bluuebunny/crossref_metadata_2025_split huggingface dataset:
Understorey vegetation in boreal Picea mariana and Populus tremuloides stands in British Columbia
Authors: Qian Hong , Klinka Karel , Økland Rune H. , Krestov Pavel , Kayahara Gordon J. 
Published: February 2009

Abstract. We compared the species composition and species density of vascular plants in the understorey vegetation of boreal forest between Picea mariana (Black spruce) and Populus tremuloides (Trembling aspen) stands in British Columbia, Canada, and related differences in species composition and species density between the two forest types to dominant canopy tree species as well as a wide variety of environmental factors. We analysed 231 stands, distributed in three different climatic regions representing drier, wetter, and milder variations of montane boreal climate. Of these stands 118 were dominated by P. mariana and 113 by P. tremuloides. P. tremuloides stands had higher species density than P. mariana stands in all climatic regions, but species density of each dominance type varied among climatic regions. The floristic composition of the understorey vegetation was markedly different for P. mariana and P. tremuloides dominated stands.A detailed study on the effect of canopy dominance and local environmental factors on the understorey vegetation of the boreal forest was conducted using 88 stands from one of the three climatic regions. Using a combination of ordination and variation partitioning by constrained ordination we demonstrated a small but unique effect of canopy dominance type on the understorey vegetation, while a larger amount of compositional variation was shared with other factors. Our results accord with a scenario in which differences in primary environmental factors and humus form properties, the latter accentuated by the canopy dominants themselves, are the most important causes of higher species density in P. tremuloides stands than in P. mariana stands, as well as differences in species composition among the two canopy dominance types. Processes and time scales involved in the small but significant direct and indirect effects of the canopy dominant on understo‐ rey species composition are discussed.
Regional patch dynamics of Cirsium arvense and possible implications for plant‐animal interactions
Authors: Eber S. , Brandl R. 
Published: February 2009

Abstract. Plant population biology considers the dynamics of plant modules within stands. However, stands themselves may have considerable regional turnover in space and time. These changes in the number, distribution and size of plant stands generate a dynamic spatial pattern with important implications for the spatial and temporal dynamics of phytophagous insects using these plants as a host. During five successive years we studied the regional distribution and patch dynamics of the creeping thistle Cirsium arvense and the distribution of associated populations of the herbivore Urophora cardui (Diptera: Tephritidae), a specialist stem gall former. The study conducted was in a 15 km2 heterogeneous, agricultural area in northeastern Bavaria.The distribution of the number of plants per patch was skewed with many more small C. arvense patches than large ones. During the five years of study, there was a 50% increase in the number of C. arvense patches, and a decrease in the mean number of plants per patch (= patch size) to less than half the patch size of the first year. Whilst patch size was randomly distributed in space, patch density showed a consistent, non‐random spatial pattern. Patch density was spatially auto‐correlated, with areas of high or low patch density having a characteristic dimension of ca. 1 km. Patch size was predictable in time and appeared to be regulated by size dependent processes, with the extinction probability of a patch being negatively correlated with its size. Correlated with the decline of C. arvense patch size during the study, the occupancy and total numbers of the herbivore U. cardui had a marked decrease, suggesting that the regional distribution of the stem gall former is not only influenced by patch number but more importantly by the mean patch size. With decreasing patch sizes, U. cardui was faced with an increasingly dynamic landscape due to higher extinction rates of small patches, although the mean distance between host plant patches decreased.
Effects of grazing on soil seed bank dynamics: An approach with functional groups
Authors: Sternberg Marcelo , Gutman Mario , Perevolotsky Avi , Kigel Jaime 
Published: February 2009

Abstract. The relationship between intensity and timing of cattle grazing on changes in the size and composition of the soil seed bank were investigated in a 3‐yr study in a Mediterranean grassland in northeastern Israel. Treatments included manipulations of stocking rates and of grazing regimes, in a factorial design.The retrieved soil seed bank community was rich in species, with 133 species accounting for 80% of the 166 species recorded at the site. Within the seed bank, 89% of the species were annuals. Seed bank dynamics was analysed in terms of plant functional groups and germination strategies. In terms of total seed bank density and including all functional groups, 42% of the seeds present in the soil did not germinate under watering conditions. The dormancy level differed greatly among functional groups. The seed bank of annual legumes, crucifers, annual thistles and annual forbs had a large fraction of non‐germinated seeds and characterized areas grazed early in the growing season under high and very high grazing intensity. These functional groups were considered to have a higher potential for persistent seed banks production. In contrast, short and tall annual grasses and tall perennial grasses, that were dominant in ungrazed or moderately grazed paddocks, generally had seed banks with a very small fraction of non‐germinated seeds. Seed bank densities varied widely between grazing treatments and years. Under continuous grazing, heavy grazing pressure reduced seed bank densities of grasses and crucifers in comparison to moderate grazing. The greatest reduction on the seed bank densities resulted from heavy grazing concentrated during the seed‐set stages.
Diversity patterns of plant functional types in relation to fire regime and previous land use in Mediterranean woodlands
Authors: Lloret Francisco , Vilá Montserrat 
Published: February 2009

Abstract. We explore patterns of diversity of plant functional types (PFTs) in Mediterranean communities subjected to landscape‐scale fire disturbances in a mosaic of uncultivated and old fields stands. We use regenerative and growth form attributes to establish two sets of PFTs of perennial species living in shrublands and pine forests of NE Spain. We test the following hypotheses: 1. Fire frequency decreases regenerative PFTs diversity by negatively selecting attributes with low regenerative efficiency. 2. Fire history has more influence on regenerative than on growth form PFTs. 3. The lowest diversity of growth form PFTs will be in old fields without recent fires.We surveyed stands of different combinations of fire and land use histories. Fire history included areas without fires in the last twenty years (unburned), sites burned in 1982 (1‐burned), and sites burned in 1982 and 1994 (2‐burned). Land use histories considered terraced old fields, and uncultivated stands on stony soils. We analysed patterns of PFT abundance and diversity at the stand level, and across the landscape (among stands absolute deviations from sample medians of the relative cover of PFTs).At the stand level, fire had more influence on the diversity patterns of regenerative PFTs than on growth form PFTs. Fire decreased the diversity of regenerative PFTs, due to the elimination of the species without effective mechanisms to post‐fire regeneration. This effect was not observed across the landscape, but seeders showed more variation in stands with longer history without fire. Land use contributed to explain the diversity patterns of growth form PFT (i.e. the number of growth form PFTs was lower in uncultivated, unburned sites), but it did not influence regenerative PFTs diversity. Patterns of PFTs diversity reflect the response to ecological processes operating at the landscape level. Overall, regenerative and growth form PFTs appear to be more sensitive to the fire history than to the past land use.
Seasonal vegetation changes in mountain pastures due to simulated effects of cattle grazing
Authors: Kohler F. , Gillet F. , Gobat J.‐M. , Buttler A. 
Published: February 2009

Cattle influence grassland dynamics in three ways: herbage removal, dung deposition and trampling. The objective of this study was to assess the effects of these factors, separately or in combination, and to compare them with cattle grazing over a one year period in a field experiment conducted in the Jura Mountains of northwestern Switzerland.A set of controlled treatments simulating the three factors was applied in a fenced area: (1) repeated mowing — three levels; (2) intensive trampling — two levels; (3) manuring with a liquid mixture of dung and urine — three levels. All treatments were applied homogeneously to the entire surface of each of the 40 plots inside the exclosure. Additionally, ten plots outside the fenced area represented reference plots with regular cattle pasturing. The multivariate response of species composition was assessed three times with the point‐intercept method: in spring before the treatments, in autumn after one season of treatments and at the beginning of the following year after winter rest.Multivariate analyses of vegetation data in the first year showed an overwhelming seasonal shift and significant differences induced by treatments. Abandoned and manured plots showed the largest deviation from the cattle grazed reference. Herbage removal, simulated by repeated mowing, appeared to be the most important factor for maintaining vegetation texture. Seasonal treatment effects were only partially carried over to the next spring, showing an unexpected resilience of the plant community, probably due to life‐history traits and competition release following climatic disturbance in winter.
Ice‐storm disturbance and long‐term forest dynamics in the Adirondack Mountains
Authors: Lafon Charles W. 
Published: February 2009

Ice storms cause periodic disturbance to temperate forests of eastern North America. They are the primary agents of disturbance in some eastern forests. In this paper, a forest gap model is employed to explore consequences of ice storms for the long‐term dynamics of Tsuga canadensis‐northem hardwoods forests. The gap model LINKAGES was modified to simulate periodic ice storm disturbance in the Adirondack Mountains of New York. To adapt the gap model for this purpose, field data on ice storm disturbance are used to develop a polytomous logistic regression model of tree damage. The logistic regression model was then incorporated into the modified forest gap model, LINK ADIR, to determine the type of damage sustained by each simulated tree.The logistic regression model predicts high probabilities of bent boles or severe bole damage (leaning, snapping, or uprooting) in small‐diameter trees, and increasing probability of canopy damage as tree size increases. Canopy damage is most likely on gentle slopes; the probability of severe bole damage increases with increasing slope angle.In the LINKADIR simulations, tree damage type determines the probability of mortality; trees with severe bole damage are assigned the highest mortality rate. LINKADIR predicts Tsuga canadensis dominance in mesophytic old‐growth forests not disturbed by ice storms. When ice storms are simulated, the model predicts Acer saccharum‐dominated forests with higher species richness. These results suggest that ice storms may function as intermediate disturbances that enhance species richness in forested Adirondack landscapes.
Comparison of statistical methods commonly used in predictive modelling
Authors: Muñoz Jesús , Felicísimo Ángel M. 
Published: February 2009

Logistic Multiple Regression, Principal Component Regression and Classification and Regression Tree Analysis (CART), commonly used in ecological modelling using GIS, are compared with a relatively new statistical technique, Multivariate Adaptive Regression Splines (MARS), to test their accuracy, reliability, implementation within GIS and ease of use. All were applied to the same two data sets, covering a wide range of conditions common in predictive modelling, namely geographical range, scale, nature of the predictors and sampling method.We ran two series of analyses to verify if model validation by an independent data set was required or cross‐validation on a learning data set sufficed. Results show that validation by independent data sets is needed. Model accuracy was evaluated using the area under Receiver Operating Characteristics curve (AUC). This measure was used because it summarizes performance across all possible thresholds, and is independent of balance between classes.MARS and Regression Tree Analysis achieved the best prediction success, although the CART model was difficult to use for cartographic purposes due to the high model complexity.
Helophyte germination in a Mediterranean salt marsh: Gut‐passage by ducks changes seed response to salinity
Authors: Espinar J.L. , García L.V. , Figuerola J. , Green A.J. , Clemente L. 
Published: February 2009

Abstract:Question: In seeds which are regularly consumed by waterbirds in the field, how does gut‐passage modify their response to salinity gradients?Location: Doñana National Park salt marsh, south‐west of Spain.Methods: Seeds of Scirpus litoralis and Scirpus maritimus were collected and force fed to mallards (Anas platyrhynchos). Both the ingested seeds (passage) and non‐ingested seeds (controls) were exposed, in germination chambers, to a salinity range similar to that observed in the field (0–32 dS/m). After 30 days, the total percentage germination, the duration of the dormancy period and the germination speed were computed. The response of the different germination parameters to ingestion and salinity was analyzed using generalized lineal models. Recovery tests on seeds that did not germinate in the various treatments and tests of the effect of ingestion on the intrinsic variability in seed response were also performed.Results: An increase in salinity reduced germinability and increased the length of dormancy, while gut pas sage increased the intrinsic variability of the temporal seed response in both species. In S. litoralis there was a significant interaction between the effects of salinity and passage on germination rate. Passage increased germination rate at low salinities (≤2 dS/m) but decreased it at high salinities (≥4 dS/m).Conclusion: Gut‐passage by ducks significantly changes seed response to salinity. The outcome of plant‐animal interactions can be influenced by environmental gradients. Studies of germination in response to gut passage that do not take such gradients into account may produce misleading results.
Influence of canopy tree phenology on understorey populations of Fagus crenata
Authors: Tomita Mizuki , Seiwa Kenji 
Published: February 2009

Abstract:Question: Is light available for subcanopy individuals of Fagus crenata spatiotemporally heterogeneous across patches with closed canopies of different foliage phenologies and gaps? Is local abundance of Sasa influenced by the composition of the canopy layer? If so, does the Sasa layer also affect the amount of light available to small F. crenata saplings? Is variation in F. crenata population structure consistent with the hypothesis that light is important?Location: Mt. Kurikoma, Japan 780 m a.s.l.Methods: Population structure of subcanopy individuals of Fagus crenata and importance of Sasa were examined in five patch types. The patch‐types were Fc (F. crenata only in the crown), Qm (Quercus mongolica var. grosseserrata only in the crown), Mo (Magnolia obovata only in the crown), Fc’ (periphery of F. crenata) and Gap. Seasonal changes in light availability above and below the Sasa layer was examined by using hemispherical photographs and quantum sensors.Results: Subcanopy individuals of F. crenata began unfolding their leaves approximately one month earlier than canopy trees of Q. mongolica var. grosseserrata and M. obovata, but a few days later than those of adult F. crenata. Accumulated photosynthetic photon flux density above the Sasa layer was greatest in Qm and Mo, and lowest in Fc. Importance of Sasa was highest in Gap. Maximum height and the number of subcanopy individuals of F. crenata were greatest in Qm, followed by Mo, and lowest in Fc.Conclusions: Differences in canopy layer composition probably influence the regeneration of F. crenata both directly through their foliage phenologies, and also indirectly by determining the importance of Sasa.
Spatial patterns and associations in a Quercus‐Betula forest in northern China
Authors: Hou J.H. , Mi X.C. , Liu C.R. , Ma K.P. 
Published: February 2009

Abstract:Question: Are species‐specific regeneration strategies and competition the dominant processes facilitating species coexistence in a Quercus liaotungensis dominated temperate deciduous forest?Location: Dongling Mountains, North China, 1300 m a.s.l.Methods: Ripley's K‐function was used to characterize the spatial patterns and spatial associations of two dominant tree species, Quercus liaotungensis and Betula dahurica, and a common subcanopy species, Acer mono, at different growth stages (adult, sapling, seedling).Results: Seedlings, saplings and adults of all three species exhibited clumped distributions at most spatial scales. Quercus seedlings and saplings were positively associated with conspecific adult trees and spatially independent of dead trees suggesting that seed dispersal and vegetative regeneration influenced the spatial patterning of Quercus trees. Betula seedlings and saplings were positively associated with both live and dead trees of conspecific adults at small scales (<5 m) but negatively associated with live and dead trees of other species indicating sprouting as an important mechanism of reproduction. Saplings of Acer had a strong spatial dependence on the distribution of conspecific adult trees indicating its limited seed dispersal range. Negative associations between adult trees of Betula and Quercus demonstrated interspecific competition at local scales (<5 m).Conclusions: Different regeneration strategies among the three species play an important role in regulating their spatial distribution patterns, while competition between individuals of Betula and Quercus at the adult stage also contributes to spatial patterning of these communities. The recruitment limitations of Betula and Quercus may affect the persistence of these species and the long‐term dynamics of the forest.
Weed vegetation of arable land in Central Europe: Gradients of diversity and species composition
Authors: Lososová Z. , Chytrý M. , Cimalová S. , Kropáč Z. , Otýpková Z. , Pyšek P. , Tichý L. 
Published: February 2009

Abstract:Question: What are the main broad‐scale spatial and temporal gradients in species composition of arable weed communities and what are their underlying environmental variables?Location: Czech Republic and Slovakia.Methods: A selection of 2653 geographically stratified relevés sampled between 1954–2003 was analysed with direct and indirect ordination, regression analysis and analysis of beta diversity.Results: Major changes in weed species composition were associated with a complex gradient of increasing altitude and precipitation and decreasing temperature and base status of the soils. The proportion of hemicryptophytes increased, therophytes and alien species decreased, species richness increased and beta diversity decreased with increasing altitude. The second most important gradient of weed species composition was associated with seasonal changes, resulting in striking differences between weed communities developed in spring and summer. In summer, weed communities tended to have more neophytes, higher species richness and higher beta diversity. The third gradient reflected long‐term changes in weed vegetation over past decades. The proportion of hemicryptophytes and neophytes increased, while therophytes and archaeophytes decreased, as did species richness over time. The fourth gradient was due to crop plants. Cultures whose management involves less disturbances, such as cereals, harboured less geophytes and neophytes, and had higher species richness but lower beta diversity than frequently disturbed cultures, such as root crops.Conclusions: Species composition of Central European weed vegetation is mainly influenced by broad‐scale climatic and edaphic factors, but its variations due to seasonal dynamics and long‐term changes in agricultural management are also striking. Crop plants and crop‐specific management affect it to a lesser, but still significant extent.
The role of disturbance in the co‐existence of the evergreen Quercus ilex and the deciduous Quercus cerrioides
Authors: Bonfil Consuelo , Cortés Pilar , Espelta Josep Maria , Retana Javier 
Published: February 2009

Abstract:Question: Which is the response of the evergreen Quercus ilex and the deciduous Q. cerrioides to repeated disturbances?Location: central Catalonia (northeastern Spain), in the areas affected by two of the largest historically recorded wildfires in NE Spain: the Bages‐Berguedà fire (24 300 ha forested area burned in July 1994), and the Solsonès fire (14 300 ha burned in 1998).Methods: Survival and growth of individuals of Quercus ilex and Q. cerrioides were evaluated in plants subjected to different fire histories and experimental disturbances (burning, cutting or clipping) applied either before or after summer.Results: Survival was high (> 99%), with both species showing a similar high resistance to disturbances. Growth after experimental disturbance was positively related to the size of the individual before the latest forest fire occurred. Fire history had a large effect on resprout growth, as the repeated incidence of disturbances lowered the capacity of individuals to grow. The type and season of experimental disturbance experienced by plants had a large effect. Individuals that experienced total above‐ground loss had lower growth rates than those with partial loss. A similar pattern was observed in individuals disturbed after the summer in relation to those disturbed before summer.Conclusions: The larger growth rates recorded in Q. cerrioides across all fire histories and experimental treatments, and the higher vulnerability of Q. ilex to increased fire frequency, intensity of experimental disturbance, and disturbance season, provide evidence for the relatively high susceptibility of the latter to repeated disturbances. This view disagrees with the larger resilience of this species compared to co‐existing deciduous oaks, as reported.
Old‐field grassland successional dynamics following cessation of chronic disturbance
Authors: Tunnell Susan J. , Engle David M. , Jorgensen Eric E. 
Published: February 2009

Abstract:Question:Does increasingFestucacanopy cover reduce plant species richness and, therefore, alter plant community composition and the relationship of litter to species richness in old‐field grassland?Location:Southeastern Oklahoma, USA.Methods:Canopy cover by species, species richness, and litter mass were collected within an old‐field grassland site on 16, 40 m × 40 m plots. Our study was conducted during the first three years of a long‐term study that investigated the effects of low‐level nitrogen enrichment and small mammal herbivory manipulations.Results:Succession was altered by an increase in abundance ofFestucaover the 3‐yr study period. Species richness did not decline with litter accumulation. Instead,Festucaincreased most on species‐poor plots, andFestucaabundance remained low on species‐rich plots.Conclusions:Festucamay act as an invasive transformer‐species in warm‐season dominated old‐field grasslands, a phenomenon associated more with invasions of cool‐season grasses at higher latitudes in North America.