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Late‐Quaternary History of High‐Elevation Vegetation in the White Mountains of New Hampshire
Author(s) -
Spear Ray W.
Publication year - 1989
Publication title -
ecological monographs
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.254
H-Index - 156
eISSN - 1557-7015
pISSN - 0012-9615
DOI - 10.2307/2937283
Subject(s) - macrofossil , tundra , tree line , vegetation (pathology) , subalpine forest , juniper , ecology , woodland , subarctic climate , alpine climate , geology , glacial period , physical geography , larch , pollen , arctic , geography , montane ecology , climate change , biology , geomorphology , medicine , pathology
The pollen and plant—macrofossil records from four small lakes in the subalpine and alpine zone of the White Mountains, New Hampshire, give a 13 000—yr paleoenvironmental history. The White Mountains were deglaciated before 13 000 yr BP. Downwasting of the continental ice sheet was rapid. The summits projected above the ice as nunataks for only a brief period of time. Residual ice may have existed in Franconia Notch until 11 000 yr BP. From 13 000 to 11 750 yr BP a barren periglacial desert covered the highest altitudes in the White Mountains. Tundra vegetation occupied the lower slopes and valleys. The mean annual temperature was roughly 5°—10°C colder than today. Sparse tundra vegetation surrounded all four high—elevation sites from 11 750 to 10 300 yr ago and several taxa, particularly Artemisia and Caryophyllaceae, indicate disturbance. The summits were subjected to intense periglacial activity. The mean annual temperature was 4—6° lower than present. By 10 300 yr BP shrubs such as willow, juniper, and dwarf birch had invaded the tundra at Lake of the Clouds. Spruce woodland dominated the lower slopes and valleys. At 10 300 yr BP spruce populations arrived at high—elevation sites. Macrofossils of fir, birch, and shrubs also occur in sediments of this age. The temperature increased to or exceeded modern levels. Tree species did not reach the Franconia Notch sites until 9750 yr BP. At these sites the establishment of subalpine forests spanned a much shorter time period. Forest with poplar, spruce, and birch replaced the spruce woodlands of low elevations. Subalpine fir forests became well established by 9000 yr BP. Evidence from the alpine site shows that the fir trees were more abundant and treeline higher than today from 10 300 to 5000 yr BP. After 5000 yr BP, the pollen percentages of alpine indicators increased and the numbers of fir macrofossils dropped. Of the three sites in subalpine fir firest, only the lowest shows any evidence of a warmer interval in the early Holocene. Treeline is apparently a poor temperature indicator because wind and moisture are the major factors determining its position. Taxa of the Northern Hardwood Forest (e.g., white pine, hemlock, yellow birch, sugar maple, and beech) arrived at lower elevations by 6500 yr BP, but the zones of modern vegetation became established only after 2000 yr BP when spruce populations expanded at low elevations between 750 and 1200 m.