Calculated Risk's Bill McBride reports that framing lumber prices were unaffected by the pickup in U.S. housing starts in 2015, and have substantially dropped year-over-year.
Early in 2013, prices reached a near-housing bubble high due to a surge in demand caused by more housing starts and supply constraints. As suppliers worked to push more inventory online, the same period in 2014 did not reflect a comparable peak due to the increase in supply and, subsequently, less demand.
Overall the decline in prices is probably due to more supply, and less demand from China. Right now Random Lengths prices are down about 13% from a year ago, and CME futures are down around 16% year-over-year.