In reply to graeme_haigh:
Trolling aside. I'm going to assume that this is a genuine question.
Sadly I don't think that there is an empirical research done on how much damage occures in a localised area depending on whether the majroity of routes are trad or bolted. There seem to be too many variables.
However, you could look at some of the examples where bolting has increased public use of an area. The first one that springs to mind is back when the right wall in Dali's Hole was bolted, producing a bunch of low grade (and rather poor quality) sport routes. There was a real problem with massive groups of people climbing there which lead to access problems in one form or another for the rest of the slate quarries. Once the hangers had been removed there was much less traffic at the area. This example would seem to indicate that because of the bolting the environmental impact would have increased.
It would have been very interesting to see if a bunch of low grade trad routes had been produced whether there would have been such an icrease in use? Is it more to do with the grade of the route rather than the style in which the route is put up.
If you look at places like Birchen Edge, Windgather and other such small crags, with easy access to the top and bottom and with the majority of routes being low graded trad line there is alot of environmental impact. People have taken it upon themselves to remove loose rock, there are normally litter problems at such places. The gear placements are always worn there is footpath erosion at the base of such crag, at the tops and especially down heavily used areas like the descent gullies or walk-offs.
In contrast to this places with higher grade routes (either sport or trad) tend to be a little tidier reflecting the reduced number of people who climb there.
I would present that it isn't necessarily the style in which a crag is climbed but the average grade of the climbs there which determines the environmental impact of people on the crag.
