These reminders of impermanence are not to be despised, for just as a fallen tree clears the view and help us see the way through the forest more clearly, perceiving impermanence helps us to see our own true nature.
In the Gakudo-Yojishu (Points to Watch in Practicing the Way), Zen Master Dogen said, "Truly, when you see impermanence, egocentric mind does not arise." The great Indian Patriarch Najaruna once said that the mind that solely sees the impermanence of this world of constant appearance and disappearance is also called the mind of wisdom (bodhi-mind).
A fallen tree does not block our path, for just as every dharma barrier is also a potential dharma gate, a tree across the trail serves to remind us of even the impermanence of the Way. The Sixth Chinese Patriarch Hui-Neng once said "Trees, grass, and bushes are impermanent and are nothing but Buddha-nature. Human beings and things, body and mind are impermanent and are nothing but Buddha-nature. The earth, mountains, and rivers are impermanent because they are Buddha-nature. Supreme awareness (Anuttara-samyak-sambodhi) is impermanent since it is Buddha-nature. The great Nirvana is Buddha-nature since it is impermanent.”
We should take a moment to thank the fallen trees for their lessons.