Shrubs generally were more resistant than forbs to the 

 immediate effects of trampling. But, none of the shrubs 

 were highly resistant. The most resistant common shrub, 

 Berberis repens, lost 80 percent of its cover after 300 

 passes. The reader should remember that these results 

 do not account for susceptibility to prolonged trampling 

 or ability to recover. Studies of established campsites 

 and trails suggest that most shrubs are relatively sus- 

 ceptible to prolonged trampling (Dale and Weaver 1974; 

 Cole 1982a, 1983). 



The two graminoids responded quite differently. The 

 bunchgrass, Festuca scabrella, was very resistant. Even 

 after 1,600 tramples, about 35 percent of the plant's 

 cover survived. This was usually the tough core of the 

 tuft (fig. 16). Calamagrostis rubescens, a rhizomatous 

 grass, was not particularly resistant and lost over 90 

 percent of its cover after 400 passes. 



Mosses were very resistant, particularly to low and 

 moderate levels of trampling (fig. 15a, b). This is the one 

 type of plant that did not exhibit a curvilinear relation- 

 ship between cover loss and amount of trampling. Two- 

 thirds of the moss cover survived 400 passes. Beyond 

 this level of trampling, cover loss was rapid and con- 

 tinued unabated; only about 5 percent survived 1,600 

 passes. Lichens were considerably more sensitive, but, 

 like mosses, consistently survived low levels of tram- 

 pling. Over 60 percent of the cover survived 100 passes. 

 Beyond this level, cover dropped rapidly to less than 5 

 percent after 400 passes. 



All of these species and 34 less widely distributed spe- 

 cies are classified according to their susceptibility in 

 table 8. This ranking can be used to predict the resis- 

 tance of vegetation types to the initial effects of tramp- 

 ling. Types dominated by resistant species will obviously 

 be more resistant than those dominated by susceptible 

 species. For example, the most resistant habitat types, 

 FESC-FEID and ABLA/XETE, have 74 and 73 percent 



cover of very resistant species, compared with and 1 

 percent cover of very susceptible species. In the 

 PSME/SYAL, ABLA/VACA, and ABLA/CLUN-VACA 

 types, very susceptible species are slightly more abun- 

 dant than very resistant species. In the ABLA/ CLUN 

 type, very sensitive species contribute 59 percent cover 

 compared to 5 percent for very resistant species. 



From table 8, graminoids have been classified as very 

 resistant, resistant, and neutral. The bunchgrass, 

 Festuca scabrella, is most resistant. Previous studies 

 have generally found graminoids to be particularly resis- 

 tant to trampling (Schreiner 1974, 1980; Nagy and Scotter 

 1974). These results, along with those of Nagy and Scotter 

 (1974), suggest that graminoids growing under shady 

 forested conditions are generally more sensitive than 

 graminoids growing in the open. Graminoids that 

 evolved under grazing pressure should also be more 

 resistant than those that did not. 



Shrubs range from sensitive to resistant; none are ex- 

 ceptionally sensitive or exceptionally resistant. The more 

 resistant shrubs are over 2 ft (0.6 m) tall (Amelanchier 

 alnifolia), very low-growing (Arctostaphylos uva-ursi, 

 Linnaea borealis), and/or have tough, flexible branches 

 and leaves {Berberis repens). The most susceptible 

 shrubs {Vaccinium caespitosum. V. globulare. Spiraea 

 betulifolia) are short, erect shrubs with brittle stems. 

 Brittleness increases with the season, making these spe- 

 cies particularly susceptible to trampling later in the 

 summer. 



These results agree with results of a series of Canadian 

 studies (Landals and Scotter 1973, 1974; Nagy and 

 Scotter 1974) in which Berberis repens and Vaccinium 

 scoparium were found more resistant than Symphoricarpos 

 albus, Vaccinium membranaceum—a morphological 

 analog to V. globulare— and Spiraea betulifolia. Differ- 

 ences were slight, however, when considering the general 

 susceptibility of these shrubs. 



Figure 16.— After 1,200 passes, Festuca scabrella is severely abraded but ttie 

 tougt) core of the tuft survives. 



26 



