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Rereading a tree-ring database to illustrate depositional histories of subfossil trees

Samuli Helama, Tomi P. Luoto, Liisa Nevalainen, and Johannes Edvardsson

Plain Language Abstract

Tree trunks can preserve over millennia in the peat and in the bottom of small lakes. Long tree-ring chronologies are built using these materials. The counts of pine trees available to such chronologies are used here to interpret the processes responsible for past variations in population density and sedimentary environments. Abundance of peatland pines around one thousand years ago was contrasted by the low number of available trees from lake sites. This interval overlaps with the Medieval Climate Anomaly with long-lasting droughts reported in the study region (southern Finland). Over the following centuries, the availability of pine trunks from lake sites increased but their number from peatland sites decreased. This change overlapped with the climatic change towards wetter Little Ice Age conditions in the study region. These dissimilarities reflect the benefit for pine trees to recruit on peatland when the climate was dry and the water table level was low, during the Medieval Climate Anomaly, whereas the potential for preservation was diminished on riparian environment for lake sites. Likewise, the recruitment of peatland pines was impaired when the water table level rose, during the Little Ice Age, while the accumulation of pine trees into the lake sediment was increased when the raising lake level drowned the riparian trees. Tree-ring data of this study was retrieved from an electronic database and the analysis highlights the potential of similar data to illustrate the depositional histories of succeeding tree generations and, when interpreted with care, to detail the picture of hydroclimate anomalies in deep time.

Resumen en Español

Releyendo una base de datos de anillos de árboles para ilustrar las historias de depósito de árboles subfósiles

Se han construido cronologías de anillos de árboles del Cuaternario tardío utilizando datos recolectados de árboles subfósiles preservados en condiciones favorables en sedimentos lacustres y depósitos de turba. Las anchuras y densidades de los anillos de árboles se usan comúnmente para reconstruir la variabilidad climática pasada. Una forma alternativa de utilizar estos datos es explorar las curvas de replicación de estas cronologías. Utilizamos los datos previamente recolectados que están actualmente disponibles en las bases de datos de los anillos de árboles para demostrar las historias de depósito de pinos una vez acumulados en el sedimento de lagos (i.e., árboles de ribera) y turberas. Se obtuvieron dinámicas divergentes para las historias de depósito respecto a diferentes entornos sedimentarios en el sur de Finlandia. La acumulación de pinos de turbera fue alta, pero la de los árboles ribereños fue baja, alrededor de 1000 años, durante la Anomalía Climática Medieval (ACM, en inglés MCA). Por el contrario, la acumulación de pinos de turbera disminuyó hacia la Pequeña Edad de Hielo (PEH, en inglés LIA), mientras que la de los árboles ribereños aumentó, con un pico máximo alrededor de 700 años. Interpretamos que estas variaciones significan cambios ambientales de transición en los hábitats correspondientes e indican un aumento de la precipitación y una subida de la capa freática desde ACM hacia el PEH. Estos resultados demuestran los papeles relativos de los potenciales de reclutamiento y preservación, y por lo tanto de los procesos paleoecológicos y tafonómicos, en el control de la acumulación de árboles en ambientes de turberas y lacustres, respectivamente. Concluimos que las cronologías de los anillos de los árboles subfósiles, incluso los extraídos de las bases de datos digitales, pueden aportar una visión significativa de la paleoecología, proporcionando nuevas perspectivas sobre el paleoclima, la paleohidrología de los lagos y las turberas, y asimismo pueden ser útiles para estudiar las respuestas de las poblaciones de árboles a los cambios climáticos del pasado.

Palabras clave: Paleobotánica; paleoclimatología; paleoecología; paleohidrología; ganancia tafonómica; anillo de árbol

Traducción: Enrique Peñalver (Sociedad Española de Paleontología)

Résumé en Français

Une seconde lecture d'une base de données de cernes de croissance d'arbres pour illustrer les histoires dépositionnelles des arbres subfossiles

Les chronologies des cernes de croissance d'arbres du Quaternaire récent ont été construites en utilisant des données collectées sur des arbres subfossiles préservés dans des conditions favorables dans des sédiments lacustres ou des dépôts de tourbières. Les épaisseurs et densités des cernes de croissance d'arbres sont généralement utilisées pour reconstituer la variabilité des climats passés. Une autre manière d'utiliser ces données est d'explorer les courbes de réplication de ces chronologies. Dans cet article, nous utilisons des données précédemment collectées et disponibles dans les bases de données de cernes de croissance d'arbres pour reconstituer l'histoire dépositionnelle des pins accumulés dans le sédiment dans des sites de lacs (i. e., des arbres proches des berges) et de tourbières. Des histoires dépositionnelles différentes ont été obtenues pour différents contextes sédimentaires du sud de la Finlande. L'accumulation des pins de tourbière était importante, mais celle des arbres de berges de lacs était faible autour de 1,0 ka pendant l'Optimum Climatique Médiéval (MCA). Au contraire, l'accumulation des pins de tourbière a diminué autour du Petit Âge Glaciaire (LIA), alors que celle des arbres de berges de lacs a augmenté, avec une culmination vers 0,7 ka. Nous interprétons ces variations en termes de changements environnementaux transitionnels dans les habitats correspondants, indiquant des précipitations plus importantes et une nappe phréatique plus haute du MCA au LIA. Ces résultats illustrent les rôles relatifs des potentiels de recrutement et préservation, et donc des processus paléoécologiques et taphonomiques, contrôlant l'accumulation d'arbres dans des environnements de lacs et de tourbières, respectivement. Nous concluons que les chronologies de cernes de croissance d'arbres subfossiles, même celles extraites des bases de données électroniques, peuvent fournir des connaissances approfondies de la paléoécologie, fournissant de nouvelles perspectives sur les paléoclimats, la paléohydrologie des lacs et des tourbières, et sur l'étude des réponses des populations d'arbres aux changements climatiques passés.

Mots-clés : paléobotanique ; paléoclimatologie ; paléoécologie ; paléohydrologie ; gain taphonomique ; cernes de croissance d'arbres

Translator: Antoine Souron

Deutsche Zusammenfassung

Neue Leseart einer Jahresringe-Datenbank zur Darstellung der Ablagerungshistorie subfossiler Bäume

Mit Daten subfossiler Bäume, erhalten unter günstigen Bedingungen in Seesedimenten und Moorablagerungen, wurde eine spätquartäre Jahresring-Chronologie aufgebaut. Üblicherweise werden die Abstände und Dichte der Jahresringe zur Rekonstruktion der vergangenen Klimavariabilität genutzt. Die Replikationskurven dieser Chronologie zu untersuchen, ist eine alternative Möglichkeit diese Daten zu verwenden. Hier bedienen wir uns zuvor gesammelter Daten die aktuell aus Jahresring-Datenbänken verfügbar sind, um die Ablagerungsgeschichte von Kiefern zu demonstrieren, sobald sie in einem Seesediment (Uferbäume) oder Moorgebiet abgelagert sind. Es wurden verschiedene Ablagerungsmöglichkeiten für verschiedene Ablagerungsbedingungen in Südfinnland ermittelt. Die Anhäufung von Kiefern aus Moorgebieten war hoch, jedoch die von Uferbäumen war mit 1.0 ka während der mittelalterlichen Klimaanomalie (MCA) niedrig. Dagegen nahm die Anhäufung von Kiefern aus Moorgebieten gegen die Kleine Eiszeit hin ab, während die der Uferbäume zunahm, mit einem Höhepunkt bei um die 0.7 ka. Wir interpretieren diese Variationen als vorübergehende Umweltveränderungen in den dementsprechenden Habitaten, die erhöhten Niederschlag und einen steigenden Grundwasserspiegel von der MCA hin zur Kleinen Eiszeit anzeigen. Diese Ergebnisse zeigen die jeweiligen Rollen von Rekrutierung und Erhaltungspotential und daher von paläontologischen und taphonomischen Prozessen bei der Kontrolle von Baumakkumulation in Moor – bzw. Seegebieten. Wir folgern, dass subfossile Baum-Chronologien, auch diese aus elektronischen Datenbänken, wichtige Erkenntnisse über die Paläoökologie und darüber wie Baumpopulationen auf Klimaveränderungen reagieren, liefern und neue Perspektiven über das Paläoklima und die Paläohydrologie von Seen und Moorgebieten geben.

Schlüsselwörter: Paläobotanik; Paläoklimatologie; Paläoökologie; Paläohydrologie; taphonomischer Gewinn; Jahresring

Translator: Eva Gebauer

Arabic

Translator: Ashraf M.T. Elewa

 

 

TABLE 1. Characteristics of the eight lake sites (L1-L8) and one peatland site (P9) and their tree-ring data. Abbreviations: LA, Latitude; LO, longitude; NR, the number of rings, NS, the number of tree-ring series; NT, the number of trees; LS, the mean length of the series in years; FY and LA, the first (FY) and last (LY) calendar year (A.D.) of the site chronology; and LC, the total length of the chronology in years.

Site name Code LA LO NR NS NT LS FY LY LC
Alakieluu Louhi Kerimäki L1 61.93 28.98 3424 21 13 163 1144 1705 562
Liippilampi Louhi Kerimäki L2 61.92 29.03 23579 158 95 149 595 1816 1222
Kaivanto Louhi Kerimäki L3 61.93 28.98 28707 160 94 179 535 1744 1210
Isokortteikko Kerimäki L4 61.97 28.87 6464 36 19 180 844 1693 850
Valkeajarvi Makkola Kerimäki L5 61.97 28.87 26703 150 78 178 582 1742 1161
Herajärvi Makkola Kerimäki L6 61.97 28.83 31863 214 170 149 559 1732 1174
Hiisjärvi Kerimäki L7 61.90 29.02 7251 57 35 127 885 1698 814
Valkiajärvi Riikola Kerimäki L8 62.03 29.17 2244 12 7 187 1233 1831 599
Purujärvi Suursuo Kesälahti P9 61.80 29.75 21788 131 79 166 845 1330 486
 

author 1Samuli Helama. Natural Resources Institute Finland, P.O. Box 16, 96301 Rovaniemi, Finland. This email address is being protected from spambots. You need JavaScript enabled to view it.

Samuli Helama is a geoscientist with special interest in time-series of annually resolved natural archives and documentary evidence, especially tree-ring chronologies and climatic records. Originally trained as Quaternary geologist, later completing his PhD thesis (University of Helsinki, 2004) on dendrochronology, studying mid and late Holocene tree-ring chronologies as indicators of past climate variability, he is interested in analyzing proxy records of various types in paleoecologic and paleoclimatic contexts. In addition to tree rings, these data include sedimentary records of microfossils, annual shell growth increments, varves, and historical (written) evidence of past environmental changes. He is currently working in a dendroisotope project (QUANOMAL; Quantifying the Past – Environmental anomalies through multi-proxy tree-ring analyses) funded by the Academy of Finland, at the Natural Resources Institute Finland, in Rovaniemi.

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author 2Tomi P. Luoto. Division of Aquatic Sciences, Department of Biological and Environmental Science, University of Jyvaskyla, P.O. Box 35, 40014, Finland. This email address is being protected from spambots. You need JavaScript enabled to view it.

Tomi Luoto is a paleolimnologist with a special interest in reconstructing paleoclimate and past environmental conditions in lakes using modeling approaches. He received his PhD degree in Geology in 2010. His current research focus on biogeochemical cycling and landscape dynamics in the Arctic. He also works in several lake management projects using paleolimnological methods to assess ecological and limnological baseline conditions to set targets for restoration efforts in boreal lakes.

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author 3Liisa Nevalainen. Division of Aquatic Sciences, Department of Biological and Environmental Science, University of Jyvaskyla, P.O. Box 35, 40014, Finland. This email address is being protected from spambots. You need JavaScript enabled to view it.

Liisa Nevalainen is a Senior Lecturer of Aquatic Sciences in Department of Biological and Environmental Science, University of Jyväskylä. She is a paleolimnologist and aquatic ecologist with a research focus in understanding lake ecosystem dynamics and lake-catchment coupling processes under natural climate fluctuations and anthropogenic disturbances. She is interested in Holocene-Anthropocene scale changes and boreal, arctic and alpine biomes.

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author 4Johannes Edvardsson. Quaternary Sciences, Department of Geology, Lund University, Sölvegatan 12, SE-223 62 Lund, Sweden. This email address is being protected from spambots. You need JavaScript enabled to view it.

Johannes Edvardsson is a dendrochronologist and geoscientist with solid history in tree-ring research, climate reconstructions, palaeohydrology, and peatland development. He received his PhD thesis at the Department of Geology, Lund University, Sweden, in March 2013. In his PhD thesis he examined hydroclimatic changes during the Holocene using subfossil peatland trees and stratigraphic records from Swedish peatlands. Johannes Edvardsson continued his hydroclimatic research using subfossil trees from the Baltic region during his three years postdoc employment at the Swiss Tree-Ring Laboratory, Bern University in Switzerland. As a complement to basic tree-ring width data he also has been working with stable isotopes in tree rings and has experience from working with non-invasive analysis of wooden objects, an important aspect when examining art objects. Apart from climatic studies, Johannes Edvardsson has been using tree-ring data to date Flemish 17th Century paintings on oak panels, standing constructions, and archaeological material. 

 

FIGURE 1. Map of North Europe showing the locations of the study site in southern Finland (filled circle) and other late Quaternary palaeoclimate-data producing sites (open circles) mentioned in this study. Lake Iso Lehmälampi is the site of water level reconstructions based on subfossils of the chironomid midge and cladoceran water flea (Luoto, 2009; Nevalainen et al., 2011; Nevalainen and Luoto, 2012). Lit-1 and Lit-2 are tree-ring sites studied by Pukienė (1997) and Edvardsson et al. (2016), respectively.

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FIGURE 2. Replication curves of the subfossil tree-ring chronologies. 1, lake sites; and 2, the peatland site. Data are given in Table 1.

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FIGURE 3. Comparisons of the proxy indications from southern Finland from AD 600 to 1800. 1, the Palmer Drought Severity Index (PDSI) reflecting spring-summer soil moisture conditions (Cook et al., 2015); 2, the water level reconstruction based on subfossil chironomid midge (dashed line) and cladoceran water flea (solid lines; calibrations from intra-site by thick line and multi-site training sets by thin line) communities in Lake Iso Lehmälampi (Luoto, 2009; Nevalainen et al., 2011; Nevalainen and Luoto, 2012); and 3, the replication curves of the subfossil tree-ring chronologies constituting a peatland and eight lake sites (this study).  

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