comparing before and after impacts

We are trying to assess impacts of single day intensive horse riding events on recreation trails. We have used 1x1 m quadrats laid across the track to estimate condition before and after the event. Since it is in the forest, edge of the track is characterised by undisturbed leaf litter while middle section has very limited litter as is the usually the troden area. The difference in litter cover between edge and middle of track can vary with as much as 80% to 2%. We have about 20 sites and each has been assessed this way. My problem is analysis. Averaging litter in all quadrats within a site does not seem ok because of the large variation between the edge and the centre of the track. Is it ok to assume the duadrats are independent and compare before and after at quadrat level instead of site level?

Thanks
Mike