Measured indicators of reproductive activity did not vary significantly between grazed and ungrazed drainages. Grazing might affect survival of young water voles and should be studied further. Jonathan H. Titus and Shiro Tsuyuzaki Ski slope vegetation on Mount Hood, Oregon, U.S.A. was surveyed to assess vegetation that has developed under a constant disturbance regime and the environmental factors that are important in structuring the vegetation. Ski runs extend from 1200 to 2200 m on the south face of Mount Hood. Elevation, which is correlated to temperature, precipitation, depth of snowpack, and timing of snow melt, is the most important variable structuring the vegetation.
Soil texture is also important.
Distance to the forest boundary influences the vegetation only at lower elevations. Most of the slopes we examined were thickly vegetated, except above treeline where vegetation is typically sparse. Non-native species were detected only at the lowest elevations and were infrequently dominant. Non-native species cover and richness were correlated with percent bare area. Above treeline there was no detectable difference in vegetative composition on and off the ski run, probably due to extensive trampling of the vegetation in the summer.