while researching the Wellman Nixon study (which I haven't found[yet])I came across this article which kind of sheds light on some of our issues.
http://www.rbbi.com/white/conflict/litrev.htm
Who Hates Whom in the Great Outdoors: The Impact of Recreational Specialization and Technologies of Play
by Bill Devall and Joseph Harry
Leisure Sciences Vol. 4 (1981) No.4
Pages 399-418
The authors offer the concept that social relationships in outdoor recreation setting are heavily influenced by recreational technologies. Recreationists participate in clusters of technological similar recreations. They hypothesized users of more physically obtrusive technologies are resented by users of less obtrusive technologies.
A questionnaire was used to obtain data from participants in many different recreational activities in the Williamette Basin of Oregon. The study found distinct clusters of recreational technologies did exist, resenting relationships were found between users of different technologies, but these resentments were directed toward both obtrusive and non-obtrusive technologies. Conflicts were surprisingly found to be between clusters rather than within their own principle cluster.
The authors suggest that a significant portion of user perceived crowding does not simply result from too many users at a site, but is due to mixing various technologies at the site. Problems may be particularly severe when one activity involves quiet, slow speed, and an appreciation for nature and the other activity requires speed and noise ("oar power" vs. "motor power").
Diversification in recreational technologies occurs in hybridization or combination of pre-existing devices and activities. An example of this is water skiing, a combination of skiing and motor boating. This kind of hybridization tends to give rise to technological clusters of related activities. The activities of boating and fishing yield a variety of activities including: motor boat fishing, rowboat fishing, shore fishing, motor boating, rowing, etc. The authors suggest that an individual will tend to participate in activities within a cluster much more frequently than those of other clusters.
Newer technologies such as snowmobiles, all-terrain vehicles and hovercraft tend to be much more "sensory obtrusive" than older technologies. Resenting relationships between devices of different technologies tends to be asymmetrical (one way). For example, canoeists resent boaters, but boaters haven no objection to canoeists.
When speed is involved an additional problem may enter the system. Users of fast moving recreational equipment may feel constrained by the presence of slower moving equipment. While slower moving recreationists may fear being "ran over."