The snowy forests of northern Idaho demonstrate how alternating patches of trees allows sustainable harvesting of older trees while younger patches regrow.

An astronaut aboard the International Space Station captured this distinctive checkerboard pattern along the Priest River in northern Idaho. It was taken just before sunset so southfacing mountain sides glow while the north faces are shadowed. The checkerboard of white squares is snow visible on deforested ground where trees have been removed for logging. These alternate with the dark squares of dense forest that obscure the snow from the astronaut's view.
The checkerboard pattern resulted from an agreement in the early 1800s where alternate one-square-mile parcels of land were granted by the US Federal government to the Northern Pacific Railroad. These parcels were later sold to private companies and stripped for timber. This pattern is now seen as a method of maintaining the sustainability of forested tracts while still enabling logging companies to harvest trees. The forested squares are reserves now managed by the US Forest Service.
Dense vegetation acts as a natural filtration system for nearby rivers, preserving water quality from degradation by soil eroded off deforested hillsides. The Priest River, winding through the scene from top to bottom, is bordered on both sides by forest to further protect the quality of its water. Prior to 1968, the river was used to transport logs for nearly a century. Its function changed when the river's entire main stem was added to the list of Wild and Scenic Rivers in 1968 to preserve its "...outstanding natural, cultural, and recreational values in a free-flowing condition for the enjoyment of present and future generations". Whitetail Butte next to the river (at image center) was historically used by the US Forest Service as a lookout point for forest fires.

Image Credit: NASA/Johnson Space Center