| 1. |
- Ballesteros-Cánovas, Juan Antonio, et al.
(författare)
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Estimation of recent peat accumulation with tree saplings
- 2022
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Ingår i: Progress in Physical Geography. - : SAGE Publications. - 0309-1333. ; 46:4, s. 515-529
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this paper is to develop an approach to estimate peat accumulation rates (PAR) over recent decades based on the age and burial depths of roots from pine sapling and to use the newly developed approach to estimate spatial variations of PAR. To this end, we sampled 120 pine saplings growing in three plots at Rėkyva peatland in Lithuania and accounted for the microtopography around each specimen. In the lab, all saplings were cut into 1-cm segments, sanded and analysed. The counting of annual rings allowed dating the germination of each sapling with a yearly resolution and thus also enabled estimation of peat accumulation. The latter was derived by measuring the distance from the original root collar at germination to the ground level (or peat surface) at the time of sampling. The large number of samples selected from three plots also enabled determination of spatial variations in PAR. We obtain averaged PAR values of 1.6 ± 0.72 cm yr−1 across the three plots and over the last decades, but also observe strong spatial heterogeneity in PAR resulting from differences in local hydrology and vegetation. To validate the results, we compared tree-ring derived PAR with radiocarbon-based (14C) estimates at one of the plots. The results are consistent between the two approaches with PAR estimated to 0.8 and 0.79 cm yr−1, respectively, over the last 20 years. We conclude that PAR can be assessed accurately with tree-ring approaches and that they have clear advantages over radiocarbon dating for shorter timescales as they can be replicated more easily. For longer timescales and larger depths (> 15 cm), however, 14C dating remains the preferred approach.
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| 2. |
- Ebert, Karin, 1976-
(författare)
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Terminology of long-term geomorphology: a Scandinavian perspective
- 2009
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Ingår i: Progress in physical geography. - : Sage publications. - 0309-1333 .- 1477-0296. ; 33:2, s. 163-182
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Tidskriftsartikel (refereegranskat)abstract
- In this paper the terminology used in long-term geomorphology is evaluated. Long-term geomorphology is the study of landforms that are of mostly pre-Quaternary, Cenozoic, Mesozoic or even Palaeozoic age. Many terms have been introduced to name the long-term large-scale landforms that persist to the present. The definitions of many of these terms are ambiguous, have changed over time, and their use and meaning is consequently often unclear. An attempt is made to clarify definitions, when possible, and to facilitate more concise usage of these terms. Long-term geomorphology deals in great parts with the lowering of a land surface to the base level (mostly sea level), leaving a new land surface. The largest group of terms concerns descriptions and genetic models for these kinds of new land surfaces collectively called “base level surfaces” here. Other terms discussed here relate to relict and preglacial landforms and regional terms for stepped surfaces. Terminology is discussed with particular reference to examples from and its use in Scandinavia. There is a long history of long-term geomorphology study in this region. Scandinavia is unique in the respect that pre-Quaternary landforms where repeatedly covered by Quaternary ice-sheets but often survived with different degrees of glacial modification. The usage of the terms in question is discussed from the view of long-term geomorphology in that area.
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| 3. |
- Heikkinen, Risto K., et al.
(författare)
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Methods and uncertainties in bioclimatic envelope modelling under climate change
- 2006
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Ingår i: Progress in Physical Geography. - : SAGE Publications. - 1477-0296. ; 30:6, s. 751-777
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Forskningsöversikt (refereegranskat)abstract
- Potential impacts of projected climate change on biodiversity are often assessed using single-species bioclimatic 'envelope' models. Such models are a special case of species distribution models in which the current geographical distribution of species is related to climatic variables so to enable projections of distributions under future climate change scenarios. This work reviews a number of critical methodological issues that may lead to uncertainty in predictions from bioclimatic modelling. Particular attention is paid to recent developments of bioclimatic modelling that address some of these issues as well as to the topics where more progress needs to be made. Developing and applying bioclimatic models in a informative way requires good understanding of a wide range of methodologies, including the choice of modelling technique, model validation, collinearity, autocorrelation, biased sampling of explanatory variables, scaling and impacts of non-climatic factors. A key challenge for future research is integrating factors such as land cover, direct CO2 effects, biotic interactions and dispersal mechanisms into species-climate models. We conclude that, although bioclimatic envelope models have a number of important advantages, they need to be applied only when users of models have a thorough understanding of their limitations and uncertainties.
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| 4. |
- MacDonald, G. M., et al.
(författare)
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Impacts of climate change on species, populations and communities : palaeobiogeographical insights and frontiers
- 2008
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Ingår i: Progress in physical geography. - : SAGE Publications. - 0309-1333 .- 1477-0296. ; 32:2, s. 139-172
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Forskningsöversikt (refereegranskat)abstract
- Understanding climate change and its potential impact on species, populations and communities is one of the most pressing questions of twenty-first-century conservation planning. Palaeobiogeographers working on Cenozoic fossil records and other lines of evidence are producing important insights into the dynamic nature of climate and the equally dynamic response of species, populations and communities. Climatic variations ranging in length from multimillennia to decades run throughout the palaeo-records of the Quaternary and earlier Cenozoic and have been shown to have had impacts ranging from changes in the genetic structure and morphology of individual species, population sizes and distributions, community composition to large-scale bio-diversity gradients. The biogeographical impacts of climate change may be due directly to the effects of alterations in temperature and moisture on species, or they may arise due to changes in factors such as disturbance regimes. Much of the recent progress in the application of palaeobiogegraphy to issues of climate change and its impacts can be attributed to developments along a number of still advancing methodological frontiers. These include increasingly finely resolved chronological resolution, more refined atmosphere-biosphere modelling, new biological and chemical techniques in reconstructing past species distributions and past climates, the development of large and readily accessible geo-referenced databases of biogeographical and climatic information, and new approaches in fossil morphological analysis and new molecular DNA techniques.
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| 5. |
- Malhotra, Avni, et al.
(författare)
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The landscape of soil carbon data : emerging questions, synergies and databases
- 2019
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Ingår i: Progress in physical geography. - : SAGE Publications. - 0309-1333 .- 1477-0296. ; 43:5, s. 707-719
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Tidskriftsartikel (refereegranskat)abstract
- Soil carbon has been measured for over a century in applications ranging from understanding biogeochemical processes in natural ecosystems to quantifying the productivity and health of managed systems. Consolidating diverse soil carbon datasets is increasingly important to maximize their value, particularly with growing anthropogenic and climate change pressures. In this progress report, we describe recent advances in soil carbon data led by the International Soil Carbon Network and other networks. We highlight priority areas of research requiring soil carbon data, including (a) quantifying boreal, arctic and wetland carbon stocks, (b) understanding the timescales of soil carbon persistence using radiocarbon and chronosequence studies, (c) synthesizing long-term and experimental data to inform carbon stock vulnerability to global change, (d) quantifying root influences on soil carbon and (e) identifying gaps in model-data integration. We also describe the landscape of soil datasets currently available, highlighting their strengths, weaknesses and synergies. Now more than ever, integrated soil data are needed to inform climate mitigation, land management and agricultural practices. This report will aid new data users in navigating various soil databases and encourage scientists to make their measurements publicly available and to join forces to find soil-related solutions.
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| 6. |
- Sam, Lydia, et al.
(författare)
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Remote sensing flow velocity of debris-covered glaciers using Landsat 8 data
- 2016
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Ingår i: Progress in physical geography. - : SAGE Publications. - 0309-1333 .- 1477-0296. ; 40:2, s. 305-321
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Tidskriftsartikel (refereegranskat)abstract
- Changes in ice velocity of a glacier regulate its mass balance and dynamics. The estimation of glacier flow velocity is therefore an important aspect of temporal glacier monitoring. The utilisation of conventional ground-based techniques for detecting glacier surface flow velocity in the rugged and alpine Himalayan terrain is extremely difficult. Remote sensing-based techniques can provide such observations on a regular basis for a large geographical area. Obtaining freely available high quality remote sensing data for the Himalayan regions is challenging. In the present work, we adopted a differential band composite approach, for the first time, in order to estimate glacier surface velocity for non-debris and supraglacial debris covered areas of a glacier, separately. We employed various bandwidths of the Landsat 8 data for velocity estimation using the COSI-Corr (co-registration of optically sensed images and correlation) tool. We performed the accuracy assessment with respect to field measurements for two glaciers in the Indian Himalaya. The panchromatic band worked best for non-debris parts of the glaciers while band 6 (SWIR – short wave infrared) performed best in case of debris cover. We correlated six temporal Landsat 8 scenes in order to ensure the performance of the proposed algorithm on monthly as well as yearly timescales. We identified sources of error and generated a final velocity map along with the flow lines. Over- and underestimates of the yearly glacier velocity were found to be more in the case of slow moving areas with annual displacements less than 5 m. Landsat 8 has great capabilities for such velocity estimation work for a large geographic extent because of its global coverage, improved spectral and radiometric resolutions, free availability and considerable revisit time.
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| 7. |
- Virkkala, Anna Maria, et al.
(författare)
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The current state of CO2 flux chamber studies in the Arctic tundra : a review
- 2018
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Ingår i: Progress in Physical Geography. - : SAGE Publications. - 0309-1333. ; 42:2, s. 162-184
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Tidskriftsartikel (refereegranskat)abstract
- The Arctic tundra plays an important role in the carbon cycle as it stores 50% of global soil organic carbon reservoirs. The processes (fluxes) regulating these stocks are predicted to change due to direct and indirect effects of climate change. Understanding the current and future carbon balance calls for a summary of the level of knowledge regarding chamber-derived carbon dioxide (CO2) flux studies. Here, we describe progress from recently (2000–2016) published studies of growing-season CO2 flux chamber measurements, namely GPP (gross primary production), ER (ecosystem respiration), and NEE (net ecosystem exchange), in the tundra region. We review the study areas and designs along with the explanatory environmental drivers used. Most of the studies were conducted in Alaska and Fennoscandia, and we stress the need for measuring fluxes in other tundra regions, particularly in more extreme climatic, productivity, and soil conditions. Soil respiration and other greenhouse gas measurements were seldom included in the studies. Although most of the environmental drivers of CO2 fluxes have been relatively well investigated (such as the effect of vegetation type and soil microclimate on fluxes), soil nutrients, other greenhouse gases and disturbance regimes require more research as they might define the future carbon balance. Particular attention should be paid to the effects of shrubification, geomorphology, and other disturbance effects such as fire events, and disease and herbivore outbreaks. An improved conceptual framework and understanding of underlying processes of biosphere–atmosphere CO2 exchange will provide more information on carbon cycling in the tundra.
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