In a milestone victory for trees and forest advocates, the office-supply giant Staples announced yesterday that it would phase out paper goods made from threatened forests and increase the average amount of recycled material in its paper products to 30 percent, up from the current average of less than 10 percent. No timetable has been set for the changes. Enviros fought for two years to win the gains from the Massachusetts-based chain. ForestEthics, based in California, and the Dogwood Alliance, based in North Carolina, say they staged more than 600 demonstrations at Staples stores nationwide, barraged the company’s top brass with letters, and even got the rock band R.E.M. to help sway public opinion. The enviros now have their sights set on other brand names in the industry. Kristy Chester Vance of ForestEthics, said, “We expect this to happen in the office-supply sector with companies such as Office Max, Office Depot, and Corporate Express.”