Actors Michael Douglas and Melanie Griffith stood on the banks of the Spree River in Berlin Saturday and planted a tree as part of a campaign for environmental protection. Douglas said the action supported a campaign by Berlin artist Ben Wargin for the protection of nature, although Douglas said it seemed to him that Berlin already had more trees than any other city in the world. Douglas and Griffith are filming "Shining Through," a World War II spy story in which Griffith plays a German-American who infiltrates Berlin with Douglas as her boss.