Organic material will lead to plant growth between rails. That will attract water. When it freezes, the stones will get working - leading to instability of the track.
On the same note: Around here, they seem to love feces:
All along the river on an rainy day i see geese and doves spreading all kinds of desease with their droppings...
When the sun comes out young people seem LOVE lying in the shite.
...nearly fell off my brompton running over one of these air-rats.
(, Tue 19 Apr 2022, 10:15, Reply)