Using Fir Waves and Flag Trees to Map Winter Windflow on Mt Washington, NH

Authors: Gray Trumbore, Colin Beier

SUNY Campus: SUNY ESF

Presentation Type: Poster

Location: UU 111

Presentation #: 75

Timeslot: Session A 9:00-10:00 AM

Abstract: The harsh climate and severe weather in the White Mountains of New Hampshire create a variety of forest structures and rare phenomena in the region. Trees at high elevations exposed to rime icing and winter winds are defoliated and stunted, creating flag trees that grow in the direction of the local wind patterns. The harsh winter winds also drive fir waves, bands of dieback and regeneration in montane forests that travel in the direction of the prevailing winds. While the prevailing winds on Mt. Washington blow from the west year round, fir waves on the western slopes move to the Northwest. This discontinuity suggests that the terrain in the region may alter the windflow direction by up to 300 degrees. I measured wind flagging on Abies balsamea (Balsam Fir) and Picea spp. (Spruce) trees near treeline on Mt. Washington to identify local wind currents driving fir wave motion on the west face of the mountain. Flagging direction was measured using a hand compass and severity was determined using the Griggs-Putnam Index. Fir waves at the study site were aged using increment cores, and the direction of fir wave motion was confirmed using orthophoto imagery. Fir wave speed, terminal age, and flagging severity at wave edges fell within the ranges found by previous studies. The flagging measurements were used to develop a surface windflow map, revealing a complex pattern of surface winds that drive fir wave motion nearly antiparallel to the prevailing winds measured at the summit of Mt. Washington.