| 1. |
- Bergstedt, Johan, et al.
(författare)
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In the eye of the beholder : bias and stochastic variation in cover estimates
- 2009
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Ingår i: PLANT ECOLOGY. - : Springer Science and Business Media LLC. - 1385-0237 .- 1573-5052. ; 204:2, s. 271-283
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Tidskriftsartikel (refereegranskat)abstract
- Cover estimates by eye is a prevailing method to assess abundance. We examined cover estimates with regard to bias and random variation. Ten observers working with a national forest vegetation survey estimated sixteen 100 m(2)-plots, placed in two different vegetation types. These had similar species composition but were clearly distinguishable in the field. In species-wise analyses, observer bias varied greatly, with Dicranum spp., Vaccinium vitis-idaea and Vaccinium myrtillus having the largest bias. Experience had a surprisingly small impact on variation. Power analysis revealed only small differences between observers in the ability to distinguish the two vegetation types, and little value in averaging the assessments from two, three or four observers. Cover estimates did better than presence/absence data in separating the two vegetation types and multivariate analyses were more powerful than univariate ones.
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| 2. |
- Carlsson, Georg, et al.
(författare)
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N-2 fixation in three perennial Trifolium species in experimental grasslands of varied plant species richness and composition
- 2009
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Ingår i: Plant Ecology. - : Springer Science and Business Media LLC. - 1385-0237 .- 1573-5052. ; 205, s. 87-104
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Tidskriftsartikel (refereegranskat)abstract
- This study is the first to investigate quantitative effects of plant community composition and diversity on N-2 fixation in legumes. N-2 fixation in three perennial Trifolium species grown in field plots with varied number of neighbouring species was evaluated with the N-15 natural abundance method (two field sites, several growing seasons, no N addition) and the isotope dilution method (one site, one growing season, 5 g N m(-2)). The proportion of plant N derived from N-2 fixation, pNdfa, was generally high, but the N addition decreased pNdfa, especially in species-poor communities. Also following N addition, the presence of grasses in species-rich communities increased pNdfa in T. hybridum and T. repens L., while legume abundance had the opposite effect. In T. repens, competition for light from grasses appeared to limit growth and thereby the amount of N-2 fixed at the plant level, expressed as mg N-2 fixed per sown seed. We conclude that the occurrence of diversity effects seems to be largely context dependent, with soil N availability being a major determinant, and that species composition and functional traits are more important than species richness regarding how neighbouring plant species influence N-2 fixation in legumes.
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| 3. |
- Csergoe, Anna-Maria, et al.
(författare)
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Two-scale modelling of Saponaria bellidifolia Sm. (Caryophyllaceae) abundance on limestone outcrops from its northern range periphery (Southeastern Carpathians)
- 2009
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Ingår i: PLANT ECOLOGY. - : Springer Science and Business Media LLC. - 1385-0237 .- 1573-5052. ; 203:2, s. 229-242
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Tidskriftsartikel (refereegranskat)abstract
- We modelled the effect of habitat heterogeneity on the abundance of the submediterranean Saponaria bellidifolia, a red list species in Romania. The study was designed at two scales: 100 and 0.5 m(2). At larger scale, generalized additive models and canonical correspondence analysis were used to model the density of ramets, whereas at microscale, binomial logistic regression was employed to model the species' occurrence. S. bellidifolia abundance responded sensitively to habitat type (classified as "grassy", "rocky" and "scree"), rather than to microclimatic variables. At both scales, habitat type was the best predictor of ramet abundance, followed by slope and vegetation cover. At 0.5 m(2), soil depth was also a good predictor of species occurrence. The data revealed that screes are the most suitable habitats for hosting relatively large populations of this rare species, because of occasional natural disturbances and presumably lower interspecific competition.
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| 4. |
- Graae, Bente J., et al.
(författare)
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The impact of temperature regimes on development, dormancy breaking and germination of dwarf shrub seeds from arctic, alpine and boreal sites.
- 2008
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Ingår i: Plant Ecology. - : Springer Science and Business Media LLC. - 1385-0237 .- 1573-5052. ; 198, s. 275-284
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Tidskriftsartikel (refereegranskat)abstract
- It has been suggested that the infrequent sexual reproduction of arctic dwarf shrubs might be related to the harsh environmental conditions in which they live. If this is the case, then increases in temperature resulting from global climate change might drastically affect regeneration of arctic species. We examined whether recruitment of Empetrum nigrum ssp. hermaphroditum and Vaccinium uliginosum (hereafter E. nigrum and V. uliginosum) was affected by temperature during three reproductive stages: seed development, dormancy breakage and germination. Seeds were collected from an arctic, an alpine (only E. nigrum) and a boreal site with different climates; stored at different winter temperatures and incubated for germination at different temperatures. Seeds of V. uliginosum developed in the boreal region had a higher percentage germination than did seeds developed in the Arctic. In contrast, seeds of E. nigrum from the arctic site had a higher or similar percentage germination than did seeds from the alpine and boreal sites. Increased winter temperatures had no significant effect on resulting germination percentage of E. nigrum. However, V. uliginosum seeds from the arctic site suffered increased fungal attack (and thus decreased germination) when they were stratified under high winter temperatures. Seeds of both species increased germination with increased incubation temperatures. Our results suggest that both species would increase their germination in response to warmer summers. Longer summers might also favour the slow-germinating E. nigrum. However, increased winter temperatures might increase mortality due to fungal attack in V. uliginosum ecotypes that are not adapted to mild winters.
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| 5. |
- Hagenah, Nicole, et al.
(författare)
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Interacting effects of grass height and herbivores on the establishment of an encroaching savanna shrub
- 2009
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Ingår i: Plant Ecology. - : Springer Science and Business Media LLC. - 1385-0237 .- 1573-5052. ; 201:2, s. 553-566
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Tidskriftsartikel (refereegranskat)abstract
- Shrub encroachment is a widely observed problem in Southern African savannas. Although the effects of herbivory and grass height on woody species recruitment have been studied individually, little information exists about how these factors interact. In this study seeds and seedlings of the encroaching shrub Dichrostachys cinerea were planted in clipped and unclipped grass plots, with and without large herbivores present. Seed germination, seedling survival and seedling predation were monitored for 8 months. Germination started earlier in plots where herbivores were excluded. Overall, the earlier the seeds germinated, the longer the seedlings survived. Clipping positively affected the number of germinated seeds, seedling growth and survival but effects varied among herbivore exclusion treatments and sites. Invertebrates caused the majority of the seedling damage. We conclude the recruitment of D. cinerea is influenced by the interplay of grass height and herbivory. In this study, the presence of large herbivores early in the wet season, and the absence of simulated grazing later on, affected the regeneration of D. cinerea negatively. However, differences in effects among sites suggest that the mechanisms found here may work differently in other habitats.
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| 6. |
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| 7. |
- Manzaneda, AJ, et al.
(författare)
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Effects of microsite disturbances and herbivory on seedling performance in the perennial herb Helleborus foetidus (Ranunculaceae)
- 2005
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Ingår i: Plant Ecology. - : Springer Science and Business Media LLC. - 1385-0237 .- 1573-5052. ; 179:1, s. 73-82
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Tidskriftsartikel (refereegranskat)abstract
- The impact of small scale disturbances on the early seedling performance components of Helleborus foetidus (Ranunculaceae) was studied through a transplant experiment. The aims of this study were: (i) to determine if the herbivory pattern depends on microsite disturbance, by the analysis of two of its components, seedling encounter (the probability of at least one seedling being harmed) and seedling exploitation (the proportion of seedling tissue removed once encountered); (ii) to test if seedlings of H. foetidus in disturbed microsites will survive in a greater proportion than seedlings in undisturbed microsites; (iii) to investigate if seedling survival is correlated with the degree of herbivory. Microsite disturbances had a large effect on the herbivory pattern. Seedlings growing in undisturbed vegetation had a 2-fold higher likelihood of being grazed and suffered 1.38-fold higher damage than those growing in disturbed plots. At the end of this experiment, after fourteen months, only 10.4% of the seedlings transplanted were still alive due to seedling desiccation, but no differences on seedling survival were found between disturbed and undisturbed plots. The effect of herbivory and the interactive effect of herbivory and disturbance on seedling survival only reached statistical significance dependent upon site. We concluded that although small scale disturbances had a large impact on herbivory patterns; they had only a minor role in the early seedling survival of H. foetidus. Only locally, small scale disturbances showed an effect on seedling survival through herbivory. Abiotic factors like summer drought and spatial variations determined the early survival of H. foetidus seedlings to a major extent.
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| 8. |
- Rozema, Jelte, et al.
(författare)
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Stratospheric ozone depletion: High arctic tundra plant growth on Svalbard is not affected by enhanced UV-B after 7 years of UV-B supplementation in the field
- 2006
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Ingår i: Plant Ecology. - : Springer Science and Business Media LLC. - 1573-5052 .- 1385-0237. ; 182:1-2, s. 121-135
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Tidskriftsartikel (refereegranskat)abstract
- The response of tundra plants to enhanced UV-B radiation simulating 15 and 30% ozone depletion was studied at two high arctic sites (Isdammen and Adventdalen, 78 degrees N, Svalbard).The set-up of the UV-B supplementation systems is described, consisting of large and small UV lamp arrays, installed in 1996 and 2002. After 7 years of exposure to enhanced UV-B radiation, plant cover, density, morphological (leaf fresh and dry weight, leaf thickness, leaf area, reproductive and ecophysiological parameters leaf UV-B absorbance, leaf phenolic content, leaf water content) were not affected by enhanced UV-B radiation. DNA damage in the leaves was not increased with enhanced UV-B in Salix polaris and Cassiope tetragona. DNA damage in Salix polaris leaves was higher than in leaves of C. tetragona. The length of male gametophyte moss plants of Polytrichum hyperboreum was reduced with elevated UV-B as well as the number of Pedicularis hirsuta plants per plot, but the inflorescence length of Bistorta vivipara was not significantly affected. We discuss the possible causes of tolerance of tundra plants to UV-B (absence of response to enhanced UV-B) in terms of methodology (supplementation versus exclusion), ecophysiological adaptations to UV-B and the biogeographical history of polar plants.
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| 9. |
- Wikberg, Sofie, et al.
(författare)
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Ramet dynamics in a centrifugally expanding clonal sedge: a matrix analysis
- 2006
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Ingår i: Plant Ecology. - : Springer Science and Business Media LLC. - 1573-5052 .- 1385-0237. ; 183:1, s. 55-63
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Tidskriftsartikel (refereegranskat)abstract
- Carex humilis is a clonal sedge that can form distinct rings of densely aggregated ramets. We hypothesize that rings form because both production of new ramets and ramet dispersal are positively correlated to ramet size. This would lead to an overrepresentation of fast-moving and large ramets with high ramet production at the periphery, whereas slow-moving and small ramets with low ramet production would mainly be found in the interior of rings. We use matrix models to analyse how ramet populations both at the periphery and in the interior develop in the absence of ramet dispersal. We found that the stable size class distributions of ramets predicted by the models were not different from the distributions found in the field. Also, the asymptotic ramet population growth rates (lambda(1)) were the same. Hence, we conclude that rings would form even in the absence of a link between ramet dispersal and ramet production. Further analysis of the matrix models showed that the ramet population increases at the periphery but decreases in the interior of rings because medium and large ramets produce fewer large ramets in the interior than at the periphery. We also found that the temporal variance in lambda(1) and transitions rates during the four study years was much higher at the periphery than in the interior. Our results suggest that rings may form because C. humilis ramets use below-ground resources from a much larger area than the one covered by the shoots. As the clone grows larger, the soil volume available to the ramets in the interior decreases because their access to soil outside the ring is cut-off by the ramets at the periphery. Ramet density in the interior is therefore decreasing.
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| 10. |
- Odnevall Wallinder, Inger, et al.
(författare)
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Corrosion-induced release and environmental interaction of chromium, nickel and iron from stainless steel
- 2006
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Ingår i: Water, Air and Soil Pollution. - : Springer Science and Business Media LLC. - 0049-6979 .- 1573-2932. ; 170:1-4, s. 17-35
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Tidskriftsartikel (refereegranskat)abstract
- A cross-disciplinary research project has been implemented because of increased awareness of the potential environmental effects caused by dispersion of metals from external applications into the environment. The work comprises a 4-year (1998-2002) field exposure of grades 304 and 316 stainless steels, and a laboratory percolation study simulating 20-25 years of chromium and nickel containing runoff water interactions with soil. Total metal annual release rates varied between 0.2 and 0.7 mg m(-2) yr(-1) for Cr, between 0.1 and 0.8 mg m(-2) yr(-1) for Ni and between 10 and 200 mg m(-2) yr(-1) for Fe. Most Cr and Ni is present in an ionic form as a result of the limited presence of organic matter at the immediate release situation. Metal ion concentrations in the runoff water are far below reported ecotoxic concentrations. Studies of the environmental interaction between runoff water from stainless steel and soil show the majority of released Cr and Ni to be retained and their concentrations in percolation water to be very low (0.5-1 mu g L-1 and 1-5.5 mu g L-1 for Cr and Ni, respectively). Speciation calculations showed Cr to be primarily complexed to dissolved organic carbon while Ni also was present in an ionic form in the solution phase. Soil extractions showed Cr and Ni to be very strongly retained within the soil.
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