umu.sePublications
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Gradients of time and complexity: understanding how riparian and instream ecosystems recover after stream restoration
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Landscape Ecology)ORCID iD: 0000-0003-2152-245X
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 [en]
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: urn:nbn:se:umu:diva-108079ISBN: 978-91-7601-302-1 (print)OAI: oai:DiVA.org:umu-108079DiVA: diva2:851012
Public defence
2015-09-25, Älgsalen, Uminova Science Park, Umeå, 09:00 (English)
Opponent
Supervisors
Available from: 2015-09-04 Created: 2015-09-03 Last updated: 2015-09-03Bibliographically approved
List of papers
1. Time for recovery of riparian plants in restored northern Swedish streams: a chronosequence study
Open this publication in new window or tab >>Time for recovery of riparian plants in restored northern Swedish streams: a chronosequence study
Show others...
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.

Keyword
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:nbn:se:umu:diva-106561 (URN)10.1890/14-1102.1 (DOI)000356898400017 ()
Available from: 2015-07-20 Created: 2015-07-20 Last updated: 2017-12-04Bibliographically approved
2. Changes in nitrogen cycling in riparian zones along a chronosequence of restored streams in northern Sweden
Open this publication in new window or tab >>Changes in nitrogen cycling in riparian zones along a chronosequence of restored streams in northern Sweden
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Understanding how stream restoration affects nitrogen (N) cycling in riparian zones is crucial for setting realistic performance criteria for restored streams. Most streams in northern Sweden were channelized for timber floating, and many streams have now been restored. Channelization disconnected streams from the riparian zone, and reduced the flooding that creates anoxic conditions necessary for many N-cycling reactions. We used a space-for-time substitution consisting of stream reaches restored 2 to 25 years ago, unrestored channelized and natural reference reaches to determine how N-cycling in riparian zones changes with time after restoration. Using stable isotopes of N (δ15N), we found that restoration caused more enriched foliar and root δ15N in recently restored sites, suggesting more gaseous losses of N in younger sites. This enrichment in foliar and root δ15N decreased over the 25-year chronosequence suggesting that the N-cycle becomes tighter and loses less N as it ages. Although the [N] in foliage, roots, and soils did not change over time, understory biomass decreased over time, suggesting that more N was available to plants in younger compared to older sites. Changes in the mechanism of N acquisition (i.e., mycorrhizal colonization, as shown by Δδ15N), plant species richness, and cover of deciduous trees (carbon source), were the most important factors explaining variation in δ15N along with time after restoration. It is clear that the restoration of these streams causes a large and rapid change in nitrogen processing in the riparian zone and this alteration persists for at least 25 years.

Keyword
boreal, chronosequence, nitrogen cycling, stream restoration, space-for-time substitution, stable isotopes, succession, time gradient
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-108075 (URN)
Funder
Swedish Research Council Formas
Available from: 2015-09-03 Created: 2015-09-03 Last updated: 2015-09-03
3. Potential and actual geomorphic complexity of restored headwater streams in northern Sweden
Open this publication in new window or tab >>Potential and actual geomorphic complexity of restored headwater streams in northern Sweden
2014 (English)In: Geomorphology, ISSN 0169-555X, E-ISSN 1872-695X, Vol. 210, 98-118 p.Article in journal (Refereed) Published
Abstract [en]

Stream restoration usually relies on ecological theories presuming that increased habitat heterogeneity leads to higher biodiversity. However, to test this hypothesis a quantitative metric of overall geomorphic complexity is needed. We quantified geomorphic complexity using 29 metrics over five dimensions (sediment distribution, longitudinal profile, cross section, planform, and instream wood) of headwater streams in northern Sweden. We examined reaches with four different restoration statuses after a century of timber floating (channelized, restored, demonstration restored, and unimpacted) to determine (1) whether restoration increases complexity in all dimensions, (2) whether a complexity gradient can be quantified and which metrics can serve as proxies for the gradient, and (3) levels of potential complexity based on large-scale controls (drainage area, glacial legacy sediment, valley slope, valley confinement old-growth forest/buffer zone, and beaver activity). We found a significantly higher complexity in unimpacted and demonstration restoration sites than in channelized sites in all five dimensions except the cross section (based on the two metrics quantifying variability in the cross section). Multivariate analyses were able to elucidate an apparent complexity gradient driven by three complexity metrics: longitudinal roughness, sediment sorting, and cross section chain and tape ratio. The large-scale factors of valley and channel gradient as well as median grain size, along with restoration status, drive differences in complexity composition. Restoring a reach to its potential complexity is beneficial in regions without reference systems or sufficient data to model flow and sediment processes. Unimpacted and demonstration restoration reaches displayed not only more intrareach variability than channelized reaches but also greater interreach heterogeneity in complexity composition, which supports a focus on reach-scale controls on potential complexity and a landscape-scale view on restoration. (C) 2014 Elsevier B.V. All rights reserved.

Keyword
Geomorphic complexity, Stream restoration, Sweden, Boreal, Headwater streams, Channelization
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:umu:diva-88319 (URN)10.1016/j.geomorph.2013.12.025 (DOI)000332820800009 ()
Available from: 2014-06-17 Created: 2014-04-30 Last updated: 2017-12-05Bibliographically approved
4. Contrasting effects of geomorphic complexity on diversity of three aquatic organism groups after stream restoration
Open this publication in new window or tab >>Contrasting effects of geomorphic complexity on diversity of three aquatic organism groups after stream restoration
Show others...
(English)Manuscript (preprint) (Other academic)
Abstract [en]
  1. Ecological theory states that greater habitat heterogeneity should support higher biodiversity. Many stream restoration projects aim to increase geomorphic complexity, assuming that this increases habitat heterogeneity and, thus, biodiversity. However, little evidence has been published that supports this theory, especially with respect to stream restoration and aquatic organisms.
  2. Previous assessments of stream habitat restoration have suffered from four major limitations: (1) incomplete quantification of habitat complexity metrics, (2) assessment of the responses of only one organism group, most often macroinvertebrates, (3) mismatch between scale of restoration and scale of disturbance, and (4) limited number of restoration measures applied.
  3. We used 12 metrics of geomorphic complexity spanning five dimensions of complexity (sediment grain size distribution, longitudinal profile, cross section, planform, and instream wood) to evaluate if the diversity, abundance and community composition of three aquatic organism groups (benthic macroinvertebrates, diatoms and macrophytes) relate positively to complexity along near-natural, restored and channelised stream reaches in rural northern Sweden where disturbance to the streams has been primarily reach-scale channelisation to facilitate timber floating.
  4. We found that the variation in biodiversity and abundance within each of the three organism groups could be described by multiple regression models that included only geomorphic complexity metrics, but the variation within an organism group could rarely be described by only one metric of complexity in isolation. Rather, three metrics were needed on average to describe the variation in biodiversity and abundance, and rarely did all metrics relate positively to diversity. Sediment grain size distribution metrics were most often significant as explanatory variables, but were inconsistent in the direction of influence. The other four dimensions of complexity were less consistently significant but were nearly all positively related to our diversity metrics.
  5. Most of the variation in these metrics was driven by advanced restoration techniques and to a lesser extent older best practice techniques. Three complexity metrics were most often included in multiple regression models as well as described community composition in ordinations:  a metric quantifying heterogeneity of small sediment sizes, a metric that represents the variation in stream depth along the longitudinal profile, and instream wood metrics. Therefore, specifically these metrics could be targets for future restoration. The organism groups were not concordant in their patterns of diversity, abundance, or community composition; thus, none can be used as a surrogate in monitoring biodiversity of these sites.
  6. Synthesis and applications. Geomorphic complexity should be measured in multiple dimensions, and ideally in all five dimensions, to understand the full breadth of restoration impacts to which organisms could be responding. More than one organism group should be used in monitoring to ensure biodiversity goals are met. Finally, even though the scale of the restorations matched the scale of the disturbance at the reach scale, the older best practice methods of restoration rarely restored the large-scale features necessary to bring the sites up to their potential levels of complexity as these elements (large boulders, bedrock, log jams) had been destroyed or removed from the system. Although the advanced restoration sites were the youngest, advanced restoration techniques that added big boulders, coarse gravel and instream wood increased complexity to a level that elicited a biological response. Finally, the complexity level needed to elicit a biological response could be difficult to understand for a given system, so we suggest doing restoration work in an experimental way in collaboration with geomorphologists to determine what level of complexity is needed.
Keyword
boreal, bioassessment, bryophyte, substrate heterogeneity, hydromorphological, large wood, river
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-108076 (URN)
Funder
Swedish Research Council Formas
Available from: 2015-09-03 Created: 2015-09-03 Last updated: 2015-09-03

Open Access in DiVA

fulltext(2071 kB)121 downloads
File information
File name FULLTEXT01.pdfFile size 2071 kBChecksum SHA-512
40f3ebcc4903b2ec1cd282795562dc0b22da57a62f072b21c120334bfb547fef2f711b1cc4090e8f51fab0dbb64296d6f78c4684028314b89fe4bd83143da3a0
Type fulltextMimetype application/pdf
spikblad(64 kB)5 downloads
File information
File name SPIKBLAD01.pdfFile size 64 kBChecksum SHA-512
09d70560072ecf0021db0ef9ddd1b037bdebe6c8daff67eeaf562506ba88c74c41487484461fedf6347ecd63c1ddfd48dc1c374dd9ce83537b551349b9f9a3bb
Type spikbladMimetype application/pdf
omslag(5396 kB)11 downloads
File information
File name COVER01.pdfFile size 5396 kBChecksum SHA-512
a601578d240a9e2e59b8a729b2873515c1cc81e256ff72ab0eec9db9e53a3fa4818f60caed0c74a0dcae8ee0f96b238013bf23b0b2381b1b2bfe5f33a9c353d1
Type coverMimetype application/pdf

Authority records BETA

Hasselquist, Eliza Maher

Search in DiVA

By author/editor
Hasselquist, Eliza Maher
By organisation
Department of Ecology and Environmental Sciences
Ecology

Search outside of DiVA

GoogleGoogle Scholar
Total: 121 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 1241 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf