The Department of Foreign Affairs and International Trade runs and monitors an export permit regime. With each shipment every lumber exporter obtains an export permit. This keeps track of a number of things, including the volume of the shipment. These are posted on a daily basis so that the industry can watch as the volumes accumulate over time, and they can be notified as they get near the end of a month if they're approaching a surge.
On April 27th, 2010. See this statement in context.