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Zale, Rolf
Publications (5 of 5) Show all publications
Klaminder, J., Fassl, M., Baudet, M., Östlund, L., Linderholm, J. & Zale, R. (2023). Landscape of ice and fire: uniquely well-preserved scots pine trunks reveal forest fires near the retreating weichselian ice margin. Vegetation History and Archaeobotany
Open this publication in new window or tab >>Landscape of ice and fire: uniquely well-preserved scots pine trunks reveal forest fires near the retreating weichselian ice margin
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2023 (English)In: Vegetation History and Archaeobotany, ISSN 0939-6314, E-ISSN 1617-6278Article in journal (Refereed) Epub ahead of print
Abstract [en]

Environmental conditions for trees that established in central Fennoscandia shortly after the final retreat of the Weichselian ice sheet remain poorly understood. In this study we examine tree rings of five well-preserved Pinus sylvestris (Scots pines) that grew in the area in front of the retreating ice sheet in northern Sweden. They became buried in flood sediments deposited by a glacial outburst flood (jökulhlaup) about 9.5–9.9 kyr cal bp and the aim of our study was to search for information regarding damage from fires and bioclimatic conditions in their ancient tree ring records. Our analysis, providing a glimpse into the local early Holocene environment in north-central Sweden, suggests that: 1, there were repeated fires (four fire events detected) during the early Holocene; and 2, bioclimatic conditions when the ancient pines were growing resembled those of modern sub-alpine pine woods. The latter is indicated by their patterns of tree ring growth (growth rate and variation), which were statistically similar to those of pines growing in sub-alpine woods with an open canopy, but different from pines in protected and managed boreal forests. Lower δ13C for the ancient latewood in comparison to pine wood from trees growing near the Scandinavian mountains before the 1850s were probably caused both by stomata fractionation due to lower atmospheric CO2 during the early Holocene and by the moist local environment created by the nearby ancient Ancylus lake, which preceded the Baltic Sea. Periods with cloudy and cold summers were also indicated by the occurrence of ‘false rings’. Finds of charred fragments of Calluna vulgaris (heather, ling), an understory shrub that can burn even with a relatively high moisture content, suggest that heath vegetation was crucial to make fire a reoccurring ecological factor in the area during the early Holocene.

Place, publisher, year, edition, pages
Springer, 2023
Climate, Early Holocene, Forest fires, Forest history, Lycksele, Pinus sylvestris
National Category
Forest Science
urn:nbn:se:umu:diva-218105 (URN)10.1007/s00334-023-00974-6 (DOI)2-s2.0-85178969112 (Scopus ID)
Swedish Research Council, 2017–04548Wallenberg Foundations, WAF
Available from: 2023-12-15 Created: 2023-12-15 Last updated: 2023-12-15
Olajos, F., Bokma, F., Bartels, P., Myrstener, E., Rydberg, J., Öhlund, G., . . . Englund, G. (2018). Estimating species colonization dates using DNA in lake sediment. Methods in Ecology and Evolution, 9(3), 535-543
Open this publication in new window or tab >>Estimating species colonization dates using DNA in lake sediment
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2018 (English)In: Methods in Ecology and Evolution, E-ISSN 2041-210X, Vol. 9, no 3, p. 535-543Article in journal (Refereed) Published
Abstract [en]
  1. Detection of DNA in lake sediments holds promise as a tool to study processes like extinction, colonization, adaptation and evolutionary divergence. However, low concentrations make sediment DNA difficult to detect, leading to high false negative rates. Additionally, contamination could potentially lead to high false positive rates. Careful laboratory procedures can reduce false positive and negative rates, but should not be assumed to completely eliminate them. Therefore, methods are needed that identify potential false positive and negative results, and use this information to judge the plausibility of different interpretations of DNA data from natural archives.
  2. We developed a Bayesian algorithm to infer the colonization history of a species using records of DNA from lake-sediment cores, explicitly labelling some observations as false positive or false negative. We illustrate the method by analysing DNA of whitefish (Coregonus lavaretus L.) from sediment cores covering the past 10,000 years from two central Swedish lakes. We provide the algorithm as an R-script, and the data from this study as example input files.
  3. In one lake, Stora Lögdasjön, where connectivity with the proto-Baltic Sea and the degree of whitefish ecotype differentiation suggested colonization immediately after deglaciation, DNA was indeed successfully recovered and amplified throughout the post-glacial sediment. For this lake, we found no loss of detection probability over time, but a high false negative rate. In the other lake, Hotagen, where connectivity and ecotype differentiation suggested colonization long after deglaciation, DNA was amplified only in the upper part of the sediment, and colonization was estimated at 2,200 bp based on the assumption that successful amplicons represent whitefish presence. Here the earliest amplification represents a false positive with a posterior probability of 41%, which increases the uncertainty in the estimated time of colonization.
  4. Complementing careful laboratory procedures aimed at preventing contamination, our method estimates contamination rates from the data. By combining these results with estimates of false negative rates, our models facilitate unbiased interpretation of data from natural DNA archives.
Place, publisher, year, edition, pages
British Ecological Society, 2018
ancient DNA, colonization, Coregonus lavaretus, detection probability, divergence, environmental DNA, lake sediment, population age
National Category
Environmental Sciences
urn:nbn:se:umu:diva-143248 (URN)10.1111/2041-210X.12890 (DOI)000426867600010 ()2-s2.0-85030156606 (Scopus ID)
Swedish Research Council, 2013-5110
Available from: 2017-12-19 Created: 2017-12-19 Last updated: 2024-05-20Bibliographically approved
Zale, R., Huang, Y.-T. -., Bigler, C., Wood, J. R., Dalén, L., Wang, X.-R., . . . Klaminder, J. (2018). Growth of plants on the Late Weichselian ice-sheet during Greenland interstadial-1?. Quaternary Science Reviews, 185, 222-229
Open this publication in new window or tab >>Growth of plants on the Late Weichselian ice-sheet during Greenland interstadial-1?
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2018 (English)In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 185, p. 222-229Article in journal (Refereed) Published
Abstract [en]

Unglaciated forelands and summits protruding from ice-sheets are commonly portrayed as areas where plants first establish at the end of glacial cycles. But is this prevailing view of ice-free refugia too simplistic? Here, we present findings suggesting that surface debris supported plant communities far beyond the rim of the Late Weichselian Ice-sheet during Greenland interstadial 1 (GI-1 or Bolling-Altered interstadial). We base our interpretations upon findings from terrigenous sediments largely resembling 'plant-trash' deposits in North America (known to form as vegetation established on stagnant ice became buried along with glacial debris during the deglaciation). In our studied deposit, we found macrofossils (N = 10) overlapping with the deglaciation period of the area (9.5-10 cal kyr BP) as well as samples (N = 2) with ages ranging between 12.9 and 13.3 cal kyr BP. The latter ages indicate growth of at least graminoids during the GI-1 interstadial when the site was near the geographic center of the degrading ice-sheet. We suggest that exposure of englacial material during GI-1 created patches of supraglacial debris capable of supporting vascular plants three millennia before deglaciation. The composition and resilience of this early plant community remain uncertain. Yet, the younger group of macrofossils, in combination with pollen and ancient DNA analyses of inclusions, imply that shrubs (Salix sp., Betula sp. and Ericaceae sp) and even tree species (Larix) were present in the debris during the final deglaciation stage. 

Place, publisher, year, edition, pages
Elsevier, 2018
Holocene, Pleistocene, Glaciology, Paleolimnology, Scandinavia, Vegetation dynamics, MIS-3
National Category
Geology Physical Geography
urn:nbn:se:umu:diva-148634 (URN)10.1016/j.quascirev.2018.02.005 (DOI)000428830400015 ()2-s2.0-85042352763 (Scopus ID)
Knut and Alice Wallenberg FoundationCarl Tryggers foundation
Available from: 2018-06-26 Created: 2018-06-26 Last updated: 2023-03-24Bibliographically approved
Gibson, R. A. & Zale, R. (2006). Holocene development of the fauna of Lake Boeckella, northern Antarctic Peninsula. THe Holocene, 16, 625-634
Open this publication in new window or tab >>Holocene development of the fauna of Lake Boeckella, northern Antarctic Peninsula
2006 (English)In: THe Holocene, Vol. 16, p. 625-634Article in journal (Refereed) Published
urn:nbn:se:umu:diva-7418 (URN)
Available from: 2008-01-09 Created: 2008-01-09 Last updated: 2018-06-09Bibliographically approved
Zale, R. (1993). Lake sediments around the Antarctic Peninsula: archives of climatic and environmental changes. (Doctoral dissertation). Umeå: Umeå Universitet
Open this publication in new window or tab >>Lake sediments around the Antarctic Peninsula: archives of climatic and environmental changes
1993 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Lakes and lake sediments from four areas around the Antarctic Peninsula are described.

The concentrations of trace metals in sediment are found to be a useful tool in distinguishing between the different sedimentary phases during a transition from marine to limnic environment.

A tephrochronology based on Deception Island tephra is developed, and used to cross date sediments from different lakes in order to overcome the radiocarbon dating problem of the area.

The fluctuating concentrations of copper and phosphorus from penguin guano in the sediment of Lake Boeckella are used as a proxy for the penguin inpact on the sediment, and the size of the penguin rookery on the shores of the lake. Anthropogenic activities in the area, as well as climatic changes are discussed in relation to the rookery size.

A radiocarbon dating model developed for the sediment of Lake Boeckella showed that the radiocarbon correction factor in the sediment depends on the amount and apparent age of the penguin guano washed down into the lake, and the amount of particulate carbon from the watershed present in the sediment. Neither the "old" meltwater from the glaciers nor dissolved carbonates contributes significantly to the correction factor. The model is used to achieve more accurate radiocarbon dates of the Lake Boeckella sediment. This model, or a modified version, may contribute to a higher dating accuracy and a better understanding of the dating problems in Antarctica.

Deglaciation dates, as well as data on the climatic and environmental history of Byers Peninsula on Livingston Island, South Shetland Islands, of Hope Bay, Antarctic Peninsula and of Hidden Lake area, James Ross Island are given.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet, 1993. p. 21
GERUM. Naturgeografi, ISSN 0282-5597 ; 17
Lake sediments, Antarctic Peninsula, radiocarbon dating, climatic and environmental changes, sediment chemistry
National Category
Physical Geography
Research subject
Physical Geography
urn:nbn:se:umu:diva-96890 (URN)91-7174-790-7 (ISBN)
Public defence
1993-05-27, hörsal 1, Skogshögskolan, SLU, Umeå universitet, Umeå, 10:00

Diss. (sammanfattning) Umeå : Umeå universitet, 1993, härtill 6 uppsatser.

Available from: 2015-02-09 Created: 2014-12-05 Last updated: 2018-06-07Bibliographically approved

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