bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of repeated burning on Mediterranean communities of the northeastern Iberian Peninsula
Authors: Eugenio Màrcia , Lloret Francisco 
Published: February 2009

AbstractQuestion:In relation to a single fire, do repeated wildfires in Mediterranean type ecosystems (1) reduce plant species richness or diversity; (2) modify patterns of abundance or dominance of plant species or (3) alter plant composition?Location:Pinus halepensisdominated communities of Catalonia, northeastern Iberian Peninsula, western Mediterranean Basin.Methods:Regional, paired design with 14 study sites, each consisting of a once burnt area (1994) and a twice burnt area (1975–1993 and 1994). Ten years after the last fire, we recorded all vascular plant species present in nested plots and quantified their relative abundances on transects. We compared species richness, diversity, dominance and relative abundance and species‐area correlations between paired once and twice burnt areas and assessed their floristic composition similarity.Results:No statistically significant differences were found in species richness or diversity. Slopes of species‐area correlations were higher in once burnt areas. In twice burnt areas, dominance by one or two species was higher.P. halepensisshowed lower relative abundance and nanophanerophytes showed higher relative abundance. No differences were found for resprouter, seeder or resprouter‐seeder species. Floristic composition similarity between paired areas tended to be higher in less productive sites.Conclusions:Fire recurrence had contrasting effects on species richness at different spatial scales. Repeated burning reduced the relative abundance of the dominant tree species, which resulted in a higher relative abundance of shrubs. It also promoted the dominance of herbs, particularlyBrachypodium retusum.However, it did not change the relative abundance of regenerative groups. Paired areas were more similar as they were more Mediterranean in terms of climatic conditions.
Plant functional group responses to fire frequency and tree canopy cover gradients in oak savannas and woodlands
Authors: Peterson David W. , Reich Peter B. , Wrage Keith J. 
Published: February 2009

AbstractQuestions: How do fire frequency, tree canopy cover, and their interactions influence cover of grasses, forbs and understorey woody plants in oak savannas and woodlands?Location: Minnesota, USA.Methods: We measured plant functional group cover and tree canopy cover on permanent plots within a long‐term prescribed fire frequency experiment and used hierarchical linear modeling to assess plant functional group responses to fire frequency and tree canopy cover.Results: Understorey woody plant cover was highest in unburned woodlands and was negatively correlated with fire frequency. C4‐grass cover was positively correlated with fire frequency and negatively correlated with tree canopy cover. C3‐grass cover was highest at 40% tree canopy cover on unburned sites and at 60% tree canopy cover on frequently burned sites. Total forb cover was maximized at fire frequencies of 4–7 fires per decade, but was not significantly influenced by tree canopy cover. Cover of N‐fixing forbs was highest in shaded areas, particularly on frequently burned sites, while combined cover of all other forbs was negatively correlated with tree canopy cover.Conclusions: The relative influences of fire frequency and tree canopy cover on understorey plant functional group cover vary among plant functional groups, but both play a significant role in structuring savanna and woodland understorey vegetation. When restoring degraded savannas, direct manipulation of overstorey tree canopy cover should be considered to rapidly reduce shading from fire‐resistant overstorey trees. Prescribed fires can then be used to suppress understorey woody plants and promote establishment of light‐demanding grasses and forbs.
Environmental and neighbourhood effects on tree fern distributions in a neotropical lowland rain forest
Authors: Jones Mirkka M. , Olivas Rojas Paulo , Tuomisto Hanna , Clark David B. 
Published: February 2009

AbstractQuestions:To what extent are the distributions of tropical rain forest tree ferns (Cyatheaceae) related to environmental variation, and is habitat specialization likely to play a role in their local coexistence?Location:Lowland rain forest at La Selva Biological Station, Costa Rica.Methods:Generalized linear (GLM) and generalized additive (GAM) logistic regression were used to model the incidence of four tree fern species in relation to environmental and neighbourhood variables in 1154 inventory plots regularly distributed across 6 km2of old‐growth forest. Small and large size classes of the two most abundant species were modelled separately to see whether habitat associations change with ontogeny.Results:GLM and GAM model results were similar. All species had significant distributional biases with respect to micro‐habitat. Environmental variables describing soil variation were included in the models most often, followed by topographic and forest structural variables. The distributions of small individuals were more strongly related to environmental variation than those of larger individuals. Significant neighbourhood effects (spatial autocorrelation in intraspecific distributions and non‐random overlaps in the distributions of certain species pairs) were also identified. Overlaps between congeners did not differ from random, but there was a highly significant overlap in the distributions of the two most common species.Conclusions:Our results support the view that habitat specialization is an important determinant of where on the rain forest landscape tree ferns grow, especially for juvenile plants. However, other factors, such as dispersal limitation, may also contribute to their local coexistence.
Regional assessment of plant invasions across different habitat types
Authors: Vilà Montserrat , Pino Joan , Font Xavier 
Published: February 2009

AbstractQuestions: 1. Which habitats have the highest degree of invasion? 2. Do native species‐rich communities have also a high degree of invasion? 3. Do the patterns of association between native and alien species richness vary between habitats.Location: Catalonia region (NE Spain).Methods: We conducted a large regional analysis of 15655 phytosociological relevés to detect differences in the degree of invasion between European Nature Information System (EUNIS) habitats representative of temperate and Mediterranean European areas.Results: Alien species were present in less than 17 % of the relevés and represented less than 2% of the total number of species per habitat. The EUNIS habitats with the highest alien species richness were arable land and gardens followed by anthropogenic forb‐rich habitats, riverine and lakeshore scrubs, southern riparian galleries and thickets and trampled areas. In contrast, the following habitats had never any alien species: surface running waters, raised and blanket bogs, valley mires, poor fens and transition mires, base‐rich fens, alpine and sub‐alpine grasslands, sub‐alpine moist or wet tall‐herb and fern habitats, alpine and sub‐alpine scrub habitats and spiny Mediterranean heaths. There was a unimodal relationship between the mean native and mean alien species richness per EUNIS habitat with a high number of aliens in habitats with intermediate number of native species and a low number of aliens at both extremes of the native species gradient. Within EUNIS habitats, the relationship was positive, negative or non‐significant depending on the habitat type without any clear pattern related to the number of native species. Alien species richness was not related to plot size, neither between habitats nor within habitats.Conclusions: The analysis emphasised that the habitats with a higher degree of invasion were the most disturbed ones and that in general habitats rich in native species did not harbour less invaders than habitats poor in native species.
Gradient analysis of reversed treelines and grasslands of the Valles Caldera, New Mexico
Authors: Coop Jonathan D. , Givnish Thomas J. 
Published: February 2009

AbstractObjective: : Treeless meadows and parks are widespread but poorly understood features of the montane vegetation of the western USA. These communities frequently form reversed treelines where grassy valleys occur below forested slopes above. Our purpose was to assess the environmental correlates of such treelines, as well as patterns in the composition and diversity of grasslands and forest margins in the Valles Caldera National Preserve.Location: Valles Caldera National Preserve (35°50′‐36°00’ N, 106°24′‐106°37’ W, 2175–3150 m), Jemez Mountains, New Mexico, USA.Methods: We conducted a gradient analysis based on 200 nested quadrats on transects crossing reversed treelines and spanning the compositional heterogeneity of grasslands. We used cluster analysis and non‐metric multidimensional scaling to assess relationships between compositional variation and environmental variables.Results: We found strong, highly significant relationships of the vegetation to gradients in slope inclination, soil texture, moisture, nutrient availability, and nighttime minimum temperatures. Reversed treelines are most strongly associated with shifts in the thermal regime, exhibit weaker relationships with soil texture and nutrient content, and show no relationship with gravimetric soil moisture. Gradients in aspect, soil moisture, and annual mean temperature are associated with compositional variation within grasslands and forest margins.Conclusions: Lower nightly minimum temperatures and fewer consecutive frost‐free days resulting from cold‐air drainage may prevent tree seedling establishment in valley bottoms via photo‐inhibition, tissue damage, or frost heaving. Fine‐textured soils may also impede tree seedling establishment in valley bottoms. These findings lay the groundwork for experimental and physiological tests of these potential causes of these reversed treelines.
Drought‐related tree death of savanna eucalypts: Species susceptibility, soil conditions and root architecture
Authors: Fensham R.J. , Fairfax R.J. 
Published: February 2009

AbstractQuestions: For eucalypt savanna in northeast Australia subject to multi‐year rainfall deficits this paper asks whether (1) dominant tree species (Ironbarks, Boxes) are more drought susceptible than the sub‐dominant Bloodwoods; (2) whether soil moisture is beyond wilting point in surface soil layers but available at depth; (3) soil conditions (moisture availability and texture) are related to tree death during drought; (4) the root systems of the Boxes and Ironbarks are shallower than the Bloodwoods; and the survivors of drought within species have deeper root systems than those that died.Location: Central Queensland, Australia.Methods: Patterns of tree death between eucalypt species were compared from field data collected after drought. Soil conditions during drought were described and compared with patterns of tree death for the Ironbark Eucalyptus melanophloia. The basal area and orientation of coarse roots were measured on upturned trees after broad‐scale tree clearing, and compared between species, and between live and dead trees with tree size as a covariate.Results: Drought‐induced tree death was higher for dominant Ironbark‐Box than for sub‐dominant Bloodwoods. During a moderate to severe drought in 2004, 41% of 100 cm deep subsoils had soil matric potential less than‐5600 kPa. The drought hardy Bloodwoods had a greater root basal area and particularly so for vertical roots compared to the drought sensitive Ironbark‐Box. Within species there was no significant difference in root basal area characteristics between trees that were recently killed by drought and those that remained relatively healthy. Surface soil moisture availability was lower where tree densities were high, and tree death increased as surface soil moisture became less available. Tree death was also greater as the clay content of sub‐soils increased.Discussion: The study suggests species with roots confined to upper soil layers will suffer severe water stress. The results strongly indicate that root architecture, and the way it facilitates water use during drought, is important for the relative dominance of the tree species. Patchiness in drought‐induced tree death seems to be at least partially a product of heterogeneity in sub‐soil conditions and competition for soil moisture.
Population dynamics of annuals in perennial grassland controlled by ants and environmental stochasticity
Authors: Dostál Petr 
Published: February 2009

AbstractQuestions:In a system of five annual plant species restricted to nest‐mounds of the antLasiusflavusin a perennial grassland: 1. Are the population dynamics influenced by ant disturbance? 2. Is the survival of the annuals at the scale of the whole grassland possible under the observed conditions of disturbance dynamics? 3. Which phases in the annuals’ life cycle and patch types contribute most to population growth?Location:Borec hill, northern Czechia, 50°31’ N, 13°59’ E, 446 m a.s.l.Methods:Local population dynamics of the annuals were analysed separately for five patch types that differed in the proportion of bare soil. Vitality rates were assessed directly in the field, but also in a garden experiment, during 2000–2001 and 2001–2002. Population dynamics at the scale of the whole grassland was analysed with a megamatrix approach, combining patch dynamics of the nest‐mounds with patch‐specific population dynamics. Contributions of different phases and patch types to growth rate were estimated by elasticity analysis.Results:Nest‐mounds differed in the percentage of bare soil. Increasing moss cover significantly reduced germination and seed production of all studied annuals and decreased their population growth rates (λ). Although successional processes dominated over ant disturbance, populations of all species could survive well (λ≫ 1) in the grassland according to the 2000–2001 megamatrix dynamics. Based on the dynamics from the following period, two species would not survive in a long‐term perspective due to random environmental variation. Whereas the A‐A transition (adult plants originating from adults of the previous year) had the highest elasticity under open conditions and ‘good period’ demography, the importance of persistent seeds increased under reverse conditions. This, however, differed among species.Conclusions:Ant‐disturbance was shown to be critical for the population survival of five annual species in the studied grassland. The fate of the annual populations in the grassland system also depends on random environmental variation, which may override the effect of ant activity.
Mapping the floristic continuum: Ordination space position estimated from imaging spectroscopy
Authors: Schmidtlein S. , Zimmermann P. , Schüpferling R. , Weiß C. 
Published: February 2009

AbstractObjective: To present a non‐classificatory technique of map representation of compositional patterns of vegetation as no two plant species assemblages are completely alike and gradations often occur. Variation is depicted as continuous fields instead of classes.Location: Murnauer Moos, Bavaria. Methods: The study combined vegetation ecology and remote sensing methods. The gradual representation of compositional patterns was based on techniques of ordination and regression, instead of mapping class fractions. The floristic field data were collected in relevés and subjected to three‐dimensional non‐metric multidimensional scaling (NMS). The reflectance information corresponding to plots was gathered from remotely sensed imagery with a high spectral resolution. Reflectance values in numerous wavelengths were related to NMS axes scores by partial least squares regression analysis. The regression equations were applied to the imagery and yielded three grey‐scale images, one for each ordination axis. These three images were transformed into a red, green, and blue colour map with a specific colour for each position in the ordination space. Similar colours corresponded to similar species compositions.Results: Compositional variation was mapped accurately (R2= 0.79), using continuous fields. The results took account of various types of stand transitions and of heterogeneities within stands. The map representation featured relatively homogeneous stands and abrupt transitions between stands as well as within‐stand heterogeneity and gradual transitions.Conclusions: The use of NMS in combination with imaging spectroscopy proved to be an expedient approach for non‐classificatory map representations of compositional patterns. Ordination is efficiently extended into the geographic domain. The approach in abandoning pre‐defined plant communities is able to reconcile mapping practice and complex reality.
Response of calcareous grassland vegetation to mowing and fluctuating weather conditions
Authors: Ingerpuu Nele , Kupper Tiiu 
Published: February 2009

AbstractQuestion: What determines the balance between the cover values of vascular plants, lichens and mosses in dry calcareous grassland communities?Location: Western Estonia.Methods: A five‐year (2001–2005) study was conducted in a dry calcareous grassland. The cover of mosses, lichens and vascular plants and all moss species was recorded in permanent plots. Vascular plants were cut in half of the plots. Data from a nearby weather station were used to calculate mean values of different weather parameters and a summer moisture index for the study years.Results: Significant differences in cover values between years were found. The fluctuations of total moss cover and the cover of the dominating moss species Ctenidium molluscum followed changes in annual precipitation. Both cover values were highest in years with high precipitation. The cover change of vascular plants was best characterized by the moisture index of the growth period (three summer months). Summers with high moisture indexes facilitated vascular plant and lichen growth. Annual precipitation and the cover of mosses had a negative influence on the cover of vascular plants. The cutting of vascular plants did not have a significant effect on moss and lichen cover.Conclusions: 1. On dry calcareous grasslands the growth of mosses is enhanced by high annual precipitation, while the growth of vascular plants and lichens is influenced rather by the high summer moisture index. The cover of vascular plants is inhibited by the large moss cover. 2. Mowing of vascular plants does not influence the cover of mosses and lichens.
The significance of small herbivores in structuring annual grassland
Authors: Peters Halton A. 
Published: February 2009

AbstractQuestion: Herbivores can play a fundamental role in regulating the composition and structure of terrestrial plant communities. Relatively inconspicuous but nevertheless ubiquitous gastropods and small mammals are usually considered to influence grassland communities through distinct modes. 1. Do terrestrial gastropods and small mammals, either alone or in combination, influence plant community composition of an intact annual grassland? 2. Do these herbivores influence the plant size structure of the dominant grass Avena?Location: Jasper Ridge Biological Preserve (37°24’ N, 122° 13’ W, elevation 150 m) in northern California.Methods: Animal exclosures were used to examine the single and combined influences of these herbivores on annual grassland production, community composition, and plant size structure during the growing season of an intact annual grassland.Results: The removal and exclusion of the herbivores increased the prevalence of grasses relative to legumes and non‐legume forbs; increased total production of above‐ground plant biomass; and increased mean plant size and exacerbated size hierarchies in populations of Avena. The effect of both gastropods and small mammals, alone and in combination, was characterized by temporal oscillations in the relative dominance of grasses in plots with vs. without herbivores.Conclusions: Both groups of herbivores are important controllers of California annual grassland that exert similar influences on production and composition. While other factors appear to determine the absolute number of individuals in this plant community, selective consumption of grasses by gastropods and small mammals partially offsets the competitive advantages associated with their early germination.
Tree establishment along an ENSO experimental gradient in the Atacama desert
Authors: Squeo Francisco A. , Holmgren Milena , Jiménez Milagros , Albán Luis , Reyes José , Gutiérrez Julio R. 
Published: February 2009

AbstractQuestions: (1) What are the roles of regional climate and plant growth rate for seedling establishment during ENSO rainy pulses along the western coast of South America? (2) What is the water threshold for tree seedling establishment in these arid ecosystems?Location: Atacama Desert, western South America: Piura (5°10’ S, 80°37’ W), Mejia (17°00’ S, 71°59’ W), Fray Jorge (30°41'S,71°37'W).Methods: We experimentally simulated a gradient of ENSO rainfall in three locations encompassing the total extent of the Atacama Desert to test the relative importance of regional climate for seedling establishment during rainy pulses. We also carried out a common garden experiment to test the role of potential interspecific differences in growth rate among two Prosopis tree species.Results: Water threshold for seedling survival increased towards the south with less than 27 mm required in Piura, 100 mm in Mejia and 450 mm in Fray Jorge. We found that seedling survival and growth rate (shoots and roots) were much higher in Piura than in the other two sites for both Prosopis species.Conclusions: Our results indicate that tree establishment during rainy pulses is more likely to be successful in regions where rain falls during warm months and stimulates fast plant growth, and where loose soil texture facilitates deep root growth and therefore access to more stable water sources.
Species richness and soil properties in Pinus ponderosa forests: A structural equation modeling analysis
Authors: Laughlin Daniel C. , Abella Scott R. , Covington W. Wallace , Grace James B. 
Published: February 2009

AbstractQuestion: How are the effects of mineral soil properties on understory plant species richness propagated through a network of processes involving the forest overstory, soil organic matter, soil nitrogen, and understory plant abundance?Location: North‐central Arizona, USA.Methods: We sampled 75 0.05‐ha plots across a broad soil gradient in a Pinus ponderosa (ponderosa pine) forest ecosystem. We evaluated multivariate models of plant species richness using structural equation modeling.Results: Richness was highest at intermediate levels of understory plant cover, suggesting that both colonization success and competitive exclusion can limit richness in this system. We did not detect a reciprocal positive effect of richness on plant cover. Richness was strongly related to soil nitrogen in the model, with evidence for both a direct negative effect and an indirect non‐linear relationship mediated through understory plant cover. Soil organic matter appeared to have a positive influence on understory richness that was independent of soil nitrogen. Richness was lowest where the forest overstory was densest, which can be explained through indirect effects on soil organic matter, soil nitrogen and understory cover. Finally, model results suggest a variety of direct and indirect processes whereby mineral soil properties can influence richness.Conclusions: Understory plant species richness and plant cover in P. ponderosa forests appear to be significantly influenced by soil organic matter and nitrogen, which are, in turn, related to overstory density and composition and mineral soil properties. Thus, soil properties can impose direct and indirect constraints on local species diversity in ponderosa pine forests.