r~\'IER!CAJ'\ Jonll'\AL OF Scn:'>n:. VoL. :25o, OcnlHEH l95H, P. 540-570] THREE POLLEN DIAGRAMS FROM CENTRAL MASSACHUSETTS MARGARET BR'fA\\ DAVIS ABSTRACT. Three pollen diagrunh' ar~ prt'sented from central Massachusetts. The di­ agrams are believed to record the n·getational sequence from the time of retreat of pre­ Valders ice to a time just previous to European colonization. They are interpreted to show that a narrow trt'elt>ss !wit along tht' t•dge of tlw retrf'ating ict• was rapidly colonized by forest. During Two Creeks timte a cool-temperate, and perhaps dry, elimate permitted the growth of a mixed SJlrllC<" and dt"ciduous forest. Tht• dima!P during tlw Val<krs stadium became cooler and more moist, and brought about a change in the frequency of the forest species. An alternative interpretation, according to which a return of park-tundra vegeta­ tion, under conditions of intense solitluction, occurred in \'alders time, is not favored by the weight of evidence. The succeeding pine pha><e has been divided into two zones, the second of which was probably warmer and drier than the first. The three deciduous forest zones described from other parts of New England have be!'n demonstrated, although only one of the diagrams contain,.; the entire sequencP. The dominant pollen types in the three zones, starting with the earliest, are: oak and hemlock; oak, pine, and hickory; birch, oak, hemlock, and chestnut. The np]Wr part of the pine zone and the first two deciduous forest zone,o; are believed to represent tlw hypsithermal interval. On the basi" of the bog plant pollen spectra, the be~inning of the third dt'eiduous forest zone is thought con­ temporaneous with the beginnin~ of the Su!J-Atlantic pollen zone in EuropP. 1.\TRODUC:TIO:\' In recent years, attention has !wen di reded to the vegetational history of glaciated regions of North America since the retreat of the ice. A knowledge of the earliest vegetation and its subsequent changes in species composition and frequency illuminates many hiogeographil'al problems and increases our knowledge of the climate and soils of the past. Analysis of the pollen and spores contained in organic deposits has proved an enormously useful technique in the study of vegetational history. Pollen diag-rams from southern l\ew England (Deevey, 1939, 1943) have demon­ strated that, following tht> retreat of the ice, there wa;;; an interval when spruce was very abundant. The spruce 11·as later replaced by pine, which in turn was replaced by three deciduous forest zones, characterized respectively by oak and hemlock. oak and hickory. and oak and chestnut. Recent studies in Con­ necticut ha1·e added more detail to this sequence. Leopold ( 1955, 1956b) has demonstrated that there was an interval of "steppe-like" vegetation immedi­ ately after deglaciation. At the southernmost site investigated, there is evi­ dence that the forest advanced and then retreated again during this interval. The spruce phase earlier described h~· Deevey has been divided into four zones. Starting with the earliest, the zones are characterized hy rising spruce per­ centages, a spruce maximum, a sprul'e minimum with higher percentages of pine and deciduous trees, and a second spruce maximum. The spruce mini­ mum has been correlated with the warmest part of the Two Creeks interstadial, and the succeeding spruce maximum is thought to represent cooling associated with glacial adyance during Valders time. This correlation is supported by radiocarbon dates. Apparently the climate in southern Connecticut during the Two Creeks interval was warm enough to permit the growth of mixed spruce, pine, and hardwood forests; during Valders time climatic cooling altered the species composition of the forest (Leopold, 1956b). The diagrams from Con- 540 Margaret Bryan Davis 541 necticut contrast sharply with the sequence in northern Maine {Deevey, 1951), Nova Scotia (Livingstone and Livingstone, 1958), and Michigan {Andersen, 1954.), where there is evidence of more seyere climate during Two Creeks and Valders time. It is thought that in northern Maine and Nova Scotia the park­ tundra established during the Two Creeks interstadial was replaced by tundra during the cold interval associated with the Valders glacial advance. In Michigan there is evidence that the spruce forests of Two Creeks time were replaced by park-tundra. The purpose of this investigation has been to study the vegetational history of central Massachusetts. On the basis of three pollen diagrams from the vicinity of the Harvard Forest it has been possible to outline the vegeta­ tional history of the area, to correlate it with sequences from other parts of New England, and to speculate on the factors which could have influenced the changes in vegetation that have occurred since the melting of the ice sheet. ACKNOWLEDGMENTS I wish to thank Prof. Hugh M. Raup for his unfailing enthusiasm for this project, and for his many valuable ideas. Prof. Elso S. Barghoorn generously allowed me to use his laboratory facilities for the greater part of this work, and gave many helpful suggestions. I am grateful to Dr. Johs. Iversen and his associates at the Danish Geological Survey for their generosity and patience while I was a student at their laboratory. Dr. Iversen and Mag. Sci. Svend Th. Andersen have given much help with the interpretation of the diagrams. I wish to thank Prof. Raup, Dr. John C. Goodlett, Prof. Daniel A. Livingstone, and Prof. John P. Miller for reading this manuseript, and to express my ap­ preciation to the many others who have helped in the field and laboratory, and provided stimulating discussion. This work was supported by grants from the l'\ational Science Founda­ tion, and by the Pennsylvania-Delaware Fellowship of the American Associa­ tion of University Women. PRESENT VEGETATION, CLD[ATE, AND SOILS OF THE REGION The three sites investigated are in the vicinity of the Harvard Forest, Petersham, Mass. (see fig. 1). This region now supports a complex, species­ rich hardwood forest. Ecological studies {Bromley, 1935; Lutz and Cline, 1947; Stout, 1952) show that the forest is dominated by red oak (Quercus rubra), ash (Fraxinus americana), red maple (Acer rubrum), black birch (Betula lenta), and sugar maple (A. saccharum). White pine (Pinus strobus) and hemlock (Tsuga canadensis) occur frequently. On some north-facing slopes and in ravines sugar maple, yellow birch {B. lutea), beech (Fagus grandifolia), and hemlock are more common. On a few well-drained slopes with thin soils, the forest is dominated by white and black oak ( Q. alba and Q. velutina), hickory {Carya a rata and C. glabra), and, formerly, chestnut (Castanea dentata) . The climate of the region {Rasche, 1958) is continental, despite the proximity (ca. 70 mi, llO km) of the Atlantic Ocean. The prevailing winds are westerly, so that the ocean has little modifying effect. The mean January 512 Margaret Bryan Davis Fig. l. \lap of southern New England. Arrow indi<'ates h)('ation of sit<'S inwstigated. temperature is about 21 °F ( -6°C)' and the mean J u]y temperature 69°F (21 °C)' a mean annual range of almost 50°F ( 27°C). The climate is moist: the average yearly precipitation is about 40 in. ( 200 mm). The irregular topography results in a variety of microdimates. Studies indicate that local temperature variations within the Harvard Forest cover from one fourth to one half the variations among stations from southern to northernmost 1\"ew England. The bedrock undnlying the Petf'rsham region is acidic granite, gneiss, and schist. Its surface is irregular and the mantle of glacial debris is thin. In the valleys, and occasionally on slopes, there are gravelly outwash deposits. The uplands are mantled with sandy till; overlying this is a loam which may he in part of eolian origin. There is evidence that frost action has modified many of the slopes. The period of most active solifluC'tion is thought to have ocC'urred prior to the deposition of the loam ( Raup, 1951; Stout, 1952). Al­ though the age of the till is not known \\'ith certainty, it is probably of Cary or late Cary age (Flint, 1953; .:VIacClintock, 1%1; Denny, 1956a). DESCRIPTION OF SITES Torn Swamp.-Tom Swamp is a large sphagnum hog located in a north· south trending bedrock valley, apparently of pre-glacial origin (exact location 42°31' l\, 72°13' W, elevation 750ft.). The valley floor is lined with outwash, and there are gravel terraces along the slopes. Glacial meltwater from the north may have drained through the Yalley, depositing the outwash. It is pos· sible that the valley was partially filled with stagnant ice during this period. The hog is about 4 km long and 0.5 km wide. On the central portion of the hog black spruce, white pine, larch, highbush blueberry, and wild raisin Three 11oflcn Diagram" from Central J1a8,mchusetts form a dense foncst. To the north and to the south, the vegetation is mon~ open. To the north, shrubs grade into a sedge meadow which is rapidly build­ ing into the open water of the artificially damned Riceville Pond. To the south, ericaceous shrubs and sphagnum are building a bog mat into the open water of Harvard Pond. The outlet here has also been dammed; early maps show the area as wet meadO\\~ (llaup and Carlson, l<JH). It was not possible to survey the botr surface, because of the dense vegetation. However, there are small ,;treams on the bog surface flowing north to the Riceville outlet, and flowing south to the Harvard Pond outlet. The presence of the two outlets and the drainage streams indicates that the bog may be slightly domed. RLceville Pond N 0 location of boring W bog, sedge meadow c.J open water o.s mi.