| 1. |
- Bejarano, Maria D., et al.
(författare)
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Hydropeaking affects germination and establishment of riverbank vegetation
- 2020
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Ingår i: Ecological Applications. - : John Wiley & Sons. - 1051-0761 .- 1939-5582. ; 30:4
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Tidskriftsartikel (refereegranskat)abstract
- Hydropeaking, defined as frequent and rapid variation in flow in regulated rivers with hydropower plants over a short period of time, usually sub-daily to weekly, alters hydraulic parameters such as water levels or flow velocity and exerts strong impacts on fluvial ecosystems. We evaluated the effects of hydropeaking on riverbank vegetation, specifically assessing the germination and establishment of seedlings and cuttings of plant species representing a variation in traits. We used seeds and seedlings and cuttings varying in size as phytometers, and transplanted them to riverbanks both above and below dams used for hydropower production in northern Sweden, selected to represent a gradient in hydropeaking intensity, and along a free-flowing reach. We also analyzed sub-daily water-level variables modified by hydropeaking to identify variables key in explaining the observed vegetation patterns. We found that plant responses to hydropeaking varied with species, with flood-intolerant species being the most strongly affected, as early as the germination stage. In contrast, seeds of flood-tolerant species managed to germinate and survive the early establishment phase, although strong erosive processes triggered by hydropeaking eventually caused most of them to fail. The fate of flood-intolerant species identifies germination as the most critical life-history stage. The depth and frequency of the inundation were the leading variables explaining plant responses, while the duration of shallow inundation explained little of the variation. The rise and fall rates of water levels were key in explaining variation in germination success. Based on the results, we propose restoration measures to enhance establishment of riparian plant communities while minimizing the impact on hydropower electricity production. Given the strong decrease in the germination of species intolerant to prolonged flooding with hydropeaking, planting of seedlings, preferably of large sizes, together with restrictions in the operation of the power plant during the establishment phase to enhance survival would be the best restoration option. Given the high probability of plant uprooting with hydropeaking, bank protection measures have the potential to increase riparian plant survival of all species, including flooding-tolerant species.
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| 2. |
- Bejarano, Maria D., et al.
(författare)
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The effects of hydropeaking on riverine plants : a review
- 2018
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Ingår i: Biological Reviews. - : WILEY. - 1464-7931 .- 1469-185X. ; 93:1, s. 658-673
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Forskningsöversikt (refereegranskat)abstract
- Hydropeaking refers to frequent, rapid and short-term fluctuations in water flow and water levels downstream and upstream of hydropower stations. Such fluctuations are becoming increasingly common worldwide and are known to have far-reaching effects on riverine vegetation. Novel hydrology caused by hydropeaking has no natural correspondence in freshwater systems, and hence few species have adaptations to all its aspects. Here, we review the literature on hydropeaking effects on riverine plants and define the state of the information on this human alteration of riverine ecosystems. We focus on riparian plants, but also draw on information from aquatic plant species, which exhibit a wide variety of adaptations to inundation and associated processes. Riparian plants face both physiological and physical constraints because of the shifts between submergence and drainage, and erosion of substrates. At the population level, hydropeaking may favour dispersal within, but not between, reservoirs, but may hamper germination, establishment, growth and reproduction. At the community level, strong filtering towards easily dispersed, flexible, flood-tolerant and amphibious plants is expected, although few species share these traits. Hence, most riparian plant species are expected to disappear or be pushed towards the upper boundaries of the regulated river margin. Future research should examine more closely global variation in hydropeaking effects, including other taxonomic groups of species and the diversity of hydropeaking regimes. There is also a need for studies focusing on identifying the boundaries within which hydropeaking could operate without impairing plant life.
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| 3. |
- Catford, Jane A., et al.
(författare)
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Reducing redundancy in invasion ecology by integrating hypotheses into a single theoretical framework
- 2009
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Ingår i: Diversity & distributions. - : Wiley. - 1366-9516 .- 1472-4642. ; 15:1, s. 22-40
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Tidskriftsartikel (refereegranskat)abstract
- Aim: Invasion ecology includes many hypotheses. Empirical evidence suggests that most of these can explain the success of some invaders to some degree in some circumstances. If they all are correct, what does this tell us about invasion? We illustrate the major themes in invasion ecology, and provide an overarching framework that helps organize research and foster links among subfields of invasion ecology and ecology more generally.Location: Global.Methods: We review and synthesize 29 leading hypotheses in plant invasion ecology. Structured around propagule pressure (P), abiotic characteristics (A) and biotic characteristics (B), with the additional influence of humans (H) on P, A and B (hereon PAB), we show how these hypotheses fit into one paradigm. P is based on the size and frequency of introductions, A incorporates ecosystem invasibility based on physical conditions, and B includes the characteristics of invading species (invasiveness), the recipient community and their interactions. Having justified the PAB framework, we propose a way in which invasion research could progress.Results: By highlighting the common ground among hypotheses, we show that invasion ecology is encumbered by theoretical redundancy that can be removed through integration. Using both holistic and incremental approaches, we show how the PAB framework can guide research and quantify the relative importance of different invasion mechanisms.Main conclusions: If the prime aim is to identify the main cause of invasion success, we contend that a top-down approach that focuses on PAB maximizes research efficiency. This approach identifies the most influential factors first, and subsequently narrows the number of potential causal mechanisms. By viewing invasion as a multifaceted process that can be partitioned into major drivers and broken down into a series of sequential steps, invasion theory can be rigorously tested, understanding improved and effective weed management techniques identified.
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| 4. |
- Dietrich, Anna, 1979-, et al.
(författare)
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A long-term phytometer study to evaluate stream restoration along climate and discharge gradients
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Simplified channel morphology caused by the channelization of rivers to facilitatetimber floating resulted in a less variable flow regime with faster flows in the mainchannel. Restoration measures aiming to counteract these impacts, such as the returnof boulders to the channel and the reconnection of the riparian zone with instreamhabitats, are expected to create a higher, more natural hydrological variability andenhance riparian site quality. In this study, we analysed the number and duration offlooding events at channelized and restored river reaches with an indirect methodusing diurnal temperature oscillation. In a long-term field experiment, we evaluatedthe effect of flooding regime on riparian plant performance by measuring survival andbiomass increment of two transplanted phytometer species, a grass (Molinia caerulea)and a forb (Filipendula ulmaria). We found that flow variability was significantlyhigher at restored compared to channelized sites in medium-sized and large streams,particularly during summer months. Phytometer performance was better at restoredsites and positively correlated with summer flooding, indicating that a more variableflow after restoration improved site conditions for phytometer growth. This may notonly result from the higher heterogeneity in channel morphology caused by thereturned boulders, but can probably also be attributed to a lower flow velocity atrestored sites. Flood variables were more often correlated with other abiotic variablesat restored than at channelized sites, which points to an increased land-waterconnectivity as a result of restoration.
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| 5. |
- Dietrich, Anna L., et al.
(författare)
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A phytometer study evaluating the effects of stream restoration on riparian vegetation
- 2016
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Ingår i: Ecohydrology. - : Wiley. - 1936-0584 .- 1936-0592. ; 9:4, s. 646-658
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Tidskriftsartikel (refereegranskat)abstract
- Channelization of streams and rivers to facilitate timber floating has cut off riparian zones from the channel, covered them with coarse sediment and resulted in less flooding. Restoration measures aiming to counteract these impacts are expected to create a higher, more natural hydrological variability and enhance site quality for riparian plants. In a long-term field experiment, we evaluated the effect of flooding regime on riparian plant performance by measuring survival and biomass increment of two transplanted phytometer species, a grass (Molinia caerulea) and a forb (Filipendula ulmaria). We also analysed the number and duration of flooding events in channelized and restored stream and river reaches with an indirect method using diurnal temperature oscillation. We found that flow duration was higher, with significantly more flood events at restored compared with channelized sites in medium-sized and large watercourses, particularly during the summer months. Phytometer performance was better at restored sites, and it was positively correlated with duration and frequency of summer flooding, indicating that more but less intense floods after restoration improved site conditions for phytometer growth. This may not only result from an increased heterogeneity in channel morphology caused by the return of boulders but can probably also be attributed to a reduced current velocity at restored sites. Flood variables were more often correlated with other abiotic variables at restored than at channelized sites, which points to an increased land-water connectivity as a result of restoration.
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| 6. |
- Dietrich, Anna L., et al.
(författare)
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Restoration effects on germination and survival of plants in the riparian zone : a phytometer study
- 2015
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Ingår i: Plant Ecology. - : Springer Science and Business Media LLC. - 1385-0237 .- 1573-5052. ; 216:3, s. 465-477
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Tidskriftsartikel (refereegranskat)abstract
- Many streams that were channelized to facilitate timber floating in northern Sweden, have in recent years been restored by returning coarse sediment (cobbles and boulders) to the channel and reconnecting riparian with instream habitats. We asked if such restoration measures affect germination and survival of plants in the riparian zone, and if such potential effects depend on location in the catchment. We used a paired site approach, comparing the performance of Helianthus annuus (sunflower) phytometers (seeds and seedlings) in the riparian zone in channelized versus restored river reaches along climate and stream size gradients in the Vindel River catchment in northern Sweden. Phytometer survival, substrate availability, and soil nutrient content in large streams were enhanced by restoration, but overall, phytometer performance was negatively related to the length of the growing season, i.e. phytometers grew best at high altitudes and short growing seasons. This result may have been caused by less competition from the shorter and sparser neighbouring vegetation at these sites or to more frequent flooding events, enhancing retention of organic matter. Soil nutrient levels were lowest close to the coast and in large streams, probably due to deposition of mineral sediment. The higher availability of riparian habitat at restored than at channelized sites suggests that plant species richness and abundance may potentially increase after restoration. Seedling transplantation seems to be a preferable revegetation measure, because phytometer seedlings established better than seeds and survival was significantly higher at restored sites. The good plant performance at sites with short growing seasons and high altitudes suggests that, with limited resources, restoration measures should first be located to such sites.
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| 7. |
- Dietrich, Anna, 1979-, et al.
(författare)
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Phytometers are underutilised for evaluating ecological restoration
- 2013
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Ingår i: Basic and Applied Ecology. - Jena : Elsevier. - 1439-1791 .- 1618-0089. ; 14:5, s. 369-377
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Tidskriftsartikel (refereegranskat)abstract
- Ecological restoration increases, but evaluation of restoration efforts is inadequate because reliable performance indicators are lacking. As plants are important actors in ecological restoration, we suggest that they be used as meters, i.e. phytometers, of restoration success. Phytometer plants are transplanted to different conditions to integrate measures of the prevailing conditions. We analysed 100 studies for the use of phytometers and especially their applicability to evaluate ecological restoration. Most studies employed single species and life-stages and focused on habitat conditions and environmental impacts. Most experiments were conducted on grasslands in wet temperate regions. Growth was the dominant response variable, in long-term studies often combined with reproductive output and plant survival. Only five studies specifically evaluated ecological restoration, implying that its potential is not yet realised. We found phytometers promising in evaluating restoration outcomes given that they are easy to measure, can provide rapid results, and serve as integrative indicators of environmental conditions with the ability of covering many aspects of plant life and ecosystem processes. To evaluate restoration success with high resolution and generality, we suggest a combination of different phytometer species, life-forms and life-stages, and experimental periods >1 year to reduce effects of transplantation and between-year variation and to account for time lags in ecological processes and changes after restoration.
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| 8. |
- Dietrich, Anna, 1979-, et al.
(författare)
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The Use of Phytometers for Evaluating Restoration Effects on Riparian Soil Fertility
- 2014
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Ingår i: Journal of Environmental Quality. - : American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.. - 0047-2425 .- 1537-2537. ; 43:6, s. 1916-1925
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Tidskriftsartikel (refereegranskat)abstract
- The ecological restoration of streams in Sweden has become increasingly important to counteract effects of past timber floating. In this study, we focused on the effect on riparian soil properties after returning coarse sediment (cobbles and boulders) to the channel and reconnecting riparian with instream habitats. Restoration increases habitat availability for riparian plants, but its effects on soil quality are unknown. We also analyzed whether the restoration effect differs with variation in climate and stream size. We used standardized plant species to measure the performance of a grass (Phleum pratense L.) and a forb (Centaurea cyanus L.) in soils sampled in the riparian zones of channelized and restored streams and rivers. Furthermore, we analyzed the mass fractions of carbon (C) and nitrogen (N) along with the proportions of the stable isotopes C-13 and N-15 in the soil, as well as its grain size composition. We found a positive effect of restoration on biomass of phytometers grown in riparian soils from small streams, indicating that restoration enhanced the soil properties favoring plant performance. We suggest that changed flooding with more frequent but less severe floods and slower flows, enhancing retention, could explain the observed patterns. This positive effect suggests that it may be advantageous to initiate restoration efforts in small streams, which make up the highest proportion of the stream network in a catchment. Restoration responses in headwater streams may then be transmitted downstream to facilitate recovery of restored larger rivers. If the larger rivers were restored first, a slower reaction would be expected.
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| 9. |
- Dynesius, Mats, et al.
(författare)
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Intercontinental similarities in riparian-plant diversity and sensitivity to river regulation.
- 2004
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Ingår i: Ecological Applications. - : Wiley. - 1051-0761 .- 1939-5582. ; 14:1, s. 173-191
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Tidskriftsartikel (refereegranskat)abstract
- We asked whether assemblages of species with separate evolutionary histories differed in their response to similar human interventions. We assessed this by comparing the response of riparian plant communities to river regulation on two different continents. We compared free-flowing and regulated rivers between boreal parts of North America (Alberta and British Columbia) and Europe (Sweden), using a standardized Sampling protocol and the same field staff on both continents. Although the two regions shared few species, both riparian plant-species diversity along free-flowing rivers and the response to different kinds of flow regulation were similar between the continents. The number of riparian-plant species and their amount of cover differed among types of water-level regime, but the continental affiliation of a river-margin site did not statistically explain any of the variation. Within continents, the local flora of the regulated river-margin sites was largely similar in species composition to the free-flowing ones, but the sites along storage reservoirs were more species-poor. The similarity in the response to regulation between the continents suggests that general guidelines for rehabilitation of degraded boreal rivers are. a realistic goal.The number of species and genera, plant cover, and species numbers in most trait groups (classified according to growth form and life span) were similar between free-flowing river margins in Europe and North America. Moreover, the regional native species pools of northern Sweden and Alberta were similar in size and composition of species groups, despite the fact that only 27% of the species in Alberta were found in northern Sweden. This is presumably because the floras share a common Tertiary origin and because the regions have had largely similar late-Tertiary and Quaternary histories. The most pronounced difference between the continents was that we found no exotic species on the 183 Swedish river margin sites, whereas 9% of the species found in all 24 North American plots taken together were exotics. All North American exotics found have occurred in Europe since prehistoric times, and the difference in exotic richness most likely reflects a difference in the number of species humans have transferred from one continent to another, rather than a difference in invasibility between the regions.
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| 10. |
- Engström, Johanna, 1981-, et al.
(författare)
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Effects of river ice on riparian vegetation
- 2011
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Ingår i: Freshwater Biology. - : Blackwell Publishing. - 0046-5070 .- 1365-2427. ; 56:6, s. 1095-1105
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Tidskriftsartikel (refereegranskat)abstract
- 1. Many rivers and streams experience pronounced ice dynamics caused by the formation of anchor and frazil ice, leading to flooding and disturbance of riparian and aquatic communities. The effects of dynamic ice conditions on riverine biota are little known.2. We studied the formation of anchor ice in natural streams over 2 years, and assessed the effects of anchor ice on riparian vegetation by comparing sites with frequent or abundant and little or no anchor ice formation. We also studied the direct impact of ice on riparian plants by experimentally creating ice in the riparian zone over three winters, and by exposing plants of different life-forms to ‑18oC cold ice in the laboratory.3. Riparian species richness per 1-m2 plot was higher at sites affected by anchor ice than at sites where anchor ice was absent or rare. Dominance was lower at anchor ice sites, suggesting that ice disturbance enhanced species richness. Species composition was more homogenous among plots at anchor ice sites. Experimentally creating riparian ice corroborated the comparative results, with species richness increasing in ice-treated plots compared to controls, irrespective of whether the sites showed natural anchor ice.4. Because of human alterations of running waters, the natural effects of river ice on stream hydrology, geomorphology and ecology are little known. Global warming in northern streams will lead to more dynamic ice conditions, offering new challenges for aquatic organisms and river management. We expect that the results discussed here can stimulate new research, contributing to a better understanding of ecosystem function during winter.
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