Wave-regeneration of high elevation fir species is an example of a wind-induced disturbance. At high elevations, the regeneration of balsam-fir (Abies balsamea) forests of the northeastern United States (Sprugel 1976, Sprugel and Bormann 1981) and fir forests of central Japan (Sata and Iwasa 1993), are regulated by high winds, along with rime ice. As you look across the mountain side, green fir canopies are broken periodically by crescent-shaped 'waves' of dead fir trees. Each wave is a band of standing dead trees, with mature trees on one side and a regenerating forest on the other. The 'wave' of death and regeneration moves slowly through the forest. Trees die at the leading edge and are replaced by seedlings. The waves move in the general direction of the prevailing wind (see figure below) at constant rates of 0.5 - 4.0 m per year. Tree mortality in the dieback zone is caused by persistent high winds which desiccate the trees, and the accumulation of time ice which results in the breakage of branches. The shallow, rocky soils also contribute to the death of the fir trees. Strong winds induce tree sway and cause damage to the root system. This reduces transpiration and encourages pathgenic root fungi. After death of the canopy trees, advanced regeneration is released and in about 80 years, these trees are again susceptible to wind damage (see figure below). The wave-regenerated forest migrates across the mountain side. This is a highly predictable disturbance regime.
