bluuebunny/crossref_metadata_2025_split 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

Summary

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

SummaryFuels 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

Summary

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

Summary

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

SummaryPartitioning 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

Summary

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

Summary

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

SummaryThis 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

Summary
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.