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Dominant Grasses (dominant + grass)

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Life Sciences50%

Terms modified by Dominant Grasses

  • dominant grass species
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    Selected Abstracts

    Strong shifts in plant diversity and vegetation composition in grassland shortly after climatic change

    JOURNAL OF VEGETATION SCIENCE, Issue 3 2008
    Maria-Teresa Sebastià
    Abstract Questions: Is plant diversity in mesic grassland ecosystems vulnerable in the short-term to extreme climate change events? How rapidly can responses in vegetation composition occur in perennial grasslands? Are the expected compositional changes related to rare species losses or to shifts in the relative abundance of the dominants? Location: Subalpine mesic grasslands on limestone in the Pyrenees. Methods: Transplanting turves from the upland, with cold-temperate climate, to a lowland location, with continental Mediterranean climate. Results: Transplanting led to decreased biodiversity and strong shifts in vegetation composition. Results from both permutation tests and traditional multivariate analysis suggested different trajectories of vegetation depending on the initial species pool. Vegetation showed a tendency to converge in composition in the lowland over time, independently of initial differences. Estimated changes in relative biomass of the five most abundant species between the upland and the lowland ranged from -89 to +96 %. The ensemble of all other species was reduced by 80%. The most dominant species in the upland, Festuca nigrescens, reduced its abundance in the lowland, shifting from having mainly positive to mainly negative associations with other species. Conclusions: Mesic grassland ecosystems in the Pyrenees showed strong shifts in plant diversity and composition after a short period of warming and drought, as a consequence of acute vulnerability of some dominant grasses, losses of rare species, and aggregate and trigger effects of originally uncommon forb species. [source]

    Consequences of shrub expansion in mesic grassland: Resource alterations and graminoid responses

    JOURNAL OF VEGETATION SCIENCE, Issue 4 2003
    Michelle S. Lett
    Anon. (1986) Abstract. In the mesic grasslands of the central United States, the shrub Cornus drummondii has undergone widespread expansion in the absence of recurrent fire. We quantified alterations in light, water and N caused by C. drummondii expansion in tall-grass prairie and assessed the hypothesis that these alterations are consistent with models of resource enrichment by woody plants. Responses in graminoid species, particularly the dominant C4 grass Andropogon gerardii, were concurrently evaluated. We also removed established shrub islands to quantify their legacy effect on resource availability and assess the capability of this grassland to recover in sites formerly dominated by woody plants. The primary effect of shrub expansion on resource availability was an 87% reduction in light available to the herbaceous understorey. This reduced C uptake and N use efficiency in A. gerardii and lowered graminoid cover and ANPP at the grass-shrub ecotone relative to undisturbed grassland. Shrub removal created a pulse in light and N availability, eliciting high C gain in A. gerardii in the first year after removal. By year two, light and N availability within shrub removal areas returned to levels typical of grassland, as had graminoid cover and ANPP were similar to those in open grassland. Recovery within central areas of shrub removal sites lagged behind that at the former grass-shrub ecotone. These results indicate that the apparent alternative stable state of C. drummondii dominance in tall-grass prairie is biotically maintained and driven by reductions in light, rather than resource enrichment. Within areas of shrub removal, the legacy effect of C. drummondii dominance is manifest primarily through the loss of rhizomes of the dominant grasses, rather than any long-term changes in resource availability. C. drummondii removal facilitates grassland recovery, but the effort required to initiate this transition is a significant cost of woody plant expansion in mesic grasslands. Prevention of woody plant expansion in remnant tall-grass prairies is, therefore, a preferred management option. [source]

    Seedling resistance to herbivory as a predictor of relative abundance in a synthesised prairie community

    OIKOS, Issue 2 2003
    G. S. Burt-Smith
    In a laboratory experiment seedlings of 24 perennial herbaceous prairie species were offered to the omnivorous cricket Acheta domestica in an extended feeding trial. Leaf damage was monitored daily allowing an index of palatability to be calculated for each plant species. The index of palatability successfully predicted relative abundance within the same set of species in an independently-conducted study involving community assembly from seed in low-fertility plots. These results support the hypothesis that resistance to herbivory may be an important component of plant fitness in unproductive vegetation. However, the correlation between palatability and community composition may be interpreted as a positive association between traits that lead to high competitive ability and herbivory resistance. There is a need to establish whether the success of the dominant grasses at Cedar Creek arises from their superior ability to capture nitrogen from low external concentrations or is, rather, due to their superior ability to minimise nitrogen loss to herbivores. [source]

    Nutrient Limitation to Primary Productivity in a Secondary Savanna in Venezuela1

    BIOTROPICA, Issue 4 2002
    Nichole N. Barger
    ABSTRACT We examined nutrient limitation to primary productivity in a secondary savanna in the interior branch of the Coastal Range of Venezuela, which was converted from forest to savanna more than 100 years ago. We manipulated soil nutrients by adding nitrogen (+N), phosphorus and potassium (+PK), and nitrogen, phosphorus, and potassium (+NPK) to intact savanna. Eleven months after fertilization, we measured aboveground biomass and belowground biomass as live fine roots in the top 20 cm of soil, and species and functional group composition in response to nutrient additions. Aboveground biomass was highest in the NPK treatment ([mean g/m2]; control = 402, +N = 718, +PK = 490, +NPK = 949). Aboveground production, however, appeared to be limited primarily by N. Aboveground biomass increased 78 percent when N was added alone but did not significantly respond to PK additions when compared to controls. In contrast to aboveground biomass, belowground biomass increased with PK additions but showed no significant increase with N (depth 0,20 cm; [mean g/m2]; control = 685, +N = 443, +PK = 827, +NPK = 832). There was also a 36 percent increase in root length with PK additions when compared to controls. Whole savanna shoot:root ratios were similar for control and +PK (0.6), while those for +N or +NPK fertilization were significantly higher (1.7 and 1.2, respectively). Total biomass response (above + belowground) to nutrient additions showed a strong N and PK co-limitation ([mean g/m2]; control = 1073, +N = 1111, +PK = 1258, +NPK = 1713). Aboveground biomass of all monocots increased with N additions, whereas dicots showed no response to nutrient additions. Trachypogon spp. (T. plumosus+T. vestitus) and Axonopus canescens, the two dominant grasses, made up more than 89 percent of the total aboveground biomass in these sites. Trachypogon spp. responded to NPK, whereas A. canescens, sedges, and the remaining monocots only responded to N. Even though nutrient additions resulted in higher aboveground biomass in N and NPK fertilized plots, this had little effect on plant community composition. With the exception of sedges, which responded positively to N additions and increased from 4 to 8 percent of die plant community, no changes were observed in plant community composition after 11 months. RESUMEN En este estudio se examinaron las limitaciones nutricionales en la productividad primatia de una sabana secundaria de más de 100 años localizada en el brazo interior de la Cordillera de la Costa de Venezuela. Se manipularon los nutrientes del suelo mediante la adición de nitrógeno (+N), fósforo y potasio (+PK), y nitrógeno, fósforo, y potasio (+NPK) al suelo de la sabana. Después de once meses de iniciarse los experimentos se midió la respuesta a la adición de nutrientes en términos de producción de biomasa aérea, biomasa de raíces finas vivas en los primeros 20 cm de suelo, y cambios en la composición de especies y grupos funcionales. La biomasa aérea fue mayor en las parcelas fertilizadas con N o en combinación de NPK ([promedio g/m2]; control = 402, +N = 718, +PK = 490, +NPK = 949) indicando que la producción aéiea está limitada principalmente por N. No hubo respuesta estadísticamente significativa a la adición de PK con respecto a los controles. La biomasa de raíces finas aumentó con la adición de PK y NPK mientras que no hubo aumento significativo con N (Profundidad 0,20 cm; [promedio g/m2]; control=685, +N=443, +PK=827, +NPK=832). La adición de PK modificó la arquitectura radical con un anmento de 36 por ciento en la longitud de las raíces con respecto al control. La relación vástago/raíz fue similar en los tratmientos controly + PK (0.6), pero significativamente mayor en +N (1.7)y +NPK(1.2) indicando nuevamente una limitación principal por N. La respuesta de la biomasa total (vástago +raíces vivas) a la adición de nutrientes refleja una colimitación de N y PK ([promedio g/m2]; control=1073, +N=1111, +PK+1258,+NPK=1713). La biomasa aérea de las monocotiledóneas aumentó de N, mientras que no hubo respuesta significativa a la adición de nutrientes en las dicotiledóneas. Trachypogon spp (T. Plumosus+T. vestitus) and Axonopus canescens, las dos gramíneas dominantes, representaron más del 89 por ciento de la biomasa total en las parcelas. Trachypogon spp respondieron a NPK, mientras que A. canescens, cuoeráceas, y las otras monocotiledóneas sólo respondieron a N. No hubo cambios significativos en la composición de especies como respuesta a la adición de nutrientes, con la excepción de las ciperáceas que respondieron significativamente a la adición de N con un aumento de 4 a 8 por ciento. [source]