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Herbaceous Communities (herbaceous + community)
Selected AbstractsEffects of insects on primary production in temperate herbaceous communities: a meta-analysisECOLOGICAL ENTOMOLOGY, Issue 5 2003Malcolm D. Coupe Abstract., 1. The effects of insects on primary production in temperate herbaceous communities were investigated in a meta-analysis. The following hypotheses were tested: (1) the effect of insects on primary production depends on community type, (2) the effect of insects on primary production varies as a function of productivity, (3) insects have a greater effect on primary production in communities with low species diversity, and (4) insects have a larger effect on primary production during outbreaks. 2. Data were collected from 24 studies in which insecticides were used to suppress insects in self-sown or pastoral communities. Effect sizes were calculated from sprayed and control plot standing crop or yield, expressed as the log response ratio, ln (sprayed plot phytomass/control plot phytomass). 3. There was a significant increase in primary production as a result of insect suppression. Forb-dominated communities showed a more variable response than graminoid communities. During outbreaks, insects had a greater negative impact on primary production. Effect size was unaffected by productivity or plant species richness. 4. Although insects lower primary production in a diversity of temperate herbaceous communities, the basic measures by which such communities are often described have little effect on the proportional impact that insects have on primary production. While outbreaks are significant predictors of higher negative impact on primary production, causes of outbreaks are not always related to traits of the plant community. [source] Do biotic interactions shape both sides of the humped-back model of species richness in plant communities?ECOLOGY LETTERS, Issue 7 2006Richard Michalet Abstract A humped-back relationship between species richness and community biomass has frequently been observed in plant communities, at both local and regional scales, although often improperly called a productivity,diversity relationship. Explanations for this relationship have emphasized the role of competitive exclusion, probably because at the time when the relationship was first examined, competition was considered to be the significant biotic filter structuring plant communities. However, over the last 15 years there has been a renewed interest in facilitation and this research has shown a clear link between the role of facilitation in structuring communities and both community biomass and the severity of the environment. Although facilitation may enlarge the realized niche of species and increase community richness in stressful environments, there has only been one previous attempt to revisit the humped-back model of species richness and to include facilitative processes. However, to date, no model has explored whether biotic interactions can potentially shape both sides of the humped-back model for species richness commonly detected in plant communities. Here, we propose a revision of Grime's original model that incorporates a new understanding of the role of facilitative interactions in plant communities. In this revised model, facilitation promotes diversity at medium to high environmental severity levels, by expanding the realized niche of stress-intolerant competitive species into harsh physical conditions. However, when environmental conditions become extremely severe the positive effects of the benefactors wane (as supported by recent research on facilitative interactions in extremely severe environments) and diversity is reduced. Conversely, with decreasing stress along the biomass gradient, facilitation decreases because stress-intolerant species become able to exist away from the canopy of the stress-tolerant species (as proposed by facilitation theory). At the same time competition increases for stress-tolerant species, reducing diversity in the most benign conditions (as proposed by models of competition theory). In this way our inclusion of facilitation into the classic model of plant species diversity and community biomass generates a more powerful and richer predictive framework for understanding the role of plant interactions in changing diversity. We then use our revised model to explain both the observed discrepancies between natural patterns of species richness and community biomass and the results of experimental studies of the impact of biodiversity on the productivity of herbaceous communities. It is clear that explicit consideration of concurrent changes in stress-tolerant and competitive species enhances our capacity to explain and interpret patterns in plant community diversity with respect to environmental severity. [source] Why does the unimodal species richness,productivity relationship not apply to woody species: a lack of clonality or a legacy of tropical evolutionary history?GLOBAL ECOLOGY, Issue 3 2008Lauri Laanisto ABSTRACT Aim, To study how differences in species richness patterns of woody and herbaceous plants may be influenced by ecological and evolutionary factors. Unimodal species richness,productivity relationships (SRPRs) have been of interest to ecologists since they were first described three decades ago for British herbaceous vegetation by J. P. Grime. The decrease in richness at high productivity may be due to competitive exclusion of subordinate species, or diverse factors related to evolution and dispersal. Unimodal SRPRs are most often reported for plants, but there are exceptions. For example, unimodal SRPRs are common in the temperate zone but not in the tropics. Similarly, woody species and forest communities in the Northern Hemisphere do not tend to show unimodal SRPRs. Location, Global. Methods, We used data from the literature to test whether a unimodal SRPR applies to woody species and forest communities on a global scale. We explored whether the shape of SRPRs may be related to the lack of clonality in woody species (which may prevent their being competitively superior), or the legacy of evolutionary history (most temperate woody species originate from tropical lineages, and due to niche conservatism they may still demonstrate ,tropical patterns'). We used case studies that reported the names of the dominant or most abundant species for productive sites. Results, Woody species were indeed less clonal than herbaceous species. Both clonality and the temperate evolutionary background of dominating species were associated with unimodality in SRPRs, with woodiness modifying the clonality effect. Main conclusions, The unimodal SRPR has been common in the ecological literature because most such studies originate from temperate herbaceous communities with many clonal species. Consequently, both evolutionary and ecological factors may influence species richness patterns. [source] Recovery of sandy beach and maritime forest vegetation on Phuket Island (Thailand) after the major Indian Ocean tsunami of 2004APPLIED VEGETATION SCIENCE, Issue 2 2009D. Hayasaka Abstract Question: How rapidly has the sandy beach and maritime forest vegetation on Phuket recovered and regenerated after the impact of the major Indian Ocean tsunami of 2004? What are the characteristics of sandy beach species for regenerating their populations and the invasion patterns of originally non-sandy beach species or other newcomers after the tsunami? Location: Phuket Island, southern Thailand. Methods: Species composition of beaches was studied on the same research plots 6 months before and 9 months after the tsunami. The changes in individual species cover before and after the tsunami were determined by ,2 tests. Change in community composition was analysed by detrended correspondence analysis. The relationship between species and environmental factors was analysed by canonical correspondence analysis. Results: The sites disturbed by the tsunami were often invaded by annuals, especially grasses and asteraceous plants, rather than by perennials. In contrast, species with clonal growth by stolons decreased significantly. Factors determining the species habitat differences were soil hardness (penetration resistance of sandy soil), per cent silt content, soil water content and beach management. Habitat differences among originally non-sandy beach herbaceous species that expanded their population or moved to the coast after the disaster were defined by sand accretion or erosion caused by the tsunami. Many sandy beach herbaceous communities changed into Dactyloctenium aegyptium communities because of the tsunami were originally constituted by non-sandy beach D. aegyptium with Cenchrus echinatus. Although the forest floors of most maritime forests were invaded by originally non-sandy beach Tridax procumbens, Eleusine indica or D. aegyptium because of the tsunami, this did not result in a change in the vegetation unit, because species' loss was restricted to the understorey. In time, these forests will recover their previous community composition. Conclusions: Our results suggest that originally non-sandy beach native species invaded the disturbed beaches rapidly after the tsunami but their habitats differ. Sites where sand accumulated on a beach because of the tsunami were invaded by D. aegyptium and E. indica, whereas soil erosion permitted invasion by Digitania adscendens. Tridax procumbens establishes rapidly on wet sites with hard soil, high per cent silt content and low beach management pressure. Sandy beach species with subterranean long rhizomes are strongly tolerant of such disasters. We concluded that the species composition of the beaches disturbed by a temporary large disaster is determined by dormancy and growth forms, with radicoid form being influential. [source] Characterization of diverse plant communities in Aspen Parkland rangeland using LiDAR dataAPPLIED VEGETATION SCIENCE, Issue 3 2007Jason G. Su Moss (1983) Abstract Question: How effective is high-resolution airborne LiDAR technology for quantifying biophysical characteristics of multiple community types within diverse rangeland environments? Location: Native Aspen Parkland vegetation in central Alberta, Canada. Methods: Vegetation within 117 reference plots stratified across eight types, including forest, shrubland, upland grassland and lowland meadow communities, were assessed in 2001 for the height, cover and density of vegetation within various strata (herb, shrub and tree layers). Actual ground data were subsequently compared against modelled values for each community type and strata derived from the analysis of airborne LiDAR data obtained in 2000. Results: LiDAR data were effective for quantifying vegetation height, cover and density of the overstory within closed- and open Populus forest communities. However, LiDAR measurements typically underestimated the height and cover of shrublands, as well as most of the herbaceous communities. Analysis of LiDAR intensity data indicated reflectance generally decreased as LiDAR sampling points moved upwards from the ground to the vegetation canopy. Conclusions: While LiDAR technology is useful for characterizing deciduous forest properties, the quantification of understory vegetation characteristics, as well as those of individual shrublands and grasslands, was more limiting. Further refinements in analysis methods are necessary to increase the reliability of characterizing these communities. [source] Dormancy and germination characteristics of herbaceous species in the seasonally dry tropics of northern AustraliaAUSTRAL ECOLOGY, Issue 3 2000JohN. G. McIvor Abstract This study investigated changes in dormancy and germination over 8 months for 23 common species (annual and perennial grasses, legumes and other dicotyledons) from herbaceous communities in northern Australia. Seeds were exposed to three storage treatments: relatively constant laboratory conditions, an oven with fluctuating temperatures similar to those found on the soil surface (25/60°C), or exposed on the soil surface at Townsville. There were wide ranges of initial levels of dormancy (9,100%), rates of change of dormancy and response to the different storage conditions showing that species with several types of dormancy characteristics are able to coexist in these communities. The general trend in dormancy levels was a decline with time with the rate of decline greatest for seeds exposed on the soil surface and least for those stored in the laboratory. The species were divided into groups based on dormancy levels in seeds on the soil surface during the late dry and mid wet seasons. The dormancy characteristics of the groups were related to the ecology of the species in the groups. There was an approximately linear increase in germination rate (i.e. a decrease in the number of days to 50% of final germination) over time for all storage treatments; rates for seeds on the soil surface increased more rapidly than those of seeds in laboratory and oven samples. [source] Dormancy and germination characteristics of herbaceous species in the seasonally dry tropics of northern AustraliaAUSTRAL ECOLOGY, Issue 3 2000JOHN. G. MCIVOR Abstract This study investigated changes in dormancy and germination over 8 months for 23 common species (annual and perennial grasses, legumes and other dicotyledons) from herbaceous communities in northern Australia. Seeds were exposed to three storage treatments: relatively constant laboratory conditions, an oven with fluctuating temperatures similar to those found on the soil surface (25/60°C), or exposed on the soil surface at Townsville. There were wide ranges of initial levels of dormancy (9,100%), rates of change of dormancy and response to the different storage conditions showing that species with several types of dormancy characteristics are able to coexist in these communities. The general trend in dormancy levels was a decline with time with the rate of decline greatest for seeds exposed on the soil surface and least for those stored in the laboratory. The species were divided into groups based on dormancy levels in seeds on the soil surface during the late dry and mid wet seasons. The dormancy characteristics of the groups were related to the ecology of the species in the groups. There was an approximately linear increase in germination rate (i.e. a decrease in the number of days to 50% of final germination) over time for all storage treatments; rates for seeds on the soil surface increased more rapidly than those of seeds in laboratory and oven samples. [source] Sampling Techniques Influence Understory Plant Trajectories After Restoration: An Example from Ponderosa Pine RestorationRESTORATION ECOLOGY, Issue 4 2003Julie E. Korb Abstract Although there is no one correct technique for sampling vegetation, the sampling design chosen may greatly influence the conclusions researchers can draw from restoration treatments. Considerations when designing vegetation sampling protocol include determining what sampling attributes to measure, the size and shape of the sampling plot, the number of replicates and their location within the study area, and the frequency of sampling. We installed 20 point-intercept transects (50-m long), 8 belt transects (10 × 50 m), 10 adapted Daubenmire transects (four 0.5 × 2-m plots), and 4 modified-Whittaker plots (20 × 50 m with smaller nested plots) in treatment and control units to measure understory herbaceous response in a forest restoration experiment that tested different treatments. Point-intercept transects on average recorded at least twice as much plant cover as did adapted Daubenmire transects and modified-Whittaker plots taken at the same location for all control and treatment units. Point-intercept transects and adapted Daubenmire plots on average captured fewer rare and exotic species in the control and treatment units in comparison with the belt transects and modified-Whittaker plots. Modified-Whittaker plots captured the highest species richness in all units. Early successional understory response to restoration treatments was likely masked by the response of the herbaceous community to yearly climatic variation (dry vs. wet years). Species richness and abundance were higher in wet years than dry years for all control and treatment units. Our results illustrate that sampling techniques can greatly influence perceptions of understory plant trajectories and therefore the interpretation of whether restoration goals have been achieved. In addition, our results suggest that restoration monitoring needs to be conducted for a sufficient length of time so that restoration treatment responses can be detected. [source] Herbaceous vegetation change in variable rangeland environments: The relative contribution of grazing and climatic variabilityAPPLIED VEGETATION SCIENCE, Issue 2 2001Samuel D. Fuhlendorf Hatch et al. (1990) Abstract. A 44-yr record of herbaceous vegetation change was analysed for three contrasting grazing regimes within a semi-arid savanna to evaluate the relative contribution of confined livestock grazing and climatic variability as agents of vegetation change. Grazing intensity had a significant, directional effect on the relative composition of short- and mid-grass response groups; their composition was significantly correlated with time since the grazing regimes were established. Interannual precipitation was not significantly correlated with response group composition. However, interannual precipitation was significantly correlated with total plant basal area while time since imposition of grazing regimes was not, but both interannual precipitation and time since the grazing regimes were established were significantly correlated with total plant density. Vegetation change was reversible even though the herbaceous community had been maintained in an altered state for ca. 60 yr by intensive livestock grazing. However, ca. 25 yr were required for the mid-grass response group to recover following the elimination of grazing and recovery occurred intermittently. The increase in mid-grass composition was associated with a significant decrease in total plant density and an increase in mean individual plant basal area. Therefore, we failed to reject the hypotheses based on the proportional change in relative response group composition with grazing intensity and the distinct effects of grazing and climatic variability on response group composition, total basal area and plant density. Long-term vegetation change indicates that grazing intensity established the long-term directional change in response group composition, but that episodic climate events defined the short-term rate and trajectory of this change and determines the upper limit on total basal area. The occurrence of both directional and non-directional vegetation responses were largely a function of (1) the unique responses of the various community attributes monitored and (2) the distinct temporal responses of these community attributes to grazing and climatic variation. This interpretation supports previous conclusions that individual ecosystems may exist in equilibrial and non-equilibrial states at various temporal and spatial scales. 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