bluuebunny/crossref_metadata_2025_split huggingface dataset:
The hare, the tortoise and the crocodile: the ecology of angiosperm dominance, conifer persistence and fern filtering
Authors: COOMES DAVID A. , ALLEN ROBERT B. , BENTLEY WARREN A. , BURROWS LARRY E. , CANHAM CHARLES D. , FAGAN LAURA , FORSYTH DAVID M. , GAXIOLA‐ALCANTAR AURORA , PARFITT ROGER L. , RUSCOE WENDY A. , WARDLE DAVID A. , WILSON DEBORAH J. , WRIGHT ELAINE F. 
Published: September 2005

SummaryAngiosperm trees often dominate forests growing in resource‐rich habitats, whereas conifers are generally restricted to less productive habitats. It has been suggested that conifers may be displaced by angiosperms except where competition is less intense, because conifer seedlings are inherently slow growing, and are outpaced by faster‐growing angiosperm species. Here we investigate whether competition with ferns and deeply shading trees also contributes to a failure of conifers to regenerate in resource‐rich habitats.We examined how changes in soil nutrient availability and drainage affected vegetation along the retrogressive stages of a soil chronosequence in southern New Zealand. Vegetation composition shifted from angiosperm‐tree dominance on ‘recent’ alluvial terraces (< 24 ky), via coniferous‐tree dominance on older marine terraces (79–121 ky), to coniferous‐shrub dominance on the oldest marine terraces (291 ky). Soil drainage deteriorated along the sequence, and N : Pleavesand N : Psoilindicate increasing P‐limitation. Conifer species appear to be adapted to persistence on infertile and poorly drained soils.The floor of the relatively fertile alluvial forests was deeply shaded (∼1% light transmission) by dense groves of tree‐ferns and ground‐ferns, and by large‐leaved subcanopy trees. Few seedlings of any type were found on the forest floor, even in tree‐fall gaps, and establishment was restricted to rotting logs and tree‐fern trunks. Angiosperms were particularly successful at colonizing these raised surfaces.Less shade was cast by the conifer‐dominated forests on infertile marine terraces (∼5% light transmission), which lacked tall ferns. There were many opportunities for conifer establishment, with high seedling densities recorded on the forest floor and on logs. By contrast, angiosperm seedlings were mainly restricted to logs.Our results suggest that several mechanisms act in concert to reduce regeneration opportunities for conifers in productive habitats. In particular, we suggest that tall ferns and deep shade are responsible for a restriction of regeneration opportunities in relatively productive forests in New Zealand, diminishing the opportunities for conifers to escape the competitive effects of fast‐growing angiosperms. Thus ‘crocodiles’ may alter the outcome of the race between ‘hares’ and ‘tortoises’.
Differential genetic influences on competitive effect and response in Arabidopsis thaliana
Authors: F. CAHILL JAMES , KEMBEL STEVEN W. , GUSTAFSON DANNY J. 
Published: September 2005

Summary

Competition plays an important role in structuring populations and communities, but our understanding of the genetic basis of competitive ability is poor. This is further complicated by the fact that plants can express both competitive effect (target plant influence upon neighbour growth) and competitive response (target plant growth as a function of a neighbour) abilities, with these ecological characteristics potentially being independent.
Using the model plant species Arabidopsis thaliana, we investigated patterns of intraspecific variation in competitive effect and response abilities and their relationships to other plant traits and resource supply rates.
Both competitive effect and response were measured for 11 genotypes, including the Columbia ecotype and 10 derived mutant genotypes. Plants were grown alone, with intragenotypic competition, and with intergenotypic competition in a replicated blocked design with high nutrient and low nutrient soil nutrient treatments. We quantified competitive effect and response on absolute and per‐gram bases.
Competitive effect and response varied among genotypes, with the relative competitive abilities of genotypes consistent across fertilization treatments. Overall, high rates of fertilization increased competitive effect and competitive response abilities of all genotypes. Both competitive effect and response were correlated with neighbour biomass, though genotype‐specific traits also influenced competitive response.
At the genotype level, there was no correlation between competitive effect and response in either fertilization treatment. Overall patterns in competitive response appeared consistent among inter‐ and intragenotypic competition treatments, indicating that a target genotype's response to competition was not driven by the genetic identity of the competitor.
These findings indicate that within A. thaliana, there is the potential for differential selection on competitive effect and response abilities, and that such selection may influence different sets of plant traits. The concept of a single competitive ability for a given plant is not supported by these data, and we suggest continued recognition of these dual competitive abilities is essential to understanding the potential role of competition in influencing intra‐ and interspecific processes.
Seed limitation in a Panamanian forest
Authors: SVENNING JENS‐CHRISTIAN , WRIGHT S. JOSEPH 
Published: September 2005

SummaryThe role of seed limitation in tropical forests remains uncertain owing to the scarcity of experimental evidence. We performed seed addition experiments to assess seed limitation for 32 shade‐tolerant tropical forest species and monitored the natural seed rain of 25 of these species for 17 years.One, two or five seeds were sown into 0.0079‐m2plots for large‐ (n = 5 species), medium‐ (n = 5) and small‐seeded species (n = 22), respectively. The experiment was replicated at 69 sites, placed in groups of three at 23 locations. Seedling establishment was evaluated after 1 and 2 years in paired seed addition and control plots. Natural seedling emergence and understorey plant density were also measured.Median natural seed rain was 0.31 seeds m−2 year−1per focal species.Seed addition enhanced seedling establishment in 31 and 26 of the 32 species after 1 and 2 years, respectively. Mean number of focal species’ seedlings after 2 years was 0.002 seedlings in control plots and 0.12, 0.37 and 0.60 seedlings in seed addition plots for large‐, medium‐ and small‐seeded species, respectively.A 25 seeds added treatment increased seedling establishment by ≥ 2.0‐fold over the five seeds added treatment after 2 years.Community‐wide recruitment and understorey plant density were strongly seed‐limited. The natural density of understorey plants averaged 12 plants m−2and was significantly less than for seedlings of the single focal species in plots with ≥ 2 seeds added 2 years earlier.The number of established seedlings per seed added was independent of seed size.Treatment (adding zero or five seeds), species identity and location all affected seedling establishment for the 11 small‐seeded species represented at all sites, with treatment and its interactions accounting for 86% of the explained variation.Our results suggest that seed limitation plays a dominant role in seedling recruitment and understorey plant community assembly in tropical forests. Although strong seed limitation may set the stage for species‐neutral community assembly, the species differences in seedling establishment rate and its spatial variation demonstrate an important role for species‐specific processes.
A mechanistic model for secondary seed dispersal by wind and its experimental validation
Authors: SCHURR FRANK M. , BOND WILLIAM J. , MIDGLEY GUY F. , HIGGINS STEVEN I. 
Published: September 2005

Summary

Secondary seed dispersal by wind, the wind‐driven movement of seeds along the ground surface, is an important dispersal mechanism for plant species in a range of environments.
We formulate a mechanistic model that describes how secondary dispersal by wind is affected by seed traits, wind conditions and obstacles to seed movement. The model simulates the movement paths of individual seeds and can be fully specified using independently measured parameters.
We develop an explicit version of the model that uses a spatially explicit representation of obstacle patterns, and also an aggregated version that uses probability distributions to model seed retention at obstacles and seed movement between obstacles. The aggregated version is computationally efficient and therefore suited to large‐scale simulations. It provides a very good approximation of the explicit version (R2 > 0.99) if initial seed positions vary randomly relative to the obstacle pattern.
To validate the model, we conducted a field experiment in which we released seeds of seven South African Proteaceae species that differ in seed size and morphology into an arena in which we systematically varied obstacle patterns. When parameterized with maximum likelihood estimates obtained from independent measurements, the explicit model version explained 70–77% of the observed variation in the proportion of seeds dispersed over 25 m and 67–69% of the observed variation in the direction of seed dispersal.
The model tended to underestimate dispersal rates, possibly due to the omission of turbulence from the model, although this could also be explained by imprecise estimation of one model parameter (the aerodynamic roughness length).
Our analysis of the aggregated model predicts a unimodal relationship between the distance of secondary dispersal by wind and seed size. The model can also be used to identify species with the potential for long‐distance seed transport by secondary wind dispersal.
The validated model expands the domain of mechanistic dispersal models, contributes to a functional understanding of seed dispersal, and provides a tool for predicting the distances that seeds move.
Mesoscale distribution patterns of Amazonian understorey herbs in relation to topography, soil and watersheds
Authors: COSTA FLÁVIA R. C. , MAGNUSSON WILLIAM E. , LUIZAO REGINA C. 
Published: September 2005

SummaryMany authors have suggested that topography and soils are the major determinants of species distributions and community patterns at small or regional scales, but few studies addressed the patterns at mesoscales. We used Reserva Ducke (100 km2) as a model to analyse the effects of soil, topography and watersheds on the variation of the herb community composition, and to determine the relative importance of the environmental factors on species composition.Taxonomic groups are frequently used as surrogates in studies of biodiversity distribution and complementarity, but their efficacy is controversial. We therefore studied the correlations between the distributional patterns of three different herb groups (Marantaceae, pteridophytes and ‘others’) and their responses to environmental predictors.Terrestrial herbs were sampled in 59 plots of 250 × 2 m, systematically distributed over the reserve. Plots followed isoclines of altitude, to minimize the internal variation of soil. Composition of the total herb community and of the three herb groups was summarized with PCoA.Soil structure, represented by PCA axes, was the main determinant of the variation in herb composition for all groups, but slope affected only pteridophytes. Soil and topography explained less than one‐third of the variance in community data. Herb composition was significantly different between watersheds, but watersheds differ only slightly in soil parameters. Our results indicate high turnover in species composition, on spatial scales of 5–10 km in central Amazonia, which is not necessarily associated with soil change.Compositional patterns of the three groups analysed were significantly correlated, but with low values for the correlation coefficient. Although composition was correlated, the responses to environmental predictors differed among groups, and the use of one group as a surrogate will miss around 50% of the variation in other groups.Although important, soil and topography alone cannot predict herb community structure. Knowledge of geographical, historical or other landscape features, such as watershed morphology, may therefore be necessary to predict the turnover patterns over mesoscales. Moreover, the same factors may not have the same effectiveness as predictors of the structure of seemingly similar biological groups.
Rapid responses of high‐mountain vegetation to early Holocene environmental changes in the Swiss Alps
Authors: TINNER WILLY , KALTENRIEDER PETRA 
Published: September 2005

Summary

The Early Holocene sediment of a lake at tree line (Gouillé Rion, 2343 m a.s.l.) in the Swiss Central Alps was sampled for plant macrofossils. Thin (0.5 cm) slices, representing time intervals of c. 50 years each from 11 800 to 7800 cal. year bp, were analysed and the data compared with independent palaeoclimatic proxies to study vegetational responses to environmental change.
Alpine plant communities (e.g. with Salix herbacea) were established at 11 600–11 500 cal. year bp, when oxygen‐isotope records showed that temperatures increased by c. 3–4 °C within decades. Larix decidua trees reached the site at c. 11 350 cal. year bp, probably in response to further warming by 1–2 °C. Forests dominated by L. decidua persisted until 9600 cal. year bp, when Pinus cembra became more important.
The dominance of Larix decidua for two millennia is explained by dry summer conditions, and possibly low winter temperatures, which favoured it over the late‐successional Pinus cembra. Environmental conditions were a result of variations in the earth's orbit, leading to a maximum of summer and a minimum of winter solar radiation. Other heliophilous and drought‐adapted species, such as Dryas octopetala and Juniperus nana, could persist in the open L. decidua forests, but were out‐competed when the shade‐tolerant P. cembra expanded.
The relative importance of Larix decidua decreased during periods of diminished solar radiation at 11 100, 10 100 and 9400 cal. year bp. Stable concentrations of L. decidua indicate that these percentage oscillations were caused by temporary increases of Pinus cembra, Dryas octopetala and Juniperus nana that can be explained by increases in moisture and/or decreases in summer temperature.
The final collapse of Larix decidua at 8400 cal. year bp was possibly related to abrupt climatic cooling as a consequence of a large meltwater input to the North Atlantic. Similarly, the temporary exclusion of Pinus cembra from tree line at 10 600–10 200 cal. year bp may be related to slowing down of thermohaline circulation at 10 700–10 300 cal. year bp.
Our results show that tree line vegetation was in dynamic equilibrium with climate, even during periods of extraordinarily rapid climatic change. They also imply that forecasted global warming may trigger rapid upslope movements of the tree line of up to 800 m within a few decades or centuries at most, probably inducing large‐scale displacements of plant species as well as irrecoverable biodiversity losses.
Manipulation of nutrients and grazing levels on heather moorland: changes inCallunadominance and consequences for community composition
Authors: HARTLEY S. E. , MITCHELL R. J. 
Published: September 2005

SummaryExperimental studies of the combined effects of herbivory and the availability of nutrients on semi‐natural communities remain relatively scarce. Here we report the effects of 6 years of nutrient addition (N, P and K) and protection from grazing on moorland plant communities in the Scottish uplands, particularly on the cover of the dominantCalluna vulgaris. We also recorded the cover of vascular plants and bryophytes, to assess the impact of changes inCallunadominance on competing species.Grazing in combination with nitrogen addition caused the greatest decline inCallunacover, typically 40–50%, but nitrogen addition did not cause a significant decline inCallunaon plots protected from grazing. MoreCallunashoots were browsed on nitrogen‐treated plots than on unfertilized ones, presumably because grazing animals preferred fertilizedCalluna.Nitrogen addition allowed grasses to increase in cover, especially on grazed plots. However,Nardus stricta,Festuca ovinaandAgrostissp. all declined in fenced areas but increased in grazed plots, whereasDeschampsia flexuosaandFestuca rubraincreased in fenced plots.The effects of grazing and nutrient addition varied markedly between sites, possibly because of differences in soil moisture and organic matter. Nitrogen addition, however, increased soil nitrogen mineralization rates in both glens.Fencing increased the cover of grazing‐intolerant plants with low nutrient demands (as classified by Ellenberg and suited species scores) that were categorized as competitive plants by Grime's CSR model. Plots receiving nitrogen and phosphorus had more nutrient‐demanding plants able to tolerate high grazing pressure that were often classified as ruderals.The impact of nitrogen addition on the cover ofCallunaand on competing grass species in the community critically depends on the level of grazing. Changes in community composition caused by grazing and fertilizer addition can be explained in terms of the ecological tolerances of individual species, allowing us to predict the types of plants that are likely to increase or decrease in cover.
Effects of competition, resource availability and invertebrates on tree seedling establishment
Authors: LADD BRENTON M. , FACELLI JOSÉ M. 
Published: September 2005

Summary

We studied the establishment of tree seedlings in Mediterranean‐type old fields in South Australia in different biotic environments and under different levels of resource availability. Specifically we wanted to: (a) test for a logarithmic relationship between the relative intensity of competition (RCI) and resource availability; (b) assess the potential of confounding resource competition with invertebrate herbivory; and (c) assess whether the architecture of the plant community had any qualitative or quantitative effects upon the relationship between resource availability and RCI.
Our glasshouse experiment showed that RCI increased with resource availability at low levels of resources, but not at higher levels, consistent with a logarithmic relationship.
The effects of resource competition and invertebrate herbivory were heavily confounded in the field experiment.
Plant architecture significantly affected the behaviour and abundance of invertebrates and we therefore conclude that it has the potential to modify the relationship between resource availability and competitive intensity.
Although the habitat templet/C‐S‐R model appears reasonably robust, modification of its general framework may be required because one of its basic underlying assumptions is most accurate when competition is defined phenomenologically.
Establishment of an emerging generalist pathogen in redwood forest communities
Authors: MALONEY P. E. , LYNCH S. C. , KANE S. F. , JENSEN C. E. , RIZZO D. M. 
Published: September 2005

Summary

Phytophthora ramorum (causal agent of sudden oak death) is an emerging generalist pathogen in coastal forests of California and Oregon, USA, that causes lethal stem infections on oaks (Quercus spp.) and tanoak (Lithocarpus densiflorus) as well as non‐lethal foliar infections on a broad range of trees and shrubs.
We studied P. ramorum over its known range in coastal redwood forests to determine forest compositional variables that are important to its epidemiology within the geographical area that it has already invaded. Redwood forests are dominated by coast redwood (Sequoia sempervirens), tanoak and California bay laurel (Umbellularia californica).
A total of 120 permanent plots (500 m2 each) were established in redwood forests at 12 sites within the main epidemic area in California. Over 5000 trees were mapped and examined for the presence of P. ramorum during spring 2002 and resampled in spring 2003.
Mean incidence of P. ramorum across all plots was 0.17 ± 0.01 in 2002 and 0.24 ± 0.02 in 2003. The highest infection levels by P. ramorum were found on California bay laurel (range 0.42–0.69) and tanoak (0.32–0.45). The highest levels of mortality were associated with tanoak and ranged from 0 to 66%, with 62.5% of that mortality associated with P. ramorum infection.
Disease incidence above 30% was most often associated with bay laurel importance value. In plots with few bay laurel stems, high disease levels were associated with the presence of understorey tanoaks. Bay laurel and small tanoaks are thought to represent the main source of inoculum for further spread of P. ramorum.
Differential host mortality due to this emerging generalist pathogen will exert considerable influence on redwood forest dynamics, with potentially dramatic shifts in forest composition and structure and subsequent cascading ecological and evolutionary effects.
Interactions among tree‐line conifers: differential effects of pine on spruce and larch
Authors: DULLINGER S. , DIRNBÖCK T. , KÖCK R. , HOCHBICHLER E. , ENGLISCH T. , SAUBERER N. , GRABHERR G. 
Published: September 2005

SummaryPlant–plant interactions are increasingly considered as complex phenomena involving both negative and positive components. Within a community, the relative importance of these components is probably species‐specific and may also vary among life‐history stages and along environmental gradients.We used the tree line of the north‐eastern Calcareous Alps of Austria, composed of shrubbyPinus mugoand uprightPicea abiesandLarix decidua, as a simple system in which to investigate these interactions. We focused on the largely unknown effects of pines on spruce and larch, rather than onP. mugo, which is known to be competitively displaced by the two tree species.We used regression models on observational data to analyse the responses of the trees to a gradient of pine cover in terms of recruitment, growth, fecundity and browsing damage, and to determine whether effects involved both competitive and facilitative components, if they depended on the life‐history stage of the trees and if they were species‐specific.We detected a pronounced negative effect of pine cover on recruitment and growth of both spruce and larch, whereas seed production was unaffected. Larch turned out to be more sensitive to pine competition: its recruitment and growth are superior to that of spruce in open habitats but this advantage vanishes in dense pine thickets.Contrary to expectations, the effects of pine cover on growth rates of spruce and larch did not depend on the life‐history stage of the trees.Pine cover is a major determinant of browsing damage for both spruce and larch, indicating that it does have a positive effect in providing shelter against herbivores.The differential effects of pines on spruce and larch are likely to favour spruce at the expense of larch in realizing potential habitat expansion as a result of climate change. Disregarding the complex details of plant–plant interactions may thus result in unrealistic predictions of species responses to environmental changes.