Holocene vegetation patterns in the Adirondack Mountains

Pollen and plant macrofossil date from six sites along an elevational gradient (661-1320 m) in the east-central Adirondack Mountains (New York) reveal the history of six tree taxa (Picea, Abies, Pinus strobus, Tsuga, Betula papyrifera,B. lutea) in the region during the past 10 000 yr. Space-time plots of the data show how spatial patterns of vegetation along the elevational gradient changed during the Holocene in response to climatic, biotic, and other changes. The plots also illustrate the contrasting spatial scales at which pollen and plant macrofossil data sense forest composition. Vegetational patterns along the gradient changed substantially during the Holocene. Responses of the six tree taxa to temporal changes in environment were individualistic, resulting in continual changes in the spatial vegetation patterns. The modern elevational zonation developed only within the past 3000 yr. Each tree taxon has a unique abundance pattern along the spatial and temporal gradients. Pollen percentages of Picea, Pinus, Tsuga, and Betula did not vary systematically with elevation, but changed substantially with time, indicating changes in abundance of these taxa at a regional scale. Macrofossil percentages of all six taxa varied with both time and elevation, revealing temporal changes in abundance of these taxa along the elevational gradient. Abies populations were concentrated at a higher elevations, while Pinus strobus, Tsuga, and Betula lutea trees were most abundant at lower elevations. The elevational distributions and low-elevation abundance of the latter three taxa changed substantially during the Holocene. Picea trees were rare at all elevations during the early and mid-Holocene, and increased in abundance at mid-elevation sites within the past 3000 yr.