Late Glacial fossil leaves of Thuja occidentalis from ...

Late Glacial fossil leaves of Thuja occidentalis from Manitoulin Island, Ontario BARRYG. WARNER

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Department of Biological Sciences, Simon Fraser Universiv, Burnaby, B.C., Canada V5A IS6 Received August 17, 1981 WARNER,B. G. 1982. Late Glacial fossil leaves of Thuja occidentalis from Manitoulin Island, Ontario. Can. J. Bot. 60: 1352- 1356. A leafy twig fragment of Thuja occidentalis L. was isolated from sediments dating about 10 000 years before present (B.P.) from Manitoulin Island, Ont. This is the earliest known record of Thuja leaves in postglacial deposits in eastern North America. Thuja may have arrived in Ontario in association with boreal spruce forests, but was a component of early pine forests. WARNER,B. G. 1982. Late Glacial fossil leaves of Thuja occidentalis from Manitoulin Island, Ontario. Can. J. Bot. 60: 1352-1356. Un fragment de rameau feuill6 du Thuja occidentalis L. a CtC isole de s6diments 2gCs d'environ 10 000 ans B.P. sur l'ile Manitoulin (Ontario). I1 s'agit de la plus vieille mention de feuilles de Thuja dans des dCp8ts post-glaciaires de l'est de 1'AmCrique du Nord. Le Thuja a pu atteindre llOntario en association avec la forCt boreale d7Cpinettes, mais il faisait partie des prernikres forCts de pins. [Traduit par le journal]

Introduction Successive immigrations of trees are reflected in postglacial pollen diagrams throughout northeastern North America. These migrations are time transgressive in response to the northward recession of the ice. Several workers have mapped migration patterns of dominant tree Species (Davis 1976; Bernabo and Webb 1977; Kapp 1977; Jacobson 1979). It appears that individual species migrated at different rates from different refugia, ultimately culminating in modem forest associations favouring similar growth regimes (Davis 1976). Modem associations did not ~ersistintact in southern refugia, which strengthens the need to consider migration of tree species individually. The history of tree species with a less abundant pollen record is more difficult to ascertain. Thuia occidentalis L. presents one such problem. Early workers speculated that Thuja swamps in southern Ohio, lying south of the modem continuous range, are relics of previously extensive northern coniferous forests ( ~ r a u n1928). While not commenting specifically, Catling et al. (1975) recorded Thuja as an important component of alvar communities which thev surmised are remnants of an eastward extension of prairie vegetation into Ontario during a mid-Holocene climatic optimum. The occurrence of this event in Ontario with respect to the vegetation has been discussed recently by McAndrews (1981). There is little hope that the fossil pollen record will illuminate the history of Thuja. Palynologists cannot confidently distinguish Thuja pollen from that of other members of the subfamily Cupressineae, such as Juniperus. Juniperus needles and seeds from mid- and late-Wisconsinan sediments confirms its presence (Berti

1975a, 1975b; Karrow et al. 1975; Miller and Thompson 1979) and possible contribution to the pollen record. Richard (1980) attempted to differentiate the two pollen types recognizing that Thuja pollen is usually folded and crumpled, while Juniperus pollen is usually broken by a longitudinal slit. There are intermediate forms, but given a large number of grains, Richard is confident that trends can be recognized in the pollen record of the two species. McAndrews and King (1976) caution that there may even be confusion with the pollen of some members of the subfamily Taxodioideae. Cupressineae pollen may be confused with some algal or bryophyte spores which may split in the same characteristic manner when viewed in slide preparations (Moore 1980). Cupressineae pollen is often poorly preserved except under ideal conditions, and inaperturate, nondiagnostic forms may result (Miller and Thompson 1979). The problem is further complicated with Thuja because it readily reproduces by vegetative layering (Fowells 1965; Collins et al. 1979). It is possible that populations of Thuja might have existed in postglacial environments without contributing pollen or seeds to a potential fossil record. Vegetative macrofossils hold more promise in establishing the presence of Thuja largely because macrofossils may be identified to the species level, generally provide conclusive proof of local presence, and define the earliest certain time of arrival for migrating species (Watts 1978). Wood remains of Thuja have been recovered from Sangamonian interglacial beds at Toronto (Terasmae 1960; Karrow 1969), possibly from mid-Wisconsinan sediments from Ellesmere Island (Lowden et al. 1971),

0008-4026/82/08 1352-05$01 .OO/O

01982 National Research Council of Canada/Conseil national de recherches du Canada

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WEST

EAST

Torasmas's

woody p e a t

sedge peat H g y t t a

0

stlty clay

sllty gravel

FIG. 1. Cross section of Greenbush Swamp showing the relative distance between sampling sites, sediment stratigraphy, and radiocarbon dates.

late Pleistocene deposits (Penhallow 1896; Szabo and Hodges 1980), and Holocene deposits (Lowden et al. 1977; Karrow 1980). Watts (1979) recovered Thuja macrofossils (presumably seeds) from south central Pennsylvania, in sediments dating between 12 000 and 13 000 years before present (B.P.). Leafy twig fragments of Thuja were reported by Brown (1938) from Louisiana. Delcourt and Delcourt (1977) reexamined Brown's sampling site and could find no Thuja, but rather abundant Chamaecyparis thyoides leaves. The similarity in the leaves of the two species led them to question Brown's identification. Leaves of Thuja were recovered from Sangamonian deposits in New York (McAndrews 1972). Ami (1899) reported well-preserved Thuja branches of undetermined age (possibly late Glacial) from a site near Ottawa; however, to my knowledge, there have been no recent reports of Thuja leaves from late Glacial sediments in eastern North America. During a study of the postglacial paleoecology of Greenbush swamp, a Thuja swamp on Manitoulin Island, a leafy twig fragment was recovered from sediments dating about 10 000 years B.P. as suggested by radiocarbon dates and pollen chronology. The following is a report on this fossil and its significance to the postglacial distribution of Thuja in eastern North America.

Location and stratigraphy of the site Greenbush Swamp lies 7 km southwest of Little Current on Manitoulin Island, Ont. (45'56' N; 82"00f30" W), at an elevation of 312 m (1023 ft) above sea level. An east-west transect midway across the swamp basin revealed the sediments to be a few centimetres deep at the eastern edge. Two pits were hand dug on this transect. The basal 5 cm of sediment in the eastern and shallower pit consisted of silty gravel resting on bedrock. These clastic sediments contained a Thuja occidentalis leafy twig. Four radiocarbon dates were obtained from organic sedi-

ments (Fig. 1). A basal organic sample (presumably gyttja) collected by J. Terasmae from Greenbush Swamp at 1.881.98-m depth was dated 9450 300 (I-GSC-3) years B.P. (Walton et al. 1961). My studies on sediment stratigraphy and depth indicate that the sample was probably collected from near the centre of the swamp. The agreement between Terasmae's date and the basal date at the western pit suggests synchronous sedimentation of clastic sediments across the basin. The 7570 2 170 years B.P. date from the eastern pit was collected from the centre of the gyttja unit, and in light of the dates bracketing the gyttja unit in the western pit, it is probably a protracted age estimate where gyttja accumulation appears to have been slower than in deeper parts of the basin. The possibility that the clastic sediments in the eastern pit represent a beach deposit contemporaneous with gyttja deposition in the western pit is unlikely. The eastern deposit contained clasts ranging from silt to cobble size with no indication of rounding or sorting as is characteristic of wave-washed beaches. Gyttja deposits suggest little erosion of upland soils, as well as productive lake waters. Organic content of the clastic deposits was minimal indicating soil instability and little vegetation.

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Pollen chronology Abbreviated relative pollen diagrams for the lower sediments are presented (Fig. 2) simply for the purpose of chronological comparison. The diagrams are divided into recognizable pollen assemblage zones primarily on the basis of changes in frequencies of the Picea, Pinus, and herb taxa. The zonation designations apply to Manitoulin Island only and do not have regional significance. An early spruce-pine pollen transition is characteristic of most pollen profiles throughout the Great Lakes region. The western pit, as well as other sites on Manitoulin Island, are unusual in showing an early and a later spruce-pine pollen transition (Lee 1957;Warner et al. 1982). It was not possible to radiocarbon date the earlier transition since it occurs within clastic sediments; however, an upper 9930 ? 90 years B .P. date suggests

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the upper clastic sediments from the western pit. This similarity in pollen assemblages suggests the upper clastic sediments from the western pit and the clastic unit in the eastern pit are contemporaneous. The radiocarbon dates, sediment stratigraphy, and pollen record indicate that clastic sediment deposition ceased by 10 000 years B.P. The Thuja fossil, therefore is presumed to be about 10 000 years old. Isolation and identification of the fossil Bulk samples of the clastic sediments from the eastern pit were collected from a clean surface. Samples were washed on a 300-km-mesh sieve with water. The fossil was isolated from the concentrate and stored in ethanol. The fossil was dark brown in colour and well preserved (Fig. 3). The individual, small, scalelike, pointed leaves on the flattened twig compare with modem herbarium specimens of Thuja occidentalis.

Discussion At present, Thuja is widespread throughout the mixed Eastern Pit coniferous-deciduous forest in eastern North America (Fig. 4). Thuja occupies both swamps and uplands, growing best on calcareous terrain in shallow, welldrained swamps, and on shallow, dry soils overlying limestone rock (Fowells 1965; Hosie 1969). The paleogeography of Thuja can be discussed in light of the sites so far known to contain macrofossils. It 1 0 X exaggeration is not known where Thuja persisted during the glacial FIG.2. Picea, Pinus, and total herbs relative pollen profiles maximum; however, as the climate began to warm after for the lower sediments in the swamp. Symbols for lithology about 14 000 years B .P., Thuja was a component of the are the same as those given in Fig. 1. local vegetation at Crider's Pond in south central Pennsylvania, at least by 12 000 years B.P. (Watts the regional date of 10 500 (Karrow et al. 1975) is 1979). Ohio was probably ice free shortly after 13 000 applicable to the earlier transition. An age of 8000 years years B.P. (Dreimanis and Goldthwait 1973), and by is estimated for the later spruce-pine transition. The inability to sample for pollen the basal 15 cm in 12 500 years B.P. Thuja probably occupied shallow the eastern pit at close intervals resulted in a somewhat glacial depressions, which appear to have succeeded to compressed pollen diagram. General trends are evident Thuja swamps by 9800 years B.P. (Szabo and Hodges and permit zones 3 and 4 to be recognized with a 1980). Thuja appears to have been very much a part of suggestion for the beginning of zone 2. The upper two the early Holocene vegetation in more eastern areas. The pollen samples from the eastern pit were gyttja which discovery of Thuja in Leda clay deposits suggests that appears to contain abundant Pinus strobus and moderate quantities of Picea, similar to lower pollen assemblages of zone 4, also within gyttja at the western pit. The middle three samples consisted of a mixture of gyttja and clastic sediments representing a depositional transition. The samples indicate a marked increase in Picea pollen and a slight decline in Pinus pollen. These samples are comparable to zone 3 pollen assemblages which include the lower gyttja and upper clastic deposits. The basal sample from the eastern pit was co1l;cted from clastic sediments immediately lying on bedrock. This sample contained a preponderance of Pinus banksiana - resinosa, continued representation of P. strobus, and a trend FIG.3. Photograph of fossil Thuja leafy twig fragment to declining Picea frequencies, as zone 2 assemblages in recovered from the eastern pit.

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remained an important element of the Greenbush Swamp vegetation to the present. Recently, I recovered leafy twig remains of Thuja from Lake Nipissing deposits dated 6490 + 100 (BGS-373) years B.P. from north of Sault Ste. Marie, Ont. (Cowan 1978). These fossils, leaves at Edward Lake (McAndrews 198l), wood on St. Joseph's Island (Lowden et al. 1977) and at Kettle Point (Karrow 1980), indicate that Thuja was common along or near the Lake Nipissing shore. Thuja appears to have become widespread throughout the eastern Great Lakes region by mid-Holocene time. Vegetative plant remains from additional sites in eastern North America are needed for a more complete understanding of the early history and migratory trends of Thuja occidentalis. It appears that macrofossils may provide the most useful information on its history. NOTEADDED IN PROOF: Anderson (1982) has recently reported fossil leaves of Thuja in sediments as old as 12500 years B.P. from Kitchener, Ont. These Thuja fossils are associated with forest-tundra elements, which further confirms the rapid northward migration of Thuja in late Glacial environments.

Acknowledgements Versions of this paper greatly benefited from critical readings by Drs. R. J. Hebda, R. W. Mathewes, J. H. McAndrews, J. Terasmae, and journal reviewers. I am FIG.4. Stippled area indicates the modern distribution of Thuja occidentalis (after Little 1971). Fossil localities are: indebted to R. J. Hebda for his assistance both in the x , Manitoulin site; 0 , Holocene; W , late Pleistocene; 0, laboratory and the field. The radiocarbon dates from Greenbush Swamp were provided by J. Berry and R. J. Sangarnonian. Drimrnie of the University of Waterloo radiocarbon these trees occupied the shores of the Champlain Sea. laboratory. Mr. J. Eadie, Mr. B. Wilson, and Mrs. E. Although the age of the Champlain Sea is debated Roadhouse kindly permitted access to the swamp for among geologists, approximate dates of 11 000 to 12 000 sampling. R. G. Long of the Biological Sciences and 10 000 to 11 000 years B.P., date the occupation of Department at Simon Fraser University photographed the Ottawa and St. Lawrence valleys, respectively, by the fossil. This study is derived from graduate research undertaken in the Department of Biology, University of the Champlain Sea (Karrow et al. 1975; Gadd 1980). The spruce-pine pollen transition in south central Waterloo. Ontario is estimated to occur about 10 500 years B.P. (Karrow et al. 1975), and probably about 10 000 years AMI, H. M. 1899. List of fossils to accompany report by Dr. R. B.P. in the Ottawa area (Terasmae 1980). Thus, Thuja W. Ells on the city of Ottawa map. Geol. Surv. Can. Annu. probably arrived in Ontario with the boreal spruce Rep. New Ser. 7: 51G-56G. forests, or under drier climates with early pine forests. ANDERSON, T. W. 1982. Pollen and plant macrofossil analyThe Thuja fossils from Manitoulin Island indicate that it ses on late Quaternary sediments at Kitchener, Ontario. Geol. Surv. Pap. (Geol. Surv. Can.), No. 82-1A. pp. reached the island during the latter phases of Lake 131-136. Algonquin, also during the expansion of pine forests in J. C., and T. WEBB111. 1977. Changing patterns in the region. A radiocarbon date of 9940 + 16 (GSC- BERNABO, the Holocene pollen record of northeastern North America: 1397) years B.P. on peat in association with in situ tree a mapped summary. Quat. Res. (N.Y.), 8: 64-96. stumps from the drowned scarp between the Bruce BERTI,A. A. 1975a. Paleobotany of Wisconsinan interstadPeninsula and Manitoulin Island (Tovell 1978), indiials, eastern Great Lakes region, North America. Quat. Res. cates that Lake Algonquin levels dropped to allow trees (N.Y.), 5: 591-619. to become established on this isthmus. Seed and leafy 19756. Pollen and seed analysis of the Titusville twig macrofossils at intervals throughout the entire Section (mid-Wisconsinan), Titusville, Pennsylvania. Can. J. Earth Sci. 12: 1675-1684. sediment sequence in the western pit indicate that Thuja


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