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  • 1.
    Backéus, Ingvar
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology. Växtekologi.
    Rehabilitation for whom? The case of Kondoa Irangi Hills, Tanzania2001In: Dryland Biodiversity, Vol. 4, p. 16-18Article in journal (Refereed)
  • 2.
    Backéus, Ingvar
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    The late Quaternary vegetation history of Sweden1999In: Swedish plant geography: dedicated to Eddy van der Maarel on his 65th birthday / [ed] Rydin, Håkan; Snoeijs, Pauli; Diekmann, Martin, Uppsala: Uppsala universitet, 1999, Vol. 4, p. 15-20Chapter in book (Refereed)
  • 3.
    Backéus, Ingvar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Tekle, Kebrom
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Experiences from a project on landscape ecology and ecological rehabilitation in Southern Wello, Ethiopia2001In: Sustainable development of dryland areas of East Africa: EC Directorate General XII. Proc. of the Int. Workshop, Addis Ababa 1998, European Commission, Directorate General XII. , 2001, p. 283-289Chapter in book (Refereed)
  • 4.
    Bengtsson, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Long-term demographic variation in range-margin populations of Gypsophila fastigiata2000In: Folia Geobotanica, ISSN 1211-9520, E-ISSN 1874-9348, Vol. 35, p. 143-160Article in journal (Refereed)
    Abstract [en]

    Disjunct populations of the perennial herb Gypsophilafastigiata L. (Caryophyllaceae) on the Balticisland of Oland were monitored during a thirteen-year study. The main objectives were to analyze the dynamicfeatures of G. fastigiata within and among sub-populations in shorter and longer time perspectives, and torelate this to habitat characteristics and patterns in local weather variation. The total number of individualsdecreased and the proportion of reproductive individuals increased throughout the study period. Recruitmentand mortality on a fine spatial scale (0.25 m 2) were negatively correlated to species richness and vegetationcover. Rapid changes in population sizes were observed during and after summers with low precipitation. Thehighest mortality rates were found in pre-reproductive stages whereas relatively many of the aduk plantssurvived the droughts. The long-term trend of population decline in G. fastigiata could be a result of changesin vegetation structure due to changing grazing regimes. It might also be an effect of more frequent dry summersduring the second half of the observation period or of an interaction between weather and changes in management.Another interpretation is that dynamic processes are taking place on a geographic scale not covered in thepresent study.

  • 5.
    Berg, H
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Redbo-Torstensson, P
    Offspring performance in Oxalis acetosella, a cleistogamous perennial herb2000In: Plant Biology, ISSN 1435-8603, E-ISSN 1438-8677, Vol. 2, no 6, p. 638-645Article in journal (Refereed)
    Abstract [en]

    Seed weight, seed germination, seedling survival, and juvenile/adult fitness in chasmogamously (CH) and cleistogamously (CL) derived offspring of Oxalis acetosella were compared during three growing seasons, to test hypotheses of fitness differences between the offspring types accounting for the maintenance of cleistogamy. In plots at three field sites, CH and CL seeds originating from all sites were sown to compare the performance of offspring growing in their habitat of origin and offspring growing in new habitats. Seeds were also sown in pots in a common garden, to test for effects of sibling competition. CL seeds had significantly lower germination than CH seeds in the field, possibly because of lower mean seed weight due to later flowering. Since the outcrossing rate in the CH flowers of O. acetosella is not known, it is uncertain whether the lower CL germination is a consequence of inbreeding depression. CH seeds had higher germination if sown at their home sites than at new sites, while for CL seeds this made no difference; this contradicts the local adaptation hypothesis for cleistogamy. No other fitness differences were found between the offspring types, and the findings did not support the sibling competition or local adaptation hypotheses. We suggest that the maintenance of the dimorphic reproductive system in O. acetosella is not explained by offspring characteristics, but rather by the two flowering phases complementing each other in maximizing annual seed production in the face of environmental variability. It is, therefore, important to include temporal and spatial variation in studies of reproductive strategies.

  • 6.
    Berg, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Differential seed dispersal in Oxalis acetosella, a cleistogamous perennial herb2000In: Acta Oecologica, ISSN 1146-609X, E-ISSN 1873-6238, Vol. 21, no 2, p. 109-118Article in journal (Refereed)
    Abstract [en]

    Explosive seed dispersal in the cleistogamous perennial forest herb Oxalis acetosella was studied during two growing seasons, to determine whether seeds derived from chasmogamous (CH) and cleistogamous (CL) flowers differ in dispersal distance. Seed dispersal distance, seed weight, and height of fruits were measured for both flower types, and the effects of phenology and year were also taken into account. The dispersal experiment was performed indoors, using plants transplanted from natural populations to pots. CL seeds were thrown significantly further than were CH seeds, though there was a considerable overlap in dispersal distances. There was also a significant positive relationship between seed weight and dispersal distance. No relationship was found between fruit height and dispersal distance. The results of this study contradict the common view that CL progeny should always be dispersed closer to the mother plant than CH progeny. The ecological implications of the dispersal difference are unclear, especially since it is uncertain whether CH seeds are generally outcrossed or not. Variation in dispersal distance in O. acetosella seems to be mainly dependent on a combination of reproductive mode and variation in seed weight.

  • 7.
    Busse, Svenja
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Benthic diatoms in the Gulf of Bothnia: Community analysis and diversity2002Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Benthic diatoms are valuable tools for biological monitoring and paleo-ecological reconstruction of past environmental conditions. This thesis aims at describing size-related properties of benthic diatoms and suggests that data assessment for community analysis can be improved by considering the importance of scale. It investigates which environmental factors structure epilithic diatom communities on the coast of the Gulf of Bothnia and identifies environmental factors correlated with phytobenthic biomass. It also contributes to the floristic knowledge of the Baltic Sea.

    Diatom species show large variation in size. The responses of large species (≥1000 μm3) in diatom communities to environmental factors are underestimated if solely measured as relative abundance, as is the common practice. However, relative abundance gives the best gradient resolution, as compared to surface area and biovolume, if species are counted separately in two biovolume classes. Small and large species in the same community may respond differently to the same environmental factors.

    To assess the principal environmental factors structuring diatom communities in the Gulf of Bothnia, 270 quantitative samples were collected from submerged stones. Sampling was carried out in spring in four areas of the Bothnian Bay, characterized by a stable north-south salinity gradient (0.4-3.3 psu), and in three areas of the Bothnian Sea which has a rather uniform salinity of ca. 5 psu. Canonical correspondence analysis (CCA) identified salinity and exposure to wave action as the principal factors structuring the diatom communities of the Bothnian Bay, whereas exposure to wave action was the principal factor in the Bothnian Sea. Measurements of relative ignition loss suggested that the cover of macroalgae, and thereby the higher abundance of epiphytic diatoms in the epilithic samples, was positively correlated with salinity in the Bothnian Bay and with water movement in the Bothnian Sea.

    Two new brackish water species are described, Navicula sjoersii S. Busse & Snoeijs and N. bossvikensis S. Busse & Snoeijs. The new species are compared with N. perminuta Grunow, a common brackish-water species.

  • 8.
    Dai, Xiaobing
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Impact of cattle dung deposition on the distribution pattern of plant species in an alvar limestone grassland2000In: Journal of Vegetation Science, ISSN 1100-9233, E-ISSN 1654-1103, Vol. 11, no 5, p. 715-724Article in journal (Refereed)
    Abstract [en]

    Seed banks in cattle dung, soil under cattle dung and soil under vegetation and growth response of plant species to the changes in soil nitrogen availability were studied in an alvar limestone grassland on Öland, Sweden, in order to analyse the impact of dung deposition and decomposition on the formation of patches of plant species. Results suggest that patches of four plant species could result from cattle dung deposition and decomposition. Impact of dung could proceed in three ways: (1) by changing the relative abundance of species in the soil seed bank under dung, and/or (2) by influencing the deposition of seeds in the dung, and/or (3) by intensifying the growth of some species through nutrient release. Species patches could result from one or more of these aspects. For instance, patches of Arenaria serpyllifolia may be induced by dung deposition because of the dominance of its seeds in dung, while the pattern of Cerastium semidecandrum and Festuca ovina may be due to the abundance of their seeds in the soil seed bank under dung and their positive growth response to increased nitrogen availability.

  • 9. Ecke, F
    et al.
    Rydin, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Succession on a land uplift coast in relation to plant strategy theory2000In: Annales Botanici Fennici, ISSN 0003-3847, E-ISSN 1797-2442, Vol. 37, no 3, p. 163-171Article in journal (Refereed)
    Abstract [en]

    Plant strategies under succession were evaluated for communities on rising seashores of the northern Gulf of Bothnia, Sweden, representing sites of primary succession. The succession could not be explained by Grime's CSR model. Early successional stages were neither characterized by high incidence of ruderals as proposed for secondary successions, nor by the dominance of stress tolerators, as proposed for primary successions. Short-lived species were almost totally absent. Instead, the shore habitat was characterized by species with an ability to tolerate and vegetatively recover from disturbance. The way in which different species experience one and the same form of stress or disturbance is an important reason why the classification on the basis of stress and disturbance seems to be insufficient to explain the course of this succession. Dominants of early and late successional stages differed with respect to root system, breeding system, leaf longevity and growth form (graminioid, herb).

  • 10. Eriksson, B.K
    et al.
    Johansson, G
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Effects of sedimentation on macroalgae: species-specific responses are related to reproductive traitsArticle in journal (Refereed)
  • 11. Eriksson, B.K
    et al.
    Johansson, G
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Snoeijs, P
    Long-term changes in the sublittoral zonation of brown algae in the southern Bothnian Sea1998In: European Journal of Phycology, Vol. 33, p. 241-249Article in journal (Refereed)
  • 12.
    Eriksson, Britas Klemens
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Long-term changes in macroalgal vegetation on the Swedish coast: An evaluation of eutrophication effects with special emphasis on increased organic sedimentation2002Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis I examine and evaluate the effects of a documented large-scale eutrophication on macroalgal vegetation on the Swedish coast. During the past century the load of nutrients has increased manifold in the Baltic Sea area, increasing primary production and organic sedimentation significantly. By re-investigating a unique reference material of macroalgal vegetation from the 1940-60s and by conducting new diving studies at the same sites, I showed that long-term trends in macroalgal community composition and species’ distributions are consistent with changes expected from an increased nutrient availability. In the Öregrund archipelago (northern Baltic Sea), I documented a declined depth distribution of the dominant canopy forming alga, Fucus vesiculosus, and an increased abundance of opportunistic ephemeral algae compared to 52-53 years ago. In the Gullmar Fjord area (Skagerrak), trends included increased abundances of functional groups with opportunistic algae, decreased abundances of large perennial algae and a general decline in the depth distribution of the vegetation compared to 36-57 years ago. Sediment removal experiments in the northern Baltic Sea confirmed the hypothesis that sedimentation influences macroalgal community composition. Species depending on short periods of reproduction were clearly favoured by sediment removal, especially F. vesiculosus that seemed limited in depth by the local sediment load. Species with long continuous periods of dispersal by spores and/or fragments (for example the ephemerals Cladophora glomerata, Ceramium tenuicorne and Enteromorpha spp.) were more tolerant to the natural sediment load. In general, sediment removal favoured macroalgal establishment and development, indicating that variation in the natural sediment load is an important constraint for sublittoral rocky-shore macroalgal community development. I conclude by suggesting that the documented long-term changes in macroalgal vegetation on the Swedish coast partly are explained by an increased organic sedimentation in these areas.

    List of papers
    1. Long-term changes in the sublittoral zonation of brown algae in the southern Bothnian Sea
    Open this publication in new window or tab >>Long-term changes in the sublittoral zonation of brown algae in the southern Bothnian Sea
    1998 In: European Journal of Phycology, Vol. 33, p. 241-249Article in journal (Refereed) Published
    Identifiers
    urn:nbn:se:uu:diva-90010 (URN)
    Available from: 2002-10-04 Created: 2002-10-04Bibliographically approved
    2. Long-term changes of macroalgal vegetation in the Skagerrak area
    Open this publication in new window or tab >>Long-term changes of macroalgal vegetation in the Skagerrak area
    1998 In: Hydrobiologia, Vol. 385, p. 121-138Article in journal (Refereed) Published
    Identifiers
    urn:nbn:se:uu:diva-90011 (URN)
    Available from: 2002-10-04 Created: 2002-10-04Bibliographically approved
    3. Long-term changes in the macroalgal vegetation of the inner Gullmar Fjord, Swedish Skagerrak coast
    Open this publication in new window or tab >>Long-term changes in the macroalgal vegetation of the inner Gullmar Fjord, Swedish Skagerrak coast
    2002 In: Journal of Phycology, Vol. 38, p. 284-296Article in journal (Refereed) Published
    Identifiers
    urn:nbn:se:uu:diva-90012 (URN)
    Available from: 2002-10-04 Created: 2002-10-04Bibliographically approved
    4. Sedimentation reduces recruitment success of Fucus vesiculosus in the Baltic Sea
    Open this publication in new window or tab >>Sedimentation reduces recruitment success of Fucus vesiculosus in the Baltic Sea
    Article in journal (Refereed) Submitted
    Identifiers
    urn:nbn:se:uu:diva-90013 (URN)
    Available from: 2002-10-04 Created: 2002-10-04Bibliographically approved
    5. Effects of sedimentation on macroalgae: species-specific responses are related to reproductive traits
    Open this publication in new window or tab >>Effects of sedimentation on macroalgae: species-specific responses are related to reproductive traits
    Article in journal (Refereed) Submitted
    Identifiers
    urn:nbn:se:uu:diva-90014 (URN)
    Available from: 2002-10-04 Created: 2002-10-04Bibliographically approved
  • 13.
    Eriksson, Britas Klemens
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Johansson, Gustav
    Effects of sedimentation on macroalgae: species-specific responses are related to reproductive traitsArticle in journal (Refereed)
  • 14.
    Eriksson, Britas Klemens
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Johansson, Gustav
    Sedimentation reduces recruitment success of Fucus vesiculosus in the Baltic SeaArticle in journal (Refereed)
  • 15.
    Eriksson, Britas Klemens
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Johansson, Gustav
    Snoeijs, Pauli
    Long-term changes in the macroalgal vegetation of the inner Gullmar Fjord, Swedish Skagerrak coast2002In: Journal of Phycology, Vol. 38, p. 284-296Article in journal (Refereed)
  • 16.
    Eriksson, Britas Klemens
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Johansson, Gustav
    Snoeijs, Pauli
    Long-term changes in the sublittoral zonation of brown algae in the southern Bothnian Sea1998In: European Journal of Phycology, Vol. 33, p. 241-249Article in journal (Refereed)
  • 17.
    Frost, Ingela
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Rydin, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Spatial pattern and size distribution of the animal-dispersed tree Quercus robur in two spruce-dominated forests2000In: Ecoscience, ISSN 1195-6860, Vol. 7, no 1, p. 38-44Article in journal (Refereed)
    Abstract [en]

    We investigated the degree to which the spatial distribution of oaks (Quercus robur L.) was related to habitat conditions, as reflected by vegetation type and structural features presumed to attract animal dispersers (trails, community borders). We hypothesized that the distribution pattern of oaks, with their potential to establish in many habitats, depends on the behaviour of the dispersing animals to a greater extent than micro-habitat conditions. One 100 m x 100 m plot was surveyed in each of two coniferous forests in east-central Sweden. No adult oak trees grew in the forests; all oaks were considered as dispersed into the plots by animals. We tested whether oak distribution was clumped with spatial autocorrelation analyses and whether oak distribution was related to vegetation type, species composition, tree cover, distance to nearest fertile oak tree, or distance to animal trails. Our study showed that oak trees were also spatially aggregated in a small-scale context. The spatial distribution of seedlings and older trees were associated with species richness and tree cover but not with any specific vegetation type, even though fewer oaks than expected grew in spruce forest habitats. Furthermore, we found that oak trees were associated with trails. There were differences in oak distribution between the two study sites in total number of oaks, the number of first-year seedlings, caches, and oak occurrence in relation to species richness and distance to nearest fertile oak. Seed-dispersing animals seem to be of importance for oak distribution even though animal activities seem to differ between sites.

  • 18.
    Gunnarsson, Urban
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Malmer, N.
    Rydin, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Dynamics or constancy in Sphagnum dominated mire ecosystems? A 40-year study2002In: Ecography, ISSN 0906-7590, E-ISSN 1600-0587, Vol. 25, no 6, p. 685-704Article in journal (Refereed)
    Abstract [en]

    Traditionally mire ecosystems (especially bogs) have been viewed as stable systems with slow changes in the vegetation over time. In this study the mire Akhultmyren, south-central Swedenw as re-investigatedin 1997 after 40 yr of continued natural development. The results show a high degree of dynamics in a Sphagnum dominated bog and fen. Altogether 97 vascular plant and bryophyte species were recorded in the two inventories of the bog and poor fen vegetation ,p H and electrical conductivity in the mire water were also surveyed. In 1997 we found 10 new species and that 8 species had disappeared since 1954 but the over-all mean number of species per plot (size 400 m2) had hardly changed. However, 21% of the species increased and 21% decreased significantly in frequency. Most of the species that decreased in frequency were low-grown vascular plants, most common in wet microhabitats. Vascular plant species that increased in frequency included trees (defined as > 1.3 m in height) and were generally taller than the unchanged or decreasing species. The frequency of dwarf shrubs and hummock bryophytes increased too. Areas with an initial pH of 4.5-5.0 showed the strongest decrease in pH, coinciding with an enlarged distribution of some Sphagnum species. The species diversity increased on the bog, but decreased in the wettest parts of the fen, where the pH also decreased. Species with unchanged or increasing frequency often showed high capacity to colonise new plots. On average the sum of gains and losses of species in the plots in 1997 was ca 50% of the species number in 1954. The vegetation changes indicate a drier mire surface and anincreaseda vailability of nitrogen. The increased tree cover may have triggered further changes in the plant cover.

  • 19.
    Gunnarsson, Urban
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology.
    Rydin, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Nitrogen fertilization reduces Sphagnum production in bog communities2000In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 147, no 3, p. 527-537Article in journal (Refereed)
    Abstract [en]

    The effects of increased nitrogen influx on Sphagnum growth and on interspecific competition between Sphagnum species were studied in a 3-yr experiment in mires situated in two areas with different rates of airborne N deposition. Sphagnum growth was recorded after various supplementary N influxes (0, 1, 3, 5 and 10 g m −2 yr−1) in hummocks and lawn communities. Sphagnum biomass production decreased with increasing N influx in both areas. After the first season at the low-deposition site, Sphagnum showed an increased growth in length with the intermediate N treatment, but in the second and third seasons the control treatment had the highest growth in length. Capitulum dry mass increased with increasing N influx. Sphagnum N concentration and N/P quotient were higher at the high- than at the low-deposition site. The low quotient at the low-deposition site, together with the initial growth increase with intermediate N supplements, indicates that growth was N-limited at this site, but our lowest N supplement was sufficient to reduce growth. The N treatments had no effect on interspecific competition between the Sphagnum species. This indicates that the species have similar responses to N. The species studied all occur naturally on ombrotrophic, N-poor sites and show low tolerances to increased N influx. Reduced Sphagnum production may affect the carbon balance, changing the mires from C sinks to sources.

  • 20.
    Gunnarsson, Urban
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology.
    Rydin, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Sjörs, Hugo
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Diversity and pH changes after 50 years on the boreal mire Skattlosbergs Stormosse, Central Sweden2000In: Journal of Vegetation Science, ISSN 1100-9233, E-ISSN 1654-1103, Vol. 11, no 2, p. 277-286Article in journal (Refereed)
    Abstract [en]

    The Skattlosbergs Stormosse min was reinvestigated in 1995 after 50 years of natural development since the previous investigation. The undrained mire is situated in an area with low anthropogenic deposition. The distribution of 106 plant species was mapped in detail and pH was measured at 251 locations, providinga unique opportunity to quantify long-term mire dynamics. The resultss how decreased pH in the richer (high-pH) parts of the mire, but little or no change in the poor fen andombrotrophipca rts.1 4 species had disappeared while two news pecies were recorded. Most species had a more restricted distribution in the mire area in 1995 than in 1945. Species richness in lOm x 0Omp lots had decreased, especially in plots with higher pH. Most Sphagnum species had unchanged distributions over the mire, while 7 3 % of other bryophyt sepecies and 3 8% of vascular plant species had decreased by more than 20 % in plot frequency. There was a strong relationship between number of species and pH-value. The mean and standard eviation of pH in plots where the species occurred have both decreased since 1945. We interpret the changes in species richness in the richer fens to be mainly caused by acidification. This could partly be an autogenic succession, but may be enhanced by increased atmospheric deposition. The mire represents an almost untouched site which can act as a reference for mires in morepolluted areas.

  • 21. Hambäck, PA
    et al.
    Ågren, Jon
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Ericson, L
    Associational resistance: insect damage to purple loosestrife reduced in thickets of sweet gale2000In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 81, no 7, p. 1784-1794Article in journal (Refereed)
    Abstract [en]

    Associational resistance occurs when herbivore damage to a focal plant is reduced by the presence of other plant species. Neighboring plants can reduce herbivore damage (1) by their effects on the predator community, (2) by reducing the ability of herbivores to find their host plants, and (3) by reducing the time herbivores remain on their host plants. We examined how the presence of the aromatic low shrub Myrica gale and of predatory lady beetles affected herbivore damage and reproductive output in a population of the perennial herb Lythrum salicaria in northern Sweden. An observational study showed that L. salicaria growing in Myrica thickets were less damaged by herbivores, had a lower abundance of the monophagous, leaf-feeding, chrysomelid beetle Galerucella calmariensis, and had higher flower and seed production than L. salicaria outside Myrica thickets. To test whether these differences could be explained by (a) differences in some aspect of plant quality, or (b) differences in predator abundance, we placed potted L. salicaria within and outside Myrica thickets. To determine whether differences in the abundance of G. calmariensis were primarily the result of different rates of colonization or emigration, we marked adult beetles and placed them on a second set of potted plants in the two micro-habitats. The results show that differences in herbivore abundance, plant damage, and reproductive output between potted L. salicaria placed within and outside Myrica thickets were in the same direction and of the same magnitude as those observed for naturally occurring plants, indicating that the observed patterns were not an effect of differences in the chemical composition of the host plant. Moreover, we found no support for the hypothesis that a higher abundance of insect predators could explain the lower abundance of G. calmariensis on L. salicaria in Myrica thickets. On the contrary, lady beetles (Coccinella quinqempunctata and Coccinella septempunctata) were observed on a greater proportion of the plants placed outside the Myrica thickets. The monitoring of marked beetles indicated that differences in the abundance of G. calmariensis were the result of a markedly higher colonization rate and a somewhat lower emigration rate from L. salicaria outside Myrica thickets. Outside the Myrica thickets, the survival of G. calmariensis and the magnitude of herbivore damage were lower, and fruit and seed output were higher on plants with observations of lady beetles than on plants without lady beetles. The results indicate that the abundance of the specialist herbivore G. calmariensis, and the herbivore damage and reproductive output of its host plant, L. salicaria, are affected both by the presence of the nonhost Myrica and by predation from lady beetles. We suggest that the most likely mechanism causing decreased feeding on L. salicaria growing in Myrica thickets is that Myrica affects the ability of G. calmariensis to find its host, either through visual or olfactory interference.

  • 22.
    Johansson, G
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Eriksson, B.K
    Reattachment of macroalgal fragments enables population persistence in a suboptimal environmentArticle in journal (Refereed)
  • 23.
    Johansson, G
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Eriksson, B.K
    Pedersén, M
    Snoeijs, P
    Long-term changes of macroalgal vegetation in the Skagerrak area1998In: Hydrobiologia, Vol. 385, p. 121-138Article in journal (Refereed)
  • 24.
    Johansson, G
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Snoeijs, P
    Macroalgal photosynthetic responses to light in relation to thallus morphology and depth zonation2002In: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599, Vol. 244, p. 63-72Article in journal (Refereed)
    Abstract [en]

    We show how photosynthesis and UV sensitivity of algae are related to thallus morphology and depth distributions. This was studied for typical depth zonations of red and brown macroalgae in the Skagerrak (ca. 25 psu) and the Baltic Sea (6.5 psu). The algae were collected from the water surface down to 20.5 m of depth, whereby each species was sampled at its maximum abundance depth. Altogether, we measured photosynthetic and respiratory rates of 19 red and 13 brown algal species as O2 evolution at different light intensities. Photosynthesis versus irradiance curves (PI curves) showed that light-saturated net photosynthetic rates (Pmax), respiratory rates in darkness (Rd) and the initial slope (α) were strongly related to algal morphology with higher values for thinner species. The compensation irradiance (Ic) and saturating irradiance (Ik) were strongly related to water depth with lower values at greater depth. A novel approach to analyse PI data with principal component analysis (PCA) is presented. The method makes it possible to assign a quantitative morphological gradient to algal species based on photosynthetic properties. Such a gradient can be used in ecological studies as an alternative to more subjective discrete subdivisions into functional-form groups. Another type of PCA analysis, with the relative shapes of the PI curves as input data, summarises α and convexity but discards all interference of morphology. This results in a gradient of genuine physiological responses, which in our study was strongly correlated to maximum abundance depth. The UV sensitivity of the same 32 algal species was determined as the change in net O2 evolution after exposure to UV light and the recovery after this treatment. Deeper-growing algae were more sensitive to UV and species with thinner thalli recovered better after UV treatment in the Skagerrak. No such trends were observed for the algae in the northern Baltic Sea, which suggests that no real deep-water species occur here. This is further supported by the lack of a clear pattern in Ic and Ik values with depth for the algae in the Baltic Sea. Our results advocate that the reduced species diversity of the Baltic Sea is also coupled to a loss of functional groups in the sense of general photosynthetic performance and not only in the sense of pure morphology (loss of canopy-forming species).

  • 25.
    Johansson, G
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Sosa, P.A
    Snoeijs, P
    Genetic variability and level of differentiation in North Sea and Baltic Sea populations of the green alga Cladophora rupestrisArticle in journal (Refereed)
  • 26.
    Johansson, Gustav
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Factors Affecting the Distribution of Rocky-Shore Macroalgae on the Swedish Coast: Morphological, Physiological, Reproductive and Genetic Aspects2002Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The aim of this thesis was to examine factors affecting the distribution of macroalgal species both vertically (depth zonation) and geographically along the Baltic Sea salinity gradient. Interactions between the physical environment and basic biological traits of the algae are emphasised.

    Previously well-described macroalgal vegetation profiles were re-investigated. Long-term changes of the vegetation that can be coupled to an increased large-scale eutrophication were recorded in both the Baltic Sea and in the Skagerrak.

    Photosynthetic properties of macroalgae with different morphologies from typical depth zonations in the Skagerrak and the Baltic Sea were assessed. A novel method that makes it possible to classify macroalgal species along a morphological gradient based on photosynthetic properties is presented. Such a gradient can be used as an alternative to more discrete subdivisions into functional-form groups.

    Small-scale variation in the natural sediment load was shown to affect the composition of sublittoral rocky-shore macroalgal communities in a long-term field experiment. Generally, species with an extended reproductive period were more tolerant to sedimentation than species depending on short periods of spore release. The effect of the sediment treatments increased with depth.

    Field experiments in the Baltic Sea showed that fragments of Furcellarialumbricalis, Polysiphoniafucoides and Rhodomela confervoides are able to reattach to the substrate under field conditions. This enables persistence of populations since these species are practically sterile in the area. Field observations suggested that sessile animals can facilitate the fixation of algal fragments to the substrate.

    Genetic variation of the chlorophyte Cladophorarupestris was assessed by allozyme electrophoresis. Two genetically differentiated groups of populations were found, one Baltic Sea group and one North Sea group, with a distinct border in the southern Kattegat near the entrance to the Baltic Sea.

    List of papers
    1. Long-term changes in the sublittoral zonation of brown algae in the southern Bothnian Sea
    Open this publication in new window or tab >>Long-term changes in the sublittoral zonation of brown algae in the southern Bothnian Sea
    1998 In: European Journal of Phycology, Vol. 33, p. 241-249Article in journal (Refereed) Published
    Identifiers
    urn:nbn:se:uu:diva-90026 (URN)
    Available from: 2002-10-16 Created: 2002-10-16Bibliographically approved
    2. Long-term changes of macroalgal vegetation in the Skagerrak area
    Open this publication in new window or tab >>Long-term changes of macroalgal vegetation in the Skagerrak area
    1998 In: Hydrobiologia, Vol. 385, p. 121-138Article in journal (Refereed) Published
    Identifiers
    urn:nbn:se:uu:diva-90027 (URN)
    Available from: 2002-10-16 Created: 2002-10-16Bibliographically approved
    3. Macroalgal photosynthetic responses to light in relation to thallus morphology and depth zonation
    Open this publication in new window or tab >>Macroalgal photosynthetic responses to light in relation to thallus morphology and depth zonation
    2002 (English)In: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599, Vol. 244, p. 63-72Article in journal (Refereed) Published
    Abstract [en]

    We show how photosynthesis and UV sensitivity of algae are related to thallus morphology and depth distributions. This was studied for typical depth zonations of red and brown macroalgae in the Skagerrak (ca. 25 psu) and the Baltic Sea (6.5 psu). The algae were collected from the water surface down to 20.5 m of depth, whereby each species was sampled at its maximum abundance depth. Altogether, we measured photosynthetic and respiratory rates of 19 red and 13 brown algal species as O2 evolution at different light intensities. Photosynthesis versus irradiance curves (PI curves) showed that light-saturated net photosynthetic rates (Pmax), respiratory rates in darkness (Rd) and the initial slope (α) were strongly related to algal morphology with higher values for thinner species. The compensation irradiance (Ic) and saturating irradiance (Ik) were strongly related to water depth with lower values at greater depth. A novel approach to analyse PI data with principal component analysis (PCA) is presented. The method makes it possible to assign a quantitative morphological gradient to algal species based on photosynthetic properties. Such a gradient can be used in ecological studies as an alternative to more subjective discrete subdivisions into functional-form groups. Another type of PCA analysis, with the relative shapes of the PI curves as input data, summarises α and convexity but discards all interference of morphology. This results in a gradient of genuine physiological responses, which in our study was strongly correlated to maximum abundance depth. The UV sensitivity of the same 32 algal species was determined as the change in net O2 evolution after exposure to UV light and the recovery after this treatment. Deeper-growing algae were more sensitive to UV and species with thinner thalli recovered better after UV treatment in the Skagerrak. No such trends were observed for the algae in the northern Baltic Sea, which suggests that no real deep-water species occur here. This is further supported by the lack of a clear pattern in Ic and Ik values with depth for the algae in the Baltic Sea. Our results advocate that the reduced species diversity of the Baltic Sea is also coupled to a loss of functional groups in the sense of general photosynthetic performance and not only in the sense of pure morphology (loss of canopy-forming species).

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:uu:diva-90028 (URN)10.3354/meps244063 (DOI)
    Available from: 2002-10-16 Created: 2002-10-16 Last updated: 2017-12-14Bibliographically approved
    4. Effects of sedimentation on macroalgae: species-specific responses are related to reproductive traits
    Open this publication in new window or tab >>Effects of sedimentation on macroalgae: species-specific responses are related to reproductive traits
    Article in journal (Refereed) Submitted
    Identifiers
    urn:nbn:se:uu:diva-90029 (URN)
    Available from: 2002-10-16 Created: 2002-10-16Bibliographically approved
    5. Reattachment of macroalgal fragments enables population persistence in a suboptimal environment
    Open this publication in new window or tab >>Reattachment of macroalgal fragments enables population persistence in a suboptimal environment
    Article in journal (Refereed) Submitted
    Identifiers
    urn:nbn:se:uu:diva-90030 (URN)
    Available from: 2002-10-16 Created: 2002-10-16Bibliographically approved
    6. Genetic variability and level of differentiation in North Sea and Baltic Sea populations of the green alga Cladophora rupestris
    Open this publication in new window or tab >>Genetic variability and level of differentiation in North Sea and Baltic Sea populations of the green alga Cladophora rupestris
    Article in journal (Refereed) Submitted
    Identifiers
    urn:nbn:se:uu:diva-90031 (URN)
    Available from: 2002-10-16 Created: 2002-10-16Bibliographically approved
  • 27. Johansson, Gustav
    et al.
    Eriksson, Britas Klemens
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Pedersén, Marianne
    Snoeijs, Pauli
    Long-term changes of macroalgal vegetation in the Skagerrak area1998In: Hydrobiologia, Vol. 385, p. 121-138Article in journal (Refereed)
  • 28.
    Karlsson, Staffan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Eckstein, Lutz
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Weih, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Seasonal variation in 15-N natural abundance in subarctic plants of different life-forms2000In: Ecoscience, ISSN 1195-6860, Vol. 7, no 3, p. 365-369Article in journal (Refereed)
    Abstract [en]

    Plants can be expected to utilize different sources of nitrogen with different proportions of 15N at different times of the year. It was hypothesized that this may be reflected in a seasonal variation in the natural abundance of plant 15N, and that this pattern would vary among life-forms or species. To test this hypothesis, we studied the δ15N of eight different life-forms, selecting two representatives from each of four categories (woody deciduous, woody evergreen, graminoid, and cryptogam life-forms) at two locations in N. Sweden having different levels of precipitation, over a six-month period. Sampling was conducted in mid-winter, during snowmelt in May, after leaf emergence, in mid-August, and in September. The sampled species showed a highly significant seasonal pattern in the natural abundance of 15N. Within each species and site, the δ15N showed a difference on average of 3.6% (range from 2.1 to 5.3%) between minimum and maximum over the sampling period. In most cases δ15N was highest in mid-winter and lowest at the start of the growing season. Most species studied showed some common trends: (i) a decline in δ15N from mid-winter to pre-snowmelt (May); (ii) an increase from snowmelt to mid-June (mainly in plants sampled at one site); and (iii) a late-season decline in δ15N (August to September). Life-forms differed from each other in terms of their pattern of seasonal variation (harvest×life-form interaction) and between sites (site×life-form interaction). Thus, the outcome of comparisons of natural δ15N within and among species or sites depends on the time of year of sampling.

  • 29.
    Karlsson, Staffan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Schleicher, L
    Weih, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Seedling growth characteristics in three birches originating from different environments2000In: Ecoscience, ISSN 1195-6860, Vol. 7, no 1, p. 80-85Article in journal (Refereed)
    Abstract [en]

    The mountain birch (Betula pubescens ssp. czerepanovii) is considered to have originated through introgressive hybridization between B. pubescens and B. nana. It is intermediate between the putative parent species in terms of growth form and distribution. Consequently, we hypothesized that the mountain birch should have growth characteristics intermediate between the other two birch forms. This hypothesis was tested in an experiment using first-year seedlings. Only in three out of 15 characteristics studied were mountain birch characteristics clearly intermediate between B. pubescens and B. nana. In some cases the mountain birch was most similar to B. pubescens, while in others it resembled B. nana most closely. In certain other respects, B. pubescens and B. nana were more similar to each other than to mountain birch. In three measures of plant productivity, i.e. , relative growth rate, leaf area productivity, and plant nitrogen productivity, mountain birch showed the highest values. Cluster analyses of thirteen growth-related characteristics indicate that at a low fertilizer supply, B. pubescens and B. nana are more similar to each other than to the mountain birch. At a high fertilizer supply, mountain birch was more similar to B. pubescens. The results indicate that the growth characteristics of mountain birch seedlings are not inherited from its two ?parent? species in any simple way.

  • 30.
    Kebrom, Tekle
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Tesfaye, Bekele
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    The role of soil seed banks in the rehabilitation of degraded hill slopes in Southern Wello, Ethiopia2000In: Biotropica, ISSN 0006-3606, E-ISSN 1744-7429, Vol. 32, no 1, p. 23-32Article in journal (Refereed)
    Abstract [en]

    The species composition in the soil seed bank of degraded hillslopes in southern Wello, Ethiopia, was assessed using the seedling emergence method and compared with that of the standing vegetation. Surface soils were sampled at 0-to 5-cm depth from 49 plots of four physiognomic vegetation classes (hereafter vegetation classes): forests, shrublands, grasslands, and degraded sites. Soils were spread on sterile sand in a glasshouse and watered. Emerging seedlings were recorded for five months until no new seedlings emerged. A total of 3969 seedlings belonging to 71 species and 30 families germinated. The species composition of the seed bank was dominated by 53 herb species (75%) compared to 2 tree species which accounted for only 3 percent of the total number of species. Seedling density differed significantly among vegetation classes and ranged from 391 to 7807 seeds/m2. Mean species richness also differed significantly among the vegetation classes. Forty-two species were found to be common to the seed banks and the standing vegetation; however, correspondence between species numbers and composition of the seed banks and the standing vegetation was poor. Although most of the species that germinated in the seed banks were herbs and grasses, they can develop a vegetative cover and contribute to reduction of soil erosion. Regeneration of the tree species (some of which have seed viability up to four years) however, requires both time and the presence of mature individuals. Together with hillside closure and soil conservation measures (e.g., terracing), planting of native woody seedlings might help to expedite rehabilitation of degraded hillslopes devoid of trees and shrubs.

  • 31.
    Lyaruu, Herbert
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Backéus, Ingvar
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Soil seed bank and regeneration potential on eroded hill slopes in the Kondoa Irangi Hills, central Tanzania1999In: Applied Vegetation Science, ISSN 1402-2001, E-ISSN 1654-109X, Vol. 2, p. 209-214Article in journal (Refereed)
    Abstract [en]

    The soil seed bank of the severely eroded Kondoa Irangi Hills, Tanzania was studied in order to determine the seed density and composition and to establish the relationshiop between seed bank and standing vegetation. The area had not been grazed for 15 yr prior to the study. A recently grazed area was used for comparison. The seed bank density (at 0-5 cm depth) ranged from 344 to 9158 seeds/m2 in the dry season and 172 to 5107 seeds/m2 in the wet season. The seed bank was very heterogeneous, both spatially and temporally, and it showed significant variation in size and composition in both sampling periods. The species similarity between the seed bank and the above-ground vegetation in all plots was low (Sørensen's index = 0.00 – 0.44). The highest similarity was found in the recently grazed area. The seed bank was dominated by annuals and by early successional species. It is concluded that re-vegetating the hill slopes with woody vegetation by using the seed bank will be difficult because seeds of woody species were not found in the soil.

  • 32.
    Lyaruu, Herbert V. M.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Eliapenda, Shadrack
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Backéus, Ingvar
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Floristic, structural and seed bank diversity of a dry Afromontane forest at Mafai, central Tanzania2000In: Biodiversity and Conservation, ISSN 0960-3115, E-ISSN 1572-9710, Vol. 9, no 2, p. 241-263Article in journal (Refereed)
    Abstract [en]

    Flora, vegetation and seed bank were studied in a dry Afromontane forest in the Kondoa Irangi Hills, Tanzania with the objective to obtain information necessary for the promotion of conservation of this forest, which is rapidly degenerating due to human pressure. A preliminary checklist of 104 vascular plants occurring in the forest is provided. Based on 27 plots, each of 400 m2, the forest had the following ecological features: mean tree density 408 stems·ha−1; basal area 66.56 m2·ha−1; Shannon and Wiener diversity 2.6406; evenness 0.7585 and species richness 31 tree species per 1.08 ha. The seed bank was dominated by woody species, including mature forest tree species, and had several species in common with the standing vegetation. The forest contains species that are phytogeographically linked to Madagascan, Western and Southern African floras and also species disjunctly distributed in this forest and the Eastern Arc Mountains of Tanzania. Correspondence Analysis of tree species based on size classes showed that the timber species had declining populations, indicating the possibility of genetic erosion, while other species showed expanding or interrupted populations. Some DBH-size classes (e.g. 145.0– 189.9 cm) have disappeared from the forest, presumably due to their selective removal. We recommend detailed integrated floristic and faunistic studies of the forest, targeting the ecologically sensitive indicators of habitat change such as orchids, birds, reptiles and amphibians. Finally, a proposal to conserve the forest under a community-based forest conservation scheme is put forward.

  • 33. Mitchell, E. A. D
    et al.
    Buttler, A
    Grosvernier, P
    Rydin, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Siegenthaler, A.
    Gobat, J.-M.
    Contrasted effects of increased N and CO2 supply on two keystone species in peatland restoration and implications for global change2002In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 90, no 3, p. 529-533Article in journal (Refereed)
    Abstract [en]

    1  Significant areas of temperate bogs have been damaged by peat harvesting but may regenerate. These secondary mires, if well managed, may act as strong C sinks, regulate hydrology and buffer regional climate.2 The potential effects of bog regeneration will, however, depend on the successful establishment of the principal peat formers –Sphagnum mosses. The influence of hydrology and microclimate on Sphagnum re-growth is well studied but effects of elevated CO2 and N deposition are not known.3 We carried out two in-situ experiments in a cutover bog during three growing seasons in which we raised either CO2 (to 560 p.p.m.) or N (by adding NH4NO3, 3 g m−2 year−1). The two treatments had contrasting effects on competition between the initial coloniser Polytrichum strictum (favoured by high N) and the later coloniser Sphagnum fallax (favoured by high CO2).

    4  Such changes may have important consequences for bog regeneration and hence for carbon sequestration in cutover bogs, with potential feedback on regional hydrological and climatic processes.

  • 34. Mitchell, EAD
    et al.
    Buttler, A
    Grosvernier, P
    Rydin, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Albinsson, C
    Greenup, AL
    Heijmans, MMPD
    Hoosbek, MR
    Saarinen, T
    Relationships among testate amoebae (Protozoa), vegetation and water chemistry in five Sphagnum-dominated peatlands in Europe2000In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 145, no 1, p. 95-106Article in journal (Refereed)
    Abstract [en]

    To study the relationships between groups of organisms and the degree to which these relationships are consistent across major climatic gradients, we analysed the testate amoeba (Protozoa) communities, vegetation and water chemistry of one peatland in five countries: Switzerland, The Netherlands, Great Britain, Sweden and Finland, as part of the BERI (Bog Ecosystem Research Initiative) project. The relationships between the different data sets and subsets were investigated by means of detrended correspondence analysis, canonical correspondence analysis and Mantel permutation tests. The comparison of data on vegetation and testate amoebae showed that inter-site differences are more pronounced for the vegetation than for the testate amoebae species assemblage. Testate amoebae are a useful tool in multi-site studies and in environmental monitoring of peatlands because: (1) the number of species in Sphagnum-dominated peatlands is much higher than for mosses or vascular plants; (2) most peatland species are cosmopolitan in their distributions and therefore less affected than plants by biogeographical distribution patterns, thus differences in testate amoeba assemblages can be interpreted primarily in terms of ecology; (3) they are closely related to the ecological characteristics of the exact spot where they live, therefore they can be used to analyse small-scale gradients that play a major role in the functioning of peatland ecosystems. This study revealed the existence of small-scale vertical gradients within the vegetation and life-form niche separation in response to water chemistry. The deep-rooted plants such as Carex spp. and Eriophorum spp. are related to the chemistry of water sampled at or near the ground water table, whereas the mosses are not. Testate amoebae were shown to be ecologically more closely related to the chemistry of water sampled at or near the water table level and to the mosses than to the deep-rooted plants.

  • 35.
    Niva, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Life History Strategies in Linnaea borealis2003Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    About 70% of the plant species in the temperate zone are characterised by clonal growth, clonal species are also in majority in the Arctic and Subarctic where they affect the structure and composition of the vegetation. It is therefore of great importance to increase our knowledge about clonal plants and their growth and life histories. I have investigated how ramets of the stoloniferous plant Linnaea borealis are affected by the naturally occurring variation in environmental factors, such as: light, nutrient and water availability. Moreover, I examined the seed set and how supplemental hand pollination affects seed set in L. borealis, and also investigated the significance of the apical meristem for shoot population fitness. All studies were performed under field conditions in northern Sweden in a Subarctic environment and most are experimental.

    The results show that nutrient resorption from senescing leaves is not significantly affecting the growth and nutrient pools of the ramet. This implies that the growth of L. borealis ramets is not governed by micro-site resource availability. However, removal of light competition resulted in increased branching and number of lateral meristems produced, reduced growth, and decreased root:shoot ratio on a per ramet basis. Thus, ramets of L. borealis can efficiently exploit favourable light patches through plastic growth. Apical dominance exerts a significant effect on shoot population fitness and can be lost through rodent grazing. However, loss of apical dominance is dependent on the timing of grazing, if the apical meristem is removed early in the autumn the ramet can repair the loss until the next summer. If grazing occur during spring the dry weight and leaf area production is affected negatively. Seed production in L. borealis in the Abisko area varies between years and sites, and was unaffected by supplemental hand pollination treatment, implying that there is no lack of pollinator activity.

    List of papers
    1. Nutrient resorption from senescing leaves of the clonal plant Linnaea borealis in relation to reproductive state and resource availability
    Open this publication in new window or tab >>Nutrient resorption from senescing leaves of the clonal plant Linnaea borealis in relation to reproductive state and resource availability
    2003 In: Functional Ecology, Vol. 17, p. 438 - 444Article in journal (Refereed) Published
    Identifiers
    urn:nbn:se:uu:diva-90896 (URN)
    Available from: 2003-10-08 Created: 2003-10-08Bibliographically approved
    2. Effects of light and water availability on shoot dynamics of the stoloniferous Linnaea borealis
    Open this publication in new window or tab >>Effects of light and water availability on shoot dynamics of the stoloniferous Linnaea borealis
    2006 (English)In: Ecoscience, ISSN 1195-6860, Vol. 13, no 3, p. 318-323Article in journal (Refereed) Published
    Abstract [en]

    Many stoloniferous plant species have the ability to exploit resource-rich patches via plastic growth responses. The most efficient responses are shortened spacers and increased branching frequency. Here we experimentally investigate the ability of the stoloniferous plant Linnaea borealis to respond to patches of increased light intensity and reduced water availability in natural systems. The significance of contrasts between patches was also investigated. A three-level factorial design was used, with light, water availability, and site as the factors. Increased light intensity was achieved through mowing of the surrounding vegetation, and reduced water availability was achieved by placing wooden ledges under the stolons. The treatments were applied at three subarctic sites that differ in light conditions. Branching frequency, number of new meristems, average internode length, leaf area, and dry weight production were studied 14 months after the manipulations. Increased light intensity increased branching frequencies; the strongest effects were obtained at the site with a closed canopy. Average intemode length decreased 19% in response to increased light intensity. Root:shoot ratios decreased under increased light intensity and reduced water availability. A reduction in water availability alone did not affect any other investigated traits. We conclude that ramets of L. borealis are able to respond efficiently to small-scale variations in light intensity in natural systems, an ability of great importance for the performance of a prostrate species on shady forest floors.

    Keywords
    branching frequency, clonal plant, division of labour, foraging, patch quality
    National Category
    Biological Sciences
    Identifiers
    urn:nbn:se:uu:diva-90897 (URN)10.2980/i1195-6860-13-3-318.1 (DOI)000240960500004 ()
    Available from: 2003-10-08 Created: 2003-10-08 Last updated: 2017-12-14Bibliographically approved
    3. Shoot population dynamics of the stoloniferous Linnaea borealis: the significance of apical dominance
    Open this publication in new window or tab >>Shoot population dynamics of the stoloniferous Linnaea borealis: the significance of apical dominance
    Article in journal (Refereed) Submitted
    Identifiers
    urn:nbn:se:uu:diva-90898 (URN)
    Available from: 2003-10-08 Created: 2003-10-08Bibliographically approved
    4. Field experiments and observations concerning pollination and seed set in the clonal plant Linnaea borealis
    Open this publication in new window or tab >>Field experiments and observations concerning pollination and seed set in the clonal plant Linnaea borealis
    Manuscript (Other academic)
    Identifiers
    urn:nbn:se:uu:diva-90899 (URN)
    Available from: 2003-10-08 Created: 2003-10-08 Last updated: 2010-01-13Bibliographically approved
  • 36.
    Niva, Mikael
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Svensson, Brita M.
    Field experiments and observations concerning pollination and seed set in the clonal plant Linnaea borealisManuscript (Other academic)
  • 37.
    Niva, Mikael
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Svensson, Brita M.
    Shoot population dynamics of the stoloniferous Linnaea borealis: the significance of apical dominanceArticle in journal (Refereed)
  • 38.
    Niva, Mikael
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Svensson, Brita M.
    Karlsson, P. Staffan
    Nutrient resorption from senescing leaves of the clonal plant Linnaea borealis in relation to reproductive state and resource availability2003In: Functional Ecology, Vol. 17, p. 438 - 444Article in journal (Refereed)
  • 39. Nordin, A
    et al.
    Gunnarsson, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
    Amino acid accumulation and growth of Sphagnum under different levels of N deposition2000In: Ecoscience, ISSN 1195-6860, Vol. 7, no 4, p. 474-480Article in journal (Refereed)
    Abstract [en]

    Nitrogen (N) is a critical nutrient for Sphagnum mosses dominating mire ecosystems. We simulated N deposition by adding doses of NH4NO3 (0, 1, 3, 5 and 10 g m-2 yr-1) to two Swedish mires with different levels of background atmospheric N deposition, i.e., on Luttumyren in central Sweden 0.3-0.4 g N m-2 yr-1 and 0.7-1.1 g N m-2 yr-1 on Åkhultmyren in south Sweden. After two years of NH4NO3 additions, free amino acid concentrations of S. fuscum, S. magellanicum and S. rubellum from the two mires were analyzed and length growth of the mosses were measured. N additions increased amino acid concentrations in Sphagnum capitula, whereas it decreased Sphagnum length growth. In general, we found that when Sphagnum amino acid N concentrations exceeded 2.0 mg amino acid N g-1 dry mass, Sphagnum length growth was reduced. The decreased growth did not explain the variation in amino acid concentrations. Hence, increased Sphagnum N assimilation in N treated plots was most likely the factor causing tissue amino acid concentrations to increase. Significant differences among control plots between the two mires in Sphagnum total amino acid N concentrations did not occur. Total amino acid N concentrations of Sphagnum are thus not sensitive enough to reflect differences in N deposition rates when they are below 1.0 g m-2 yr-1.