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  • 1.
    Bergstedt, Johan
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Boreal vegetation responses to forestry as reflected in field trial and survey data2004Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis had two objectives: the first objective was to evaluate the response of forest ground vegetation to selected forestry operations, i.e. cutting of different intensities and scarification; the second objective was to compare the use of survey data in vegetation research with that of more traditional research using field trials - i.e. can survey data be used and produce results that comply with those emerging from field trials? Here, the results from an analysis of survey data has been compared with results emerging from a field trial.

    Survey data was analysed from the National Forest Inventory (NFI), using 789 sample plots in central and northern Sweden visited twice at an interval of 10-11 years, 294 of which had been subjected to logging between inventories. This was compared with a field trial in central Sweden: a complete block design with four replicates - three treatments and conventional harvesting as the control.

    The cutting intensity was found to have an impact on the ground-layer flora, the change being mostly differences in abundance rather than change in species richness. Those increasing were early successional species, i.e. crustose lichens, Deschampsia flexuosa. In contrast, Vaccinium myrtillus was decreasing substantially in response to increased cutting intensity. A number of species appeared to be indifferent to cutting, i.e. Vaccinium vitisidaea, Trientalis europaea.

    Scarification had a different impact on the flora than cutting: only Polytrichum spp. increased substantially, while many decreased.

    For those effects that were possible to compare in both studies, the results from survey data comply with those from the field trial, indicating that survey data is possible to use in forest vegetation research.

  • 2.
    Bergstedt, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Ecology . Linköping University, The Institute of Technology.
    Boreal vegetation responses to forestry as reflected in field trial and survey data and the quality of cover estimates and presence/absence in vegetation inventory2008Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis has two main focuses; first, the response of forest ground layer flora on forestry, mainly harvesting and secondly, the quality of the vegetation assessment methods, cover estimates by eye and presence/absence data.

    The effect of harvesting intensity was evaluated with survey data from permanent plots as well as vegetation data from a field trial fourteen years after harvesting. Both data sets confirmed that response of ground layer flora increased with increasing logging intensity. Thereby, indicating that survey data is possible to use in research. From the survey data set, existence of a time lag was evident for several species and also a threshold level was evident in cutting intensity needed to affect a number of species. Logging had a modest, but significant positive effect on the change in species number per plot. Species turnover was influenced by the proportion of Picea abies in the tree canopy; site productivity; and logging intensity. In the field trial scarification had a strong effect that was different from the one created by cutting.

    In plant ecology cover estimate by eye and presence/absence recording are the two most frequent methods used. The methods were evaluated with survey data and a field trial.

    In the first data set vegetation was recorded independently by two observers in 342 permanent 100-m2 plots. Overall, one third of each occurrence was missed by one of the two observers, but with large differences among species. Species occurring at low abundance tended to be frequently overlooked. Observer-explained variance in cover estimates was <10% in 15 of 17 species.

    In the second data set, 10 observers independently estimated cover in sixteen 100-m2 plots in two different vegetation types. The bias connected to observer varied substantially between species. The estimates of missing field and bottom layer had the highest bias, indicating that missing layers are problematic to use in analysis of change. Experience had a surprisingly small impact on the bias connected to observer. Analyses revealed that for the statistical power, cover estimates by eye carries a higher information value than do presence/absence data when distinguishing between vegetation types, differences between observers is negligible, and using more than one observer had little effect.

    List of papers
    1. The impact of logging intensity on field-layer vegetation in Swedish boreal forests
    Open this publication in new window or tab >>The impact of logging intensity on field-layer vegetation in Swedish boreal forests
    2001 (English)In: Forest Ecology and Management, ISSN 0378-1127, Vol. 154, no 1-2, p. 105-115Article in journal (Refereed) Published
    Abstract [en]

    The relationship between logging intensity and changes in ground cover vegetation was studied in 16 species and groups of species recorded at 10- or 11-year intervals in mature conifer-dominated forests. The 789 plots located in northern and central Sweden had been surveyed by the National Forest Inventory and the National Survey of Forest Soil and Vegetation. Thirty-seven percent of the plots had been subjected to a thinning or clear-cutting between the inventories. A principal components analysis showed that, of the variables considered, logging intensity had the highest explanatory power regarding change in ground cover vegetation between the inventories (the other variables were sum of temperatures, age of stand, timber volume, percentage Pinus sylvestris and site productivity). A multivariate direct gradient analysis technique (Redundancy analysis) showed that the logging intensity significantly affected the change in cover. This analysis also ranked the species in their responsiveness to logging. Epilobium angustifolium, narrow-leaved grasses and broad-leaved grasses, increased most with logging intensity. The response was not linear and only detectable at high logging intensities (>80%). In contrast, Vaccinium myrtillus seemed to decrease linearly with increased logging intensity. There was several years time-lag in the response to logging of E. angustifolium, V. myrtillus and narrow-leaved grasses. Several species and groups of species seemed unaffected by the logging. In sample plots unaffected by logging the cover of most species decreased.

    Keywords
    Clear cut, Community, Cutting, Multivariate analysis, Sweden, Thinning
    Identifiers
    urn:nbn:se:liu:diva-13278 (URN)10.1016/S0378-1127(00)00642-3 (DOI)
    Available from: 2008-05-07 Created: 2008-05-07 Last updated: 2018-07-03
    2. Composition of vegetation after a modified harvesting and propagation method compared with conventional clear-cutting, scarification and planting: evaluation 14 years after logging
    Open this publication in new window or tab >>Composition of vegetation after a modified harvesting and propagation method compared with conventional clear-cutting, scarification and planting: evaluation 14 years after logging
    2008 (English)In: Applied Vegetation Science, ISSN 1402-2001, Vol. 11, no 2, p. 159-168Article in journal (Refereed) Published
    Abstract [en]

    Question: How does the vegetation of boreal forests respond to harvesting and scarification?

    Location: 650 m a.s.l., central Sweden (61°38' N).

    Methods: The response of boreal forest vegetation to cutting and scarification was studied in a field trial, which consisted of three treatments plus conventional harvesting as a control in a complete block design with four replicates. The cutting was done 14 years prior to vegetation inventory and scarification and planting were conducted the first or second years after cutting.

    Results: The species most abundant at higher cutting intensities were crustose lichens, Cladonia spp., Cladina arbuscula, Polytrichum spp. and pioneer mosses, the grass Deschampsia flexuosa, and the tree Betula pubescens, A few species had substantially lower abundance in treatments with higher cutting intensity, notably Hylocomium splendens and Vaccinium myrtillus. Scarification had a strong effect that was different from the one created by cutting. In scarification treatments, Polytrichum spp. were the only species with high abundance; most species had low abundance, i.e. Barbilophozia lycopodioides, Vaccinium vitis-idaea, Pleurozium schreberi, Carex globularis, Empetrum nigrum, Cladina arbuscula, Sphagnum spp.

    Conclusions: Our results elaborate on the details of the well-known effect of cutting on ground-layer flora, and also give support for the profound and long-lasting effect that soil scarification has on forest vegetation.

    Keywords
    Boreal forest, Cutting intensity, Field trial, Forest understorey, Logging, Propagation, Sweden
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-13279 (URN)10.3170/2007-7-18343 (DOI)
    Available from: 2008-05-07 Created: 2008-05-07 Last updated: 2014-10-08
    3. Turnover of ground layer species in Swedish boreal forests and its response to logging
    Open this publication in new window or tab >>Turnover of ground layer species in Swedish boreal forests and its response to logging
    Manuscript (Other academic)
    Identifiers
    urn:nbn:se:liu:diva-13280 (URN)
    Available from: 2008-05-07 Created: 2008-05-07 Last updated: 2010-01-13
    4. Systematic and random variation in vegetation monitoring data
    Open this publication in new window or tab >>Systematic and random variation in vegetation monitoring data
    Show others...
    2008 (English)In: Journal of Vegetation Science, ISSN 1100-9233, E-ISSN 1654-1103, Vol. 19, p. 633-644Article in journal (Refereed) Published
    Abstract [en]

    Question: Detecting species presence in vegetation and making visual assessment of abundances involve a certain amount of skill, and therefore subjectivity. We evaluated the magnitude of the error in data, and its consequences for evaluating temporal trends.

    Location: Swedish forest vegetation.

    Methods: Vegetation data were collected independently by two observers in 342 permanent 100-m2 plots in mature boreal forests. Each plot was visited by one observer from a group of 36 and one of two quality assessment observers. The cover class of 29 taxa was recorded, and presence/absence for an additional 50.

    Results: Overall, one third of each occurrence was missed by one of the two observers, but with large differences among species. There were more missed occurrences at low abundances. Species occurring at low abundance when present tended to be frequently overlooked. Variance component analyses indicated that cover data on 5 of 17 species had a significant observer bias. Observer-explained variance was < 10% in 15 of 17 species.

    Conclusion: The substantial number of missed occurrences suggests poor power in detecting changes based on presence/absence data. The magnitude of observer bias in cover estimates was relatively small, compared with random error, and therefore potentially analytically tractable. Data in this monitoring system could be improved by a more structured working model during field work.

    Place, publisher, year, edition, pages
    Institutionen för fysik, kemi och biologi, 2008
    Keywords
    Forest, Observer error, Permanent plot, Statistical power, Sweden
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-11872 (URN)10.3170/2008-8-18423 (DOI)
    Note
    Original publication: Milberg, P., Bergstedt, J., Fridman, J., Odell, G & Westerberg, L., Systematic and random variation in vegetation monitoring data, 2008, Journal of Vegetation Science, (19), 633-644. http://dx.doi.org/10.3170/2008-8-18423. Copyright: Opulus Press, http://www.opuluspress.se/index.phpAvailable from: 2008-05-22 Created: 2008-05-22 Last updated: 2017-12-13
    5. In the eye of the beholder: bias and stochastic variation in cover estimates
    Open this publication in new window or tab >>In the eye of the beholder: bias and stochastic variation in cover estimates
    Manuscript (Other academic)
    Identifiers
    urn:nbn:se:liu:diva-13282 (URN)
    Available from: 2008-05-07 Created: 2008-05-07 Last updated: 2010-01-13
  • 3.
    Bergstedt, Johan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Ecology . Linköping University, The Institute of Technology.
    Hagner, M.
    Milberg, P.
    Linköping University, Department of Physics, Chemistry and Biology, Ecology . Linköping University, The Institute of Technology.
    Composition of vegetation after a modified harvesting and propagation method compared with conventional clear-cutting, scarification and planting: evaluation 14 years after logging2008In: Applied Vegetation Science, ISSN 1402-2001, Vol. 11, no 2, p. 159-168Article in journal (Refereed)
    Abstract [en]

    Question: How does the vegetation of boreal forests respond to harvesting and scarification?

    Location: 650 m a.s.l., central Sweden (61°38' N).

    Methods: The response of boreal forest vegetation to cutting and scarification was studied in a field trial, which consisted of three treatments plus conventional harvesting as a control in a complete block design with four replicates. The cutting was done 14 years prior to vegetation inventory and scarification and planting were conducted the first or second years after cutting.

    Results: The species most abundant at higher cutting intensities were crustose lichens, Cladonia spp., Cladina arbuscula, Polytrichum spp. and pioneer mosses, the grass Deschampsia flexuosa, and the tree Betula pubescens, A few species had substantially lower abundance in treatments with higher cutting intensity, notably Hylocomium splendens and Vaccinium myrtillus. Scarification had a strong effect that was different from the one created by cutting. In scarification treatments, Polytrichum spp. were the only species with high abundance; most species had low abundance, i.e. Barbilophozia lycopodioides, Vaccinium vitis-idaea, Pleurozium schreberi, Carex globularis, Empetrum nigrum, Cladina arbuscula, Sphagnum spp.

    Conclusions: Our results elaborate on the details of the well-known effect of cutting on ground-layer flora, and also give support for the profound and long-lasting effect that soil scarification has on forest vegetation.

  • 4.
    Bergstedt, Johan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Ecology . Linköping University, The Institute of Technology.
    Milberg, Per
    Linköping University, Department of Physics, Chemistry and Biology, Ecology . Linköping University, The Institute of Technology.
    The impact of logging intensity on field-layer vegetation in Swedish boreal forests2001In: Forest Ecology and Management, ISSN 0378-1127, Vol. 154, no 1-2, p. 105-115Article in journal (Refereed)
    Abstract [en]

    The relationship between logging intensity and changes in ground cover vegetation was studied in 16 species and groups of species recorded at 10- or 11-year intervals in mature conifer-dominated forests. The 789 plots located in northern and central Sweden had been surveyed by the National Forest Inventory and the National Survey of Forest Soil and Vegetation. Thirty-seven percent of the plots had been subjected to a thinning or clear-cutting between the inventories. A principal components analysis showed that, of the variables considered, logging intensity had the highest explanatory power regarding change in ground cover vegetation between the inventories (the other variables were sum of temperatures, age of stand, timber volume, percentage Pinus sylvestris and site productivity). A multivariate direct gradient analysis technique (Redundancy analysis) showed that the logging intensity significantly affected the change in cover. This analysis also ranked the species in their responsiveness to logging. Epilobium angustifolium, narrow-leaved grasses and broad-leaved grasses, increased most with logging intensity. The response was not linear and only detectable at high logging intensities (>80%). In contrast, Vaccinium myrtillus seemed to decrease linearly with increased logging intensity. There was several years time-lag in the response to logging of E. angustifolium, V. myrtillus and narrow-leaved grasses. Several species and groups of species seemed unaffected by the logging. In sample plots unaffected by logging the cover of most species decreased.

  • 5.
    Bergstedt, Johan
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Ecology .
    Milberg, Per
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Ecology .
    The impact of logging on species richness and turnover of field layer species in Swedish boreal forests2008In: Open environmental & biological monitoring journal, ISSN 1875-0400, Vol. 1, p. 48-57Article in journal (Refereed)
    Abstract [en]

     On two occasions, with a 10- or 11-year interval, species occurring in 650 plots (100 m2) in boreal production forests in Sweden were recorded within a monitoring program. During this interval, many of the plots had been subjected to varying degrees of timber extraction. The presence of 49 vascular plant species or species groups was recorded and we evaluated how species number varied over time. There was an overall increase in species number, probably partly reflecting changing attitudes and strategies for fieldwork. Logging had a modest, but significant positive effect on the change in species number per plot. When analysing individual species, three of 18 showed a differential response along the logging gradient: Linnea borealis was more likely to appear at low logging intensities while the opposite pattern was present in Epilobium angustifolium and Calluna vulgaris. A species turnover index was calculated per plot and used as the dependent variable in a multiple regression with six independent variables. Three of these contributed significantly to the model: turnover increased (i) with decreasing amounts of Pinus sylvestris in the tree canopy; (ii) with increasing site productivity; and (iii) with increasing logging intensity. Hence, greatest changes over time occurred in stands lacking P. sylvestris (consequently dominated by Picea abies) that occurred on fertile soil, and was amplified by logging.

  • 6.
    Bergstedt, Johan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Ecology . Linköping University, The Institute of Technology.
    Westerberg, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Ecology . Linköping University, The Institute of Technology.
    Milberg, Per
    Linköping University, Department of Physics, Chemistry and Biology, Ecology . Linköping University, The Institute of Technology.
    In the eye of the beholder: bias and stochastic variation in cover estimates2009In: PLANT ECOLOGY, ISSN 1385-0237, Vol. 204, no 2, p. 271-283Article in journal (Refereed)
    Abstract [en]

    Cover estimates by eye is a prevailing method to assess abundance. We examined cover estimates with regard to bias and random variation. Ten observers working with a national forest vegetation survey estimated sixteen 100 m(2)-plots, placed in two different vegetation types. These had similar species composition but were clearly distinguishable in the field. In species-wise analyses, observer bias varied greatly, with Dicranum spp., Vaccinium vitis-idaea and Vaccinium myrtillus having the largest bias. Experience had a surprisingly small impact on variation. Power analysis revealed only small differences between observers in the ability to distinguish the two vegetation types, and little value in averaging the assessments from two, three or four observers. Cover estimates did better than presence/absence data in separating the two vegetation types and multivariate analyses were more powerful than univariate ones.

  • 7.
    Callaghan, Terry V.
    et al.
    Royal Swedish Academy of Sciences, Stockholm, Sweden .
    Tweedie, Craig E.
    University of Texas at El Paso, USA .
    Åkerman, Jonas
    Royal Swedish Academy of Sciences, Stockholm, Sweden .
    Andrews, Christopher
    Centre for Ecology & Hydrology, Penicuik, UK .
    Bergstedt, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Ecology. Linköping University, The Institute of Technology.
    Butler, Malcolm G.
    North Dakota State University, Fargo, ND, USA .
    Christensen, Torben R.
    Lund University, Sweden.
    Cooley, Dorothy
    Department of Environment, Yukon Territorial Government, Dawson City, YT, Canada.
    Dahlberg, Ulrika
    Lantmäteriet, Gävle, Sweden .
    Danby, Ryan K.
    Queen’s University, Kingston, ON, Canada.
    Daniëls, Fred J. A.
    Institute of Biology and Biotechnology of Plants, Münster, Germany .
    de Molenaar, Johannes G.
    Maurik, The Netherlands .
    Dick, Jan
    Centre for Ecology & Hydrology, Penicuik, UK .
    Mortensen, Ebbe
    Alterra, Wageningen University, The Netherlands .
    Ebert-May, Diane
    Michigan State University, East Lansing, MI, USA .
    Emanuelsson, Urban
    Swedish Biodiversity Centre, Uppsala, Sweden.
    Eriksson, Håkan
    Umeå University, Sweden .
    Hedenås, Henrik
    Abisko Scientific Research Station, Sweden.
    Henry, Greg. H. R.
    University of Alberta, Edmonton, Canada .
    Hik, David S.
    University of Alberta, Edmonton, Canada .
    Hobbie, John E.
    Ecosystems Center, Marine Biological Laboratory, Woods Hole, MA, USA.
    Jantze, Elin J.
    Stockholm University, Sweden.
    Jaspers, Cornelia
    DTU Aqua, Charlottenlund, Denmark .
    Johansson, Cecilia
    Uppsala University, Sweden .
    Johansson, Margareta
    Lund University, Sweden.
    Johnson, David R.
    University of Texas at El Paso, USA .
    Johnstone, Jill F.
    University of Saskatchewan, Canada.
    Jonasson, Christer
    Abisko Scientific Research Station, Sweden.
    Kennedy,, Catherine
    Department of Environment, Yukon Territorial Government, Whitehorse, YT, Canada .
    Kenney, Alice J.
    University of British Columbia, Vancouver, Canada .
    Keuper, Frida
    VU University Amsterdam, The Netherlands.
    Koh, Saewan
    University of Alberta, Edmonton, Canada .
    Krebs, Charles J.
    University of British Columbia, Vancouver, Canada .
    Lantuit, Hugues
    Alfred Wegener Institute, Potsdam, Germany .
    Lara, Mark J.
    University of Texas at El Paso, USA .
    Lin, David
    University of Texas at El Paso, USA .
    Lougheed, Vanessa L.
    University of Texas at El Paso, USA .
    Madsen, Jesper
    Aarhus University, Roskilde, Denmark .
    Matveyeva, Nadya
    Department of Vegetation of the Far North, Komarov Botanical Institute, St. Petersburg, Russia .
    McEwen, Daniel C.
    Minnesota State University, Moorhead, MN, USA .
    Myers-Smith, Isla H.
    University of Alberta, Edmonton, Canada .
    Narozhniy, Yuriy K.
    Tomsk State University, Russia .
    Olsson, Håkan
    Swedish university of Agricultural Sciences, Umeå, Sweden .
    Pohjola, Veijo A.
    Uppsala University, Sweden .
    Price, Larry W.
    Portland State University, OR, USA .
    Rigét, Frank
    Minnesota State University, Moorhead, MN, USA .
    Rundqvist, Sara
    Umeå Univerity, Sweden .
    Sandström, Anneli
    Gävle, Sweden .
    Tamstorf, Mikkel
    Minnesota State University, Moorhead, MN, USA .
    Van Bogaert, Rik
    Flanders Research Foundation, Brussels, Belgium .
    Villarreal, Sandra
    University of Texas at El Paso, USA .
    Webber, Patrick J.
    Michigan State University, East Lansing, MI, USA .
    Zemtsov, Valeriy A.
    Tomsk State University, Russia.
    Multi-Decadal Changes in Tundra Environments and Ecosystems: Synthesis of the International Polar Year-Back to the FutureProject (IPY-BTF)2011In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 40, no 6, p. 705-716Article in journal (Refereed)
    Abstract [en]

    Understanding the responses of tundra systemsto global change has global implications. Most tundraregions lack sustained environmental monitoring and oneof the only ways to document multi-decadal change is toresample historic research sites. The International PolarYear (IPY) provided a unique opportunity for such researchthrough the Back to the Future (BTF) project (IPY project#512). This article synthesizes the results from 13 paperswithin this Ambio Special Issue. Abiotic changes includeglacial recession in the Altai Mountains, Russia; increasedsnow depth and hardness, permafrost warming, andincreased growing season length in sub-arctic Sweden;drying of ponds in Greenland; increased nutrient availabilityin Alaskan tundra ponds, and warming at mostlocations studied. Biotic changes ranged from relativelyminor plant community change at two sites in Greenland tomoderate change in the Yukon, and to dramatic increasesin shrub and tree density on Herschel Island, and in subarcticSweden. The population of geese tripled at one sitein northeast Greenland where biomass in non-grazed plotsdoubled. A model parameterized using results from a BTFstudy forecasts substantial declines in all snowbeds andincreases in shrub tundra on Niwot Ridge, Colorado overthe next century. In general, results support and provideimproved capacities for validating experimental manipulation,remote sensing, and modeling studies.

  • 8.
    Hedenas, Henrik
    et al.
    Abisko Science Research Stn.
    Olsson, Hakan
    Swedish University of Agriculture Science.
    Jonasson, Christer
    Abisko Science Research Stn.
    Bergstedt, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Ecology. Linköping University, The Institute of Technology.
    Dahlberg, Ulrika
    Royal Swedish Academic Science.
    Changes in Tree Growth, Biomass and Vegetation Over a 13-Year Period in the Swedish Sub-Arctic2011In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 40, no 6, p. 672-682Article in journal (Refereed)
    Abstract [en]

    This study was conducted in the Swedish sub-Arctic, near Abisko, in order to assess the direction and scale of possible vegetation changes in the alpine-birch forest ecotone. We have re-surveyed shrub, tree and vegetation data at 549 plots grouped into 61 clusters. The plots were originally surveyed in 1997 and re-surveyed in 2010. Our study is unique for the area as we have quantitatively estimated a 19% increase in tree biomass mainly within the existing birch forest. We also found significant increases in the cover of two vegetation types-"birch forest-heath with mosses and "meadow with low herbs, while the cover of snowbed vegetation decreased significantly. The vegetation changes might be caused by climate, herbivory and past human impact but irrespective of the causes, the observed transition of the vegetation will have substantial effects on the mountain ecosystems.

  • 9.
    Milberg, Per
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Ecology . Linköping University, The Institute of Technology.
    Bergstedt, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Ecology . Linköping University, The Institute of Technology.
    Fridman, Jonas
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Odell, Gunnar
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Westerberg, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Ecology . Linköping University, The Institute of Technology.
    Systematic and random variation in vegetation monitoring data2008In: Journal of Vegetation Science, ISSN 1100-9233, E-ISSN 1654-1103, Vol. 19, p. 633-644Article in journal (Refereed)
    Abstract [en]

    Question: Detecting species presence in vegetation and making visual assessment of abundances involve a certain amount of skill, and therefore subjectivity. We evaluated the magnitude of the error in data, and its consequences for evaluating temporal trends.

    Location: Swedish forest vegetation.

    Methods: Vegetation data were collected independently by two observers in 342 permanent 100-m2 plots in mature boreal forests. Each plot was visited by one observer from a group of 36 and one of two quality assessment observers. The cover class of 29 taxa was recorded, and presence/absence for an additional 50.

    Results: Overall, one third of each occurrence was missed by one of the two observers, but with large differences among species. There were more missed occurrences at low abundances. Species occurring at low abundance when present tended to be frequently overlooked. Variance component analyses indicated that cover data on 5 of 17 species had a significant observer bias. Observer-explained variance was < 10% in 15 of 17 species.

    Conclusion: The substantial number of missed occurrences suggests poor power in detecting changes based on presence/absence data. The magnitude of observer bias in cover estimates was relatively small, compared with random error, and therefore potentially analytically tractable. Data in this monitoring system could be improved by a more structured working model during field work.

  • 10.
    Petersson, Linda K.
    et al.
    Swedish Univ Agr Sci, Sweden.
    Milberg, Per
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Bergstedt, Johan
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Dahlgren, Jonas
    Swedish Univ Agr Sci, Sweden.
    Felton, Annika M.
    Swedish Univ Agr Sci, Sweden.
    Gotmark, Frank
    Univ Gothenburg, Sweden.
    Salk, Carl
    Swedish Univ Agr Sci, Sweden.
    Lof, Magnus
    Swedish Univ Agr Sci, Sweden.
    Changing land use and increasing abundance of deer cause natural regeneration failure of oaks: Six decades of landscape-scale evidence2019In: Forest Ecology and Management, ISSN 0378-1127, E-ISSN 1872-7042, Vol. 444, p. 299-307Article in journal (Refereed)
    Abstract [en]

    Many tree species worldwide are suffering from slow or failed natural regeneration with dramatic consequences for biodiversity and ecosystem services. However, it is difficult to disentangle the complex effects of factors influencing regeneration processes on long-lived tree species at large scales. In this study, we use long-term data from the Swedish National Forest Inventory (1953-2015) combined with deer hunting data (1960-2015) to reveal experimentally-intractable processes impeding oak (Quercus spp.) regeneration in southern Sweden. Oak-dominated ecosystems are widespread in northern temperate regions, where oaks are foundation species with disproportionate importance for biodiversity and ecosystem functions. Our study reveals that during the last six decades, oak tree numbers and standing volume have continuously increased, while natural regeneration of oak declined steeply after the early 1980s. We connect this decline to denser and darker forests, combined with increased abundance of deer. Land use changes during the six decades, such as abandonment of traditional practices and large-scale introduction of forest management oriented towards high volume production, led to continuously denser forests and thereby reduced the oak regeneration niche. In addition, the impact of changed game management was evident. This was particularly clear from a natural experiment on Gotland, a large island free of deer until roe deer were introduced in the late 20th century, at which point oak regeneration began a steep decline. At the stand level, natural oak regeneration could be expected to mainly occur in pulses after disturbance events, followed by a period of low regeneration success as the cohort ages. However, at a landscape scale one would expect a mix of successional stages that would even out such demographic patterns. A prolonged period of low regeneration at a landscape scale will eventually lead to a large gap in the oak size distribution as was observed in this study. This could eventually hurt the many species dependent on old and large oak trees. Active management to restore the oak regeneration niche, i.e. forest habitats with more light and less browsing pressure, therefore seems essential. The latter includes developing strategies that manage both deer populations and their available food across landscapes. Our study is the first to link oak regeneration failure to long-term changes in land use and increased deer populations at a landscape scale in this region. Furthermore, our study show how historical data can clarify confounded processes impacting long-lived forest species.

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