bluuebunny/crossref_metadata_2025_split huggingface dataset:
Floristic composition of a Swedish semi‐natural grassland during six years of elevated atmospheric CO2
Authors: Marissink Mark , Hansson Margareta 
Published: February 2009

Abstract. A semi‐natural grassland in Sweden was exposed to an elevated CO2 concentration during a six‐year open‐top chamber experiment. Vegetation composition was assessed twice a year using the point‐intercept method. The field had been grazed previously, but when the experiment started this was replaced with a cutting regime with one cut (down to ground level) each year in early August. From the third to the sixth year of the study the harvested material was divided into legumes, non‐leguminous forbs and grasses, dried and weighed.Elevated CO2 had an effect on species composition (as analysed by Principal Component Analysis) that increased over time. It also tended to increase diversity (Shannon index) in summer, but reduce it in spring. However, the effects of the weather and/or time on species composition and diversity were much more prominent than CO2 effects. Since the weather was largely directional over time (from dry to wet), with the exception of the fifth year, it was difficult to distinguish between weather effects and changes caused by a changed management regime.In all treatments, grasses increased over time in both mass and point‐intercept measurements, whereas non‐leguminous forbs decreased in mass, but not in point‐intercept measurements. Legumes increased in the point‐intercept measurements, but not in biomass, at elevated CO2, but not in the other treatments.Overall, we found that elevated CO2 affected species composition; however, it was only one of many factors and a rather weak one.
Altitudinal gradients in seed dynamics of Calluna vulgaris in eastern Scotland
Authors: Cummins Roger P. , Miller Gordon R. 
Published: February 2009

Abstract. Relationships between seed deposition, size of soil seed banks and some of the environmental factors affecting them were assessed for Calluna vulgaris throughout its altitudinal range (150–960 m a.s.l.) in eastern Scotland. Seed rain was assessed using pitfall traps, collected every 5–10 wk for 3 yr; germinability was determined by laboratory incubation. Seed bank size was estimated, once only, by counting seedlings emerging from soil cores kept for 50 wk in a glasshouse.Seed deposition varied annually, was related to parent plant cover but always declined with altitude, falling sharply above 600 m a.s.l. Seed bank size was more closely correlated with the proportion of organic matter in the soil than with the amount of seed rain. Seed bank sizes declined gradually with altitude but did not differ significantly between four altitudinal zones. The mean density of buried seeds was less than half the mean annual seed rain at sites below 300 m a.s.l. but was over 200 × greater than annual seed rain above 800 m, suggesting that seeds buried at high altitudes remain viable for much longer than those at lower altitudes.
BOOK REVIEWS
Authors: Grime J.P. 
Published: February 2009

Book reviewed in this article:Weiher, E. & Keddy, P. (eds.) 2001. Ecological Assembly Rules: Perspective, Advances, and Retreats. xii + 418 pp. Cambridge University Press, Cambridge. ISBN 0‐521‐65533‐1 (paperback). Price: USD 37.95.
Patterns of plant species composition on Amazonian sandstone outcrops in Colombia
Authors: Arbeláez Maria V. , Duivenvoorden Joost F. 
Published: February 2009

Vascular plant species compositional patterns of the low forest, scrub, and herbaceous vegetation on white sand soils and sandstone substrates were studied at six sandstone plateaus in Colombian Amazonia, by means of a field survey according to the Braun‐Blanquet relevé method. Canonical Correspondence Analysis (CCA) was applied to separate effects of habitat and spatial configurations of the plateaus on species patterns. Also, information on dispersal ability and phytogeographic affinity of species was used to test explanations for between plateau differences.Low trees, shrubs and herbs were the main species recorded in 212 relevés. The main gradients in the species patterns were linked to the spatial configuration of the plateaus. Spatially controlled species patterns were mainly related to soil depth and soil organic matter. The association between phytogeographic affinity and the habitat controlled spatial link of species pointed at insufficient sampling at one plateau. Dispersal ability did not explain the habitat controlled spatially distributed occurrences of plant species. This might indicate a low frequency of local extinctions at the sandstone plateaus, especially of the poorly dispersed species, possibly because plant populations survive fire or drought disturbances in local sheltered places. Space and habitat controlled species patterns at one plateau were quite distinct from patterns at the other plateaus. This might be due to unmeasured habitat factors (e.g. unrecorded soil variation or human disturbance history) or the preferential, surveyor biased sampling procedure.
Primary succession on lava domes on Terceira (Azores)
Authors: Elias Rui B. , Dias Eduardo 
Published: February 2009

Abstract:Questions: Are the vegetation attributes significantly different among lava domes and among geomorphologic units as a result of age and soil features? Are the successional rates equal in all the geomorphologic units of the domes? Are the colonizer species of lava domes totally replaced by other species in the late successional stages?Location: Terceira Island, Azores (Portugal).Methods: Three comparable domes of 240, 370 and 2080 yr old were selected. Data on floristic composition, vegetation bioarea (area occupied by plant species in transects), structure, demography and soil nutrients were collected. Quantitative and qualitative changes along the succession gradient were also analyzed.Results: Vegetation attributes were consistent with the successional stage of each dome in the primary sere; however, the geomorphologic units did not follow the same pattern. The influence of the rates of plant colonization and soil formation are responsible for the decrease of the successional rates from footslopes, to summits, to slopes. The vegetation successionally changes from Juniperus scrub, to Juniperus wood and forest, and there is little species replacement since the similarity in species composition is high between the 3 domes.Conclusions: This is a special type of direct succession that takes place mainly through an increase in biomass and structural complexity. We observed small wooded areas in the fissures of very young domes that are samples of later successional forests — a phenomenon that we call ‘zoom effect’.
Non‐destructive dry matter estimation of Alhagi sparsifolia vegetation in a desert oasis of Northwest China
Authors: Siebert S. , Gries D. , Zhang X. , Runge M. , Buerkert A. 
Published: February 2009

Abstract:Question: Can above‐ground biomass of naturally growing Alhagi sparsifolia shrubs be estimated non‐destructively?Location: Qira oasis (37° 01′N, 80° 48′E, 1365 ma.s.l.) at the southern fringe of the Taklamakan desert, Xinjiang, NW China.Methods: Two methods were compared to estimate above‐ground biomass (AGB) of Alhagi. At first shrub AGB was estimated by manual ground measurements (called ‘allometric approach’) of length, width and height of 50 individuals. Subsequently regression equations were established between calculated shrub canopy volume and shrub AGB (r2= 0.96). These equations were used to calculate AGB from manual ground measurements in 20 sample plots within the Alhagi field. Secondly, kite‐based colour aerial photography coupled with the use of a Geographic Information System (called ‘GIS approach’) was tested. First and second order polynomial regressions between AGB data of the 50 individual shrubs and their respective canopy area allowed to automatically calculate the AGB of all remaining shrubs covered by the photograph (r2= 0.92 to 0.96). The use of non‐linear AGB regression equations required an automatised separation of shrubs growing solitary or in clumps. Separation criteria were the size and shape of shrub canopies.Results: The allometric approach was more reliable but also more time‐consuming than the GIS‐based approach. The latter led to an overestimation of Alhagi dry matter in densely vegetated areas. However, this systematic error decreased with increasing size of the surveyed area. Future research in this field should focus on improvements of AGB estimates in areas of high shrub density.
Small‐scale spatial autocorrelation and the interpretation of relationships between phenological parameters
Authors: Almeida‐Neto Mário , Lewinsohn Thomas M. 
Published: February 2009

Abstract:Question:Are flower production and associated phenological variables (onset, end, duration, and three measures of flowering synchrony) randomly distributed in space or, alternatively, is there a neighbourhood structure (spatial autocorrelation) in the values of these variables? To which extent does spatial autocorrelation affect the correlation tests between phenological traits?Location:A tree savanna reserve in Southeastern Brazil (22°15′S,47°08′W).Methods:The flowering season ofChromolaena odoratawas followed for all (96) individuals in a completely mapped area of 3000 m2. The phenological traits were estimated by counting flower heads in anthesis on individual plants every seven days for 14 weeks.Results:Flowering time was unimodally distributed, but with different peak dates depending on whether individual flower heads or plants were counted. Three phenological traits and canopy closure above the plants showed some degree of spatial autocorrelation, which caused loss of up to 35% of degrees of freedom in nine of 36 correlation tests. Such a decrease in the degrees of freedom resulted in loss of significance for correlations in three pairs of variables.Conclusions:We hypothesize that the spatial autocorrelation in phenological traits betweenC. odorataneighbours may be driven by genetic similarity among neighbouring plants and/or spatial structuring of environmental factors. Because location and distance between samples may affect their statistical independence, we suggest that spatial autocorrelation should be taken into account in future studies of plant phenology, e.g. by using effective sample size in statistical tests.
Subdominant species distribution in microsites around two life forms at a desert grassland‐shrubland transition zone
Authors: Hochstrasser T. , Peters D.P.C. 
Published: February 2009

Abstract:Question: In the same landscape context — at a desert grassland‐shrubland transition zone, how does subdominant plant abundance vary in microsites around dominant grasses and shrubs?Location: Sevilleta LTER, New Mexico, USA (34°21’N; 106°53’W; 1650 m a.s.l.).Methods: We compared the distribution of subdominant plants in canopy, canopy edge and interspace microsites around individual shrubs (Larrea tridentata) and grasses (Bouteloua eriopoda) at a transition zone that has been encroached by shrubs within the past 50 ‐ 100 a. Plots of variable size according to microsite type and dominant plant size were sampled.Results: Subdominant abundance was higher in microsites around L. tridentata shrubs than in microsites around B. eriopoda. Furthermore, differences in species abundance and composition were higher among microsites around grasses than among microsites around shrubs. The distribution of subdominants was mostly explained by their phenological characteristics, which indicates the importance of temporal variation in resources to their persistence.Conclusions: This study of coexistence patterns around dominants revealed ecological contrasts between two dominant life forms, but other factors (such as disturbances) have to be taken into consideration to evaluate landscape‐scale diversity.
Seed bank dynamics and tree‐fall gaps in a northwestern Mexican Quercus‐Pinus forest
Authors: Arriaga Laura , Mercado Carmen 
Published: February 2009

Abstract:Questions: How does the seed bank respond to different types of tree‐fall gaps and seasonal variations? How does the soil seed bank influence recovery of the standing vegetation in the mature forest and tree‐fall gaps?Location: 1800 — 2020 m a.s.l., Quercus‐Pinus forest, Baja California Sur, Mexico.Methods: Seed size, species composition and germination were estimated under different environmental conditions during dry and rainy seasons: a mature forest plot and gaps created by dead standing trees, snapped‐of f trees and uprooted trees. The soil seed bank was investigated using direct propagule emergence under laboratory conditions, from soil cores obtained during both seasons.Results: 21 species, 20 genera and 14 families constitute the seed bank of this forest community. Fabaceae, Asteraceae, Euphorbiaceae and Lamiaceae were the most frequently represented families in the seed bank. Floristic composition and species richness varied according to the different modes of tree death. Species composition of seed banks and standing vegetation had very low similarity coefficients and were statistically different. Seed bank sizes varied between 164 and 362 ind.m‐2 in the mature forest plot for the dry and rainy seasons, respectively, while soil seed bank sizes for gaps ranged between 23–208 ind.m‐2 forthe dry season and between 81–282 ind.m‐2 for the rainy season.Conclusions: Seed bank sizes and germination response were always higher in the rainy season under all the environmental conditions analysed. Results suggest that timing responses to gap formation of the soil seed bank could be more delayed in this temperate forest than expected.
Recruitment limitation in secondary forests dominated by an exotic tree
Authors: Lichstein Jeremy W. , Grau H. Ricardo , Aragón Roxana 
Published: February 2009

AbstractQuestion: What factors limit woody plant recruitment in a mosaic landscape where former agricultural lands are dominated by the invasive tree Ligustrum lucidum (Oleaceae)?Location: Subtropical northwestern Argentina.Methods: In secondary forest patches, we measured (1) tree, shrub and liana abundance in different size classes; (2) seed rain of Ligustrum and two native trees and (3) topographic, soil and light variables. We used spatial autoregressive models to test for effects of Ligustrum dominance and environment on native plant abundance in each size class. We used multiple regression on resemblance matrices to quantify the relative importance of spatial (e.g. dispersal) and environmental effects on native species composition.Results: Native tree abundance in the smallest size class was unrelated to Ligustrum canopy dominance, while native tree abundance in larger size classes and native liana abundance were negatively correlated with Ligustrum dominance. Native species composition was both environmentally and spatially structured, suggesting that some species are dispersal limited. Seed rain was spatially correlated with conspecific basal area for one of two native species, but not for Ligustrum.Conclusions: Native tree recruitment appears to be limited primarily by sapling mortality in patches dominated by the invasive Ligustrum. Ligustrum does not appear to be dispersal limited in our study area and is likely to continue spreading. Invaded patches may persist for hundreds of years.
Distribution and abundance of trees in floodplain forests of the Wisconsin River: Environmental influences at different scales
Authors: Turner Monica G. , Gergel Sarah E. , Dixon Mark D. , Miller James R. 
Published: February 2009

AbstractQuestions: 1. How do physiography, flooding regime, landscape pattern, land‐cover history, and local soil conditions influence the presence, community structure and abundance of overstorey trees? 2. Can broad‐scale factors explain variation in the floodplain forest community, or are locally measured soil conditions necessary?Location: Floodplain of the lower 370 km of the Wisconsin River, Wisconsin, USA.Methods: Floodplain forest was sampled in 10 m × 20 m plots [n= 405) during summers of 1999 and 2000 in six 12‐ to 15‐km reaches.Results: Species observed most frequently were Fraxinus pennsylvanica, Acer saccharinum and Ulmus americana. Physiography (e.g. geographic province) and indicators of flooding regime (e.g. relative elevation and distance from main channel) were consistently important in predicting occurrence, community composition, and abundance of trees. Correspondence analysis revealed that flood‐tolerant and intolerant species segregated along the primary axis, and late‐successional species segregated from flood‐tolerant species along the secondary axis. Current landscape configuration only influenced species presence or abundance in forests that developed during recent decades. Land‐cover history was important for tree species presence and for the abundance of late‐successional species. Comparison of statistical models developed with and without soils data suggested that broad‐scale factors such as geographic province generally performed well.Conclusions: Physiography and indicators of flood regime are particularly useful for explaining floodplain forest structure and composition in floodplains with a relatively high proportion of natural cover types.
Effects of fire severity in a north Patagonian subalpine forest
Authors: Kitzberger Thomas , Raffaele Estela , Heinemann Karin , Mazzarino María Julia 
Published: February 2009

Abstract. Question: What is the relative importance of fire‐induced canopy mortality, soil burning and post‐fire herbivory on tree seedling performance?Location: Subalpine Nothofagus pumilio forests at Challhuaco valley (41°13'S, 71°19'W), Nahuel Huapi National Park, Argentina.Methods: We fenced and transplanted soils of three burning severities along a fire severity gradient produced by a fire in 1996. Over two growing seasons we monitored soil water, direct incoming solar radiation, seedling survival, final seedling total biomass and root/shoot ratio. Additionally, we assessed severity‐related changes in soil properties.Results: Incoming radiation (an indicator of the amount of canopy cover left by the fire) was the primary factor influencing spring and summer top soil water availability, first and second‐year seedling survival and seedling growth. While seedling survival and soil water content were negatively affected by increased radiation, seedling final biomass was highest in very open microsites. Burned soils showed lower water holding capacity and soil carbon; however these changes did not affect topsoil water, and, contrary to expectation, there was a slight tendency toward higher seedling survival on more heavily burned soils. Herbivory significantly reduced seedling survival, but only under high‐radiation conditions. While the effect of radiation on final seedling biomass was not affected by herbivory, R/S ratios were significantly reduced by herbivory in high radiation micro sites.Conclusions: Despite inducing faster aerial growth, increased radiation and herbivory in severely burned sites may effectively prevent post‐fire regeneration in north Patagonian subalpine forest where seed sources are not limiting.
Determinants of community organization of a South African mesic grassland
Authors: Fynn Richard W.S. , O'Connor Timothy G. 
Published: February 2009

Abstract.Question:What is the long‐term influence of nutrient availability, productivity and soil pH on grassland community organization?Location:Ukulinga research farm, KwaZulu‐Natal, South Africa.Methods:The influence of fertilization on soil pH, nitrogen (N) and phosphorus (P) on variation in plant traits, community composition and species richness were examined in a 50‐year grassland fertilization experiment.Results:Averaged over 30 years, above‐ground net primary production (ANPP) was 337, 428 and 518 g.m‐2in sites not fertilized, fertilized with N, and fertilized with N plus P respectively. ANPP depended directly on N‐fertilization but not on P‐fertilization or liming, and responded positively to the interaction of N (first limiting nutrient) and P (second limiting nutrient). Short narrow‐leaved grass species —Themeda triandra, Tristachya leucothrixandSetaria nigrirostris— dominated sites of lowest ANPP where N was limiting (unfertilized, P‐fertilized or limed sites). A tall narrow‐leaved species,Eragrostis curvula, dominated sites of intermediate ANPP where P was limiting (N‐fertilized sites). By contrast, a tall broad‐leaved species,Panicum maximum, dominated the most productive sites where neither N nor P were limiting (N‐ and P‐fertilized sites). Certain species responded to liming and type of N‐fertilizer apparently because of their effects on soil pH. N‐fertilization reduced the density of herbaceous dicots (forbs) from 14 (unfertilized) to two (high N, no P, no lime) and five species per m2(high N, no P, limed). This effect was attributed to increased ANPP and a decrease in soil pH from 4.6 (KCl) in unfertilized sites to 3.49 (high N, no lime) and 4.65 (high N and lime). Soil acidification had no effect on grass species richness but influenced the abundance of certain species.Conclusions:Grassland community organization is determined not only by the influence of N availability, but also by the hierarchical interaction of N and P availability, in part through their compounded effect on ANPP, and by individualistic species responses to soil pH.
Oscillating vegetation dynamics in a wet heathland
Authors: Urban Katharina E. 
Published: February 2009

Abstract. Question: The significance of disturbances caused by periodical inundation was investigated with respect to its effects on vegetation dynamics, species richness and fluctuations, and to the relevance of certain plant properties.Location and Method: At a sod‐cut stand within nutrient‐poor inland sand dunes, permanent plots along a transect were surveyed over a period of up to nine years after sod cutting.Results: In contrast to never inundated plots, periodically inundated plots were characterized by low vegetation cover and by high numbers of species belonging to many different communities, each of them with a low cover. Periodical inundations favoured the presence of pioneers, species tolerant of disturbances, species adapted to wet conditions and stoloni‐ferous species. Furthermore, annual fluctuations of species within each plot were higher and most species occurred only sporadically.Discussion: A comprehensive model is presented describing the relevant processes identified in the littoral zone. Changing water tables result in the creation of gaps. The re‐colonization of these gaps follows mainly from vegetative regeneration and less to the dispersion of diaspores. Highest species numbers in the zone of moderate disturbances result from a high rate of re‐colonization in spite of local extinctions following each disturbance event. It is suggested that colonization abilities are among the most important features for species occurrence at a site rich in disturbances (more important than competitive abilities and more important than a slow rate of displacement). For nature conservation such sites are very important, because they allow (rare) pioneer species to survive for longer periods of time.