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The Effect of Snow on Plants and Their Interactions with Herbivores.
Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The ongoing climate changes are predicted to accelerate fast in arctic regions with increases in both temperatures and precipitation. Although the duration of snow cover is generally expected to decrease in the future, snow depth may paradoxically increase in those areas where a large amount of the elevated precipitation will fall as snow. The annual distribution and duration of snow are important features in arctic ecosystems, influencing plant traits and species interactions in various ways. In this thesis, I investigated the effect of snow on plants and their interactions with herbivores by experimentally increasing the snow cover by snow fences in three different habitats along an environmental gradient in Abisko, northern Sweden.

I found that the snow cover mattered for plant quality as food for herbivores and herbivore performance. An enhanced and prolonged snow cover increased the level of insect herbivory on dwarf birch leaves under field conditions. Autumnal moth larvae feeding on leaves that had experienced increased snow-lie grew faster and pupated earlier than larvae fed with leaves from control plots. These findings indicated that plants from snow-rich plots produced higher-quality food for herbivores. My studies showed that differences in snow-lie explained parts of the within-year spatial and seasonal variation in plant chemistry and patterns of herbivory in this arctic landscape. The relationship between leaf nitrogen concentration and plant phenology was consistent between treatments and habitats, indicating that snow per se, via a delayed phenology, was controlling the nitrogen concentration. The relationship between leaf age and level of herbivory was positive in the beginning of the growing season, but negative in the end of the growing season, indicating an increasing importance of plant palatability and a decreasing importance of exposure time in determining the level of herbivory throughout the growing season. The concentrations of phenolics varied among habitats, treatments and sampling occasions, suggesting that these plants were able to retain a mosaic of secondary chemical quality despite altered snow conditions. Furthermore, the nutrient limiting plant growth, according to N:P ratio thresholds, appeared to shift from nitrogen to phosphorus along the topographic gradient from snow-poor ridges to more snow-rich heathlands and fens. Snow addition had, however, no significant effect on other nutrient concentrations than nitrogen and no significant effect on the leaf N:P ratio, indicating that differences in snow cover could not explain the variation in plant nutrient concentrations among habitats. In a five-year study, I found opposing inter-annual effects of increased snow on plant chemistry. In contrast to earlier results, the effect of snow-lie on plant nitrogen concentration was predominantly negative. However, the effect of increased snow cover on the level of herbivory remained predominantly positive. The strong within-year relationship between snow-melt date (via plant phenology) and plant nitrogen concentration and level of herbivory could not predict inter-annual variation in the effect of snow manipulation. I did not find any conclusive evidence for a single factor causing the inter-annual opposing effect of snow addition, but the results indicated that interactions with summer and winter temperatures might be important.

In conclusion, this thesis showed that climate-induced changes in snow conditions will have strong effects on plant traits and plant-herbivore interactions. However, alterations in snow cover do not influence all plant traits and the effect may vary in time and space.

Place, publisher, year, edition, pages
Umeå: Print&Media , 2010. , 59 p.
Keyword [en]
Snow, arctic ecosystem, plant-herbivore interactions, phenology, nitrogen, phenolics, experimental manipulation, natural gradient, inter-annual variability
National Category
Biological Sciences
Identifiers
URN: urn:nbn:se:umu:diva-30444ISBN: 978-91-7264-923-1 (print)OAI: oai:DiVA.org:umu-30444DiVA: diva2:283015
Public defence
2010-01-22, Lilla Hörsalen (KB3A9), KBC-huset, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2009-12-29 Created: 2009-12-22 Last updated: 2009-12-29Bibliographically approved
List of papers
1. Snow-induced changes in dwarf birch chemistry increase moth larval growth rate and level of herbivory
Open this publication in new window or tab >>Snow-induced changes in dwarf birch chemistry increase moth larval growth rate and level of herbivory
2010 (English)In: Polar Biology, ISSN 0722-4060, E-ISSN 1432-2056, Vol. 33, no 5, 693-702 p.Article in journal (Refereed) Published
Abstract [en]

Changes in snow cover might influence arctic ecosystems to the same extent as increased temperatures. Although the duration of snow cover is generally expected to decrease in the future as a result of global warming, the amounts of snow might increase in arctic areas where much of the elevated precipitation will fall as snow. We examined the effects of an increased snow cover, as a result of a snow fence treatment, on soil nitrogen mineralization, plant phenology, plant chemistry (nitrogen and potential defense compounds), the level of invertebrate herbivory, and performance of invertebrate herbivores in an arctic ecosystem, using dwarf birch (Betula nana) and the autumnal moth (Epirrita autumnata) as study organisms. An enhanced and prolonged snow cover increased the level of herbivory on dwarf birch leaves. Larvae feeding on plants that had experienced enhanced snow cover grew faster and pupated earlier than larvae fed with plant material from control plots, indicating that plants from enhanced snow-lie plots produce higher-quality food to herbivores. The increased larval growth rate was strongly correlated with higher leaf nitrogen concentration in plants subjected to snow manipulation, and also to certain phenolic acids. Snow manipulation did not change net nitrogen mineralization rates in the soil or total carbon concentration in leaves, but it altered the within-season fluctuating pattern of leaf phenolic compounds. This study demonstrates a positive relationship between increased snow cover and level of herbivory on deciduous shrubs, thus proposing a negative feedback on the climate-induced dwarf shrub expansion in arctic areas.

Place, publisher, year, edition, pages
Springer, 2010
Keyword
Climate change, Snow fence, Plant phenology, Nitrogen, Epirrita autumnata, Betula nana
National Category
Biological Sciences
Identifiers
urn:nbn:se:umu:diva-30414 (URN)10.1007/s00300-009-0744-9 (DOI)000276615400013 ()
Available from: 2009-12-22 Created: 2009-12-21 Last updated: 2017-12-12Bibliographically approved
2. The effect of snow on plant chemistry and invertebrate herbivory: Experimental manipulations along a natural snow gradient
Open this publication in new window or tab >>The effect of snow on plant chemistry and invertebrate herbivory: Experimental manipulations along a natural snow gradient
2010 (English)In: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Vol. 13, no 5, 741-751 p.Article in journal (Refereed) Published
Abstract [en]

Changing snow conditions have strong effects onnorthern ecosystems, but these effects are rarelyincorporated into ecosystem models and our perceptionof how the ecosystems will respond to awarmer climate. We investigated the relationshipsbetween snow cover, plant phenology, level ofinvertebrate herbivory and leaf chemical traits inBetula nana in four different habitats located along anatural snow cover gradient. To separate the effectof snow per se from other differences, we manipulatedthe snow cover with snow fences in threehabitats. The experimentally prolonged snow coverdelayed plant phenology, but not as much as expectedbased on the pattern along the natural gradient.The positive effect of the snow treatment onplant nitrogen concentration was also weaker thanexpected, because plant nitrogen concentrationclosely followed plant phenology. The level ofherbivory by leaf-chewing invertebrates increasedin response to an increased snow cover, at least atthe end of the growing season. The concentrationof phenolic substances varied among habitats,treatments and sampling occasions, indicating thatB. nana shrubs were able to retain a mosaic ofsecondary chemical quality despite altered snowconditions. This study shows that the effect of thesnow cover period on leaf nitrogen concentrationand level of herbivory can be predicted based ondifferences between habitats, whereas the effect ofa changed plant phenology on plant nitrogenconcentration is better explained by temporaltrends within habitats. These results have importantimplications for how northern ecosystemsshould respond to future climate changes.

Place, publisher, year, edition, pages
Springer, 2010
Keyword
Tundra, snow, natural gradient, experimental manipulation, nitrogen, phenolics, herbivory, phenology, Betula nana
National Category
Biological Sciences
Identifiers
urn:nbn:se:umu:diva-30410 (URN)10.1007/s10021-010-9351-4 (DOI)000280260100009 ()
Available from: 2009-12-22 Created: 2009-12-21 Last updated: 2017-12-12Bibliographically approved
3. Inter-annual variation in the effect of snow on plants and their interactions with herbivores.
Open this publication in new window or tab >>Inter-annual variation in the effect of snow on plants and their interactions with herbivores.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Plant traits and patterns of herbivory are influenced by environmental conditions and annual variability in climatic parameters is thus of great importance for plant-herbivore interactions in arctic ecosystems. Although many environmental manipulations are carried out as long-term experiments, the direct effect on plants and herbivores is often described for one year only. Snow manipulation experiments have often demonstrated a positive relationship between snow cover and plant nitrogen concentration, and studies have suggested that the higher nitrogen concentration in plants from snow-rich sites results in increased plant quality as food for herbivores. However, recent experiments indicate that the effect of snow on plants and herbivores may vary between years. In a five-year study in northern Sweden, where we used snow fences to manipulate the snow accumulation in winter, we found opposing effects of increased snow cover on plant carbon and nitrogen concentrations between years and in contrast to earlier findings, the effect of snow-lie on plant nitrogen concentration was predominantly negative. The effect of snow on the level of leaf damage by invertebrate herbivores remained predominantly positive. We found no conclusive evidence for any single factor causing the inter-annual variation in the effect of snow-lie manipulation on plant chemical traits and level of herbivory. However, our results indicate that interactions with summer and winter temperatures might be important. These findings highlight the importance of long-term studies when trying to understand vegetation responses and plant-herbivore interactions in a changing climate, and advocate that longer time series and more accurate measurements of both environmental and plant characteristics are needed in order to find the mechanisms causing the inter-annual variation in the effect of increased snow cover.

National Category
Biological Sciences
Identifiers
urn:nbn:se:umu:diva-30411 (URN)
Available from: 2009-12-22 Created: 2009-12-21 Last updated: 2009-12-22Bibliographically approved
4. Effects of snow manipulation on nutrient concentrations in plants growing in habitats with contrasting snow cover.
Open this publication in new window or tab >>Effects of snow manipulation on nutrient concentrations in plants growing in habitats with contrasting snow cover.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Most studies on plant nutrition and plant quality as food for herbivores in arctic ecosystems have focused on the significance of nitrogen alone. However, several other macro- and micro-nutrients are of vital importance, for both plants and herbivores, all of which are thought to be affected by snow cover. We have investigated the effect of experimental snow addition using snow fences, on the concentrations of a number of nutrients (N, P, Ca, Fe, Mg, K, Na) in two dwarf shrub species (Betula nana and Salix glauca), in three different habitats along a natural gradient of snow cover. Our study revealed that although there were large differences in plant nutrition between both species and habitats, snow addition had only a minor, non-significant, effect on the leaf concentrations of most nutrients. Further, although the nutrient limiting plant growth, according to N:P ratio thresholds, appeared to shift from nitrogen to phosphorus along the topographic gradient from snow-poor ridges to more snow-rich heathlands and fens, experimental snow addition had no significant effect on plant N:P ratios. The observed stoichiometric shift must thus be caused by other factors varying between habitats rather than by differences in snow cover. Our results support previous studies showing that herbivores, such as reindeer, can optimize their nutrient uptake by foraging in different habitats. However, our study also demonstrates that climate-induced changes in snow conditions will probably have only minor effects on nutrient limitation of plant growth and leaf concentrations of most nutrients, and consequently the nutritional quality of plants as food for herbivores.

National Category
Biological Sciences
Identifiers
urn:nbn:se:umu:diva-30412 (URN)
Note
Submitted manuscript.Available from: 2009-12-22 Created: 2009-12-21 Last updated: 2009-12-22Bibliographically approved
5. Increased snow cover causes a shift towards negative neighbor interactions in tundra plant communities.
Open this publication in new window or tab >>Increased snow cover causes a shift towards negative neighbor interactions in tundra plant communities.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Gradients of increasing environmental harshness are associated with a shift from negative to positive interactions between plants. In alpine ecosystems, the severity of the environment generally increases with altitude and positive interactions between neighboring plants dominate at higher altitudes, while negative interactions dominate at lower altitudes. Similar shifts occur along local topographic gradients, where positive interactions predominate on exposed ridges, while negative interactions are more common in protected habitats. In a recent experiment, it was found that earlier snow-melt caused a shift towards more positive interactions between neighboring plants. This result suggests that differences in the duration of snow cover are responsible for differences in interactions between plants within such habitats. We examined this hypothesis by investigating the effect of longer-lasting snow cover on the intensity and direction of interactions between plants along an environmental gradient from exposed ridges with little natural snow cover to more sheltered fens and heathlands. We recorded a shift from positive interactions with neighbors on exposed ridges to negative interactions with neighbors in heathlands and fens. In accordance with previous studies, the increased snow cover resulted in more negative netinteractions between plants, but the effect was similar in all habitats. Other factors such as nutrient availability, soil humidity or wind exposure might explain these differences between habitats with respect to plant–plant interactions. These results improve our understanding of how abiotic conditions shape species interactions and thus add to our ability to predict how interactions between plants, and thus the composition of plant communities, will change in response to climate change.

National Category
Biological Sciences
Identifiers
urn:nbn:se:umu:diva-30413 (URN)
Note
Submitted manuscript.Available from: 2009-12-22 Created: 2009-12-21 Last updated: 2009-12-22Bibliographically approved

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