| 1. |
- Ammann, Birgitta, et al.
(författare)
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The potential of stomata analysis inconifers to estimate presence of conifer trees: examples from the Alps
- 2014
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Ingår i: Vegetation History and Archaeobotany. - : Springer Science and Business Media LLC. - 0939-6314 .- 1617-6278. ; 23:3, s. 249-264
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Tidskriftsartikel (refereegranskat)abstract
- To estimate whether or not a plant taxon found in the fossil record was locally present may be difficult if only pollen is analyzed. Plant macrofossils, in contrast, provide a clear indication of a taxon’s local presence, although in some lake sediments or peats, macrofossils may be rare or degraded. For conifers, the stomata found on pollen slides are derived from needles and thus provide a valuable proxy for local presence and they can be identified to genus level. From previously published studies, a transect across the Alps based on 13 sites is presented. For basal samples in sandy silt above the till with high pollen values of Pinus, for example, we may distinguish pine pollen from distant sources (samples with no stomata), from reworked pollen (samples with stomata present). The first apparent local presence of most conifer genera based on stomata often but not always occurs together with the phase of rapid pollen increase (rational limit). An exception is Larix, with its annual deposition of needles and heavy poorly dispersed pollen, for it often shows the first stomata earlier, at the empirical pollen limit. The decline and potential local extinction of a conifer can sometimes be shown in the stomata record. The decline may have been caused by climatic change, competition, or human impact. In situations where conifers form the timberline, the stomata record may indicate timberline fluctuations. In the discussion of immigration or migration of taxa we advocate the use of the cautious term “apparent local presence” to include some uncertainties. Absence of a taxon is impossible to prove.
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| 2. |
- Ammar, Yosr, et al.
(författare)
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The rise of novelty in marine ecosystems : The Baltic Sea case
- 2021
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 27:7, s. 1485-1499
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Tidskriftsartikel (refereegranskat)abstract
- Global environmental changes have accelerated at an unprecedented rate in recent decades due to human activities. As a consequence, the incidence of novel abiotic conditions and biotic communities, which have been continuously emerging in the Earth system, has rapidly risen. Despite growing attention to the incidence and challenges posed by novelty in terrestrial ecosystems, novelty has not yet been quantified in marine ecosystems. Here, we measured for the rate of novelty (RoN) in abiotic conditions and community structure for three trophic levels, i.e., phytoplankton, zooplankton, and fish, in a large marine system - the Baltic Sea. We measured RoN as the degree of dissimilarity relative to a specific spatial and temporal baseline, and contrasted this with the rate of change as a measure of within-basin change over time. We found that over the past 35 years abiotic and biotic RoN showed complex dynamics varying in time and space, depending on the baseline conditions. RoN in abiotic conditions was smaller in the open Central Baltic Sea than in the Kattegat and the more enclosed Gulf of Bothnia, Gulf of Riga, and Gulf of Finland in the north. We found a similar spatial pattern for biotic assemblages, which resulted from changes in composition and stock size. We identified sea-surface temperature and salinity as key drivers of RoN in biotic communities. Hence, future environmental changes that are expected to affect the biogeochemistry of the Baltic Sea, may favor the rise of biotic novelty. Our results highlighted the need for a deeper understanding of novelty development in marine ecosystems, including interactions between species and trophic levels, ecosystem functioning under novel abiotic conditions, and considering novelty in future management interventions.
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| 3. |
- de Jong, Rixt, et al.
(författare)
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Climate and Peatlands
- 2010
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Ingår i: Changing Climates, Earth Systems and Society. - Dordrecht : Springer Netherlands. - 9789048187157 - 9789048187164 ; , s. 85-121
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Peatlands are an important natural archive for past climatic changes, primarily due to their sensitivity to changes in the water balance and the dating possibilities of peat sediments. In addition, peatlands are an important sink as well as potential source of greenhouse gases. The first part of this chapter discusses a range of well-established and novel proxies studied in peat cores (peat humification, macrofossils, testate amoebae, stomatal records from subfossil leaves, organic biomarkers and stable isotope ratios, aeolian sediment influx and geochemistry) that are used for climatic and environmental reconstructions, as well as recent developments in the dating of these sediments. The second part focuses on the role that peatland ecosystems may play as a source or sink of greenhouse gases. Emphasis is placed on the past and future development of peatlands in the discontinuous permafrost areas of northern Scandinavia, and the role of regenerating mined peatlands in north-western Europe as a carbon sink or source.
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| 4. |
- Finsinger, Walter, et al.
(författare)
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Human impacts and eutrophication patterns during the past similar to 200 years at Lago Grande di Avigliana (N. Italy)
- 2006
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Ingår i: Journal of Paleolimnology. - Dordrecht : Springer. - 0921-2728 .- 1573-0417. ; 36:1, s. 55-67
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Tidskriftsartikel (refereegranskat)abstract
- A short sediment core from Lago Grande di Avigliana (Piedmont, Italy), the second most eutrophied lake in Italy, was analysed for pollen and diatoms to reconstruct land-use changes and to estimate baseline conditions for total phosphorus (TP) in the water column. Varve counts on sediment thin-sections and (210)Pb, (226)Ra, and (137)Cs dating provided a reliable chronology for the past similar to 200 years. The main pollen-inferred land-use changes showed a sharp decrease of hemp retting around AD 1900, as well as a gradual change to less intensive agriculture and increasing abundance of exotic plants since AD similar to 1970. Diatom-inferred TP reconstructions indicated stable TP concentrations until AD similar to 1950, revealing baseline mesotrophic conditions (TP < 25 mu g l(-1)). After AD similar to 1950, TP values increased distinctly and continuously, culminating in the late 1960s with concentrations of 150 mu g l(-1). Subsequently, diatoms implied a linear decrease of TP, with an inferred value of 40 mu g l(-1) in the surface sediment sample. Comparison with instrumental TP measurements from the water column since AD 1980 showed a rapid recovery and allowed a direct validation of the diatom TP inference. However, although the TP concentration has decreased considerably, baseline conditions have not yet been reached. When compared to the limnological effects of sewage discharges on inferred-TP concentration, our results indicated that agricultural land use played a minor role in the lake's eutrophication.
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| 5. |
- Finsinger, Walter, et al.
(författare)
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Rates of palaeoecological change can inform ecosystem restoration
- 2024
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Ingår i: Biogeosciences. - : Copernicus Publications. - 1726-4170 .- 1726-4189. ; 21:7, s. 1629-1638
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Tidskriftsartikel (refereegranskat)abstract
- Accelerations of ecosystem transformation raise concerns, to the extent that high rates of ecological change may be regarded amongst the most important ongoing imbalances in the Earth system. Here, we used high-resolution pollen and diatom assemblages and associated ecological indicators (the sum of tree and shrub pollen and diatom-inferred total phosphorus concentrations as proxies for tree cover and lake-water eutrophication, respectively) spanning the past 150 years to emphasize that rate-of-change records based on compositional data may document transformations having substantially different causes and outcomes. To characterize rates of change also in terms of other key ecosystem features, we quantified for both ecological indicators: (i) the percentage of change per unit time, (ii) the percentage of change relative to a reference level, and (iii) the rate of percentage change per unit time relative to a reference period, taking into account the irregular spacing of palaeoecological data. These measures document how quickly specific facets of nature changed, their trajectory, as well as their status in terms of palaeoecological indicators. Ultimately, some past accelerations of community transformation may document the potential of ecosystems to rapidly recover important ecological attributes and functions. In this context, insights from palaeoecological records may be useful to accelerate ecosystem restoration.
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| 6. |
- Giesecke, Thomas, et al.
(författare)
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The pace of Holocene vegetation change : testing for synchronous developments
- 2011
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 30:19-20, s. 2805-2814
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Forskningsöversikt (refereegranskat)abstract
- Mid to high latitude forest ecosystems have undergone several major compositional changes during the Holocene. The temporal and spatial patterns of these vegetation changes hold potential information to their causes and triggers. Here we test the hypothesis that the timing of vegetation change was synchronous on a sub-continental scale, which implies a common trigger or a step-like change in climate parameters. Pollen diagrams from selected European regions were statistically divided into assemblage zones and the temporal pattern of the zone boundaries analysed. The results show that the temporal pattern of vegetation change was significantly different from random. Times of change cluster around 8.2, 4.8, 3.7, and 1.2 ka, while times of higher than average stability were found around 2.1 and 5.1 ka. Compositional changes linked to the expansion of Corylus avellana and Alnus glutinosa centre around 10.6 and 9.5 ka, respectively. A climatic trigger initiating these changes may have occurred 0.5 to 1 ka earlier, respectively. The synchronous expansion of C avellana and A. glutinosa exemplify that dispersal is not necessarily followed by population expansion. The partly synchronous, partly random expansion of A. glutinosa in adjacent European regions exemplifies that sudden synchronous population expansions are not species specific traits but vary regionally.
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| 7. |
- Giesecke, Thomas, et al.
(författare)
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Towards mapping the late Quaternary vegetation change of Europe.
- 2014
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Ingår i: Vegetation History and Archaeobotany. - : Springer Science and Business Media LLC. - 0939-6314 .- 1617-6278. ; 23:1, s. 75-86
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Tidskriftsartikel (refereegranskat)abstract
- The number of well-dated pollen diagrams in Europe has increased considerably over the last 30 years and many of them have been submitted to the European Pollen Database (EPD). This allows for the construction of increasingly precise maps of Holocene vegetation change across the continent. Chronological information in the EPD has been expressed in uncalibrated radiocarbon years, and most chronologies to date are based on this time scale. Here we present new chronologies for most of the datasets stored in the EPD based on calibrated radiocarbon years. Age information associated with pollen diagrams is often derived from the pollen stratigraphy itself or from other sedimentological information. We reviewed these chronological tie points and assigned uncertainties to them. The steps taken to generate the new chronologies are described and the rationale for a new classification system for age uncertainties is introduced. The resulting chronologies are fit for most continental-scale questions. They may not provide the best age model for particular sites, but may be viewed as general purpose chronologies. Taxonomic particularities of the data stored in the EPD are explained. An example is given of how the database can be queried to select samples with appropriate age control as well as the suitable taxonomic level to answer a specific research question.
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| 8. |
- Kaufman, Darrell, et al.
(författare)
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A global database of Holocene paleotemperature records
- 2020
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Ingår i: Scientific Data. - : Springer Science and Business Media LLC. - 2052-4463. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- A comprehensive database of paleoclimate records is needed to place recent warming into the longer-term context of natural climate variability. We present a global compilation of quality-controlled, published, temperature-sensitive proxy records extending back 12,000 years through the Holocene. Data were compiled from 679 sites where time series cover at least 4000 years, are resolved at sub-millennial scale (median spacing of 400 years or finer) and have at least one age control point every 3000 years, with cut-off values slackened in data-sparse regions. The data derive from lake sediment (51%), marine sediment (31%), peat (11%), glacier ice (3%), and other natural archives. The database contains 1319 records, including 157 from the Southern Hemisphere. The multi-proxy database comprises paleotemperature time series based on ecological assemblages, as well as biophysical and geochemical indicators that reflect mean annual or seasonal temperatures, as encoded in the database. This database can be used to reconstruct the spatiotemporal evolution of Holocene temperature at global to regional scales, and is publicly available in Linked Paleo Data (LiPD) format.
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| 9. |
- Wagner-Cremer, Friederike, et al.
(författare)
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Tracing growing degree-day changes in the cuticle morphology of Betula nana leaves : a new micro-phenological palaeo-proxy
- 2010
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Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 25:6, s. 1008-1017
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Tidskriftsartikel (refereegranskat)abstract
- Changing growing-season properties in the northern latitudes are among the most obvious consequences of ongoing global change. Available techniques including satellite monitoring and phenological observations enable the detection of changes over the last few decades to centuries, but the full range of natural variability is still difficult to capture. Here we introduce a new approach to reconstruct growing season properties, by studying imprints of prolonged growing season on epidermal cell growth in Betula nana. A high correlation between cell expansion determined in annually collected B. nana leaves and subfossil leaf fragments collected from recent peat sections in northern Scandinavia, and climatic indices such as budburst date, growing-season degree-days and May–September mean temperatures, enable the establishment of a new micro-phenological proxy for growing season characteristics. The applicability of the epidermal cell undulation index (UI) is tested by comparison with historical instrumental records of growing-season degree-days for the last 200 a. The results demonstrate the potential of the new leaf-morphology-based technique to reconstruct and quantify past changes in growing degree-days beyond instrumental data series. Applied to abundant B. nana leaf remains from peat and lake sediments, the UI may enable a reconstruction of growing degree-days throughout the Holocene and other parts of the late Quaternary.
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