Columbia subject headings:
Acid rain--Environmental aspects--Congresses.
Air--Pollution--Environmental aspects--Congresses.
Forest ecology--Congresses.
Plants--Effect of air pollution on--Congresses.
Harvard subject headings:
Forest ecology--Congresses
Plants--Effect of acid deposition on--Congresses.
Plants--Effect of air pollution on--Congresses
Trees--Effect of acid deposition on--Congresses.
Trees--Effect of air pollution on--Congresses.
Princeton subject headings: