| 1. |
- Bjelke, Ulf, et al.
(författare)
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Dieback of riparian alder caused by the Phytophthora alni complex: projected consequences for stream ecosystems
- 2016
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Ingår i: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 61, s. 565-579
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Forskningsöversikt (refereegranskat)abstract
- 1. Alder trees (Alnus spp.) are key nitrogen-fixing riparian species in the northern hemisphere. Inputs of nitrogen-rich leaf litter from alder into stream food webs can contribute significantly to nitrogen dynamics at local and landscape scales. Alder trees also provide habitats for terrestrial and aquatic organisms, and help stabilize river banks. 2. Recently, substantial declines in alder stands have occurred along streams in Europe, with damages observed in some parts of North America also. A major driver has been the invasive oomycete pathogen Phytophthora alni species complex, which can spread rapidly along stream networks. 3. This review synthesises information on the pathogen, processes of spread and infection, and its impacts on alder. We further address the potential ecosystem-level and management consequences of the decline of alder, and highlight research needs. 4. The alder dieback caused by P. alni is associated with reductions in shade and quality and quantity of leaf litter. A decline in the structural integrity of branches and roots further threatens bank stability. Stream banks dominated by other tree species or no trees at all will result in ecosystem-level changes both above and below the waterline. 5. The P. alni taxonomic complex includes different species with varying phenotypes. An improved understanding of their environmental tolerances, virulence and evolution, along with the processes regulating the spread and impacts of the pathogen, would assist in identification of the riparian and stream systems most vulnerable not only to invasion but also to the heaviest disease outbreaks and ecosystem-level impacts. 6. Within the P. alni complex, the highly pathogenic hybrid species P. x alni is favoured by mild winters and warm, but not excessively hot summer temperatures suggesting possible changes in distribution and level of impact under future global climate change.
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| 2. |
- Marbuah, George, et al.
(författare)
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Management of an Aquatic Invasive Weed with Uncertain Benefits and Damage Costs: The Case of Elodea Canadensis in Sweden
- 2019
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Ingår i: Water Economics and Policy. - 2382-624X .- 2382-6258. ; 5
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Tidskriftsartikel (refereegranskat)abstract
- The invasive aquatic weed Elodea canadensis (Mich) (Canadian pondweed) might provide benefits for nature and society when present in low abundance by contributing to nutrient regulation in lakes, particularly in more degraded environments where native species are unable to persist, but can cause damage when it forms extensive monocultures that choke lake littoral zones. Using a bioeconomic model developed to describe the population dynamics and uncertain spatial dispersion of the weed in Lake Lot in Sweden, we conducted an analysis of optimal management of the species as regards good and bad effects on society. A theoretical finding was that the level of control required depends on the benefits, damage costs, control costs, and uncertainty in dispersal of the weed. Lake Lot was chosen as the case because data on dynamics of the weed are available for this lake. The empirical results showed that the total net benefits were sensitive to inclusion of uncertainty and benefits of the species, but uncertainty had little effect on the level and timing of optimal control of the weed. However, the cost of no action with associated damage costs net of benefits of the weed proved to be considerably larger than the control costs, irrespective of inclusion of benefits and uncertainty.
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| 3. |
- Mckie, Brendan, et al.
(författare)
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A long-established invasive species alters the functioning of benthic biofilms in lakes
- 2023
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Ingår i: Freshwater Biology. - : John Wiley & Sons. - 0046-5070 .- 1365-2427. ; 68:12, s. 2068-2083
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Tidskriftsartikel (refereegranskat)abstract
- Invasive species often transform environmental conditions, exclude native species and alter ecosystem functioning, including key ecosystem processes underpinning nutrient and energy cycles. However, such impacts have been most documented during periods of invasive species dominance; their influences on functioning at lower relative abundances and after long-term establishment are less well-known. We investigated the effects of Elodea canadensis, a macrophyte native to North America with a long invasion history in many regions of the world, on the biomass accrual and metabolism of littoral zone biofilms growing on organic and inorganic substrates. We deployed nutrient diffusing substrates (NDS) in 18 replicate transects distributed across six lakes, comprising three invaded by E. canadensis and three uninvaded reference lakes. NDS were amended with nitrogen (N), phosphorus (P) or N + P together, or were deployed as unamended controls. E. canadensis relative abundance varied widely in the invaded transects, ranging from 13% to 93% of all macrophyte cover. On control substrates, algal biomass, quantified as Chlorophyll-a, and gross primary production (GPP) were 42% and 78% greater in the invaded compared to uninvaded lakes, respectively. Respiration rates, attributable to responses of both autotrophs and heterotrophs, were 45% greater on control substrates in invaded lakes. By contrast, N-limitation of both biofilm GPP and respiration was 25% and 35% greater in uninvaded compared with invaded lakes. There was no evidence for differences in nutrients, light availability or grazing pressure between invaded and uninvaded transects. Rather, the observed differences in metabolism suggest that the presence of E. canadensis increases availability of N at local scales, reducing N-limitation of biofilms and resulting in elevated rates of biofilm productivity. Our results demonstrate that invasive elodeids might have significant impacts on biofilms and processes associated with the cycling of nutrients, even when long-established and present at lower relative abundances.
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| 4. |
- Stephan, Jörg, et al.
(författare)
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Long-term deer exclosure alters soil properties, plant traits, understory plant community and insect herbivory, but not the functional relationships among them
- 2017
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Ingår i: Oecologia. - : Springer Science and Business Media LLC. - 0029-8549 .- 1432-1939. ; 184, s. 685-699
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Tidskriftsartikel (refereegranskat)abstract
- Evidence of the indirect effects of increasing global deer populations on other trophic levels is increasing. However, it remains unknown if excluding deer alters ecosystem functional relationships. We investigated how sika deer exclosure after 18 years changed soil conditions, the understory plant community, the traits of a dominant understory plant (Sasa palmata), herbivory by three insect-feeding guilds, and the functional relationships between these properties. Deer absence decreased understory plant diversity, but increased soil organic matter and ammonium concentrations. When deer were absent, S. palmata plants grew taller, with more, larger, and tougher leaves with higher polyphenol concentrations. Deer absence led to higher leaf area consumed by all insect guilds, but lower insect herbivory per plant due to increased resource abundance (i.e., a dilution effect). This indicates that deer presence strengthened insect herbivory per plant, while in deer absence plants compensated losses with growth. Because plant defenses increased in the absence of deer, higher insect abundances in deer absence may have outweighed lower consumption rates. A path model revealed that the functional relationships between the measured properties were similar between deer absence versus presence. Taken together, deer altered the abiotic and biotic environment, thereby changing insect herbivory, which might impact upon nutrient cycling and primary productivity. These results provide evidence that deer can alter interactions between trophic levels, but that functional relationships between certain ecosystem components may remain constant. These findings highlight the need to consider how increasing global deer populations can have cascade effects that might alter ecosystem dynamics.
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| 5. |
- Tattersdill, Kristina, et al.
(författare)
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A head start for an invasive species in a strongly seasonal environment? Growth of Elodea canadensis in boreal lakes
- 2017
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Ingår i: Aquatic Invasions. - : Regional Euro-Asian Biological Invasions Centre Oy (REABIC). - 1798-6540 .- 1818-5487. ; 12, s. 487-498
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Tidskriftsartikel (refereegranskat)abstract
- Many invasive species are expanding northwards into boreal and subarctic habitats, but research on the factors favoring their establishment in these regions remains limited. In three Swedish lakes we investigated the growth of Elodea canadensis Michx, a highly invasive macrophyte that is spreading northwards in Europe and Alaska. We conducted an in situ growth experiment, maintained for ten months, in concert with two field macrophyte surveys, undertaken in summer and spring. We further compared the performance of propagules established during summer with those established under less favorable conditions in late autumn. We found that E. canadensis grew throughout the autumn, followed by winter dieback, with regrowth occurring early in the spring when water temperatures remained under 5 degrees C. Elodea canadensis plants were frequently found in our spring field survey, soon after ice melt, when almost all other species were still dormant. In the growth experiment, growth of individual shoots was positively associated with key abiotic variables (especially alkalinity) and also with increasing cover of E. canadensis. The tendency of propagule shoots to fragment from the main stems was also positively associated with increasing E. canadensis length and ambient population cover. Although propagules established in November initially did worse the following spring than those established in August, by the start of the following summer both groups were growing equally well, and had converged in morphology. The growth of E. canadensis throughout autumn and its early re-growth in spring, the capacity of propagules established even in late autumn to regrow well the following year, and the apparently self-reinforcing effect of increasing local population size on shoot growth all have the potential to benefit E. canadensis as it spreads north into boreal and subarctic regions.
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