The Supra-Long Scots Pine Tree-Ring Record for Finnish Lapland
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TheHolocene 12,6(2002) pp. 673– 680 Thesupra-long Scots pine tree-ring record forFinnish Lapland: Part 1, chronologyconstruction and initial inferences Matti Eronen, 1*Pentti Zetterberg, 2 Keith R.Briffa, 3 Markus Lindholm, 1 Jouko Merila¨inen 4 and Mauri Timonen 5 (1Department ofGeology, POBox 64, FIN-00014 University ofHelsinki, Finland; 2KarelianInstitute, University ofJoensuu, POBox 111, FIN 80101 Joensuu, Finland; 3ClimaticResearch Unit, University ofEast Anglia, Norwich NR4 7TJ, UK; 4Saima Centre forEnvironmental Sciences, University of Joensuu, Linnankatu11, FIN-57130 Savonlinna, Finland; 5FinnishForest Research Institute, POBox 16, FIN-96301 Rovaniemi, Finland) Abstract: Thispaper reviews thedevelopment of thecurrent ‘ supra-long’pine chronology for northern Finnish Lapland.In the forest-tundra ecotone region of northernFinnish Lapland over 250 samples fromliving Scots pines (Pinussylvestris L.)and over 1700 samples ofsubfossilpines have been collected for dendrochronological studies.In addition, over 1400 subfossils have been sampled fromthe forested area ofFinnish Lapland. The goalof the research was tobuild a more than7000-year long continuous pine ring-width chronology. The constructionof the chronology is nowcompleted. The intensive phase of the data collectionand chronology buildinglasted about10 years, 1989to 1999. The major partof the Finnish Lapland master curvewas con- structedseveral years ago,but it was extremely difcult to bridge the c. 300-yeargap, prior to 165 bc between the‘ absolute’younger part of thechronology and the ‘ oating’older part. The crucial samples were identied andassembled inthe chronology in early 1999,and there is nowan unbroken pine chronology about 7500 years longconstructed from the subfossil forest-limit pines of northern Finnish Lapland. The severe growth depressioncentred on 330 bc is likelyto have been caused byincreased wetness. Abriefsummary is presented ofinferred tree-line changesfrom the location of thesamples. Key words: Dendrochronology, Pinussylvestris ,tree-growthvariability, climatic change,Finnish Lapland, Holocene. Introduction andNesje, 1996). The dated tree megafossils are valuable tools inmapping the former expanse of pine. Subfossil remnants can Manyearly naturalists and explorers, who travelled in Laplandin befound from peatlands, especially at the higher elevations of thepast few centuries, made observations on pine stumps and Scandinavianmountains, where stumps can occur in exposedpos- trunkslying far beyond the present limit of pine (Eronen, 1979). itions(cf. above references). In the atareasof Finnish Lapland Theages of thesesubfossils remained unknown until the numeri- thespread and growth of mires has to a largeextent buried the caldating of treeremnants became possible after the invention of oldtrees. Subfossil trees can be discovered in peat areas only theradiocarbon method. In theNordic countries, the rstdates on occasionally,for example in sectionsmade for road construction. oldpine stumps found above the present tree-line were obtained in Duringearlier studies on the history of pine forests and the Swedenin the late 1950s (Lundqvist, 1959; 1962). Since then, coniferoustree-line (Eronen, 1979; Eronen and Hyva ¨rinen,1982; thenumber of 14Cdatedpine subfossils from the tree-line areas of Eronenand Huttunen, 1987; 1993) numerous samples of subfossil theScandinavian mountains and Lapland has expanded to several pineswere collected from many lakes in northern Lapland, and hundreds(Eronen and Huttunen, 1987; 1993; Kullman, 1993; radiocarbondated. The eldnotes and dates resulting from that 1995;2000; Karle ´n,1993; Karle ´nandKuylenstierna, 1996; Dahl workwere valuable when an intensied collectionof samplesfor dendrochronologicalpurposeswas started in 1989. In 1990–96 it *Authorfor correspondence(e-mail: [email protected].) waspossible to continue the eldworkand dendrochronologica l Ó Arnold 2002 10.1191/0959683602hl580rp 674 TheHolocene 12 (2002) researchas part of the Finnish Research Programme on Climate Samplesfrom the old Sodankyla ¨parishchurch, nine beams in all, Change(SILMU). Themain purpose of collecting samples was werealso used (Lindholm et al., 1999). toacquirematerial for building a 7000-yearor longercontinuous pinetree-ring chronology for northern Finnish Lapland and use it Subfossilsamples fordendroclimatological studies. The basis for de ning the goal Inthe eld,subfossil pines were collected by a teamusually of asthat time period was the age of the oldest radiocarbon dated veor six people, including one or two divers. The divers made pinesubfossil in the Finnish Lapland data, 6930 6 170 BP itpossible to sample almost all megafossils preserved in each (Hel-835),which is around 7680 cal. BP (Eronen,1979; Eronen studiedlake. During earlier work in the1970s, the subfossils were andHuttunen, 1993). foundonly by making observations from the shore. These were Inthestudy being described here, only a verysmall proportion usuallyfew in number, perhaps 10 or 12 at most. In the same ofthe subfossils were collected from peat sections. The great lakes,divers found many more logs, including those buried deep majorityof sampleswere recovered from small lakes in northern- inthe mud, stamping on them through mud or crawling in the mostFinland (Figure 1). During the eldworkin northernFinland, shallowwater and probing by hand.Logs were pulled to theshore itwas observed that the lake levels had risen during the past bymanpower, using logging tongs connected to a heavy-duty thousandsof years, which also partly explained the good preser- rope.When the logs were tightly stuck in the mud, it was vationof logs.Lithostratigraphical and microfossil studies of lake necessaryto use a combinationof one or two winches and an sedimentsin the areas where old pines were collected con rmed aluminiumtripod (Figure 2). The winches were usually xedto thatlakes had risen to theirpresent levels during the latter part the mountainbirches growing close to the shore. These techniques Holocene(Hyva ¨rinenand Alhonen, 1994; Eronen et al., 1999a). failedonly in a veryfew occurrences, when trying to move very largeand deep-seated trunks. Onthe shore, sample discs, usually 5– 10 cm thick, were cut Materials witha chainsaw;where possible, the samples were taken from the basalpart of the trunk. However, this part was often decayed, or Livingtrees and construction timber thelog broke while being removed from the lake and in these Inorder to getaccurately dated long tree-ring chronologies, they casesthe sample was cut from the lowermost well-preserved part. mustbe ‘anchored’to the absolute calendar timescale by overlap Sometimesthat was several metres above the original root system, withtree-ring series from living trees. Even though several whichmeant that many of the oldest annual rings of a treewere chronologies,constructed using living pines, already existed in missed.Logs which were badly decayed or contained fewer than FinnishLapland, additional living trees were cored in thevicinity 50treerings were rejected as notusable for accurate cross-dating. ofthe coniferous tree-line area to establish climatically sensitive Aftersampling the logs were pushed back into the lake. localand regional chronologies for the present research: 474 cores Fromlong-lived well-preserved trees, some larger samples from258 living trees were collected, measured and cross-dated werecollected for possible further analyses and demonstration toyield 12 site chronologies and one regionally representative purposes.All samples were wrapped in plastic bags, given code series(Lindholm, 1996; Lindholm et al.,1996a;1996b). The old- labelsand, depending on eldconditions, transported by back- estring of alivingpine, cored in thetree-line area, started growth pack,ATV, boator small aeroplane. in ad 1398at Karhunpesa ¨kivi,Inari, thus having 600 annual Thenumbers of sample discs from different subareas in the rings. tree-linezone are reported in Eronen and Zetterberg (1996) and Logsused for building constitute an importantlink between the Eronen et al.(1999a).The samples collected by theFinnish Forest livingtrees and megafossils found in natural situations. Pine is Institute(METLA) teamin 1994– 98, mainly from the forested commonlyused as building material in Lapland and beams of areaof Lapland, are shown in Table 1. someold wooden buildings provided valuable data for connecting thetree-ring series made from living trees to thechronology con- structedfrom subfossil logs preserved in lakes(Zetterberg, 1990). Constructionof themaster chronology Inthelaboratory, the samples were dried slowly at roomtempera- 7800 ture.For tree-ring measurement, one surface of the slab was 50km Lake Ailigasjärvi sanded.The ring widths were measured from each disc along 118 10 23 117 1 32 645 Utsjoki 1 3 2 threeor four different radii with an accuracy of 0.01 mm. All 111 1 38 measurementsfrom one tree were averaged into a singletree-ring 1 4 1 14 23 14 0 119 13 1 12 1223 1 33 144 1 36 1 14 208 Karigasniemi 1 02 671 1 4 106 5 7700 11 Sevetti- series.A tentativecross-matching of the individual tree-ring 1 3 9 1 28930 2 6 järvi Kilpis- curvesand the developing subchronologies was routinely com- järvi 13 5 pletedusing several procedures (Fritts, 1976; Holmes et al., 1986; 12 117 5 Lake Luolajärvi 1 0 4 1 47 VanDeusen and Koretz, 1988; Aniol, 1989; cf. also Briffa and 1 3 4 1 9 14 5 1 3 7 1 0 8 3 2 Ivalo Lake Kompsiojärvi 11 234 2 1 22 16 1 8 11 6 2 0 1 7 2 3 33 Jones,1990; Cook et al.,1990).The nalcorrelation was always 891 0 7 5 34