[jonashus]

Where I live in northern Europe almost all ground in the forests are soft. There is moss, small plants, grass or leaves everywhere.

I can't imagine why the mice would climb trees, but if they did and fall down, they probably gonna be fine most of the time.

In many forests there is lots of large rocks and steep slope/cliffs/precipice in the range 0-5 m where mice possibly could shorten their path by jumping. But I'd suppose they rather use a path they can go in both directions.