Did not look for national park service, but did find these with easy search:
On Camels Hump in Vermont's Green Mountains, Dr. H. Vogelmann, professor of botany at the University of Vermont, has reported startling evidence of tree damage. Conifers are most effected because the needles are bathed in acid droplets all year around.Other trees drop their leaves. Measurements of the total biomass in the balsam fir has declined 20 % from 1965 to 1983. The red spruce has declined a dramatic 73 % in the same time period. Lower on the mountain sugar maples and beech trees biomass dropped 25 %.
Forests at high altitudes maybe enshrouded by clouds or fog for much of the time. The pH of lower cloud droplets may average 3.6, which is a much lower pH than the final rain of pH 4.2.
Effects of Acid Rain on Plants and Trees
Dead or dying trees are a common sight in areas effected by acid rain. Acid rain leaches aluminum from the soil. That aluminum may be harmful to plants as well as animals. Acid rain also removes minerals and nutrients from the soil that trees need to grow.
At high elevations, acidic fog and clouds might strip nutrients from trees’ foliage, leaving them with brown or dead leaves and needles. The trees are then less able to absorb sunlight, which makes them weak and less able to withstand freezing temperatures.
Overview of the effects of acid rain on ecosystems, plant life, wildlife and man-made structures.
www.epa.gov