bluuebunny/crossref_metadata_2025 huggingface dataset:
Trends in species diversity and composition of urban vegetation over three decades
Authors: Pyšek Petr , Chocholousková Zdena , †Pyšek Antonín , Jarošík Vojtěch , Chytrý Milan , Tichý Lubomír
Published: February 2009

Question: What was the change in diversity of urban synantropic vegetation in a medium‐sized Central European city during the period of increasing urbanization (1960s‐1990s)?

Location: The city of Plzeň, an industrial centre of the western part of the Czech Republic.

Methods: Sampling of various types of synanthropic vegetation, conducted in the 1960s, was repeated by using the same methods in the 1990s. This yielded 959 relevés, of which 623 were made in the 1960s and 336 in the 1990s. The relevés were assigned to the following phytosociological classes: Chenopodietea, Artemisietea vulgaris, Galio‐Urticetea, Agropyretea repentis and Plantaginetea majoris. Total number of vascular plant species, evenness index J, number of alien species (classified into archaeophytes and neophytes), and mean Ellenberg indicator values for light, temperature, continentality, moisture, soil reaction, and nutrients were obtained for each relevé.

Results: From 1960s to 1990s, there was a significant decrease of species richness and diversity in synanthropic vegetation. The proportion of archaeophytes decreased in most vegetation types, indicating the contribution of this group of species, often confined to specific rural‐like habitats, to the observed impoverishment of ruderal vegetation. The proportion of neophytes did not change between the two periods. Comparison between 1960s and 1990s indicated a decrease in light, temperature, moisture, soil reaction and nutrient indicator values in some vegetation types. In both periods, Artemisieta, Galio‐Urticetea and Chenopodietea formed a distinct group harbouring more species than Agropyretea and Plantaginetea. Neophytes, i.e. recently introduced species, were most represented in the early successional annual vegetation of Chenopodietea, rather than in perennial vegetation of the other classes.

Conclusions: Synanthropic vegetation of Plzeň exhibited a general trend of decrease in species diversity.
The effect of fire interval on post‐fire understorey communities in Yellowstone National Park
Authors: Schoennagel T. , Waller D.M. , Turner M.G. , Romme W.H.
Published: February 2009

Questions: How does the time interval between subsequent stand‐replacing fire events affect post‐fire understorey cover and composition following the recent event? How important is fire interval relative to broad‐ or local‐scale environmental variability in structuring post‐fire understorey communities?

Location: Subalpine plateaus of Yellowstone National Park (USA) that burned in 1988.

Methods: In 2000, we sampled understorey cover and Pinus contorta density in pairs of 12–yr old stands at 25 locations. In each pair, the previous fire interval was either short (7–100 yr) or long (100–395 yr). We analysed variation in understorey species richness, total cover, and cover of functional groups both between site pairs (using paired t‐tests) and across sites that experienced the short fire intervals (using regression and ordination). We regressed three principal components to assess the relative importance of disturbance and broad or local environmental variability on post‐fire understorey cover and richness.

Results: Between paired plots, annuals were less abundant and fire‐intolerant species (mostly slow‐growing shrubs) were more abundant following long intervals between prior fires. However, mean total cover and richness did not vary between paired interval classes. Across a gradient of fire intervals ranging from 7–100 yr, total cover, species richness, and the cover of annuals and nitrogen‐fixing species all declined while the abundance of shrubs and fire‐intolerant species increased. The few exotics showed no response to fire interval. Across all sites, broad‐scale variability related to elevation influenced total cover and richness more than fire interval. Conclusions: Significant variation in fire intervals had only minor effects on post‐fire understorey communities following the 1988 fires in Yellowstone National Park.
Seedling recruitment in a semi‐arid Patagonian steppe: Facilitative effects of refuse dumps of leaf‐cutting ants
Authors: Farji‐Brener Alejandro G. , Ghermandi Luciana
Published: February 2009

Question:What is the influence of refuse dumps of leaf‐cutting ants on seedling recruitment under contrasting moisture conditions in a semi‐arid steppe?

Location:Northwestern Patagonia, Argentina.

Methods:In a greenhouse experiment, we monitored seedling recruitment in soil samples from refuse dumps of nests of the leaf‐cutting antAcromyrmex lobicornisand non‐nest sites, under contrasting moisture conditions simulating wet and dry growing seasons.

Results:The mean number of seedling species and individuals were higher in wet than in dry plots, and higher in refuse dump plots than in non‐nest soil plots. The positive effect of refuse dumps on seedling recruitment was greater under low moisture conditions. Both the accumulation of discarded seeds by leaf‐cutting ants and the passive trapping of blowing‐seeds seems not explain the increased number of seeds in refuse dumps. Conversely, refuse dumps have higher water retention capacity and nutrient content than adjacent non‐nest soils, allowing the recruitment of a greater number of species and individual seedlings.

Conclusions:Nests of A.lobicornismay play an important role in plant recruitment in the study area, allowing a greater number of seedlings and species to be present, hence resulting in a more diverse community. Moreover, leaf‐cutting ant nests may function as nurse elements, generating safe sites that enhance the performance of neighbouring seedlings mainly during the driest, stressful periods.
Bias in Ellenberg indicator values — problems with detection of the effect of vegetation type
Authors: Smart Simon M. , Scott W. Andrew
Published: February 2009

A recent analysis published in this journal found different relationships between mean Ellenberg indicator values and environmental measurements in different vegetation types. The cause was stated as bias in mean Ellenberg values between relevés which in turn suggested to reflect a bias in individual Ellenberg values. We discuss two phenomena that could explain these results without the need to invoke bias in either individual or mean Ellenberg values. Firstly, slopes of linear regression lines underestimate true relationships when analyses involve explanatory variables measured with error. Secondly, syntaxon‐specific distributions of Ellenberg values follow from the floristic definition of phytosociological units. Mean Ellenberg values per relevé therefore carry the stamp of their associated syntaxon even though associated abiotic conditions may vary between relevés. This will lead to variation in slopes and intercepts between vegetation types not because of bias in individual Ellenberg values but because of prescribed bias in the distribution of Ellenberg values between syntaxa. The residual variation in calibrations carried out across vegetation types is undoubtedly reduced by introducing vegetation type as a factor. However users should note that this is unlikely to reflect bias in individual Ellenberg values but is more likely to reflect error in environmental measurements as well the constraint imposed by phytosociological classification.
Measurement errors and regression to the mean cannot explain bias in average Ellenberg indicator values
Authors: Wamelink G.W.W. , Goedhart P.W. , van Dobben H.F.
Published: February 2009

Smart & Scott (2004, this is sue) criticized our paper (Wamelink et al. 2002) about the bias in average Ellenberg indicator values. Their main criticism concerns the method we used, regression analysis. They state the bias can be mimicked by the construction of an artificial data set and that regression analysis is not a suited tool to investigate underlying phenomena. Moreover they claim that the present bias is caused by the distribution of Ellenberg indicator values between syntaxa, instead of a bias in average Ellenberg indicator values per species. We show that their criticism of the use of regression analysis does not hold. We selected average Ellenberg values per vegetation group for several pH classes and applied an F‐test to determine whether or not the vegetation groups within each pH class differed significantly from each other. This was the case for all tested classes (P < 0.001). Moreover we simulated an artificial data set, of which the F‐test for varying measurement error could not explain the magnitude of the F‐value we found earlier. This indicates that the bias we found in average Ellenberg indicator values cannot be explained by measurement errors or by regression to the mean. In the end, Smart & Scott, as we did, come to the conclusion that there is a bias present and that separate regression lines per vegetation type are necessary, but the debate remains open on whether or not this is caused by the bias in Ellenberg indicator values per species.
Structure, dynamics and dendroecology of an old‐growth Fagus forest in the Apennines
Authors: Piovesan G. , Di Filippo A. , Alessandrini A. , Biondi F. , Schirone B.
Published: February 2009

Abstract. Question: Which are the structural attributes and the history of old‐growth Fagus forest in Mediterranean montane environments? What are the processes underlying their structural organization? Are these forests stable in time and how does spatial scale affect our assessment of stability? How do these forests compare to other temperate deciduous old‐growth forests?

Location: 1600–1850 m a.s.l., Fagus forest near the tree line, central Apennines, Italy.

Methods: An old‐growth Fagus forest was studied following historical, structural and dendroecological approaches. History of forest cover changes was analysed using aerial photographs taken in 1945, 1954, 1985 and 1994. The structural analysis was carried out in the primary old‐growth portion of the forest using 18 circular and two rectangular plots. Dendroecological analyses were conducted on 32 dominant or co‐dominant trees.

Results: These primary old‐growth Fagus remnants consist of four patches that escaped logging after World War II. Both living and dead tree components are within the range of structural attributes recognized for old‐growth in temperate biomes. Dendroecological analyses revealed the roles of disturbance, competition and climate in structuring the forest. We also identified a persistent Fagus community in which gap‐phase regeneration has led to a mono‐specific multi‐aged stand at spatial scales of a few hectares, characterized by a rotated‐sigmoid diameter distribution.

Conclusion: Even at the relatively small spatial scale of this study, high‐elevation Apennine Fagus forests can maintain structural characteristics consistent with those of old‐growth temperate forests. These results are important for managing old‐growth forests in the Mediterranean montane biome.
Spatial pattern and process in forest stands within the Virginia piedmont
Authors: Druckenbrod Daniel L. , Shugart Herman H. , Davies Ian
Published: February 2009

Abstract. Question: Underlying ecological processes have often been inferred from the analysis of spatial patterns in ecosystems. Using an individual‐based model, we evaluate whether basic assumptions of species’life‐history, drought‐susceptibility, and shade tolerance generate dynamics that replicate patterns between and within forest stands.

Location: Virginia piedmont, USA.

Method: Model verification examines the transition in forest composition and stand structure between mesic, intermediate and xeric sites. At each site, tree location, diameter, and status were recorded in square plots ranging from 0.25 to 1.0 ha. Model validation examines the simulated spatial pattern of individual trees at scales of 1–25 m within each forest site using a univariate Ripley's K function.

Results: 7512 live and dead trees were surveyed across all sites. All sites exhibit a consistent, significant shift in pattern for live trees by size, progressing from a clumped understorey (trees ± 0.1 m in diameter) to a uniform overstorey (trees > 0.25 m). Simulation results reflect not only the general shift in pattern of trees at appropriate scales within sites, but also the general transition in species composition and stand structure between sites.

Conclusions: This shift has been observed in other forest ecosystems and interpreted as a result of competition; however, this hypothesis has seldom been evaluated using simulation models. These results support the hypothesis that forest pattern in the Virginia piedmont results from competition involving species’life‐history attributes driven by soil moisture availability between sites and light availability within sites.
Short‐term changes affecting regeneration of Fagus crenata after the simultaneous death of Sasa kurilensis
Authors: Abe M. , Miguchi H. , Honda A. , Makita A. , Nakashizuka T.
Published: February 2009

Abstract. Question: The aim of the present study is to determine whether seed/seedling predation will increase and Fagus survival will decline with the recovery of the Sasa cover.

Methods: We examined Fagus crenata regeneration for seven years in an old‐growth Fagus‐Sasa forest near Lake Towada, northern Japan, by examining the effects of simultaneous death of Sasa, tree canopy gap formation, mast seeding of Fagus and seed and seedling predation by rodents on the survival of Fagus seeds and current year seedlings. We established four types of sites differing in forest canopy (closed or gap) and Sasa status (dead or alive) following the simultaneous flowering and death of Sasa kurilensis (dwarf bamboo) in 1995.

Results: Fallen Fagus seed was abundant in 1997 and 2000 (mast years). In sites with alive Sasa, survival from the first growing season was low due to high seed and seedling predation. In sites with dead Sasa, seed survival under the canopy was high for both mast years, but in gaps it varied between years. Seedling survival was highest in canopy gaps with dead Sasa (gap‐dead) in 1998, because of higher light levels and lower predation by rodents. However, seedling survival in these plots was low in 2001, apparently because rapid Sasa recovery favoured rodent predation. In both mast years, Sasa die‐back had significant positive effects on seed and seedling survival under closed canopies because the seedlings there were more successful in escaping predation.

Conclusion: The change in successful sites for the early stage of regeneration of Fagus appears to reflect the combined effects of canopy gap, seed/seedling predation and revegetation of Sasa.
Recruitment limitation along disturbance gradients in river flood plains
Authors: van Eck W.H.J.M. , van de Steeg H.M. , Blom C.W.P.M. , de Kroon H.
Published: February 2009

Abstract. Question: Along river floodplains lower distribution limits of plant species seem largely determined by their tolerance to rarely occurring floods in the growing season. Such distribution patterns remain fixed for many years suggesting additional effects of winter floods at lower positions. Our objective was to investigate the direct and indirect effects of winter floods on colonization of floodplains in a series of field experiments.

Location: River Rhine, The Netherlands.

Methods: We measured the direct effects of winter floods on seedling survival and seed removal and survival at low and high floodplain elevation. Indirect effects of winter flooding through changes in the soil were investigated by measuring seedling emergence on soil transplants that were exchanged between high and low floodplain elevation. To investigate indirect effects of floods on the germination environment through changes in the vegetation structure, we measured the effects of vegetation removal on recruitment of sown species.

Results: Recruitment was seed limited at both floodplain elevations. An additional effect of vegetation removal on seedling emergence was also observed. Soil types from both zones did not differently affect seedling emergence. Seeds were not removed from the soil surface by a single winter flood. Moreover, seeds remained viable in the soil for at least two years, while the experimental plots were flooded several times during the experimental period. During one of those floods a thick sand layer was deposited at the low zone and subsequently no seedlings were observed anymore.

Conclusions: Colonization of low floodplain zones in years between subsequent summer floods is prevented by seed limitation while the direct effects of winter floods are limited except for irregularly occurring sand depositions.
Milestones in ecological thought — A canon for plant ecology
Authors: Keddy Paul A.
Published: February 2009

Abstract. Scientific progress in plant ecology is at risk of being obscured by increasing ignorance of major works in the field. The driving force seems to be the twin seductions of novelty and crowd psychology. I illustrate this tendency with three examples from plant community ecology that span the past thirty years of ecological research. I offer, as one solution, the concept of a canon: a short list of essential books that we assume all students and co‐workers have read, a short list that summarizes the wisdom of the discipline. A canon can be likened to DNA, be it in music, art, or science, as it carries forward through time the key ideas that have worked in the past. Without a canon, there is no memory of past achievement, no context for appreciating current work, and no way of judging the quality of newer productions. I suggest 20 essential books (the short canon), and 22 complementary readings, for a total of 42 books needed in any young professional's library on plant ecology.
Dynamic tree aggregation patterns in a species‐poor temperate woodland disturbed by fire
Authors: Davis Mark A. , Curran Claudia , Tietmeyer Andrea , Miller Andy
Published: February 2009

Abstract. Question: How does fire affect the aggregation patterns of trees in a species‐poor oak woodland?

Location: East‐central Minnesota, USA.

Methods: More than 10 000 trees with DBH > 2 cm (comprising more than 11 000 stems) were monitored in a 16‐ha grid on an annual basis from 1995‐ 2001 in a species‐poor temperate woodland. Different portions of the grid experienced different frequencies of controlled burns. Aggregation indices were calculated for individual species and individual size classes within species. A community‐wide aggregation index was also calculated for different burn units. Spatial data were managed, and many of the aggregation indices calculated using a GIS ArcInfo™ (ESRI).

Results: Fire initially increased clumping, although repeated fires reduced it, a finding that suggests a corollary to the intermediate‐disturbance hypothesis, the corollary stating that intermediate levels of disturbance are expected to maximize community‐wide patterns of aggregation. Analyses also showed that all species are aggregated at small scales, that the degree of aggregation of a stem type (species or size) declines with distance from individual stems, that the degree of aggregation of large stems is usually less than that of small stems, and that rare species are more aggregated than common species. Findings from this study are consistent with those from similar studies in other temperate and tropical forests, woodlands, and savannas.

Conclusion: The spatial patterns of trees in this woodland are dynamic, continually changing in response to the relative strengths of the often opposing forces of competition, which tends to reduce clumping, and disturbance, which, at low and intermediate frequencies, tends to increase it.
Mycorrhiza and seedling establishment in a subarctic meadow: Effects of fertilization and defoliation
Authors: Pietikäinen A. , Kytöviita M.‐M. , Vuoti U.
Published: February 2009

Abstract. Question: How does changing resource availability induced by fertilization and defoliation affect seedling establishment and mycorrhizal symbiosis in a subarctic meadow?

Location: 610 m a.s.l., Kilpisjärvi (69°03’N, 20°50’E), Finland.

Methods: A short‐term full‐factorial experiment was established, with fertilization and defoliation of natural established vegetation as treatments. Seeds of two perennial herbs Solidago virgaurea and Gnaphalium norvegicum were sown in natural vegetation and their germination and growth followed. At the final harvest we measured the response in terms of arbuscular mycorrhizal (AM) colonization, biomass and nitrogen concentration of the seedlings and the established vegetation.

Results: Germination rate was negatively affected by defoliation in the unfertilized plots. The shoot biomass of S. virgaurea seedlings was reduced by the defoliation and fertilization treatments, but not affected by their interaction. In G. norvegicum, the germination rate and the seedling shoot biomass were negatively correlated with moss biomass in the plots. In the established plants the arbuscular colonization rate was low and defoliation and fertilization treatments either increased or did not affect the colonization by AM fungi. In the seedlings, the colonization rate by AM fungi was high, but it was not affected by treatments. Both seedlings and established plants were colonized by dark septate fungi.

Conclusions: Reduction of plant biomass by herbivores can have different effects on seedling growth in areas of high and low soil nutrient availability. The weak response of AM colonization to defoliation and fertilization suggests that AM symbiosis is not affected by altering plant resource availability under the conditions employed in this study.
Safe sites for tree regeneration in wooded pastures: A case of associational resistance?
Authors: Smit Christian , Béguin Daniel , Buttler Alexandre , Müller‐Schärer Heinz
Published: February 2009

Abstract. Question: Are tree saplings in wooded pastures spatially associated with specific nurse structures or plants that facilitate tree sapling survival?

Location: Wooded pastures in the Jura Mountains, Switzerland.

Methods: In two sites, 73 km apart, we sampled 294 plots of 4 m2, systematically distributed on 1 ha. We recorded number and height of all established Picea abies saplings (> 1 a of age and up to 40 cm in height), and visually estimated cover of rocks, shrubs, tree stumps, overhanging tree branches and unpalatable plant species.

Results: Despite differences in site characteristics, we found overall positive effects of cover of unpalatable plants, rocky outcrops and tree stumps on the density of Picea saplings. Plots with tree stumps and higher cover of rocky outcrops and unpalatable plants were more likely to contain Picea saplings.

Conclusions: Unpalatable plants, rocky outcrops and tree stumps seem to form safe sites for Picea saplings in this grazed system, improving their establishment and survival. Our findings support the idea that associational resistance drives the dynamics of wooded pastures, but experimental evidence for this hypothesis is still required.
Long‐term changes in semi‐arid vegetation: Invasion of an exotic perennial grass has larger effects than rainfall variability
Authors: Clarke Peter J. , Latz Peter K. , Albrecht David E.
Published: February 2009

Abstract. Questions: This paper examines the long‐term change in the herbaceous layer of semi‐arid vegetation since grazing ceased. We asked whether (1) there were differences in the temporal trends of abundance among growth forms of plants; (2) season of rainfall affected the growth form response; (3) the presence of an invasive species influenced the abundance and species richness of native plants relative to non‐invaded plots, and (4) abundance of native plants and/or species richness was related to the time it took for an invasive species to invade a plot.

Location: Alice Springs, Central Australia.

Methods: Long‐term changes in the semi‐arid vegetation of Central Australia were measured over 28 years (1976–2004) to partition the effects of rainfall and an invasive perennial grass. The relative abundance (biomass) of all species was assessed 25 times in each of 24 plots (8 m × 1 m) across two sites that traversed floodplains and adjacent foot slopes. Photo‐points, starting in 1972, were also used to provide a broader overview of a landscape that had been intensively grazed by cattle and rabbits prior to the 1970s. Species’abundance data were amalgamated into growth forms to examine their relationship with environmental variation in space and time. Environmental variables included season and amount of rainfall, fire history, soil variability and the colonization of the plots by the exotic perennial grass Cenchrus ciliaris (Buffel grass).

Results: Constrained ordination showed that season of rainfall and landscape variables relating to soil depth strongly influenced vegetation composition when Cenchrus was used as a covariate. When Cenchrus was included in constrained ordination, it was strongly related to the decline of all native growth forms over time. Univariate comparisons of non‐invaded vs impacted plots over time revealed unequivocal evidence that Cenchrus had caused the decline of all native growth form groups and species richness. They also revealed a contrasting response of native plants to season of rainfall, with a strong response of native grasses to summer rainfall and forbs to winter rainfall. In the presence of Cenchrus these responses were strongly attenuated.

Discussion: Pronounced changes in the composition of vegetation were interpreted as a response to removal of grazing pressure, fluctuations in rainfall and, most importantly, invasion of an exotic grass. Declines in herbaceous species abundance and richness in the presence of Cenchrus appear to be directly related to competition for resources. Indirect effects may also be causing the declines of some woody species from changed fire regimes as a result of increased fuel loads. We predict that Cenchrus will begin to alter landscape level processes as a result of the direct and indirect effects of Cenchrus on the demography of native plants when there is a switch from resource limited (rainfall) establishment of native plants to seed limited recruitment.
Large parts of the world are brown or black: A different view on the ‘Green World’hypothesis
Authors: Bond William J.
Published: February 2009

Abstract. Climate sets the limits to plant growth but does climate determine the global distribution of major biomes? I suggest methods for evaluating whether vegetation is largely climate or consumer‐controlled, focusing on large mammal herbivores and fire as influential consumers. Large parts of the world appear not to be at equilibrium with climate. Consumer‐controlled ecosystems are ancient and diverse. Their distinctive ecology warrants special attention.
Multi‐scale patterns and bush encroachment in an arid savanna with a shallow soil layer
Authors: Wiegand Kerstin , Ward David , Saltz David
Published: February 2009

Abstract.Question:Bush encroachment (i.e. an increase in density of woody plants often unpalatable to domestic livestock) is a serious problem in many savannas and threatens the livelihood of many pastoralists. Can we derive a better understanding of the factors causing bush encroachment by investigating the scale dependency of patterns and processes in savannas?

Location:An arid savanna in the Khomas Hochland, Namibia.

Methods:Patterns of bush, grass, and soil nutrient distribution were surveyed on several scales along a rainfall gradient, with emphasis on intraspecific interactions within the dominant woody species,Acacia reficiens.

Results:Savannas can be interpreted as patch‐dynamic systems where landscapes are composed of many patches (a few ha in size) in different states of transition between grassy and woody dominance.

Conclusions:In arid savannas, this patchiness is driven both by rainfall that is highly variable in space and time and by inter‐tree competition. Within the paradigm of patch‐dynamic savannas, bush encroachment is part of a cyclical succession between open savanna and woody dominance. The conversion from a patch of open savanna to a bush‐encroached area is initiated by the spatial and temporal overlap of several (localized) rainfall events sufficient forAcaciagermination and establishment. With time, growth and self‐thinning will transform the bush‐encroached area into a matureAcaciastand and eventually into open savanna again. Patchiness is sustained due to the local rarity (and patchiness) of rainfall sufficient for germination of woody plants as well as by plant‐soil interactions.
Long‐term dynamics of the long‐lived conifer Libocedrus bidwillii after a volcanic eruption 2000 years ago
Authors: Ogden J. , Fordham R.A. , Horrocks M. , Pilkington S. , Serra R.G.
Published: February 2009

Abstract. Question: Following a volcanic eruption of ca. 232 AD, known as the Taupo eruption, the emergent conifer Libocedrus bidwillii expanded on Mt. Hauhungatahi, upwards above the current tree‐line, and downwards into the mixed montane forest. We ask: (1) if current age‐structures at different altitudes support the patterns predicted by the temporal stand replacement model, with cohort senescence and progressively depleting recruitment at ca. 600 year intervals (average cohort age) since the eruption: and (2) if the case history of the population sheds light on the persistence of mixed conifer‐hardwood forests in general.

Location: Mt. Hauhungatahi, Tongariro National Park, New Zealand.

Methods: The species composition and structure of seven stands covering the altitudinal range of Libocedrus bidwillii, were quantified. Libocedrus trees were cored, and regression equations used to predict ages. Cohorts were identified.

Results: Libocedrus densities and basal areas, and the abundance of seedlings and saplings, peaked at different altitudes. At the species’lower limits there has been no recruitment for ca. 550 years, and the angiosperm Weinmannia racemosa has gained dominance. In the tree line and sub‐alpine forest stands, a low level of continuous regeneration has been boosted by periodic cohort recruitment following exogenous disturbances.

Conclusions: In the montane zone, the Libocedrus age structure, and its replacement by Weinmannia, are consistent with a model of depleting cohorts separated by ca. 600 years since the Taupo eruption. At higher altitudes more frequent disturbances and reduced competition have allowed Libocedrus persistence. Comparison with other studies suggests long‐term relationships between gymnosperms and angiosperms are mediated by the scale and frequency of disturbance.
Simulated distribution of vegetation types in response to climate change on the Tibetan Plateau
Authors: Song Minghua , Zhou Caiping , Ouyang Hua
Published: February 2009

Abstract. Questions: What is the relationship between alpine vegetation patterns and climate? And how do alpine vegetation patterns respond to climate changes?

Location: Tibetan Plateau, southwestern China. The total area is 2500000 km2 with an average altitude over 4000 m.

Methods: The geographic distribution of vegetation types on the Tibetan Plateau was simulated based on climatology using a small set of plant functional types (PFTs) embedded in the biogeochemistry‐biography model BIOME4. The paleoclimate for the early Holocene was used to explore the possibility of simulating past vegetation patterns. Changes in vegetation patterns were simulated assuming continuous exponential increase in atmospheric CO concentration, based on a transient ocean‐atmosphere simulation including sulfate aerosol effects during the 21st century.

Results: Forest, shrub steppe, alpine steppe and alpine meadow extended while no desert vegetation developed under the warmer and humid climate of the early Holocene. In the future climate scenario, the simulated tree line is farther north in most sectors than at present. There are also major northward shifts of alpine meadows and a reduction in shrub‐dominated montane steppe. The boundary between montane desert and alpine desert will be farther to the south than today. The area of alpine desert would decrease, that of montane desert would increase.

Conclusions: The outline of changes in vegetation distribution was captured with the simulation. Increased CO2 concentration would potentially lead to big changes in alpine ecosystems.
Production as a function of resource availability: Slopes and efficiencies are different
Authors: Verón Santiago R. , Oesterheld Martín , Paruelo José M.
Published: February 2009

Abstract. A number of investigators have interpreted the slope of a linear production‐resource relationship as a measure of efficiency of resource utilization. However, this is rarely true and may lead to incorrect conclusions. Here, by means of simple mathematical equations and conceptual definitions, we point out the theoretical differences between slope and efficiency. While a slope represents the change in the dependent variable per unit change in the independent variable, efficiency expresses the amount of output produced by a unit amount of input. Practical implications of using slopes as indicators of resource‐use efficiency are less important as the resource amount increases. Slopes may be used as indicators of the sensitivity of production to changes in input, which is by itself an interesting property of biological systems. Finally, production function intercepts determine whether the efficiency will decrease, increase, or remain constant as resources increase.
Variation in leaf traits through seasons and N‐availability levels and its consequences for ranking grassland species
Authors: Al Haj Khaled Raouda , Duru Michel , Theau Jean Pierre , Plantureux Sylvain , Cruz Pablo
Published: February 2009

Question:

Are leaf dry matter content, specific leaf area and leaf life span relevant plant traits to discriminate the fertility gradient in species‐rich natural grasslands? In other words, is species ranking conserved when nitrogen availability or growing periods change?

Location:

Toulouse Research Centre, France; 150 m a.s.l.

Methods:

Fifteen grasses and nine dicotyledons were sown in pure stands in a random block design with three replicates. Each species was cultivated at two levels of nitrogen supply, limiting and non‐limiting for growth, with three replications per nitrogen level. Leaf traits were measured across both levels of nitrogen supply and growing periods over the year.

Results:

Leaf dry matter content values separated the species into three life‐form classes (grasses, rosette forbs and upright forbs, P < 0.001). This was not the case for specific leaf area and leaf life span. The three leaf traits were variable across growing periods and nitrogen levels, but the ranking of species was conserved over N‐levels and growth periods. Furthermore leaf dry matter content was always less variable than the other leaf traits.

Conclusion:

We conclude that leaf dry matter content measured only on grasses could be used as an indicator to describe the N‐richness of the habitat where native herbaceous vegetation develops.
Biomass production, N:P ratio and nutrient limitation in a Caucasian alpine tundra plant community
Authors: Soudzilovskaia N.A. , Onipchenko V.G. , Cornelissen J.H.C. , Aerts R.
Published: February 2009

Questions:

1. To what extent is biomass production of a Caucasian alpine tundra plant community limited by soil nitrogen and/ or phosphorus? 2. Can the foliar N:P ratio predict the nutrient limitation pattern of alpine vascular plant communities?

Location:

Lichen‐rich tundra on Mt. Malaya Khatipara in the NW Caucasus, Russia (43°27’N, 41°42’E; alt. 2800 m a.s.l.).

Methods:

We conducted a 4–year fertilization experiment (N, P, N+P, lime additions and irrigation) on the alpine tundra in the northwestern Caucasus, Russia. We determined responses of biomass, tissue nutrient concentrations and nutrient pools of the above‐ground component of the plant community.

Results:

Total plant community biomass did not respond to fertilization. However, lichen biomass strongly decreased in response to the N‐ and N+P treatments, whereas vascular plant biomass increased in response to the N‐ and even more to the N+P treatment, but not to P or lime addition or irrigation. P‐concentrations in vascular plant species were very low, but their biomass production was not principally P‐limited, suggesting adaptation to low soil P‐availability. The N‐limitation of vascular plant biomass production in the community, which in lowlands usually occurs at N:P ratios below 16, could not be predicted from the mean foliar N:P mass ratio in the control (N:P = 29).

Conclusions:

This Caucasian alpine plant community is an example of N‐ and P‐co‐limitation of vascular plant biomass production, with N being the principal and P the secondary limiting nutrient. Critical N:P ratios as determined for lowland communities are not applicable here.
Species frequency dynamics in an old‐field succession: Effects of disturbance, fertilization and scale
Authors: Gibson David J. , Middleton Beth A. , Foster Kari , Honu Yohanes A.K. , Hoyer Erik W. , Mathis Marilyn
Published: February 2009

Question:

Can patterns of species frequency in an old‐field be explained within the context of a metapopulation model? Are the patterns observed related to time, spatial scale, disturbance, and nutrient availability?

Location:

Upland and lowland old‐fields in Illinois, USA.

Method:

Species richness was recorded annually for seven years following plowing of an upland and lowland old‐field subject to crossed fertilizer and disturbance treatments (mowing and rototilling). Species occupancy distributions were assessed with respect to the numbers of core and satellite species.

Results:

In both fields, species richness became higher in disturbed plots than in undisturbed plots over time, and decreased in fertilized plots irrespective of time. A bimodal pattern of species richness consistent with the Core‐satellite species (CSS) hypothesis occurred in the initial seed bank and through the course of early succession. The identity of native and exotic core species (those present in > 90% of blocks) changed with time. Some core species from the seed bank became core species in the vegetation, albeit after several years. At the scale of individual plots, a bimodal fit consistent with the CSS hypothesis applied only in year 1 and rarely thereafter.

Conclusions:

The CSS hypothesis provides a metapopulation perspective for understanding patterns of species richness but requires the assessment of spatial and temporal scaling effects. Regional processes (e.g. propagule availability) at the largest scale have the greatest impact influencing community structure during early secondary succession. Local processes (e.g., disturbance and soil nutrients) are more important at smaller scales and place constraints on species establishment and community structure of both native and exotic species. Under the highest intensity of disturbance, exotic species may be able to use resources unavailable to, or unused by, native species.
Resource use efficiency as a function of species richness and stand composition in upper montane conifer forests of the Sierra Nevada
Authors: DeClerck Fabrice A.J. , Barbour Michael G. , Sawyer John O.
Published: February 2009

Questions:

1. Does resource use efficiency increase with increased species richness in conifer forests? 2. Do patterns found in resource use support niche differentiation/complementarity between species, or is any increase indicative of a selection effect?

Location:

All data were collected from upper montane (2200–2600 m a.s.l) conifer forests of the Desolation Wilderness in the central California Sierra Nevada, USA.

Methods:

We established 281 plots of varying levels of conifer richness throughout the wilderness area. Within each plot we used hemispherical photos to measure canopy closure and LAI, total soil carbon and nitrogen from the A‐horizon, and stand basal area. We used linear regression and ANOVA to analyse the relationship between stand species richness and resource availability.

Results:

We found no correlation of either soil nitrogen or carbon with stand biomass. Nor did soil nitrogen and carbon levels change with species richness. Canopy closure increased with species richness but also varied significantly between pure stands of different species. PurePinus monticolastands had the lowest canopy closure,Tsuga mertensianastands the highest. Composition explained more canopy cover variation than did species richness. We found evidence supporting both the sampling effect and niche differentiation models at different stages of stand development.

Conclusions:

During initial stages of stand development, the interaction between the shade‐intolerantPinusspecies and shade‐tolerantAbies magnificaandT. mertensianafollowed the niche differentiation model, but switched to the sampling effect model during the competitive‐exclusion stage. In contrast, interaction betweenA. magnificaandT. mertensianafollowed the niche differentiation model.
Plant species as predictors of soil pH: Replacing expert judgement with measurements
Authors: Wamelink G.W. Wieger , Goedhart Paul W. , Van Dobben Han F. , Berendse Frank
Published: February 2009

Question:

The use of expert‐based indicator values to estimate abiotic conditions from vegetation is widespread. However, recent research has shown that expert judgement may contain considerable bias and thereby introduces a large amount of uncertainty. Could expert based indicator values be replaced by indicator values based on field measurements?

Location:

Europe.

Methods:

We developed a method to estimate species response based on measured physical data, and a method to predict abiotic conditions from the vegetation composition using these responses. This method was tested for soil pH.

Results:

We were able to estimate the pH response of 556 species of the Dutch flora. Ca. 20% of the responses were, at least, bimodal and many responses had a very wide range. The simplest method (‘raw mean’) yielded the best prediction of pH; the indicator value of a species is the mean of the soil pH values of the sites where it was observed. A list of all raw‐mean estimates per species is given. The predicted pH of a new site is the mean of the indicator values of the present species. The estimated species responses were validated on independent Dutch and European data sets. Older successional stages seem to be predicted better than younger stages.

Conclusions:

Our method performed better than the popular Ellenberg indicator system for the Dutch data set, while being just as easy to use, because it only needs a single value per species. We foresee that, when more data become available, our method has the potential to replace the Ellenberg system.
Effects of resource availability and heterogeneity on the slope of the species‐area curve along a floodplain‐upland gradient
Authors: Désilets P. , Houle G.
Published: February 2009

Question:

What are the relative effects of resource availability and heterogeneity on the slope of the species‐area curve along a floodplain‐upland gradient?

Location:

Réserve Léon‐Provancher, Québec, Canada.

Methods:

The mean and coefficient of variation of several environmental variables (soil organic matter, N and pH; irradiance; elevation) were estimated in 70 plots along a floodplain‐upland gradient. The slope of the species‐area curve was calculated from subplots nested within each plot. Path analysis was used to determine the effects of the environmental variables on the slope of the species‐area curve.

Results:

Spatial variation in flooding intensity created a complex gradient along which resource availability, but not resource heterogeneity, varied. Together, the environmental variables explained 73% of the variance in the slope of the species‐area curve. Elevation, soil variables (but not light) and heterogeneity in soil fertility (but not in light) were all significantly associated with the slope of the species‐area curve. Resource availability explained three times as much of the variance as resource heterogeneity.

Conclusion:

The expected positive relationships between resource availability, resource heterogeneity and diversity were obscured by effects of flooding stress and species dominance. Flooding intensity varies inversely with elevation and restricts the pool of species that can occupy the more fertile/heterogeneous section of the gradient, i.e. near the river. The few species combining flooding stress tolerance and competitive ability use the abundant resources near the river to grow quickly and utilize space, thereby enhancing the negative effect of the flooding stress on diversity.
Multivariate exploratory analysis of ordinal data in ecology: Pitfalls, problems and solutions
Authors: Podani János
Published: February 2009

Questions:

Are ordinal data appropriately treated by multivariate methods in numerical ecology? If not, what are the most common mistakes? Which dissimilarity coefficients, ordination and classification methods are best suited to ordinal data? Should we worry about such problems at all?

Methods:

A new classification model family, OrdClAn (OrdinalClusterAnalysis), is suggested for hierarchical and non‐hierarchical classifications from ordinal ecological data, e.g. the abundance/dominance scores that are commonly recorded in relevés. During the clustering process, the objects are grouped so as to minimize a measure calculated from the ranks of within‐cluster and between‐cluster distances or dissimilarities.

Results and Conclusions:

Evaluation of the various steps of exploratory data analysis of ordinal ecological data shows that consistency of methodology throughout the study is of primary importance. In an optimal situation, each methodological step is order invariant. This property ensures that the results are independent of changes not affecting ordinal relationships, and guarantees that no illusory precision is introduced into the analysis. However, the multivariate procedures that are most commonly applied in numerical ecology do not satisfy these requirements and are therefore not recommended. For example, it is inappropriate to analyse Braun‐Blanquet abudance/dominance data by methods assuming that Euclidean distance is meaningful. The solution of all problems is that the dissimilarity coefficient should be compatible with ordinal variables and the subsequent ordination or clustering method should consider only the rank order of dissimilarities. A range of artificial data sets exemplifying different subtypes of ordinal variables, e.g. indicator values or species scores from relevés, illustrate the advocated approach. Detailed analyses of an actual phytosociological data set demonstrate the classification by OrdClAn of relevés and species and the subsequent tabular rearrangement, in a numerical study remaining within the ordinal domain from the first step to the last.