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Vegetation patterns and processes in riparian landscapes
Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The objective of this study was to increase understanding of the processes structuring and controlling the species richness of riparian plant communities. In particular, I examined the unimodal relationship, found in many rivers, between plant species richness and location along the river corridor. The most important finding was that this pattern is dynamic and varies with time, most likely in response to large-scale flood disturbances. I also found that the sensitivity to flood disturbance varied with the environmental setting of the riparian reaches. Turbulent sections of the river retained high species richness, whereas tranquil reaches had significantly lower species richness in years following high and prolonged flooding, compared to a period without extreme flood events. Riparian soils along turbulent reaches are more resistant to oxygen depletion during floods, a factor which is likely to contribute to the maintenance of species richness.

The finding that the species richness pattern varied with time led me to ask which factors control plant diversity along riparian zones. I addressed this question by formulating three contrasting, although not mutually exclusive, hypotheses: (1) longitudinal patterns in riparian plant species richness are governed by local, river-related processes independent of the regional species richness, (2) riparian plant species richness is controlled by dispersal along the river, i.e., longitudinal control, and (3) the variation in riparian plant species richness mirrors variation in regional richness, i.e., lateral control. I found indications of all three types of control, although local factors seemed to fit most of the criteria. Riparian species richness was not significantly correlated to species richness in the surrounding upland valley. It was however significantly negatively correlated to soil pH, a local habitat factor of the reach. The fact that the species richness pattern varied in time, corresponding to the presence or absence of extreme flood events suggest that it is influenced by local disturbance regimes. The potential for control by longitudinal dispersal was found to be highest in the middle reaches of a river. Here, the similarity between upland and riparian vegetation was lowest, and invasibility (germination ability) was highest. Earlier work has shown that regulated rivers have an inverted species richness pattern compared to free-flowing rivers, with lowest species richness in the middle reaches. One potential mechanism behind this could be varying susceptibility to disturbance along the river. I tested this by experimentally disturbing the vegetation, applying the same level of disturbance along an entire free-flowing river. However, the response to experimental disturbance did not vary with location, likely because of a major flood disturbance preceding the experiment.

Place, publisher, year, edition, pages
Umeå: Ekologi och geovetenskap , 2004. , 31 p.
Keyword [en]
Ecology
Keyword [sv]
Ekologi
National Category
Ecology
Identifiers
URN: urn:nbn:se:umu:diva-342OAI: oai:DiVA.org:umu-342DiVA: diva2:143167
Public defence
2004-11-12, Sal 5, Uminova Science Park, Umeå Universitet, Umeå, 10:00
Opponent
Supervisors
Available from: 2004-10-28 Created: 2004-10-28 Last updated: 2012-06-29Bibliographically approved
List of papers
1. Connecting variation in vegetation and streamflow: the functions of large floods for riparian plant diversity and composition in boreal rivers
Open this publication in new window or tab >>Connecting variation in vegetation and streamflow: the functions of large floods for riparian plant diversity and composition in boreal rivers
In: Article in journal (Refereed) Submitted
Identifiers
urn:nbn:se:umu:diva-4173 (URN)
Available from: 2004-10-28 Created: 2004-10-28 Last updated: 2013-10-01Bibliographically approved
2. Spatial patterns of plant invasiveness in a riparian corridor
Open this publication in new window or tab >>Spatial patterns of plant invasiveness in a riparian corridor
2005 (English)In: Landscape Ecology, ISSN 0921-2973, E-ISSN 1572-9761, Vol. 20, no 2, 165-176 p.Article in journal (Refereed) Published
Abstract [en]

Analysis of landscape-scale patterns of plant invasiveness can assist in interpreting spatial patterns of plant species richness. We investigated downstream variation in plant invasiveness in the riparian corridor of the free-flowing Vindel River in northern Sweden by introducing seeds of an alien species, Helianthus annuus, in 0.25 m2 plots of natural vegetation from mountain headwaters to the coast and found a significant downstream pattern with middle reaches having the highest invasiveness. We related invasiveness to species richness, both on a reach scale (200-m long stretches of riverbank encompassing the experimental plots) and on the scale of experimental plots. We found no significant correlation between plant invasiveness and species richness, neither at the reach nor at the plot scale. The number of available soil substrates shows a significant positive quadratic relationship with location along the river and substrate fineness shows a near significant negative quadratic relationship with location along the river, with middle reaches having coarser substrates. Several studies have shown that plant species richness in riparian corridors often exhibits a quadratic pattern with highest species richness in the middle reaches of a river, similar to the pattern we found for invasiveness. Although species richness per se might not be a primary factor for invasibility, the same habitat conditions as those supporting plant species richness, can help in explaining large-scale patterns of plant invasion in riparian zones.

Place, publisher, year, edition, pages
Springer Netherlands, 2005
Keyword
Helianthus annuus, Invasiveness, Northern Sweden, Riparian vegetation, River, Species richness, Vindel River
National Category
Biological Sciences
Identifiers
urn:nbn:se:umu:diva-7723 (URN)10.1007/s10980-004-2262-z (DOI)
Available from: 2008-01-11 Created: 2008-01-11 Last updated: 2013-10-03Bibliographically approved
3. Spatial and temporal patterns of species richness in a riparian landscape
Open this publication in new window or tab >>Spatial and temporal patterns of species richness in a riparian landscape
(English)In: Article in journal (Refereed) Submitted
Identifiers
urn:nbn:se:umu:diva-4175 (URN)
Available from: 2004-10-28 Created: 2004-10-28 Last updated: 2013-10-01Bibliographically approved
4. Longitudinal variation in vegetation responses to disturbance in a riparian corridor along a boreal river
Open this publication in new window or tab >>Longitudinal variation in vegetation responses to disturbance in a riparian corridor along a boreal river
(English)Manuscript (Other academic)
Identifiers
urn:nbn:se:umu:diva-4176 (URN)
Available from: 2004-10-28 Created: 2004-10-28 Last updated: 2013-10-01Bibliographically approved

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