Day of the Animals, 1977, Starring Leslie Nielsen: A group of hikers find out the hard way that ozone depletion has caused animals above 5000 ft to go crazy. The bright side is, it doesn't seem to affect human animals...
Prophecy, 1979, Directed by John Frankenheimer: Logging industry pollutants have caused mutations in the forest, including the creation of a giant skinless bear.
Frogs, 1972, Starring Ray Milland and Sam Elliot: Jason Crockett (Milland) hates nature and poisons any creatures that find themselves on his island. For his birthday this year, nature has decided to fight back.
Night of the Lepus, 1972: A zoologist injects rabbits with mutated blood and hormones in order to disrupt their reproduction (obviously). Unfortunately all this does is create giant and bloodthirsty rabbits.
The Happening, 2008, Starring Mark Wahlberg: Humans are polluting the earth. Trees fight back and Mark Wahlberg has to outrun the wind. (Also his movie will teach you everything you need to know about hotdogs.)