Rivers across the Pacific Northwest are missing something critical to how they function, and it’s not water. It’s wood.

In late November, Tracey Forest heard loud grinding and beeping and raced down the road to find a fleet of logging trucks with giant claws and saws near where she runs Spirit Hollow, a silent retreat.

Global investment companies have quietly acquired tens of thousands of acres of historically open timberland in Washington’s Wahkiakum and Pacific counties — and they’re locking the gates behind them, ...