I have to agree with Jadbal here. Frequented routes are usually clean and without loose rock, but that isn't because routes are only established on clean solid rock, it is because routes are cleaned and trafficked. I've seen local clean solid routes have access prohibited by the powers that be and develop lichen and plant life within several years. Least frequented routes are always the dirtiest. Just like a hiking trail that is being "rested for rehabilitation". It really does come down to whether the volume of routes is a significant portion of the ecosystem. I'd imagine in the western portion of the country where the geography is still young and abound with cliffs it'd be less substantial. Over here on the east coast is different, cliffs are few and far between and climbers flock to every square foot of cliff face to get their fix, myself included.