North American softwood lumber prices surged more than 7% on Thursday as mortgage rates fell for the first time in four weeks.  The popular 30-year fixed mortgage rate fell 11 basis points to an average of 5.70% over the past week, according to Freddie Mac.  A continued decline in mortgage rates could help revitalize the housing market and stimulate demand for lumber.  North American softwood lumber prices surged more than 7% on Thursday to $638 per thousand board feet, representing the biggest daily gain for the essential building commodity in months.  ...