant species–specific soil biota rather than the plants have contributed to the plant community overyielding.

Species biomass ranking in mixtures highly differed between non‐sterilized soils of different histories of soil conditioning, whilst the ranking was more consistent in sterilized soil. Sterilized soils of different origin differed significantly in nutrient availability. These results suggest that shifts in competitive hierarchies depend on plant species–specific interactions influenced by soil biota and cannot be induced by mineral nitrogen.

Synthesis. Our results show that overyielding in four plant species mixtures can be due to species‐specific interactions between plants and their specific soil biota. Neither mixing the plant species alone nor the differential responses of species to mineral nitrogen influenced community productivity, but mixing soil biota did.
Effects of litter on seedling establishment in natural and semi‐natural grasslands: a meta‐analysis
Authors: Loydi Alejandro , Eckstein R. Lutz , Otte Annette , Donath Tobias W.
Published: May 2013

Plant litter is a key component in terrestrial ecosystems. It plays a major role in nutrient cycles and community organization. Land use and climate change may change the accumulation of litter in herbaceous ecosystems and affect plant community dynamics. Additionally, the transfer of seeds containing plant material (i.e. litter) is a widespread technique in grassland restoration.

Ecosystem responses to litter represent the outcome of interactions, whose sign and strength will depend on many variables (e.g. litter amount, seed size). A previous meta‐analysis (from 1999) reported that litter had an overall negative effect on seed germination and seedling establishment in different ecosystems. However, recent studies indicated that this might not be the case in grassland ecosystems.

We used 914 data from 46 independent studies to analyse the effects of litter on seedling (i) emergence, (ii) survival and (iii) biomass, employing meta‐analytical techniques. Each data set was stratified according to methodology, grassland type, irrigation conditions, litter amount and seed size.

We found an overall neutral effect of litter presence on seedling emergence and survival and a positive effect on seedling biomass. However, whereas for field experiments the response remained neutral, it was positive for common garden studies. In glasshouse experiments, litter effects were negative for emergence and positive for biomass.

Litter may have a positive effect on seedling recruitment in dry grasslands or under water‐limited conditions, or in the presence of low to medium litter amounts (< 500 g m−2). However, high litter amounts (> 500 g m−2) will inhibit seedling recruitment. Large seeds showed a more positive response to litter presence with respect to seedling emergence and survival, but not concerning biomass.

Synthesis. Under dry conditions (e.g. dry grasslands or dry periods) or with low to medium litter amounts, litter presence has a positive effect on seedling establishment. However, climate and land use change may promote litter accumulation and reduce seedling establishment, affecting grasslands composition and ecosystem functions.
Spatial and temporal variability in positive and negative plant–bryophyte interactions along a latitudinal gradient
Authors: Doxford Simon W. , Ooi Mark K. J. , Freckleton Robert P.
Published: May 2013

According to the Stress Gradient Hypothesis, facilitation and competition are considered to be important at opposite ends of an environmental gradient. However, recent research has questioned the generality of this idea. One limitation is that the small‐scale and short‐term nature of much research into plant interactions limits our understanding of how their strength and importance changes over large temporal and spatial scales.

Here, we experimentally measured the interactions between bryophytes and a community of winter annuals in sand dunes along a c. 1500 km latitudinal gradient over two generations. We carried out bryophyte‐removal experiments within permanent quadrates at eight field sites along the Atlantic coast of Western Europe, to measure the spatio‐temporal variation in the strength and direction of biotic interactions.

We found a striking contrast in the nature of plant–bryophyte interactions observed in consecutive years of study, using three measures of plant demographics: density, plant performance and population growth. In the first year facilitation dominated, but showed an overall decline in strength from south to north. In the following year facilitation was largely replaced by competition, which also declined in strength from south to north along the latitudinal gradient.

Interaction strengths are correlated with population growth rate, so that facilitation dominated in sites and years where population growth was low, whereas when population growth was high competition appeared to be more important. This is consistent with the Stress Gradient Hypothesis, but further to previous studies we demonstrate that this mechanism operates over time and in terms of population growth rates.

The effects of bryophyte removal were more strongly related to population density and population growth than to individual plant performance (i.e. reproductive output). This result suggests interactions are most important during germination and early establishment of annuals, and not in terms of inter‐plant competition for resources.

Synthesis: This study is one of the first to show that there may be extreme spatio‐temporal variation in the strength and direction of interactions, with substantial changes in their impact over a short time period. Our results suggest that the Stress Gradient Hypothesis may operate within and along gradients, as well as inter‐annually. This may therefore play a role in buffering population dynamics.
Enemy damage of exotic plant species is similar to that of natives and increases with productivity
Authors: Dostál Petr , Allan Eric , Dawson Wayne , van Kleunen Mark , Bartish Igor , Fischer Markus
Published: May 2013

In their colonized ranges, exotic plants may be released from some of the herbivores or pathogens of their home ranges but these can be replaced by novel enemies. It is of basic and practical interest to understand which characteristics of invaded communities control accumulation of the new pests. Key questions are whether enemy load on exotic species is smaller than on native competitors as suggested by the enemy release hypothesis (ERH) and whether this difference is most pronounced in resource‐rich habitats as predicted by the resource–enemy release hypothesis (R‐ERH).

In 72 populations of 12 exotic invasive species, we scored all visible above‐ground damage morphotypes caused by herbivores and fungal pathogens. In addition, we quantified levels of leaf herbivory and fruit damage. We then assessed whether variation in damage diversity and levels was explained by habitat fertility, by relatedness between exotic species and the native community or rather by native species diversity.

In a second part of the study, we also tested the ERH and the R‐ERH by comparing damage of plants in 28 pairs of co‐occurring native and exotic populations, representing nine congeneric pairs of native and exotic species.

In the first part of the study, diversity of damage morphotypes and damage levels of exotic populations were greater in resource‐rich habitats. Co‐occurrence of closely related, native species in the community significantly increased the probability of fruit damage. Herbivory on exotics was less likely in communities with high phylogenetic diversity.

In the second part of the study, exotic and native congeneric populations incurred similar damage diversity and levels, irrespective of whether they co‐occurred in nutrient‐poor or nutrient‐rich habitats.

Synthesis. We identified habitat productivity as a major community factor affecting accumulation of enemy damage by exotic populations. Similar damage levels in exotic and native congeneric populations, even in species pairs from fertile habitats, suggest that the enemy release hypothesis or the R‐ERH cannot always explain the invasiveness of introduced species.
Are stored carbohydrates necessary for seed production in temperate deciduous trees?
Authors: Ichie Tomoaki , Igarashi Shuichi , Yoshida Shohei , Kenzo Tanaka , Masaki Takashi , Tayasu Ichiro
Published: May 2013

Many tree species undergo large fluctuations from year to year in seed production, a phenomenon known as masting. The resource budget model, based on the assumption that abundant seeding in a masting year depends on the abundance of resources stored over several years, is a key hypothesis in explaining the mechanism of masting. But do masting species really need such long‐term storage to produce a large seed crop?

To test this hypothesis, we studied the relationship between the carbon accumulation period for seed production, as estimated by radiocarbon (14C) analyses, and the coefficient of variation of annual seed production in 10 canopy tree species in a temperate deciduous forest. These species differ widely in their reproductive intervals.

In all the species studied, the accumulation period was < 1.4 years before seed maturation. Moreover, without taking species or reproductive intervals into account, there was no significant correlation between the carbon accumulation period and the fluctuation of annual seed production; both remained at an even level.

Synthesis. Our results suggest that temperate canopy trees used photosynthates produced in the current and/or the previous year for seed production, regardless of reproductive intervals. It might therefore be necessary to reconsider the importance of stored carbohydrate resources for masting.
Trait‐based climate change predictions of plant community structure in arid steppes
Authors: Frenette‐Dussault Cédric , Shipley Bill , Meziane Driss , Hingrat Yves
Published: May 2013

Global climate change is possibly one of the most important challenges for current and future human populations due to its wide‐ranging effects on ecosystems. Global prediction models suggest that in some areas of the world (e.g. Northern Africa, Central America) an increase in aridity might strongly disturb agricultural production and affect food security. To counterbalance these negative effects, reliable predictive models are needed to anticipate ecosystem changes.

We tested the ability of the Community Assembly by Trait‐based Selection (CATS) model that is based on the principle of maximum entropy and trait‐based environmental filtering, to predict actual and future plant community composition in the arid steppes of eastern Morocco. Specifically, we asked whether this model was adequate for predicting actual community composition, based on predicted community‐weighted mean (CWM) traits, and what would be the changes in community composition under various scenarios of climate change for the period 2080—2099.

The CATS model could predict > 90% of actual community composition if the actual CWM traits were known but only ˜40% if the CWM values were predicted from estimated aridity and grazing values. The predictions of community composition for 2080—2099 suggested that, regardless of the climate change scenario considered, the dominant group in grazed and ungrazed sites would shift from ruderal species to stress‐tolerant sub‐shrubs, which would constitute up over 80% of total community composition in some cases.

Synthesis. Our findings suggest that effects of climate change will strongly modify plant community structure in arid steppes, possibly accentuating the process of desertification, and reducing the pastoral value of the vegetation. Future research efforts should concentrate on the identification of strong trait–environment relationships to improve model predictions.
Hierarchical responses of plant–soil interactions to climate change: consequences for the global carbon cycle
Authors: Bardgett Richard D. , Manning Pete , Morriën Elly , De Vries Franciska T.
Published: May 2013

Interactions between plant and soil communities play a major role in determining the impact of climate change on ecosystem functioning and the carbon cycle, and the mechanisms involved operate over a wide range of spatial and temporal scales.

We present a framework for understanding the consequences of climate‐induced changes in plant–soil feedback for the carbon cycle. The framework describes a hierarchy of mechanisms by which changes in climate impact on ecosystem carbon dynamics at three levels of response, namely individual and community reordering and species immigration and loss.

For each level, we identify the mechanisms by which climate change impacts on plant–soil interactions with consequences for the carbon cycle. We also demonstrate that the potential for decoupling of plant–soil interactions increases across the three levels of response, being greatest with species immigration and/or loss, for example, if plants were to undergo a biome shift, but their associated soil communities did not. Such decoupling is a largely unrecognized, but potentially important regulator of the future global carbon cycle.

Synthesis. The framework presented here highlights a need for a new approach to the study of climate change impacts on plant–soil interactions and carbon cycling that integrates this hierarchy of responses, and incorporates the decoupling of above‐ground and below‐ground networks, across a range of temporal and spatial scales, and ecosystems.
Complex plant–soil interactions enhance plant species diversity by delaying community convergence
Authors: Fukami Tadashi , Nakajima Mifuyu
Published: May 2013

A plant that causes specific changes to soil biota may either positively or negatively affect the performance of the plant that subsequently grows in that location. These effects, known as plant–soil feedback, can affect plant species diversity at multiple spatial scales.

It has been hypothesized that positive plant–soil feedback reduces alpha (local) diversity by allowing dominance by early‐arriving species, but increases gamma (regional) diversity by promoting community divergence (increased beta diversity) through the emergence of alternative stable states. In contrast, negative plant–soil feedback has been thought to increase alpha diversity by allowing local species coexistence, but to reduce gamma diversity by promoting community convergence (reduced beta diversity). Although widely accepted, these hypotheses do not consider the possibility that plant species differ in their effect on, and their response to, a given other species via soil biota. In reality, plant–soil interactions can be complex, with the strength of the interactions variable between plant species. Using a basic simulation model of plant community assembly, we investigated how complex plant–soil interactions might affect plant diversity during succession.

When we included only positive or negative intraspecific plant–soil feedback in the model, with no variation in the strength of interspecific plant–soil interactions, results were consistent with the conventional hypotheses. When we allowed the strength of plant–soil interactions to differ between species, plant–soil interactions enhanced alpha diversity initially and beta and gamma diversity subsequently. Diversity enhancement occurred not necessarily because alternative stable states emerged, but primarily because complex plant–soil interactions lengthened the time during which local species composition changed. Due to the longer time for changes in species composition, the high level of beta and gamma diversity at the early stage of succession was maintained for a long time despite eventual community convergence. Thus, diversity enhancement was often transient, though long‐lasting, making the conventional concept of alternative stable states inadequate for explaining diversity.

Synthesis. Based on these findings, we propose the new hypothesis that complex plant–soil interactions enhance plant species diversity by delaying community convergence. This hypothesis highlights the role of plant–soil interactions as a driver of long‐lasting transient dynamics of community assembly.
Plant–soil feedbacks: the past, the present and future challenges
Authors: van der Putten Wim H. , Bardgett Richard D. , Bever James D. , Bezemer T. Martijn , Casper Brenda B. , Fukami Tadashi , Kardol Paul , Klironomos John N. , Kulmatiski Andrew , Schweitzer Jennifer A. , Suding Katherine N. , Van de Voorde Tess F. J. , Wardle David A.
Published: May 2013

Plant–soil feedbacks is becoming an important concept for explaining vegetation dynamics, the invasiveness of introduced exotic species in new habitats and how terrestrial ecosystems respond to global land use and climate change. Using a new conceptual model, we show how critical alterations in plant–soil feedback interactions can change the assemblage of plant communities. We highlight recent advances, define terms and identify future challenges in this area of research and discuss how variations in strengths and directions of plant–soil feedbacks can explain succession, invasion, response to climate warming and diversity‐productivity relationships.

While there has been a rapid increase in understanding the biological, chemical and physical mechanisms and their interdependencies underlying plant–soil feedback interactions, further progress is to be expected from applying new experimental techniques and technologies, linking empirical studies to modelling and field‐based studies that can include plant–soil feedback interactions on longer time scales that also include long‐term processes such as litter decomposition and mineralization.

Significant progress has also been made in analysing consequences of plant–soil feedbacks for biodiversity‐functioning relationships, plant fitness and selection.

To further integrate plant–soil feedbacks into ecological theory, it will be important to determine where and how observed patterns may be generalized, and how they may influence evolution.

Synthesis. Gaining a greater understanding of plant–soil feedbacks and underlying mechanisms is improving our ability to predict consequences of these interactions for plant community composition and productivity under a variety of conditions. Future research will enable better prediction and mitigation of the consequences of human‐induced global changes, improve efforts of restoration and conservation and promote sustainable provision of ecosystem services in a rapidly changing world.
Consequences of plant–soil feedbacks in invasion
Authors: Suding Katharine N. , Stanley Harpole William , Fukami Tadashi , Kulmatiski Andrew , MacDougall Andrew S. , Stein Claudia , van der Putten Wim H.
Published: May 2013

Plant species can influence soil biota, which in turn can influence the relative performance of plant species. These plant–soil feedbacks (PSFs) have been hypothesized to affect many community‐level dynamics including species coexistence, dominance and invasion.

The importance of PSFs in exotic species invasion, although widely hypothesized, has been difficult to determine because invader establishment necessarily precedes invader‐mediated PSFs. Here, we combine a spatial simulation model of invasion that incorporates PSFs with a meta‐analysis that synthesizes published case studies describing feedbacks between pairs of native and exotic species.

While our spatial model confirmed the link between positive soil feedbacks (‘home’ advantage) for exotic species and exotic species spread, results were dependent on the initial abundance of the exotic species and the equivalence of dispersal and life history characteristics between exotic and native species.

The meta‐analysis of 52 native–exotic pairwise feedback comparisons in 22 studies synthesized measures of native and exotic performance in soils conditioned by native and exotic species. The analysis indicated that the growth responses of native species were often greater in soil conditioned by native species than in soil conditioned exotic species (a ‘home’ advantage). The growth responses of exotic species were variable and not consistently related to species soil‐conditioning effects.

Synthesis. Overlaying empirical estimates of pairwise PSFs with spatial simulations, we conclude that the empirically measured PSFs between native and exotic plant species are often not consistent with predictions of the spread of exotic species and mono‐dominance. This is particularly the case when exotic species are initially rare and share similar dispersal and average fitness characteristics with native species. However, disturbance and other processes that increase the abundance of exotic species as well as the inclusion of species dispersal and life history differences can interact with PSF effects to explain the spread of invasive species.