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Inter-annual variation in the effect of snow on plants and their interactions with herbivores.
Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
Swedish University of Agricultural Sciences, Southern Swedish Forest Research Centre, P.O. Box 49, SE-230 53 Alnarp, Sweden.
School of Biological and Biomedicinal Sciences, Institute of Ecosystem Science, University of Durham, Durham DH1 3LE, UK.
Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
(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: urn:nbn:se:umu:diva-30411OAI: oai:DiVA.org:umu-30411DiVA: diva2:282795
Available from: 2009-12-22 Created: 2009-12-21 Last updated: 2009-12-22Bibliographically approved
In thesis
1. The Effect of Snow on Plants and Their Interactions with Herbivores.
Open this publication in new window or tab >>The Effect of Snow on Plants and Their Interactions with Herbivores.
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
Snow, arctic ecosystem, plant-herbivore interactions, phenology, nitrogen, phenolics, experimental manipulation, natural gradient, inter-annual variability
National Category
Biological Sciences
Identifiers
urn:nbn:se:umu:diva-30444 (URN)978-91-7264-923-1 (ISBN)
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

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