Growth decline of wind-exposed red spruce and balsam fir in the White Mountains

Overstory red spruce (Picearubens Sarg.) and balsam fir (Abiesbalsamea (L.) Mill.) trees suddenly exposed to strong, turbulent winds along a ski trail cut in 1962 in New Hampshire showed growth (increment of basal area) reductions during 1974 through 1983 of 82 and 63%, respectively, compared with growth during 1954 through 1963. Growth of comparable trees on the upwind side of the ski trail did not decline during this period. Mechanical damage to crowns and roots during tree sway is proposed as the primary cause of the growth decline. Six downwind fir trees had smaller living crowns, fewer living fine roots, more abrasion wounds on woody roots, and more discoloration of root wood than did the six fir trees on the upwind side of the trail. Six downwind spruce trees had smaller living crowns and more root discoloration than did the six upwind spruce trees. Regression analyses were made using the 24 trees along the ski trail and 29 trees from two other poorly stocked and declining stands in the White Mountains. Of the site, stand, and tree parameters tested, only root and crown damage parameters significantly correlated with reductions in growth rate. For fir, percent root discoloration and percent roots abraded explained 82% of the variation in growth decline. For spruce, crown loss explained 70% of the variation. The symptomatology of these wind-stressed trees was consistent with that described for spruce–fir decline. Although acid deposition or some other anthropogenic stress has been proposed as the primary cause of spruce–fir decline, wind appears to be an overlooked but significant natural stress factor that could explain at least some of the growth decline and mortality of spruce and fir at high elevations in the northern Appalachian Mountains.