VANCOUVER, British Columbia — Weyerhaeuser Co., the second-largest owner of U.S. timberland, has declared a record $5.6 billion special dividend to lock in the company’s conversion this year to a real estate investment trust.

The company is making the payout to signal its determination to convert to a REIT this year and address investor concern that its shrinking market valuation could have derailed the process, Chief Executive Officer Daniel Fulton said in an interview. The dividend, limited to 10 percent cash with the balance in stock, will be paid Sept. 1, the Federal Way, Wash.-based company said Monday.

“Market conditions today are not impacting our ability to convert and we wanted to take away the uncertainty and provide the surety for our shareholders that we will complete the conversion this year,” Fulton, 61, said by phone.