After some miles the forest thinned and retreated to the north.

When the climate cooled 1.5 million years ago and the first of four ice ages occurred, the forests retreated as the ice advanced.

By about 10,000 years ago, the alpine zones had disappeared, and the spruce-fir forest had retreated to the range's highest elevations.

The tundra vegetation disappeared, and the spruce-fir forests retreated to the highest elevations.

The forest retreated from the path, the trees becoming stranger yet.

The forest retreated before this onslaught.

The forest was retreating, like a blanket being drawn back, leaving the ground bare.

The forest retreated; the grass disappeared.

Since the 1960s, the forest on the Acker crest has steadily retreated.

The forest retreated.