The 28-year old Jamaica international arrives at Portland along with goalkeeper Milos Kocic in exchange for keeper Joe Bendik, the No. 3 overall pick in next month's MLS SuperDraft and allocation money.
"After weighing our immediate needs and evaluating the college pool, we felt it was in the club's best interest to give up a draft pick to secure a talented goal-scorer and an experienced player like Ryan," Timbers GM Gavin Wilkinson said in a statement.
"He adds another weapon to our attacking group and can create goals in a number of ways. He also offers versatility in a number of positions in either a three- or two-front system."