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| 2. |
- Dynesius, Mats, et al.
(författare)
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High resilience of bryophyte assemblages in streamside compared to upland forests
- 2009
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Ingår i: Ecology. - : Ecological Society of America. - 0012-9658 .- 1939-9170. ; 90:4, s. 1042-1054
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Tidskriftsartikel (refereegranskat)abstract
- Landscape heterogeneity causes spatial variation in disturbance regimes and resilience. We asked whether the resilience of bryophyte (liverwort and moss) assemblages to clear-cutting differs between streamside and upland boreal forests in northern Sweden. We hypothesized that bryophyte survival and recolonization rates are higher in streamside areas, thus raising resilience. Conversely, disturbance-intolerant but also invading species should be more frequent here, potentially reducing resilience. In each of 18 sites, we compared two 0.1-ha plots (one streamside and one upland) located in old forest that had never been clear-cut with two matching plots in young stands established after clear-cutting of old forests 30-50 years earlier. We used the magnitude of the difference in assemblages between old and young stands as a measure of change and, therefore, resilience (large difference implying low resilience). Species assemblages were more resilient in streamside than in upland forests. Species composition changed significantly in upland but not in streamside forests. Reductions in species richness were more pronounced in upland forests for total richness and for eight subgroups of species. Two results indicated lower survival/recolonization in upland forests: (1) species had a stronger association with old stands in upland areas, and (2) among species present in both the old streamside and old upland plot in a site, fewer appeared in the young upland than in the corresponding streamside plot. Simultaneously, a higher proportion of species invaded streamside areas; 40 of the 262 species encountered in streamside forests increased their occupancy by two or more sites compared to only two of 134 species in uplands. We suggest that in boreal forests spatial variation in resilience of assemblages of forest organisms intolerant of canopy removal is related to factors governed mainly by topography. More generally, we argue that landscape-scale variation in resilience of assemblages is influenced by spatial variation in (1) stress and resource availability, (2) number of disturbance intolerant species, and (3) magnitude of environmental changes brought about by a disturbance with a specific intensity. We also suggest that rapid recovery in the short term does not necessarily imply higher long-term ability to return to the pre-disturbance state.
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| 3. |
- Dynesius, Mats, et al.
(författare)
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Microclimatic buffering by logging residues and forest edges reduces clear-cutting impacts on forest bryophytes
- 2008
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Ingår i: Applied Vegetation Science. - : Wiley. - 1402-2001 .- 1654-109X. ; 11:3, s. 345-354
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Tidskriftsartikel (refereegranskat)abstract
- Question: The practice of extracting logging residues after clear-cutting for bioenergy purposes is spreading. Logging residues constitute a shelter in clear-cut areas and therefore concerns have been expressed that their removal could make the ground and its vegetation more exposed to extreme micro¬climatic conditions. We asked whether logging residues and forest edges can protect ground-dwelling forest bryophytes from fatal microclimate events following clear-cutting.Location: Boreal forests of central Sweden.Methods: Using transplants of eight forest floor bryophyte species we experimentally analysed the sheltering effect (less solar radiation and less wind) of logging residues and forest edges in seven clear-cut areas. Transplants were placed in two contrasting positions in each area; near a north-facing forest edge and in the centre of the clear-cut area. In each position, half of the transplants were covered by a layer of spruce branches and the other half was left uncovered. We estimated proportion of apparently living shoots (apparent vitality) and measured radial growth of transplants during one growing season.Results: Position in the clear-cut area, but not cover of spruce branches, clearly influenced radial growth. Vitality scores were higher among transplants covered with branches and the lowest apparent vitality was observed in uncovered transplants in the middle of clear-cut areas. The change in area of apparently liv¬ing shoots during the course of the experiment (growth minus mortality) was unaffected by branch cover close to the edge but positively affected in the centre of the clear-cut area. In general, the effect of branch cover on bryophytes was higher in the centre of clear-cut areas. Here, climatic measurements showed that branch cover buffers during periods of extreme microclimates.Conclusions: Extraction of logging residues after clear-felling may reduce the survival of some ground-dwelling forest organisms. The additional sheltering provided by branches was unimportant close to forest edges. We suggest smaller clear-cut areas, green-tree retention and other ways to make logged areas shadier and less windy to mitigate the reduced shelter caused by harvest of logging residues.
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| 4. |
- Hylander, Kristoffer, et al.
(författare)
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Substrate form determines the fate of bryophytes in clear-cuts and buffer strips along small boreal streams
- 2005
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Ingår i: Ecological Applications. - : Wiley. - 1051-0761. ; 15:2, s. 674-688
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Tidskriftsartikel (refereegranskat)abstract
- Studies on the effectiveness of forest buffer strips left along streams after logging have long overlooked the biota of the buffers themselves, despite their high species richness. We investigated mosses and liverworts (bryophytes), abundant and species-rich groups in boreal forests, before and 2.5 years after logging along 15 small streams. In each Site, two 1000-m(2) (20 X 50 m) plots along the stream were inventoried; one plot in an area subjected to clear-cutting, and another in a buffer strip (10 m wide on each side of the stream). Ten plots along small streams in forest reserves in the same region were used as references. We found that less than half as many bryophyte species per plot disappeared after logging in the buffer strips compared to the clearcuts. The changes in bryophyte cover and in species composition were smaller in the buffer strips, and the species that were negatively affected in the clearcuts were less affected in the buffer strips. However, there was a significant change in species composition in the buffer strips compared to the references. Substrate form. and taxonomic group were important factors in understanding this turnover. Many species growing on substrates with a convex form (e.g., logs, tree bases, and mesic ground) decreased or disappeared, while species on concave substrates were rather unaffected. This held for both mosses and liverworts, although liverworts were generally more sensitive than mosses. The difference in response of assemblages on convex vs. concave substrates makes changes in microclimate due to logging a likely explanation. The species in most need of protection (i.e., the red-listed species) were among the ones with strongest declines in the 20 m wide buffer strips. In order to function optimally for bryophyte conservation, forests along small streams need to be protected from high wind-throw frequency and strong edge effects. Increasing the width of buffer strips at sites with known or potential values (e.g., large amounts of woody debris or boulders) should be considered a better strategy than using narrow buffer strips with a fixed width.
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| 6. |
- Nilsson, Christer, et al.
(författare)
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Fragmentation and flow regulation of the world's large river systems
- 2005
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 308:5720, s. 405-408
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Tidskriftsartikel (refereegranskat)abstract
- A global overview of dam-based impacts on large river systemsshows that over half (172 out of 292) are affected by dams,including the eight most biogeographically diverse. Dam-impactedcatchments experience higher irrigation pressure and about 25times more economic activity per unit of water than do unaffectedcatchments. In view of projected changes in climate and waterresource use, these findings can be used to identify ecologicalrisks associated with further impacts on large river systems.
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| 7. |
- Pallon, Jan, et al.
(författare)
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Optimization of PIXE-sensitivity for detection of Ti in thin human skin sections
- 2005
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section B: Beam Interactions with Materials and Atoms. - : Elsevier BV. - 0168-583X. ; 231:1-4, s. 274-279
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Tidskriftsartikel (refereegranskat)abstract
- Modern sunscreens contain particles like TiO2 having sizes of 25-70 nm and acting as a reflecting substance. For cosmetic reasons the particle size is minimized. Questions have been raised to what degree these nano particles penetrate the skin barrier, and how they do affect the human. The EU funded project "Quality of skin as a barrier to ultra-fine particles" - NANODERM has started with the purpose to evaluate the possible risks of TiO2 penetration into vital skin layers. The purpose of the work presented here was to find the optimal conditions for micro-PIXE analysis of Ti in thin skin sections. In the skin region where Ti is expected to be found, the naturally occurring major elements phosphorus, chlorine, sulphur and potassium have steep gradients and thus influence the X-ray background in a non-predictable manner. Based on experimental studies of Ti-exposed human skin sections using proton energies ranging from 1.8-2.55 MeV, the corresponding PIXE detection limits for Ti were calculated. The energy that was found to be the most favourable, 1.9 MeV, was then selected for future studies.
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| 8. |
- Zinko, Ursula, et al.
(författare)
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Plant species number predicted by a topography based groundwater-flow index
- 2005
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Ingår i: Ecosystems (New York. Print). - New York, N.Y. : Springer. - 1432-9840 .- 1435-0629. ; 8:4, s. 430-441
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Tidskriftsartikel (refereegranskat)abstract
- The lack of a clear understanding of the factors governing the often-great variation of species numbers over entire landscapes confounds attempts to manage biodiversity. We hypothesized that in a topographically variable boreal forest landscape the availability of shallow groundwater is a major determinant of plant species numbers. We then developed a topographically derived hydrologic index based on multidirectional flow algorithms to account for the variation in availability of such groundwater in the landscape. We found a positive correlation between species numbers of vascular plants in plots ranging from 0.01 to 200 m2 and the hydrologic index. Generally, the landscape was relatively dry and species-poor, but interspersed patches with shallow groundwater had high species numbers and high proportions of regionally uncommon plant species. The index explained 30% of the variation in vascular plant number and correlated quite well (rs = 0.50) with groundwater level, but not as well with a community H+concentration value (instead of community pH, rs = −0.31), based on species composition. In addition, we found a very strong correlation between species number and the community H+ concentration value (rs−0.84). The hydrologic index is a useful tool for the identification of spatial of species number patterns across entire landscapes. This is an important step in identifying the areas most in need of protection or restoration, designing survey techniques, and understanding the fundamental processes that control the spatial distribution of species.
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| 9. |
- Zinko, Ursula, et al.
(författare)
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The role of soil pH in linking groundwater flow and plant species density in boreal forest landscapes
- 2006
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Ingår i: Ecography. - : Wiley. - 0906-7590 .- 1600-0587. ; 29:4, s. 515-524
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Tidskriftsartikel (refereegranskat)abstract
- In hilly boreal landscapes topography governs groundwater flow which strongly influences soil development, and thus vegetation composition. Soil pH is known to correlate well with plant species density and composition, but in boreal forests this relationship has been little studied. Previously, we successfully used a topography-based hydrological index, the topographical wetness index (TWI), as an approximation of the variation in groundwater flow to predict local plant species density in a boreal forest landscape. Data on species indicator values demonstrated that soil pH can be an important soil variable linking groundwater flow and plant species density. In the present paper we explore this link by relating measured soil pH to species numbers of vascular plants and TWI in 200-m2 plots within two boreal forest landscapes, differing in average soil pH. The two landscapes showed almost identical relationships between plant species number and soil pH, implying that this relationship is robust. The landscapes also had similar relationships between soil pH and TWI as well as between plant species number and TWI except at high TWI values, which indicate groundwater discharge areas. In these areas soil pH and plant species numbers were higher in the high-pH landscape at any given TWI value. We conclude that for predictive mapping of the species density of vascular plants in boreal forests, soil pH is a major factor. However, TWI as a measure of groundwater flow is a practical alternative predictor.
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