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Time for recovery of riparian plants in restored northern Swedish streams: a chronosequence study
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Arcum)
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Arcum)
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2015 (English)In: Ecological Applications, ISSN 1051-0761, E-ISSN 1939-5582, Vol. 25, no 5, 1373-1389 p.Article in journal (Refereed) Published
Abstract [en]

A lack of ecological responses in stream restoration projects has been prevalent throughout recent literature with many studies reporting insufficient time for recovery. We assessed the relative importance of time, site variables, and landscape setting for understanding how plant species richness and understory productivity recover over time in riparian zones of northern Swedish streams. We used a space-for-time substitution consisting of 13 stream reaches restored 5-25 years ago, as well as five unrestored channelized reference reaches. We inventoried the riparian zone for all vascular plant species along 60-m study reaches and quantified cover and biomass in plots. We found that while species richness increased with time, understory biomass decreased. Forbs made up the majority of the species added, while the biomass of graminoids decreased the most over time, suggesting that the reduced dominance of graminoids favored less productive forbs. Species richness and density patterns could be attributed to dispersal limitation, with anemochorous species being more associated with time after restoration than hydrochorous, zoochorous, or vegetatively reproducing species. Using multiple linear regression, we found that time along with riparian slope and riparian buffer width (e.g., distance to logging activities) explained the most variability in species richness, but that variability in total understory biomass was explained primarily by time. The plant community composition of restored reaches differed from that of channelized references, but the difference did not increase over time. Rather, different time categories had different successional trajectories that seemed to converge on a unique climax community for that time period. Given our results, timelines for achieving species richness objectives should be extended to 25 years or longer if recovery is defined as a saturation of the accumulation of species over time. Other recommendations include making riparian slopes as gentle as possible given the landscape context and expanding riparian buffer width for restoration to have as much impact as possible.

Place, publisher, year, edition, pages
2015. Vol. 25, no 5, 1373-1389 p.
Keyword [en]
boreal forest, buffer strip, chronosequence, riparian buffer, riparian slope, river restoration, seed dispersal, space-for-time substitution, time gradient, vegetation
National Category
Ecology
Identifiers
URN: urn:nbn:se:umu:diva-106561DOI: 10.1890/14-1102.1ISI: 000356898400017OAI: oai:DiVA.org:umu-106561DiVA: diva2:842501
Available from: 2015-07-20 Created: 2015-07-20 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Gradients of time and complexity: understanding how riparian and instream ecosystems recover after stream restoration
Open this publication in new window or tab >>Gradients of time and complexity: understanding how riparian and instream ecosystems recover after stream restoration
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Why evaluations of the ecological outcomes of stream and river restoration have largely reported inconclusive or negative results has been the subject of much debate over the last decade or more. Understanding the reasons behind the lack of positive results is important for bettering future restoration efforts and setting realistic expectations for restoration outcomes. This thesis explores possible explanations for why researchers have failed to find clear and predictable biotic responses to stream restoration: recovery time has been too short, that restoration of habitat complexity is not clearly linked to instream biodiversity, that one monitored organism group is not representative of the entire community, that restoration effort was not intense enough to restore the potential habitat complexity of a system, and that reach-scale restoration done in the presence of catchment-scale degradation obscures restoration results. The overarching goal of this thesis is to study the holistic effect of reach-scale restoration of historic reach-scale simplification, due to timber floating in northern Swedish streams, thus avoiding the added pressure of catchment-scale degradation typically found at most restoration sites (e.g., non-point-source pollution and impervious cover). Using this model system, I was able to show that it took 25 years for riparian plant species richness at restored sites to increase above that of channelized sites. Furthermore, it was clear that restoration of these streams caused a large and rapid change in N-processing in the riparian zone and this alteration persists for at least 25 years. Additionally, multiple metrics of geomorphic complexity were needed to explain some of the more subtle responses of organism groups. Macroinvertebrates, diatoms, and macrophytes did not respond concordantly and cannot serve as surrogates or indicators for each other. I found that older best practice methods of restoration rarely restored the large-scale features needed to bring the sites up to their potential complexity because these elements were destroyed or removed from the system. Advanced restoration techniques used in more recent restorations added big boulders and instream wood and increased complexity to a level that elicited a biological response. By combining surveys of multiple metrics of structure, diversity of multiple organism groups, and process in this thesis I was able to get a holistic view of the effects of restoration of streams after timber floating. We now know that it takes at least 25 years for riparian plants and N-cycling to recover, we understand that multiple metrics of geomorphic complexity should be measured to be able to explain biotic responses, and that restored complexity should better match the potential complexity of the site in order to elicit a biological response. Finally, we know that multiple organism groups need to be assessed when evaluating the response of biodiversity to restoration.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2015. 36 p.
Keyword
bioassessment, biodiversity, boreal, bryophyte, chronosequence, complexity, diatom, geomorphology, habitat heterogeneity, hydromorphological, macroinvertebrate, macrophyte, nitrogen cycling, river restoration, riparian buffer, stable isotopes, succession, Sweden
National Category
Ecology
Research subject
biology, Environmental Science
Identifiers
urn:nbn:se:umu:diva-108079 (URN)978-91-7601-302-1 (ISBN)
Public defence
2015-09-25, Älgsalen, Uminova Science Park, Umeå, 09:00 (English)
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Available from: 2015-09-04 Created: 2015-09-03 Last updated: 2015-09-03Bibliographically approved

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Hasselquist, Eliza MaherNilsson, ChristerJørgensen, DollyLind, LovisaPolvi, Lina E.

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