The Supra-Long Scots Pine Tree-Ring Record for Finnish Lapland

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.)andover 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

34 7600 1234 Rajajooseppi

3 1 5

4 Hetta 2 5 basedon visual inspection of tree-ring curves. 2 7 Saariselkä Pokka Withcross-correlation it is possible to extend the chronology Lake Pitkäjärvi asfar back in time as the available tree samples with preserved Muonio

1 tree-ringpattern. Sometimes ‘ missingrings’ may occur in thepine

7500 3 5 28 Sodankylä tree-ringseries, i.e., a verynarrow annual increment may be dis-

Kolari 2 continuous,parts of it disappearing totally in a largeror smaller 29301 sectorof thesample disc. Nevertheless, the ‘ missingrings’ can be 250 300 350 400 450 500 550 600 650 detectedin most cases by careful visual examination of samples Figure 1 Mapshowing the study area innorthern Finland and the andcorrelations with other curves. However, a certainnumber of samplingsites ofsubfossilpines. The present limit of pineis marked with samplesdisplay such irregular or suppressedgrowth patterns that abrokenline. The triangles show the sites sampled bythe Helsinki- theycannot easily be measured accurately or matched positively Joensuuteam andthe circles thesites sampled bythe Finnish Forest withother samples or averagedsection of chronology.About 10– Research Institute(METLA) team. 15% ofthe samples belong in this category. ADVANCE-10KSpecial Issue: Long pinechronologies fromnorthern Fennoscandia 675

Figure 2 Asubfossilpine being pulled to the shore. Lohikoste, Utsjoki (photograph: M. Eronen).

Earlierstudies on subfossil pines in Finnish Lapland had pro- tothegrowth of atleastsome tree species and/ orperhaps also to ducedover 60 radiocarbon dates of samples collected from the thepreservation of dead trees. forest-tundraecotone (Eronen, 1979; Eronen and Hyva ¨rinen1982, Aftermany frustrating, failed attempts, crucial progress in Eronenand Huttunen, 1987; 1993). Many of those samples were bridgingthe gap was made in late 1998. A prerequisitefor the stillavailable when work began on buildingthe long pine chron- successfulcross-matching was the sharing of Finnishand Swedish ology.Many of theirtree-ring patterns could be matchedwith the pinedata. Another important factor was the radiocarbon wiggle- tree-ringseries of newsamples collected in largenumbers. In this matchdating of one Swedish wood sample (Grudd et al., this wayit was possible to build subchronologies of different age, issue).The Finnish teams changed their data-collection strategy. approximatelydated by included radiocarbon dated samples. As Untilthis point, the Joensuu and Helsinki teams had collected thesesubchronologies were developed, additional individual tree- woodsamples solely from the tree-line area, to maximize the ringseries could be datedin increasingnumbers by cross-match- potentialclimate sensitivity of thedata as regardspure palaeocli- ingthem, continuously extending them and increasing their repli- maticstudies. Subsequently, eldworkwas moved further south cation.It then became possible to cross-match the overlapping totheforested part of northwesternFinnish Lapland. The METLA partsof these oatingchronologies and join them together. The teamhad also been collecting samples from the forested areas of workeventually reached a stagewhere one large data set com- northernLapland since the beginning of theirwork, and in 1997– priseda single . 5000-yearchronology for the time preceding the 99they collected about 700 sample discs from three lakes (Lake Christianera, containing many radiocarbon dated samples, which Kompsioja¨rvi,Lake Luolaja ¨rviand Lake Pitka ¨ja¨rvi,see Figure 1) xedits position within rather narrow limits of accuracy. At the wherethey tried to select logs of suitable age for llingin the sametime, the ‘ absolute’chronology, more than 2000 years long, gap.Surprisingly, it is possible by visual inspection to estimate ranfrom the present continuously back to thesecond century bc. veryroughly the ages of the old logs because they are often Thismeant that a c.7500-yearlong dendrochronologica lcurve depositedin layers in the sediments with the younger subfossil wasalmost completed in 1994, except for one gap estimated to boleslying above the older ones. Second, it ispossibleto discern be250– 300 years long for the period running up to 165 bc. It manydifferences in theshape and status of preservation between becameevident in subsequentwork that it wasextremely dif cult olderand more recent pine subfossils. The selective sampling tobridgethe gap (Zetterberg et al.,1994;1995; 1996; Eronen and resultedin increased numbers of samples dating around the time Zetterberg,1996; Eronen et al., 1996). ofthe gap, but most often either before or after it. Samplecollection subsequently was continued in Finland by Anotherstrategy focused on concerted attempts to build a twoteams, one made up of university researchers from Helsinki separatechronology that would cross the gap, by usingthe radio- andJoensuu and the other of researchers based at the Finnish carbondated sample (FIL6201 from Lake Ailigasja ¨rvi,age 2280 ForestResearch Institute (METLA). New samplesmade it 6 130BP, Hel-834)as a basereference, but this proved unsuc- possibleto extendthe ‘ absolute’chronology until 260 bc in 1998, cessfulfor a longtime. Finally the critical data were found in buta gapstill remained. late1998 when a samplefrom Lake Kompsioja ¨rvi(KOM6724) Inthe collected data, there are pines that grew in the present containing199 tree rings was cross-matched with FIL6201 and tree-linezone and even beyond it, but still survived over that time produceda mergedseries that spanned 332 years, eventually ofhardships.The 14Cdatedsample FIL6201 collected from Lake identied as 512– 181 bc.Thisplaced the 5000-year oating Ailigasja¨rviin Utsjoki(Figure 1) isonesuch survivor (Figure 3). chronology85 yearsearlier than its tentative position at thattime. Probablypines and pine stands had declined at extreme growing Thisnew position was also in agreement with the wiggle-match sitesand the density of trees thinned over wide areas. The lack datingof the Swedish series. The new position also enabled new ofsubfossil trees around the beginning of the Christian era has cross-matchesof othertree-ring series that con rmed the connec- beenencountered in other pine megafossil data in Sweden and tionbetween the 2000-year and 5000-year Finnish series, such as Norway(Kullman, 1993; 1995; Karle ´n1993;Karle ´nand werefound using a numberof additional data from Lake Kuylenstierna,1996; Dahl and Nesje, 1996) and even in longEur- Kompsioja¨rviand some supporting Swedish data. (Figures 4 opeanoak records (Frenzel et al.,1998).This European-scale cli- and 5). maticevent produced conditions temporarily very unfavourable Itcan be seen in Figure 5 thatthe sample KOM6274 covers 676 TheHolocene 12 (2002)

Table 1 Thesites ofsubfossil pines sampled bythe Finnish Forest Research Institute(METLA) team. Thenames andcodes, locations, altitudes above sea leveland numbers of collected samples are given

Site y-coord.x-coord. Height Number of samples collectedin Total a.s.l. 19941996 1997 1998

Northern Lapland 1Vallija¨rvi 7632.3 280.3 465 – 24 – – 24 2Pa¨ttikka¨ 7625.4 286.0 400 – 22 – – 22 4 Na¨kka¨la¨ 2 7610.2 349.9 350 6 – – – 6 6 Na¨kka¨la¨ 5 7614.0 356.2 350 – 13 15 – 28 7 Na¨kka¨la¨ 1 7617.1 359.8 370 1 – – – 1 8 Na¨kka¨la¨ 4 7627.8 367.1 440 9 – – – 9 9Na¨kka¨la¨6 7620.9 363.3 345 – 5 – – 5 10Na ¨kka¨la¨PS 7610.1 356.2 350 9 – – – 9 11Pahtaja ¨rvi(Na ¨kka¨la¨3) 7617.1 361.8 390 3 – – – 3 12 Na¨kkala¨ 6 7620.9 363.3 345 – 3 – – 3 15Kalmankaltio 2 7593.9 403.8 340 – 20 – – 20 16Kalmankaltio 1 7595.6 405.3 345 2 – 4 – 6 17 Utsjoki 7751.5 475.1 100 3 – – – 3 18Kuntsavaara (Muotkanruoktu) 7698.0 496.0 190 45 – – – 45 19Petsimija ¨rvi(Muotkanruoktu) 7689.3 499.5 190 13 – – – 13 12aNa ¨kka¨la¨7 7620.3 362.8 395 – 9 – – 9 Iija¨rvi 7620.3 362.8 395 – 9 – – 9 TotalNorthern Lapland 91 96 24 0 211 Western Lapland 3Kultimaja¨rvi1 (Enontekio¨) 7604.0 335.0 334 9 – – – 9 3Kultimaja¨rvi2 (Enontekio¨) 7604.0 335.0 334 – 39 – – 39 3Kultimaja¨rvi3 (Enontekio¨) 7604.0 335.0 334 – 31 – – 31 13 Pitka¨ja¨rvi(Pallastunturi) 7578.2 376.5 290 – 30 – – 30 14Peltovuoma (Kittila ¨) 7589.9 402.5 337 5 – – – 5 26 Pahtaja¨rvi (Ylla¨s) 7512.2 367.0 235 8 – – – 0 27 A¨ ka¨sja¨rvi (Ylla¨s) 7528.5 381.5 265 5 – – – 8 28Hangasmaa (Ylla¨s) 7514.1 377.1 265 – – 153 – 5 29Pitka ¨ja¨rvi(Ylla ¨s) 7494.0 368.5 290 6 4 – – 157 30Saivoja ¨rvi(Ylla ¨s) 7497.4 170 – – 6 TotalWestern Lapland 33 104 153 0 290

Eastern Lapland 20 Koierija¨rvi(Saariselka ¨) 7602.4 512.0 250 5 – – – 5 21Riekkovaara (Saariselka ¨) 7599.0 512.0 280 70 – – – 70 22Luttojoki (Saariselka ¨) 7595.0 525.0 280 10 – – – 10 23Luolaja ¨rvi1 (Rajajooseppi) 7598.5 541.5 200 15 – – – 15 23 Luolaja¨rvi1 (Rajajooseppi) 7598.5 541.5 200 – 38 – – 38 23 Luolaja¨rvi2 (Rajajooseppi) 7598.5 541.5 200 – 30 – – 30 23 Luolaja¨rvi3 (Rajajooseppi) 7598.5 541.5 200 – 26 110 – 136 24Riekkoja ¨rvi(Rajajooseppi) 7608.0 545.3 190 – 36 10 – 46 25Kompsioja ¨rvi(Rajajooseppi) 7604.0 547.1 190 – 72 130 200 402 31Ha ¨rka¨joki(Pelkosenniemi) 7473.1 514.5 165 – 13 – – 13 32Puljunpalonlammit 1 (Pelkosenniemi) 7467.1 517.0 160 – 27 – – 27 32Pulijunpalonlammit 2 (Pelkosenniemi) 7467.1 517.0 160 – 15 – – 15 32Puljunpalonlammit 3 (Pelkosenniemi) 7467.1 517.0 160 – 14 – – 14 33Kolmiloukkonen (Salla) 7406.1 581.7 293 4 – 50 – 4 34Haltija ¨rvi(Salla) – – – 20 – 50 35Hossa (Kuusamo) – 15 15 – 50 TotalEastern Lapland 119286 320 200 925

Other (exhibitionsamples etc) 25 15 35 – 75 Summary:all samples in Northern Finland,collected byMETLA Northern Lapland 91 96 24 200 211 Western Lapland 33 104 153 290 Eastern Lapland 119 286 320 860 Other 25 15 35 75 Totalno of samples in Finnish Lapland 268 501 532 1436 ADVANCE-10KSpecial Issue: Long pinechronologies fromnorthern Fennoscandia 677

Fil6201

Kom6724

-400 -380 -360 -340 -320 -300 -280 -260 -240 -220 -200 BC -0.05 .24 .79 .16 .44 .53 .37 -.10 Figure 3 Sample FIL6201from Lake Ailigasja¨rvi,situated north of the present tree-line innorthernmost Finland, and sample KOM6724from Lake Kompsioja¨rvi,situated in the forested area ofLapland, over 150 km further south. A suddendrop in radial growth of pines occurred 330 bc and the recoveryfrom it was slow.(Note: 330 bc is shownat 329in the graph, because thescale is displaced1 year toaccount for the absence ofa year 0at the bc/ad boundary.)

Kom6131

Kom6724

-380 -370 -360 -350 -340 -330 -320 -310 -300 -290 -280 -270 -260 BC .32 .59 .41 .31 .81 .77 .52 .47 .11 .19 .56

Figure 4 Anexample showingvery similar growthpatterns in the ‘ gapsection’ . Thesamples fromLake Kompsioja¨rvi,KOM6131 and KOM6724, cover aperiod379 to 265 bc Notethe sharp drop in growth 330 bc (cf. Figure3).

1.0 Correlation between samples (RBAR)

0.5 R=0.40 0.0 PIT3125 RIE3185 KOM6707 KOM6712 KOM6810 KOM6820 PIT3142 KOM6750 KOM6740 KOM6724 KOM6827 KOM6530 KOM6131 KOM6814 KOM6724 KOM6717 KOM5975 KOM6143 KUL3006 NAK4912 PIT6568 LUO3122 LUO5624 PIT4963 RIE5640 KOM6706 NAK6047 VAL5031 VAL5022 KOM6545 VAL6087

-1200 -1000 -800 -600 -400 -200 0 200 YEAR SCALE Figure 5 Age prole ofcross-matched tree-ringseries for1200– 160 bc,showingalso the problematic period where theformer gapin the long chronology existed(box). The interseries correlation(RBAR) showsin these selected data arather highcommon growth signal. The sample KOM6724was very importantin successful bridgingof thegap. 678 TheHolocene 12 (2002) almostthe entire time period of theformer gap in thedata. There and,from a dendroclimatologicalviewpoint, adding unwanted aremany other tree-ring series, mostly from Lake Kompsioja ¨rvi, ‘noise’to the record. These include different edaphic conditions, whichoverlap each other with rather high correlations in thismore variationsin aspector elevationand the possible effect of compe- than200-year period. The replication is good enough to support tition.These effects can be partlyremoved by thestandardization theclaim that the dating of thecontinuous Finnish Lapland 7500- ofthe tree-ring records (Helama et al.,thisissue). yearpine tree-ring chronology is now complete. Data from the Therewas a suddendrop in thepine growth in 330 bc (Figures SwedishTornetra ¨skchronologywere, however, necessary to con- 3and4). A verythin ring was formed in that year and the re- rmsome critical sections of lowinternal correlations. At thetime coveryfrom the blow took about 20 years. Based on the ring ofwriting, the Finnish Lapland series is constructed from 1087 widths,this was the most unfavourable year for the growth of averagedtree-ring series from sample discs of subfossilpine trees tree-linepines in Lapland during the entire 7500-year period and51 averaged tree-ring series from living trees. The older part (Lindholm et al.,unpublisheddata). Afterwards, in the third cen- ofthechronology running up until c. 400 bc isconstructedmainly tury bc,thetrees seem to turn back to ‘ normal’growing con- fromtree-line area samples collected by the Helsinki-Joensuu ditions.The cause for the sudden fall in thegrowth rate is notyet team.The samples around the former ‘ gapsection’ c. 400–200 bc known.Detailed pollen and tephra analyses have been made from aremainly from the forested area of Laplandand collected by the apeatcore collected from northern Lapland (Saastamoinen et al,. METLA team.In the younger part of the chronology, from 200 2000).No exceptional features in pollen data were found at the bc tothe present, the material is a mixtureof data from both levelsdeposited around 330 bc andonly a fewshards of volcanic teamsand many data in the most recent part are collected from glasswere found, providing little, if any, evidence for a volcanic buildingsand living trees. Thus the record consists of rather het- eruptionor an abrupt cooling. This leaves the possibility of a erogeneoussources and in that sense should be considered far signicant change in humidity.As mentioned above, the humidity fromhomogeneous, although on short (interannual to decadal) increasedin line with the cooling trend after the warm mid- timescalesseveral studies have demonstrated wide regional simi- Holocene(Hyva ¨rinenand Alhonen, 1994; Eronen et al., 1999a). larityin ring-width variability and empirically ascribed summer- Increasedwetting of the ground would have caused conditions temperaturesensitivity (Hustich 1948; Briffa et al.,1990;1992; unfavourableto lakesidetrees, and waterlogging of thesoil would Lindholm,1996; Lindholm et al.,1999;Lindholm and Eronen, haveseverely restricted root respiration, even to the point where 2000;Kirchhefer; 1999). This chronology currently extends from itcouldkill the trees (cf. Zetterberg et al.,1994).Hence, the 330 5520 bc to1999: a totalof 7519 years. bc severeevent may be associatedwith greatly increased precipi- tationand increased stress and even mortality of tree-line pines. Whateverthe cause, the radial growth of pineswas seriously dis- Initial inferences turbedin the decades following 330 bc andthe normally strong interseriescorrelation between individual tree records weakened Growth variabilityand events around400– 100 BC inthattime. This strongly suggests that cold summer temperatures Thepine tree-ring curve calculated as thesimple arithmetic aver- werenot the sole decisive growth-determining factor. ageof the raw averaged tree measurement data is presented in Probablymany young trees germinated soon after the ‘ catas- Figure6. Because of the heterogeneity of source material, the trophe’, reachinga ‘normal’growth rate, while many old trees in variablereplication through time and the bias when relatively theregion presumably had perished in the catastrophic times. It youngtrees (with wider ring widths) predominate over older tree mustbe kept in mind that many subfossils in this part of the samples,the raw data curve cannot be usedas areliableindicator chronologyare from the forested area of Lapland, far from the ofthe full spectrum of potential climatic variations. In addition, tree-line.The samples from Lake Kompsioja ¨rvi(Figure 5) were thereare many non-climatic factors affecting the growth of trees usedto llthe gap in thechronology, and many of themhad been

1.5

1.0

0.5

0.0 -5500 -5000 -4500 -4000 -3500 -3000 1.5

1.0

0.5

0.0 -3000 -2500 -2000 -1500 -1000 -500 1.5

1.0

0.5

0.0 -500 0 500 1000 1500 2000 Figure 6 Themean raw data 7519-yearFinnish Lapland pine tree-ring chronology, extending back to 5520 bc.Theaverage ringwidth remains surprisingly constantat about0.6 mm yr 2 1 throughoutthe whole length of thechronology. The thin line indicates annual ring-width variability (in mm) andthe bold line50-year running means. ADVANCE-10KSpecial Issue: Long pinechronologies fromnorthern Fennoscandia 679 growingconsiderably more than the tree-line pines. As a whole, trendsin the raw data that do not degrade the longer timescale theformer problematic ‘ gaparea’ in thechronology building does signals.The data set should be expanded further to improve the notin retrospectstand out as aperiodradically different than the qualityof the record. As further material from the tree zone otherparts of the chronology. becomesavailable it will also be possible to enhance the hom- Thevariability of ringwidths in Figure6 maypartly re ect the ogeneityof the data, particularly in the early centuries bc where occasionallychanging ages of trees whose annual increments are moresoutherly material make up the series. assembledwithin the chronology. Today, it is known that two InPart2 ofthispaper (Helama et al.,thisissue), an alternative consecutivesummers warmer than the modern average are approachto chronology construction, aimed at preserving long- requiredfor the production of pineseed in Lapland(Mikola, 1978; timescaleinformation, is described, along with a descriptionof Pohtila;1980). During the cool period, ad 1781–1850, major pine theinferred temperature variability. regenerationin northernLapland occurred only once (Mielika ïnen et al.,1998)and according to Pohtila (1980) the regeneration of pinein northern Lapland succeeds only six times a centuryon Acknowledgements average.It canbe concluded that in thetree-line area of Lapland theyears of successful regeneration were rather rare in the past. Wethank the technica lstaffof the Karelian Institut e, Therecruitment of new tree generations after good regeneration UniversityofJoensuu, especiall yPirjoHarmaala who meas- periodswill increase the average growth for many decades and uredmost of the tree-rin gdata,and Kari Ratilaine nandIlkka thesechanges affect the shape of the raw-data curve (cf. Kinnunenwho did great work in the eld.Tauno Luosuja ¨rvi Zetterberg et al., 1994). participatedin the eldwork,measured the major part of the collectedtree-ringdataand made an important contribution to Pine tree-line changes the nalconstruction of thechronology at METLA. Amajorpart Ifwe accept that the distribution of pine forest is an indicator, ofthesamples from living pines was measured by thetechnicians albeitsomewhat lagged, of slow changes in the thermal climate, ofthe Saima Centre for Environmental Sciences. This enduring wecan infer such changes from the variations in thelocations of effortin chronology building was nancedby the EC Research thedated samples. The dendrochronologica ldatingof subfossil Programmeon Environmentand Climate, contracts ENV4-CT95- pineshas resulted in agreatexpansion in thenumber of accurately 0127(ADVANCE-10K) andEV5V-CT94-0500 (Tree-ring datedwood samples. More than 1000 records of individual evidenceof climate change in northern Eurasia during the last megafossilshave been assembled within the supra-long master 2000years). We also acknowledge support from the Academy of series,and because the large majority of themwere collected from Finland(SILMU, FinnishResearch Programme on Climate theforest-tundra ecotone they can be used to reassess long-term Change,and grants 34477, 35386 and 40962 to M. Eronen)and changesin summer warmth that are not apparent in the tree-ring theEuropean Science Foundation (European Palaeoclimate and chronologyitself. The mean ring width remains more or less the Man). same(0.6 mm) throughoutthe whole 7500-year chronology. Pinemigrated to northern Finnish Lapland by 9500– 9000 cal. BPandimmediately spread beyond its present limits (Hyva ¨rinen, 1975).The evidence of themegafossils and pollen data are mutu- References allysupportive in indicating that the time of maximum extent of pinein Finnish Lapland was between 6800 and 4500 cal. BP. Aniol, R.W. 1989: Computeraided tree ringanalysis system. User’s Afterwards,the northernmost pine tree-line and the limit of forest manual.Schleswig,Germany (stencil),20 pp. graduallyretreated. Again, both the pollen and megafossils indi- Barnekow,L. 1999:Holocene tree-line dynamicsand inferred climatic cateslow decline (Hyva ¨rinen,1975; Eronen and Huttunen, 1987). changesin the Abisko area, northernSweden, based on macrofossil and pollenrecords. TheHolocene 9, 253–65. Thedated subfossils show that pine tree-line retreated in north- Briffa,K.R. and Jones, P.D. 1990:Basic chronologystatistics and westernFinnish Lapland at most about 70 km, while at thesame assessment. InCook, E. andKairiukstis, L., editors, Methodsof dendro- timemoving 100 m loweron the mountain slopes (Eronen and chronology:applications in the environmental sciences ,Dordrecht: Huttunen,1987; Eronen et al.,1999a;1999b). The shift was less Kluwer Academic Publishers,137– 52. pronouncedin more easterly parts of Lapland, but as a whole Briffa,K.R., Bartholin, T.S., Eckstein, D., Jones, P.D., Karle ń, W., thereis evidence for a generallowering of summer temperatures Schweingruber,F.H. and Zetterberg, P. 1990:A 1400-yeartree-ring by about 2°Csincethe mid-Holocene (Donner, 1995; Barnekow, recordof summer temperatures inFennoscandia. Nature 346,434– 39. 1999).This is notdiscernible in thepine tree-ring data. 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