North American lumber prices continued to move higher this week as mills extended order files, transportation delays reduced prompt availability and buyers returned to the market to replenish inventories. Price increases are no longer limited to Canadian SPF. Traders report firmer offers across Hem-Fir, Douglas Fir and Southern Yellow Pine, with several products posting gains of US$25-40/mbf over the past week.    The latest advance is not being driven by a sudden recovery in residential construction. Instead, traders say the market has become increasingly difficult to supply. Inventories throughout the distribution chain remain ...