| 1. |
- Hasselquist, Eliza Maher, et al.
(författare)
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Changes in nitrogen cycling in riparian zones along a chronosequence of restored streams in northern Sweden
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 2. |
- Hasselquist, Eliza Maher, et al.
(författare)
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Management of non-native annual plants to support recovery of an endangered perennial forb, Ambrosia pumila
- 2013
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Ingår i: Restoration Ecology. - 1061-2971 .- 1526-100X. ; 21:2, s. 224-231
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Tidskriftsartikel (refereegranskat)abstract
- Invasive non-native plants pose a ubiquitous threat to native plant communities and have been blamed for the decline of many endangered species. Endangered species legislation provides legal instruments for protection, but identifying a general method for protecting endangered species by managing non-natives is confounded by multiple factors. We compared non-native management methods aimed at increasing populations of an endangered forb, Ambrosia pumila, and associated native plants. We compared the effects of a grass-specific herbicide (Fusilade II), hand-pulling, and mowing in two degraded coastal sage scrub sites in southern California, U.S.A. At both sites, hand-pulling had the greatest effect on non-native cover, and correspondingly resulted in the greatest increase in A. pumila stems. Fusilade II application also led to an increase in A. pumila, but was not as effective in controlling non-native plants as hand-pulling and its effect varied with the dominant non-native species. Mowing was not effective at promoting A. pumila, and its effect on non-native cover seemed to be related to rainfall patterns. Although some methods increased A. pumila, none of our treatments simultaneously increased cover of other native plants. Hand-pulling, the most effective treatment, is labor intensive and thus only feasible at small spatial scales. At larger scales, managers should take an experimental approach to identifying the most appropriate method because this can vary depending on the specific management objective (endangered species or whole native community), the dominant non-natives, yearly variation in weather, and the timing of treatment application.
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| 3. |
- Hasselquist, Eliza Maher, et al.
(författare)
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Recovery of nitrogen cycling in riparian zones after stream restoration using delta N-15 along a 25-year chronosequence in northern Sweden
- 2017
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Ingår i: Plant and Soil. - : Springer Science and Business Media LLC. - 0032-079X .- 1573-5036. ; 410:1-2, s. 423-436
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Tidskriftsartikel (refereegranskat)abstract
- Swedish boreal streams were modified to transport timber by pushing boulders to stream sides, creating levees that disconnected streams from riparian areas. Many streams have since been restored and our goal was to understand how this affects riparian nitrogen (N) cycling. We compared the natural abundance of delta N-15 isotopes in foliage and roots of Filipendula ulmaria plus soils and litter along streams restored 2-25 years ago. We measured sources of N, potential immobilization of N, namely plant diversity and biomass, and the amount and sources of carbon (C) to determine if these were important for describing riparian N cycling. The delta N-15 of F. ulmaria foliage changed dramatically just after restoration compared to the channelized, disconnected state and then converged over the next 25 years with the steady-state reference. The disturbance and reconnection of the stream with the riparian zone during restoration created a short-term pulse of N availability and gaseous losses of N as a result of enhanced microbial processing of N. With increasing time since restoration, N availability appears to have decreased, and N sources changed to those derived from mycorrhizae, amino acids, or the humus layer, or there was enhanced N-use efficiency by older, more diverse plant communities.
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| 4. |
- Kozii, Nataliia, et al.
(författare)
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Partitioning growing season water balance within a forested boreal catchment using sap flux, eddy covariance, and a process-based model
- 2020
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Ingår i: Hydrology and Earth System Sciences. - : Copernicus GmbH. - 1027-5606 .- 1607-7938. ; 24, s. 2999-3014
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Tidskriftsartikel (refereegranskat)abstract
- Although it is well known that evapotranspiration (ET) represents an important water flux at local to global scales, few studies have quantified the magnitude and relative importance of ET and its individual flux components in high-latitude forests. In this study, we combined empirical sapflux, throughfall, and eddy-covariance measurements with estimates from a process-based model to partition the water balance in a northern boreal forested catchment. This study was conducted within the Krycklan catchment, which has a rich history of hydrological measurements, thereby providing us with the unique opportunity to compare the absolute and relative magnitudes of ET and its flux components to other water balance components. During the growing season, ET represented ca. 85 % of the incoming precipitation. Both empirical results and model estimates suggested that tree transpiration (T) and evaporation of intercepted water from the tree canopy (I-C) represented 43 % and 31 % of ET, respectively, and together were equal to ca. 70 % of incoming precipitation during the growing season. Understory evapotranspiration (ETu) was less important than T and I-C during most of the study period, except for late autumn, when ETu was the largest ET flux component. Overall, our study high-lights the importance of trees in regulating the water cycle of boreal catchments, implying that forest management impacts on stand structure as well as climate change effects on tree growth are likely to have large cascading effects on the way water moves through these forested landscapes.
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| 5. |
- Laudon, Hjalmar, et al.
(författare)
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Northern landscapes in transition : Evidence, approach and ways forward using the Krycklan Catchment Study
- 2021
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Ingår i: Hydrological Processes. - : John Wiley & Sons. - 0885-6087 .- 1099-1085. ; 35:4
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Tidskriftsartikel (refereegranskat)abstract
- Improving our ability to detect changes in terrestrial and aquatic systems is a grand challenge in the environmental sciences. In a world experiencing increasingly rapid rates of climate change and ecosystem transformation, our ability to understand and predict how, when, where, and why changes occur is essential for adapting and mitigating human behaviours. In this context, long-term field research infrastructures have a fundamentally important role to play. For northern boreal landscapes, the Krycklan Catchment Study (KCS) has supported monitoring and research aimed at revealing these changes since it was initiated in 1980. Early studies focused on forest regeneration and microclimatic conditions, nutrient balances and forest hydrology, which included monitoring climate variables, water balance components, and stream water chemistry. The research infrastructure has expanded over the years to encompass a 6790 ha catchment, which currently includes 11 gauged streams, ca. 1000 soil lysimeters, 150 groundwater wells, >500 permanent forest inventory plots, and a 150 m tall tower (a combined ecosystem-atmosphere station of the ICOS, Integrated Carbon Observation System) for measurements of atmospheric gas concentrations and biosphere-atmosphere exchanges of carbon, water, and energy. In addition, the KCS has also been the focus of numerous high resolution multi-spectral LiDAR measurements and large scale experiments. This large collection of equipment and data generation supports a range of disciplinary studies, but more importantly fosters multi-, trans-, and interdisciplinary research opportunities. The KCS attracts a broad collection of scientists, including biogeochemists, ecologists, foresters, geologists, hydrologists, limnologists, soil scientists, and social scientists, all of whom bring their knowledge and experience to the site. The combination of long-term monitoring, shorter-term research projects, and large-scale experiments, including manipulations of climate and various forest management practices, has contributed much to our understanding of boreal landscape functioning, while also supporting the development of models and guidelines for research, policy, and management.
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| 6. |
- Eklöf, Karin, et al.
(författare)
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Effekter av dikesrensning och våtmarksrestaurering på kvicksilver i vatten
- 2024
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Dikning av våtmark i svenska skogsområden under de senaste 120 åren har bidragit till ökad skogsproduktion men också orsakat genomgripande förändringar i skogarnas omsättning och lagring av vatten. Med tiden ansamlas sediment och vegetation i dikena, och dikesrensning kan behövas för att upprätthålla en hög skogsproduktion. Åtgärden kan dock påverka markegenskaper och -processer, vattenkvalitet och kolbalans. Ökad avrinning av total-kvicksilver (THg) och biotillgängligt metylkvicksilver (MeHg) har pekats ut som en potentiell risk vid dikesrensning. En alternativ åtgärd för dikade områden är restaurering till mer naturliga våtmarksförhållanden. Från politiskt håll uppmuntras restaurering som en åtgärd mot översvämningar och torka, för att minska emission av växthusgaser och för att öka den biologiska mångfalden. Åtgärden, som i regel blötlägger torv, riskerar dock att öka den mikrobiella bildningen av MeHg. Mer ytliga flödesvägar i restaurerade våtmarker riskerar också att mobilisera kvicksilver (Hg) från markens övre lager. I ett experimentellt fältförsök med sex avrinningsområden och tre referensområden studerades effekter på THg och MeHg i dikesvatten, efter både dikesrensning och våtmarksrestaurering, upp till ca två år efter åtgärderna. Fältförsöket kompletterades med provtagning av THg och MeHg i rensade (n = 25; 1–4 år efter rensning) och orensade (n = 25) diken i en rumslig studie med en stor geografisk spridning. Dessutom utvärderades 15 sedimentationsdammar belägna nedströms dikesrensade områden med avseende på bildning av MeHg i dammarna. Slutligen i en litteraturstudie sammanställdes effekter av dikesrensning på skogsproduktion med syftet att väga dessa effekter mot effekter på THg och MeHg i vatten. Resultaten visar att dikesrensning inte ledde till några ökningar av THg och MeHg i avrinnande vatten. Tvärt om, minskade koncentrationen och exporten av THg och MeHg i vissa områden. Dikesrensning ledde inte heller till några tydliga ökningar av partikelbundet THg och MeHg. Risken att dikesrensning i avverkade områden kan leda till ökad mobilisering av MeHg från de avverkade områdena kunde inte påvisas genom hydrologisk modellering. Sedimentationsdammar, merparten relativt små, nedströms dikesrensade områden orsakade inga förhöjda halter av MeHg, varken i bottensediment eller i dikesvatten nedströms dammarna. Våtmarksrestaurering ledde till ökade koncentration och export av THg och MeHg i ett av de två restaurerade områdena. Sammanfattningsvis visar studierna i projektet att dikesrensning kan minska, och våtmarksrestaurering kan öka THg och MeHg i avrinnande vatten, men att det kan variera mellan områden. Det gäller åtminstone under de första åren efter åtgärderna som studierna avser. Dessa förändringar drivs troligtvis av en kombination av i) ändrade flödesvägar för vattnet och ii) förändrade redox-förhållanden i marken då grundvattenytan sänks (vid dikesrensning) respektive höjs (vid våtmarksrestaurering).
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| 7. |
- Hasselquist, Eliza Maher, et al.
(författare)
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Contrasting effects of geomorphic complexity on diversity of three aquatic organism groups after stream restoration
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- 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.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.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.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.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.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.
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| 8. |
- Hasselquist, Eliza Maher, et al.
(författare)
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Contrasting Responses among Aquatic Organism Groups to Changes in Geomorphic Complexity Along a Gradient of Stream Habitat Restoration : Implications for Restoration Planning and Assessment
- 2018
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Ingår i: Water. - : MDPI. - 2073-4441. ; 10:10
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Tidskriftsartikel (refereegranskat)abstract
- Many stream restoration projects aim to increase geomorphic complexity, assuming that this increases habitat heterogeneity and, thus, biodiversity. However, empirical data supporting these linkages remain scant. Previous assessments of stream restoration suffer from incomplete quantification of habitat complexity, or a narrow focus on only one organism group and/or one restoration measure, limiting learning. Based on a comprehensive quantification of geomorphic complexity in 20 stream reaches in northern Sweden, ranging from streams channelized for timber floating to restored and reference reaches, we investigated responses of macroinvertebrates, diatoms, and macrophytes to multiple geomorphic metrics. Sediment size heterogeneity, which was generally improved in restored sites, favored macroinvertebrate and diatom diversity and macroinvertebrate abundance. In contrast, macrophyte diversity responded to increased variation along the longitudinal stream profile (e.g., step-pools), which was not consistently improved by the restoration. Our analyses highlight the value of learning across multiple restoration projects, both in identifying which aspects of restoration have succeeded, and pinpointing other measures that might be targeted during adaptive management or future restoration. Given our results, a combination of restoration measures targeting not only sediment size heterogeneity, but also features such as step-pools and instream wood, is most likely to benefit benthic biota in streams.
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| 9. |
- Hasselquist, Eliza Maher, 1977-
(författare)
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Gradients of time and complexity : understanding how riparian and instream ecosystems recover after stream restoration
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 10. |
- Hasselquist, Eliza Maher, et al.
(författare)
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Microsite differentiation among conifer species during seedling establishment at alpine treeline
- 2006
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Ingår i: Ecoscience. - : Presses de L`Université Laval. - 1195-6860. ; 13:3, s. 334-341
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Tidskriftsartikel (refereegranskat)abstract
- Tree establishment is a potentially important factor affecting tree populations in alpine-treeline ecotones. Patterns of seedling establishment of Abies lasiocarpa, Pinus albicaulis, and Picea engelmannii were evaluated relative to neighbouring trees and herbs over two years and three treelines of the Rocky Mountains, USA. The greatest mortality rates were observed in seedlings that had just emerged from seed and were in their first year of growth and in seedlings that had the least amount of cover provided by trees or other landscape features that block exposure to the sky. Although herb cover promoted survivorship in microsites that were not near trees, no seedlings were detected at or above the upper limit of the treeline ecotone. Microsite tree cover was greatest for A. lasiocarpa and least for P. albicaulis seedlings, which matches predictions based on their relative photosynthetic tolerances to the bright sunlight and frequent frost that occur in exposed microsites. Interspecific differences in seedling requirements for neighbouring plant cover likely contribute to the apparent coexistence and possible interdependency of these conifers along a continuum of colonization and succession within treelines.
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