bluuebunny/crossref_metadata_2025 huggingface dataset:
Border and ecotone detection by vegetation composition along forest‐savanna transects in Ivory Coast
Authors: Hennenberg Klaus J. , Goetze Dethardt , Kouamé Lucien , Orthmann Bettina , Porembski Stefan
Published: February 2009

Abstract. Question: How do properties of different vegetation components vary along ecotones of semi‐deciduous forest islands, and can the depth of edge influence (DEI) of the components be detected using a novel combination of analyses?

Location: Comoé National Park (CNP), NE Ivory Coast.

Methods: Along eight transects at semi‐deciduous forest islands tree individuals > 20 cm DBH were mapped. At one transect, tree and shrub individuals down to 1 cm DBH were measured and cover of species was estimated. Split moving window dissimilarity analysis (SMWDA) and moving window regression analysis (MWRA) were combined to detect statistical significance of borders in multivariate vegetation data along continuous transects, to determine the width of associated ecotones, and, thus, the DEI towards the forest interior.

Results: For trees > 20 cm DBH, a distinct boundary formation was detected, dominated by the semi‐fire resistant tree species Anogeissus leiocarpus. The median of DEI towards the forest interior was 55 m. Ecotone detection with all species present revealed an interlocked sequence of ecotones for grasses, herbs, woody climbers, shrubs and trees, with each of these ecotones being narrower than the overall ecotone. DEI ranged from 10 m for grasses up to 120 m for trees and shrubs.

Conclusions: The coherent set of analyses applied proved to be an objective method for detecting borders and the width of associated ecotones. The patterns found may be explained by successional processes at the forest‐savanna border. The DEI measured for the forest islands in the nearly undisturbed semi‐natural system of the CNP is of relevance to concepts of core‐area analysis and the protection of forest interior species in semi‐deciduous forests in tropical West Africa.
Context‐dependent interactions between adult shrubs and seedlings in a semi‐arid shrubland
Authors: Riginos Corinna , Milton Suzanne J. , Wiegand Thorsten
Published: February 2009

Abstract. Question: In semi‐arid systems, rainfall gradients can cause plant‐plant interactions to shift from negative to positive or vice versa. However, the importance of a second major abiotic factor, soil nutrients, has rarely been considered. We consider different combinations of both factors and ask: do net adult‐seedling interactions become less competitive and more facilitative with increasing overall abiotic harshness?

Location: Succulent Karoo, Western Cape, South Africa.

Methods: We examined the interactions between seedlings and adult shrubs at two sites. Sites differ in rainfall, and each contain two habitats: Nutrient‐rich mounds associated with underground termitaria and a relatively nutrient‐poor matrix. We carried out a spatial pattern analysis of community‐wide seedling‐adult associations. We then conducted field and greenhouse experiments to test the effects of soil and the presence of neighbouring shrubs on the growth and survival of six seedling species.

Results: At the higher rainfall site, both competitive and facilitative effects of adults on seedlings were found but did not differ by habitat, despite the more benign conditions in the mound habitat. At the lower rainfall site, adult shrubs generally had neutral effects on seedlings in the matrix habitat. In the nutrient‐rich mound habitat, however, adult shrubs had strong and consistently competitive effects on seedlings.

Conclusion: Seedling‐adult interactions could not be predicted by a simple overall gradient of abiotic harshness, demonstrating the need for more complex, mechanistic models to predict plant‐plant interactions. We suggest that rainfall and soil nutrients affect seedling‐adult relations through their interactive effects on the life‐history attributes of the species involved.
Ginkgo, a multivariate analysis package
Authors: Bouxin Guy
Published: February 2009

Abstract. The Ginkgo software is a subset of the VegAna (for Vegetation edition and Analysis) package that contains three programs named Quercus, Fagus and Yucca. Ginkgo is a multivariate analysis tool; it is oriented mainly towards ordination and classification of ecological data. Quercus is a relevé table editor; it handles community data to perform a phytosociological analysis. Fagus is a floristic citation editor; it can handle data coming from field surveys, bibliographic sources or collections. Yucca is a cartographic tool; it allows plotting distributions of taxa or syntaxa.

VegAna is produced by the Department of Vegetal Biology, University of Barcelona. The general project is directed by Xavier Font I Castell, the Ginkgo module by Francesc Oliva I Cuyàs. Programmers are Miquel De Cáceres and Richard Garcia. This review deals primarily with Ginkgo.
Book Reviews
Authors: Prach Karel
Published: February 2009

Abstract. van der Maarel, E. (ed.) 2005. Vegetation ecology. 395 pp. Blackwell Publishing, Maiden, Oxford & Carlton. ISBN 0‐632‐05761‐0 (paperback). Price: GBP 34.99.
Rejecting the mean: Estimating the response of fen plant species to environmental factors by non‐linear quantile regression
Authors: Schröder Henning K. , Andersen Hans Estrup , Kiehl Kathrin
Published: February 2009

Question:

Is quantile regression an appropriate statistical approach to estimate the response of fen species to single environmental factors?

Background:

Data sets in vegetation field studies are often characterized by a large number of zeros and they are generally incomplete in respect to the factors which possibly influence plant species distribution. Thus, it is problematic to relate plant species abundance to single environmental factors by the ordinary least squares regression technique of the conditional mean.

Location:

Riparian herbaceous fen in central Jutland (Denmark).

Methods:

Semi‐parametric quantile regression was used to estimate the response of 18 plant species to six environmental factors, 95% regression quantiles were chosen to reduce the impact of multiple unmeasured factors on the regression analyses. Results of 95% quantile regression and ordinary least squares regression were compared.

Results:

The standard regression of the conditional mean underestimated the rates of change of species cover due to the selected factor in comparison to 95% regression quantiles. The fitted response curves indicated a general broad tolerance of the studied fen species to different flooding durations but a narrower range concerning groundwater amplitude. The cover of all species was related to soil exchangeable phosphate and base‐richness. A relationship between soil exchangeable potassium and species cover was only found for 11 species.

Conclusion:

Considering the characteristics of data sets in vegetation science, non‐linear quantile regression is a useful method for gradient analyses.
Supervised classification of plant communities with artificial neural networks
Authors: Černá Lenka , Chytrý Milan
Published: February 2009

Questions:

Are artificial neural networks useful for the automatic assignment of species composition records from vegetation plots to a priori established classes (vegetation units)? Is the assignment more accurate (1) if the classes are defined by numerical classification rather than by expert‐based classification; (2) if the training data set is selected to include plots that are richer in diagnostic species of particular classes?

Material:

Species composition records (relevés) from 4186 plots of Czech grasslands.

Methods:

Plots were classified into 11 phytosociological alliances (expert classification) and into 11 clusters derived from numerical cluster analysis. Some plots were used for training the classifiers, which were the multi‐layer perceptrons (MLP; a type of artificial neural network). Other plots were used for testing the performance of these classifiers. Plots used for training were selected (1) randomly; (2) according to higher representation of diagnostic species of particular classes.

Results:

Different MLP classifiers correctly classified 77–83% of plots to the classes of the expert classification and 70–78% to the classes of the numerical classification. The better result in the former case was mainly due to two classes in the expert classification, which were well recognized by the classifiers and at the same time contained a large proportion of the plots of the entire data set. Correct classification of the plots belonging to these large classes resulted in a good overall performance of the classifiers. After training with randomly chosen plots, the classifiers produced better results than after training with plots that contained more diagnostic species. This indicates that the biased selection of the training plots disables the classifiers to recognize the entire variation within the classes and results in errors when new plots are to be classified.

Conclusions:

MLP is suitable for assigning vegetation plots to already established classes. Unlike some other methods of supervised classification, it performs well even in communities that are poor in diagnostic species. However, the method does not provide clear assignment keys that could be used for class identification in field surveys. It is therefore more appropriate in applications that aim at a reliable class assignment rather than understanding the assignment rules.
Tree regeneration in a New Zealand rain forest influenced by disturbance and drainage interactions
Authors: Urlich Stephen C. , Stewart Glenn H. , Duncan Richard P. , Almond Peter C.
Published: February 2009

Question:

Does canopy tree regeneration response to different large disturbances vary with soil drainage?

Location:

Old‐growth conifer (Dacrydium and Dacrycarpus)., angiosperm (Nothofagus and Weinmannia) rain forest, Mount Harata, South Island, New Zealand.

Methods:

Trees were aged (1056 cores) to reconstruct stand history in 20 (0.12–0.2 ha) plots with different underlying drainage. Spatial analyses of an additional 805 tree ages collected from two (0.3—0.7 ha) plots were conducted to detect patchiness for five canopy tree species. Microsite preferences for trees and saplings were determined.

Results:

There were clear differences in species regeneration patterns on soils with different drainage. Conifer recruitment occurred infrequently in even‐aged patches (> 1000 m2) and only on poorly drained soils. Periodic Nothofagus fusca and N. menziesii recruitment occurred more frequently in different sized canopy openings on all soils. Weinmannia recruitment was more continuous on all soils reflecting their greater relative shade‐tolerance. Distinct periods of recruitment that occurred in the last 400 years matched known large disturbances in the region. These events affected species differently as soil drainage varied. Following earthquakes, both conifers and N. menziesii regenerated on poorly drained soils, while Nothofagus species and Weinmannia regenerated on well‐drained soils. However, Dacrydium failed to regenerate after patchy storm damage in the wetter forest interior; instead faster‐growing N. fusca captured elevated microsites caused by uprooting.

Conclusions:

Underlying drainage influenced species composition, while variation in the impacts of large disturbance regulated relative species abundances on different soils.
Leaf phenology of three dominant limestone grassland plants matching the disturbance regime
Authors: Kahlert Bettina R. , Ryser Peter , Edwards Peter J.
Published: February 2009

Question:

Does interspecific variation in leaf phenology among grassland species help to explain the differences in species'performance under contrasting disturbance regimes.

Location:

Merishausen, northern Switzerland.

Methods:

Seasonal variations in leaf production and mortality were assessed for three species of nutrient‐poor limestone grasslands: Brachypodium pinnatum, Bromus erectus and Salvia pratensis; each of these species tends to become dominant under a contrasting form of management. Their phenological characteristics were compared with their performance in plots differently managed for 21 years: (1) mowing in July; (2) mowing in October; (3) controlled burning in February; and (4) no biomass removal.

Results:

The species‐specific phenological patterns of leaf production and leaf mortality are associated with the abundance of the three species under the different management regimes. B. erectus, with relatively short‐lived leaves and leaf production late in the season dominates plots mown annually in June; it has almost disappeared from plots with winter burning. B. pinnatum, with production maxima of the long‐lived leaves early in the season, does not tolerate June mowing but is most abundant in plots burnt in winter when the species has no living leaves. S. pratensis, a species with long‐lived leaves but fast senescence of all the leaves in autumn, dominates plots mown in October. In unmown plots, all species are equally abundant.

Conclusions:

The seasonal pattern of leaf production and mortality strongly influence biomass and nutrient loss due to the management, and the growth that can be realized between the disturbances. A species may become dominant if it ‘fits’into the particular management regime, whereas a mismatch between phenological pattern and disturbance regime leads to its elimination from the community.
Linking microtopography with post‐fire succession in bogs
Authors: Benscoter Brian W. , Kelman Wieder R. , Vitt Dale H.
Published: February 2009

Questions:

Does post‐fire plant succession in boreal bogs vary microtopographically and are successional patterns reproducible among similar microtopographic features? Does succession preserve microtopography post‐fire?

Location:

Boreal bog peatlands near Sinkhole Lake and Athabasca, Alberta, Canada.

Methods:

We assessed microtopographic variation in post‐fire plant community succession through stratigraphic macrofossil analysis of bog soil cores collected from high (hummock) and low (hollow) positions. We conducted vegetation surveys and collected soil cores from ten hummocks and hollows in each bog. Pre‐fire microtopographic status was inferred based on floral composition and compared to current microtopography.

Results:

Hollow vegetation was more variable than hummocks, both in present composition and post‐fire succession. The successional trajectory of current hummocks was relatively uniform, showing relatively rapid shifts to Sphagnum fuscum dominance, but varied greatly in hollows. Hollows, although compositionally variable, were typically perpetuated following fire, while hummocks had an approximately equal chance of being perpetuated or becoming hollows.

Conclusions:

Greater compositional variability at lower microtopographic positions, both spatially and temporally, is most likely due to the ability of hollows to support a wider range of species and greater susceptibility to severe disturbance. Likewise, spatial variability in fire severity appears to be responsible for perpetuation or change in microtopographic status, favouring the creation of hollows over maintenance of hummocks.
Relationships between gap makers and gap fillers in an Arkansas floodplain forest
Authors: King Sammy L. , Antrobus Terry J.
Published: February 2009

Question:

In floodplain forests, does frequent flooding allow for self‐replacement of shade‐intolerant tree species or do small canopy gap openings lead to replacement by shade‐tolerant tree species?

Location:

Cache River, Arkansas, US; 55 m a.s.l.

Methods:

The species, diameter‐at‐breast height, and elevation of primary gap‐maker trees were determined for new gaps from 1995–1998. The size and species of gap‐filler trees were identified and placed into three classes: definitive, edge, or interior. Transition probabilities were determined.

Results:

The dominant shade‐intolerant species Quercus texana is being replaced primarily by the more shade‐tolerant A. rubrum var. drummondii, Fraxinus spp. and Ulmus americana. Only 20 of 2767 gap fillers were Q. texana. Replacement probabilities are not constant across elevations, however, as the least shade‐tolerant of the three most common species of definitive gap fillers, Fraxinus spp., occurred at lower elevations than A. rubrum var. drummondii, and U. americana.

Conclusions:

The contention that frequent flooding would allow for self‐replacement of shade‐intolerant species was only partially supported. The small canopy gaps undoubtedly influenced canopy replacement processes.
Stratified resampling of phytosociological databases: some strategies for obtaining more representative data sets for classification studies
Authors: Knollová Ilona , Chytrý Milan , Tichý Lubomír , Hájek Ondřej
Published: February 2009

Question:

The heterogeneous origin of the data in large phytosociological databases may seriously influence the results of their analysis. Therefore we propose some strategies for stratified resampling of such databases, which may improve the representativeness of the data. We also explore the effects of different resampling options on vegetation classification.

Methods:

We used 6050 plot samples (relevés) of mesic grasslands from the Czech Republic. We stratified this database using (1) geographical stratification in a grid; (2) habitat stratification created by an overlay of digital maps in GIS; (3) habitat stratification with strata defined by traditional phytosociological associations; (4) habitat stratification by numerical classification and (5) habitat stratification by Ellenberg indicator values. Each time we resampled the database, taking equal numbers of relevés per stratum. We then carried out cluster analyses for the resampled data sets and compared the resulting classifications using a newly developed procedure.

Results:

Random resampling of the initial data set and geographically stratified resampling resulted in similar classifications. By contrast, classifications of the resampled data sets that were based on habitat stratifications (2–5) differed from each other and from the initial data set. Stratification 2 resulted in classifications that strongly reflected environmental factors with a coarse grain of spatial heterogeneity (e.g. macroclimate), whereas stratification 5 resulted in classifications emphasizing fine‐grained factors (e.g. soil nutrient status). Stratification 3 led to the most deviating results, possibly due to the subjective nature of the traditional phytosociological classifications.

Conclusions:

Stratified resampling may increase the representativeness of phytosociological data sets, but different types of stratification may result in different classifications. No single resampling strategy is optimal or superior: the appropriate stratification method must be selected according to the objectives of specific studies.
Development of the cultural landscape in the forest‐grassland transition in southern Alberta controlled by topographic variables
Authors: Simonson J.T. , Johnson E.A.
Published: February 2009

Question:

How has the terrain, namely elevation, slope and aspect, controlled the cultural modification of the forest‐grassland transition in southern Alberta?

Location:

The aspen parkland region of the Rocky Mountains foothills southwest of Calgary, Alberta, Canada.

Methods:

Dominion Land Survey data, historical maps and a DEM (digital elevation model) were used to determine which decision rules settlers used to plough native grassland and parkland at the turn of the last century. Comparative measurements between historical and current vegetation patterns and GIS techniques were used to explore relationships between terrain, land use and the modification of the landscape.

Results:

Grassland at lower elevations, aspen parkland at mid elevations and closed forest at higher elevations dominated the pre‐settlement forest‐grassland transition. Elevation, hillslope angle and aspect affected which parts of the landscape were cleared and ploughed for agriculture or left in their natural state. Clearing and ploughing occurred mostly on gentle hill‐slopes (≤ 6°). At higher elevations with fewer gentle hillslopes clearing and ploughing were limited. Ca. 90% of the original vegetation at lower elevations has been cleared or ploughed, compared to ca. 30% at higher elevations. Almost all of the grassland at lower elevations has been converted to cropland. In the mid‐elevation parkland 48% of the tree cover and > 72% of the native grass have been converted to domesticated grass and cropland. Tree cover has expanded at the expense of grass on steep hillslopes and in ravines that presumably were burned frequently by wildfires in pre‐settlement times. At higher elevations, the closed forest has remained more or less intact.

Conclusions:

Terrain structure has controlled the arrangement of suitable agricultural land and consequently determined the current vegetation patterns in the forest‐grassland transition zone in southern Alberta. Tree invasion into grass has been minimal, and has been restricted to hilly topography or wet areas, even though the parkland has expanded somewhat in its distribution. Any effect the cessation of wildfires may have had on aspen expansion has been overshadowed by agriculture, which has converted vast areas of native grassland and aspen parkland to farmland. Thus, along this forest‐grassland transition, the strong elevation, slope and aspect have maintained some of the regional variation in vegetation.
Rao's quadratic entropy as a measure of functional diversity based on multiple traits
Authors: Botta‐Dukát Zoltán
Published: February 2009

Question:

Is Rao's quadratic entropy a suitable measure of functional diversity if several traits are considered?

Methods:

It is checked whether Rao's quadratic entropy (FDQ) satisfies a priori criteria suggested by Mason et al. A real data set is used to show that there are often zeros in abundance distributions which maximize functional diversity.

Results and Conclusion:

FDQ fulfils all a priori criteria and it surpasses other proposed indices, because it includes species abundances and more than one trait. Therefore, it seems to be an improvement compared to measures of functional diversity that are currently available. An unexpected property of FDQ is that its value may decrease if species richness increases. The reason is that functional diversity is influenced by both species‐abundance based diversity and differences among species. Introduction of a new species into the community increases the species‐abundance based diversity, while it may decrease the average dissimilarity among species.
Trends in the upward shift of alpine plants
Authors: Walther Gian‐Reto , Beißner Sascha , Burga Conradin A.
Published: February 2009

Questions:

The 1990s were the warmest decade since the beginning of climate measurements. Based on almost 100 years of monitoring in the Swiss Alps, we asked (1) whether the extraordinary warm climatic conditions of the 1990s are reflected in the floristic composition of Alpine summit vegetation and, if so, (2) what the magnitude and rate of species change has been over the last few decades compared to the documented increase in species richness within the first 80 years of the 20th century.

Location:

Ten high mountain summits of the Bernina area in the southeastern Swiss Alps.

Methods:

Resurvey of the floristic composition of the uppermost altitudinal 10 m of these summits, applying the same methodology of former two surveys (1905 and 1985) and recording the presence of all vascular plant species.

Results:

Whereas the continued increase in plant species richness of high alpine summit vegetation is confirmed, our results also suggest an acceleration of the trend in the upward shift of alpine plants.

Conclusion:

Vegetation change in the southeastern Swiss Alps has accelerated since 1985, consistent with a climate change explanation.
Small‐scale guild proportions and niche complementarity in a Caucasian subalpine hay meadow
Authors: Kikvidze Zaal , Khetsuriani Liana , Kikodze David
Published: February 2009

Question:

Monocot and dicot perennial herbaceous species can be considered two a priori guilds, which interact in regularly mown grasslands. Complementary resource use in space is important for diversity and productivity of perennial herbaceous communities, yet small‐scale spatial patterns of guilds and niche complementarity have rarely been linked explicitly. We ask: 1. Do guild interactions in our community generate small‐scale patterns such as guild proportionality? 2. Do these patterns coincide with overyielding of guilds, that is, can small‐scale spatial patterns of guilds be experimentally linked to niche complementarity?

Location:

Georgia, central Caucasian mountains.

Methods:

We sampled randomly placed small quadrats and used presence‐absence data to measure small‐scale spatial patterns within plots. We experimentally tested overyielding of monocots and dicots grown separately and in mixtures.

Results:

We found measurable small‐scale pattern of guilds in our community: monocots and dicots showed significant guild proportionality. However, variance deficit in the number of species per small quadrat was stronger in monocots than in dicots. Experiments found considerable overyielding, which was unaffected by water stress.

Conclusions:

Coincidence of measurable small‐scale arrangements of guilds with robust overyielding indicates that spatial arrangement is an important manifestation of niche complementarity. Stronger variance deficit of monocot species at small scale suggests that monocots compete with each other more strongly and, as a consequence, are more regularly dispersed at small spatial scale. Conversely, morphologically more diverse and more plastic dicots may more easily fit within the neighbourhood patchwork created by monocots.
Can competitive ability predict structure in experimental plant communities?
Authors: Fraser Lauchlan H. , Keddy Paul A.
Published: February 2009

Question:

Two questions were posed: 1. Can an independent measure of relative competitive ability be used to predict the abundance of species in mixtures? 2. Is the success of those predictions affected by low fertility (stress simulation) or clipping (disturbance simulation)?

Location:

Greenhouse at Carleton University, Ottawa, Canada.

Methods:

We collected adult plant ramets of 11 species from the field and transplanted one ramet of each species into 56 containers of 60 L. We applied a 4 × 2 factorial combination of fertilization (none, full nutrients except N, full nutrients except P, full nutrients) and clipping (no clipping, clipping to 10 cm above soil) with seven replicates of each treatment. After two growing seasons the above‐ and below‐ground biomass of each species was determined.

Results:

Regression analyses uncovered a significant positive relationship between plant biomass (measured in this study) and relative competitive ability (as measured in an independent study) under all experimental conditions. Both the mean slope and meanR2were lowest in treatments with low nutrients and highest in the full nutrient treatment (irrespective of clipping).

Conclusions:

Our results show that (1) at high fertility, relative competitive ability can generally predict the abundance of species in experimental plant communities, and (2) the intensity of competition (inferred from the magnitude of the slope orR2) increased with increasing nutrient supply, particularly nitrogen.
Variation in seed buoyancy of species in wetland ecosystems with different flooding dynamics
Authors: van den Broek Tom , van Diggelen Rudy , Bobbink Roland
Published: February 2009

Question:

Do species from communities with different flooding dynamics differ in seed buoyancy? Is there a trade‐off between seed buoyancy and seed longevity?

Methods:

Seeds of 55 freshwater wetland species were collected and related to communities along the hydrological gradient, ranging from constantly flooded reed beds, through tall herb fens and rich fens, to rarely flooded wet meadows. Species were experimentally tested for seed buoyancy over 210 days in standing water and moving water. Seed longevity for each species was calculated.

Results:

Community occurrence along the hydrologic gradient was mirrored by seed buoyancy. Seed buoyancy was highest for species of almost permanently inundated reed beds and lowest for species of rarely inundated wet meadows. The seed buoyancy characteristics of species of reed beds were best adapted to hydrological dynamic conditions mimicked by the treatment moving water and were the most independent of the flow rate of the water. A high percentage of the species used had a transient seed bank. Together with high buoyancy in many species, this suggests a trade‐off between dispersal capacity and seed persistence.

Conclusions:

In freshwater wetlands with rather stable water levels, many species lack a persistent seed bank and depend on dispersal for colonization of new habitats. Seed buoyancy enhances aquatic seed dispersal, and can be of great importance in both vegetation dynamics and restoration. In wetlands that are inundated for a long period during the year and with a water level above soil surface, higher seed buoyancy enhances the possibility for hydrochory.
Demographic and life‐history correlates for Amazonian trees
Authors: Nascimento Henrique E.M. , Laurance William F. , Condit Richard , Laurance Susan G. , D'Angelo Sammya , Andrade Ana C.
Published: February 2009

Questions:

Which demographic and life‐history differences are found among 95 sympatric tree species? Are there correlations among demographic parameters within this assemblage?

Location:

Central Amazonian rain forest.

Methods:

Using long‐term data from 24 1–ha permanent plots, eight characteristics were estimated for each species: wood density, annual mortality rate, annual recruitment rate, mean stem diameter, maximum stem diameter, mean stem‐growth rate, maximum stem‐growth rate, population density.

Results:

An ordination analysis revealed that tree characteristics varied along two major axes of variation, the major gradient expressing light requirements and successional status, and the second gradient related to tree size. Along these gradients, four relatively discrete tree guilds could be distinguished: fast‐growing pioneer species, shade‐tolerant sub‐canopy species, canopy trees, and emergent species. Pioneers were uncommon and most trees were canopy or emergent species, which frequently had low mortality and recruitment. Wood density was negatively associated with tree mortality, recruitment, and growth rates when all species were considered. Growth rates varied markedly among and within species, with pioneers exhibiting far faster and less variable growth rates than did the other species. Slow growth in subcanopy species relative to canopy and emergent trees was not a simple consequence of mean tree size, but apparently resulted from physiological constraints imposed by low‐light and other conditions in the forest understorey.

Conclusions:

Trees of Amazonian rain forests could be classified with some success into four relatively distinctive guilds. However, several demographic and life‐history traits, such as those that distinguish early and late successional species, probably vary along a continuum, rather than being naturally grouped into relatively discrete categories.
Reproduction of dipterocarps during low intensity masting events in a Bornean rain forest
Authors: Maycock Colin R. , Thewlis Richard N. , Ghazoul Jaboury , Nilus Reuben , Burslem David F.R.P.
Published: February 2009

Question:

The evolution of general flowering and mast fruiting of dipterocarps in tropical rain forest has been explained by different mechanisms. We studied whether the abundance of flowering conspecifics influences the recruitment success of tropical forest trees in Borneo.

Location:

Sepilok Forest Reserve, Sabah, Malaysia.

Method:

We examined the recruitment success of 17 species ofDipterocarpaceaein a 640–ha sample area over two flowering events in 2001–2002 using seed traps and quadrats. Seed predation experiments were used to investigate if post‐dispersal seed survival was density‐dependent.

Results:

We found a negative relationship between the percentage of flowers abscised per individual and the number of flowering conspecifics and a positive relationship between the percent of flowering trees that produced viable seeds and the number of flowering conspecifics. However, we found no evidence of decreasing pre‐ and post‐dispersal predation with increasing numbers of flowering conspecifics. High levels of flower abscission, and pre‐ and post‐dispersal seed mortality, resulted in near‐complete recruitment failure of most species, with only three species successfully recruiting in only one year. One of these,Parashorea tomentella, satiated seed predators over a large area, whileHopea beccarianaandShorea multifloraonly recruited in small isolated clumps. Seed predation experiments suggest that post‐dispersal seed survival was positively density‐dependent in the short‐term.

Conclusions:

Increased density of flowering conspecifics may contribute to increased likelihood of successful cross‐pollination during low intensity flowering events and, in some cases, to enhanced probability of short‐term seed and seedling survival. Both processes may contribute to the evolution of mast fruiting and general flowering in Southeast Asian lowland dipterocarp forests.
Plant invasions in undisturbed ecosystems: The triggering attribute approach
Authors: Gurvich Diego E. , Tecco Paula A. , Díaz Sandra
Published: February 2009

The invasion of a target community by a non‐indigenous plant species includes the stages of arrival, establishment and spread, which tend to depend on different characteristics of the invasive species and its context. While the mechanisms behind the invasion of highly disturbed ecosystems are well known, our understanding of the invasion process in undisturbed or weakly disturbed ecosystems is much more limited. Here we propose that, once a non‐indigenous species has arrived to a new ecosystem and become established, the likelihood that it spreads, and thus becomes invasive, may depend on just one or very few characteristics, called‘triggering attributes’(TA). We propose that a TA is a vegetative or regenerative attribute discontinuously distributed in comparison to the resident community. This attribute allows the species to benefit from a resource that is permanently or temporarily unused by the resident community. We present an original study case and examples from the literature to illustrate our approach, and we also propose some ways to test it in different ecosystems.
A test of three juvenile plant competitive response strategies
Authors: Carlyle Cameron N. , Fraser Lauchlan H.
Published: February 2009

Questions:

1. Are there competitive response strategies for light in juvenile plants? 2. If so, do plant traits (e.g. seed weight, relative growth rate, height and biomass) correlate with the strategies?

Location:

Controlled greenhouse study using perennial vegetation typical of wet meadows in Northeast Ohio, USA.

Methods:

We used two light manipulations in a greenhouse to screen ten replicates of 19 plant species for three proposed competitive response strategies (‘escape’, ‘forage’, ‘persist’). We measured the time it took a seedling to die and the maximum height achieved when grown in the dark to assess two strategies, persist and escape. The biomass of seedlings when grown under a controlled, low‐intensity, shifting light source was measured to test a third strategy, forage.

Results:

We found significant variation across species in the measurements used to assess each strategy. The species ranking for each strategy was not concordant across strategies. Traits were found that correlated with the escape strategy (seed weight, height and biomass) and persist strategy (time to reach maximum height). No traits were found that correlate with the forage strategy.

Conclusions:

There appear to be trade‐offs by plants in the three strategies tested in this study. Species which had the best performance on one strategy typically scored poorly on the other strategies. However, many species fall in the middle range, ranking similarly across the ‘persist’, ‘escape’, and ‘forage’ strategies.
Tree regeneration responses to Chusquea montana bamboo die‐off in a subalpine Nothofagus forest in the southern Andes
Authors: Holz C. Andrés , Veblen Thomas T.
Published: February 2009

Question:

The aim of the present study is to examine how a rare flowering and massive die‐off event of a dominant understorey bamboo affected tree regeneration processes in a subalpine Nothofagus forest. In particular, we assess the effects of the die‐off event on tree seedling demography (establishment and survival) and on the height growth of previously established juveniles, and we determine how these effects vary in relation to stand age and canopy conditions.

Location:

Carirriñe Pass and Choshuenco Volcano at 1200 m a.s.l. in a mixed subalpine temperate forest in northern Patagonia (40°S, 71°W), spanning the Chilean and Argentinian border.

Methods:

Regeneration processes in Nothofagus pumilio and N. dombeyi were examined under different canopy conditions (closed or gap), in both young and old stands, and in patches of flowered and non‐flowered Chusquea bamboo during the first three growing seasons following the simultaneous flowering and die‐off of Chusquea montana f. montana in November‐December 2001. We installed permanent plots under all forest conditions and measured seedling and sapling height growth and new seedling establishment following the bamboo die‐off. To assess potential variation in tree seed sources, seed fall was collected and seed viability was measured. To assess for potential variation in the understorey light conditions and infer its influence on tree regeneration, hemispherical photographs of the canopy were taken at each plot.

Results:

Bamboo die‐off triggered accelerated growth in height of Nothofagus seedlings and saplings in gaps in old stands. Bamboo die‐off did not result in new tree seedling establishment; however, die‐off did increase the survival of newly established seedlings.

Conclusion:

The predominant response of Nothofagus spp. to the bamboo die‐off event was the accelerated height growth of previously established juveniles (i.e. a re‐organization response). Successful recruitment into the canopy of these relatively shade‐intolerant tree species appears to be dependent on previously existing canopy gaps. It is likely that the release in height of previously established juveniles of Nothofagus after the bamboo die‐off will eventually result in development of even‐sized and relatively even‐aged, patches of canopy trees.
Patterns of plant invasion along an environmental stress gradient
Authors: MacDougall A.S. , Boucher J. , Turkington R. , Bradfield G.E.
Published: February 2009

Question:

Do stressful environments facilitate plant invasion by providing refuges from intense above‐ground competition associated with productive areas, or prevent it by favouring locally adapted native species?

Location:

An invaded and fragmented oak savanna ecosystem structured along a landscape‐level stress gradient associated with soil depth, elevation, and canopy openness.

Methods:

Vegetation and environmental data were collected from 184 plots in seven savanna remnants along the gradient. Using multivariate (CCA) and post‐hoc regression analyses, we determined the relationship between environment and the richness and abundance of invasives.

Results:

46 of 119 species were naturalized exotics. CCA indicated the importance of environmental variation (mostly soil depth) for community structure but not for invasion; invasive species richness was similar in all areas. However, the abundance of invasives and their impacts on native diversity appear to increase significantly in less stressful habitats. Deeper soils had lower evenness and significantly fewer native species. This result was associated with dominance by exotic perennial grasses and large increases in vegetation height, suggesting strong above‐ground competition.

Conclusions:

Low‐stress environments were not more invasible per se but appear to be more susceptible to invasion by species with strong competitive impacts. The causes of decreasing exotic impact with decreasing soil depth may reflect shifts in competitive intensity or an increased importance of stress tolerance, both of which may favour natives. Alternatively, this ecosystem may simply lack high‐impact invaders capable of dominating shallow soils. Conservation challenges are twofold for this endangered plant community: controlling invasives that currently dominate deeper‐soils and accounting for a diverse pool of invaders that proliferate when the current dominants are removed.
Facilitative succession in a boreal bryophyte community driven by changes in available moisture and light
Authors: Fenton Nicole J. , Bergeron Yves
Published: February 2009

Question:

What are the drivers of bryophyte succession in paludifying boreal Picea mariana forests?

Location:

The Clay‐Belt of Quebec and Ontario, Canada.

Methods:

The bryophyte community and habitat variables (forest floor thickness, water table, stand density, canopy openness micro‐climate and presence of ericaceous species) were analysed in a chronosequence of 13 stands from 50 to more than 350 years since fire.

Results:

Across the chronosequence, feathermosses were replaced by shade and desiccation tolerant slower growing hummock Sphagna and then by faster growing hollow Sphagna. These changes were linked with both increasing light availability and the movement of the water table into the forest floor.

Conclusions:

As water table rise is dependent on forest floor thickness, which is in turn influenced by the presence of Sphagna, this successional sequence represents an example of facilitation. Furthermore, it emphasizes the importance of water table rise in determining stand level, and landscape level variables such as carbon balance.
Seasonal shifts in competition and facilitation in subalpine plant communities of the central Caucasus
Authors: Kikvidze Zaal , Khetsuriani Liana , Kikodze David , Callaway Ragan M.
Published: February 2009

Question:

Temporal and spatial shifts in competitive and facilitative interactions among plants have important implications for species coexistence and community diversity. Many studies have focused on inter‐seasonal variation in these interactions, but very few have examined short‐term intra‐seasonal shifts between competition and facilitation. In the central Caucasus Mountains the subalpine climate changes considerably over the season, with a relatively benign (humid and cooler) first part followed by a much more stressful (drier and warmer) second part. We ask: do plant interactions shift from competitive to facilitative during the growing season as environmental conditions change from mesic to dry?

Location:

The central Caucasus Mountains, Georgia.

Methods:

We experimentally investigated shifts in the balance of positive and negative interactions in plant communities over the course of a single growing season by conducting sequential removal experiments on two co‐dominant species.

Results:

We found that during the wet and cool first half of the growing season, target plants without neighbours accumulated significantly more biomass than individuals with neighbours, indicating competition. However, in the drier second half of the growing season competitive interactions were shifted to facilitation as individuals without neighbours accumulated significantly less biomass.

Conclusions:

In general, these results support the view that competitive and facilitative effects exist in dynamic tension in plant communities with facilitation intensifying as abiotic stress increases, also within a growing season.
Biogeographical determinants of lichen species diversity on islets in the West‐Estonian Archipelago
Authors: Jüriado Inga , Suija Ave , Liira Jaan
Published: February 2009

Questions:

Do islet area, number of biotopes and distance from the mainland shape lichen species richness on islets? Are there any species‐ or substrate group‐specific trends associated with these factors?

Location:

Islets of the west Estonian Archipelago, Estonia.

Methods:

A species list was compiled for each of the 32 islets and the relative abundance of each species was estimated. The lichens were divided into seven groups according to their substrate preferences. Generalized linear model (GLIM) analysis was applied to test the effect of the islet traits on the number of lichen species on the islets and in the substrate groups. The probability of presence/absence and abundance of the most frequent species according to the islet traits were tested with GLIM and general linear mixed model.

Results:

The lichen flora of the islets consisted of 326 taxa, the number of lichen species per islet varied from 2 to 197. Total number of species per islet and within the substrate groups was positively correlated with islet area and with number of biotopes, and negatively correlated with distance from the mainland; however, these relationships varied among the substrate groups. Although individual lichen species showed variation in responses, general trends in island biogeography were evident.

Conclusions:

The distribution pattern of lichens on the studied islets follows the theory of island biogeography: the number of species per islet depends on isolation, area and biotope diversity. Species specific traits, such as dispersal strategy and growth form, as well as availability of a particular substrate are important for formation of the lichen flora on islets.
Edge influence on the old‐growth forest indicator lichen Alectoria sarmentosa in natural ecotones
Authors: Esseen Per‐Anders
Published: February 2009

Question:

Is the pendulous epiphytic indicator lichen Alectoria sarmentosa influenced by proximity to forest edge in natural old‐growth forests?

Location:

Large (28 400 ha), naturally heterogeneous boreal landscape in northern Sweden dominated by old‐growth Picea abies forest in a matrix of open wetland.

Methods:

The abundance of A. sarmentosa and forest structure were quantified in ten edge‐interior transects (0–100 m) at southern to western forest edges. Four 10 m × 50 m plots were sampled along each transect. Mass of A. sarmentosa in the lower canopy (0–5 m) of P. abies was estimated from maximum thallus length.

Results:

The maximum length of A. sarmentosa was four times lower, and the lichen mass 16 times lower, at the forest edge compared to the forest interior. Lichen mass showed a monotonic decrease from the interior to the edge. Mean distance of edge influence was 58 m for lichen mass, and extended longer into the forest than changes in stand structural variables. The response of A. sarmentosa to edges is a result of a combination of changes in microclimate and substrate availability.

Conclusions:

The indicator species A. sarmentosa is strongly affected by proximity to forest edge in natural old‐growth forests. Edge influence is thus important in controlling the abundance of this group of pendulous lichens in natural forest ecosystems. Distance of edge influence was longer in natural wetland‐forest ecotones than previously reported for fragmented forests; this was probably due to higher lichen abundance and lower site productivity in the study area. Understanding lichen response to natural landscape structure may help us to improve conditions for epiphytes in managed forests.