Late-Quaternary history of high-elevation vegetation in the White Mountains of New Hampshire

The White Mountains were deglaciated before 13 000 yr BP. From 13 000 to 11 750 yr BP a barren periglacial desert covered the highest altitudes. Tundra vegetation occupied the lower slopes and valleys. Mean annual temperature was 5-10°C colder than today. Sparse tundra vegetation surrounded all 4 high-elevation sites from 11 750 to 10 300 yr ago and several taxa, particularly Artemisia and Caryophyllaceae, indicate disturbance. Summits were subjected to intense periglacial activity. The mean annual temperature was 4-6°C lower than present. By 10 000 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 establishment of subalpine forests spanned a much shorter time period. Forests with poplar, spruce, and birch replaced the spruce woodlands of low elevations. Subalpine fir forests became well established by 9000 yr BP. At the alpine site, 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 numbers of fir macrofossils dropped. Treeline is a poor temperature indicator because wind and moisture are the major factors determining its position. Taxa of the Northern Hardwood Forest 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. -from Autho