Forbs are most divergent in their response. All the 

 very sensitive species are forbs, but so are three of the 

 six very resistant species. Tough leaves in a basal 

 rosette or tuft and a woody base are characteristics that 

 make some forbs particularly resistant. Taller, caulescent 

 forbs are most sensitive. Schreiner (1974) found Arenaria 

 capillaris, a species similar morphologically to A. congesta, 

 to be resistant. Nagy and Scotter (1974) found Xerophyllum 

 tenax to be resistant and Thalictrum venulosum. Aster 

 conspicuus, and Galium triflorum to be highly sensitive. 



The resistance of mosses has been noted many times 

 (Schreiner 1974, 1980; Landals and Scotter 1974; Nagy 

 and Scotter 1974; Holmes and Dobson 1976; Studlar 

 1980). Lichens have been found to be sensitive when 

 trampled in high-elevation and high-latitude vegetation 

 types (Schreiner 1974, 1980). In the midelevation types 

 trampled in this study, hchens were only moderately 

 susceptible to damage. 



With only six exceptions, these fragility ratings 

 (table 8) are comparable to ratings based on a compari- 

 son of species response on campsites in the Bob Marshall 

 Wilderness and neighboring undisturbed control plots 

 (Cole 1983). Compared to the study of existing camp- 

 sites, this experimental study overestimates the fragility 

 of Smilacina stellata and Disporum trachycarpum. These 

 species appear to be highly resilient, recovering rapidly 

 after disturbance from rhizomes. The experimental study 

 underestimates the fragility of Carex geyeri, 

 Arctostaphylos uva-ursi, Linnaea borealis, and mosses. 

 Apparently, the initial resistance of these species 

 declines when subjected to prolonged trampling. These 



hypotheses will be tested after following the response of 

 these species to subsequent years of trampling. 



EFFECT OF TRAMPLING ON 

 MINERAL SOIL EXPOSURE 



In addition to eliminating vegetation cover, trampling 

 also can erode the surface organic horizons of the soil, 

 exposing mineral soil beneath. Before trampling, all of 

 the habitat types had a mean mineral soil exposure of 

 percent, although seven of the 34 subplots on the FESC- 

 FEID type and one of the subplots on the PSME/SYAL 

 type had traces of exposed mineral soil. The increase in 

 exposure resulting from trampling was expressed simply 

 as the percentage of exposure after trampling minus the 

 percentage before— usually zero. No correction for 

 changes on the control lanes was necessary because 

 these lanes had no mineral soil exposure. 



Table 9 shows the relationship between trampling in- 

 tensity and increase in mineral soil exposure for each 

 habitat type and for all types combined. Because most 

 values were zeros, the distribution of values was so 

 highly skewed that nonparametric statistics were used 

 to draw inferences about the statistical significance of 

 these results. 



A Friedman two-way analysis of variance (Siegel 1956) 

 suggested that increase in exposure differs both with 

 amount of trampling and with habitat type (p < 0.001). 

 Page's test for ordered alternatives based on Friedman 

 rank sums was used to test whether or not mineral soil 

 exposure increased with trampling. Multiple comparisons 



Table 9.— The relationship between number of passes and percentage increase in mineral soil exposure for 

 each habitat type and for all types combined'' 



Habitat type^ 



Number ABLA/CLUN- All 



of ABLA/CLUN VACA phase ABLA/VACA ABLA/XETE PSME/SYAL FESC FEID types 



passes Mean S.d. Mean S.d. Mean S.d. Mean S.d. Mean S.d. Mean S.d. Mean S.d. 





 5 



15 

 25 

 40 

 75 

 80 

 100 

 200 

 300 

 400 

 600 

 800 

 900 

 1,200 

 1,600 

 Mean 



— 1 



1 4 1 



— — — 3 



— — — 6 



0.5 3 0.1 



9 

 16 



4.6 



























+ 



1 



+ 



1 



+ 



1 



3 



5 







1 



2 











-1- 



-1- 



4- 



2 



2 



5 



1 



4 



1 



2 



1 



3 



2 



9 



4 



8 



-1- 



1 



+ 

 1 



+ 

 5 



1 



4 



3 



6 







1 



3 



1 



1 



7 



11 



3 



9 



2 



7 







1 



4 



3 



5 



1 



3 



4 



5 



15 



22 



4- 



1 



4 



11 



1 



1 



8 



9 



3 



4 



4 



8 



1 



1 



14 



21 



13 



14 



6 



12 



0.9 



3.7 



3.5 



9.4 



1.3 



4.5 



1.4 



5.1 



'Increase in mineral soil exposure is percentage mineral soil exposure after trampling minus percentage mineral soil ex- 

 posure before trampling. A + indicates less than 0.5 percent. 

 ^Habitat types are: 



ABLA/CLUN = Abies lasiocarpa/Clintonia uniflora 



ABLA/CLUN-VACA = Abies lasiocarpa/Clintonia uniflora-Vaccinium caespitosum phase 

 ABLA/VACA = Abies lasiocarpa/Vaccinium caespitosum 

 ABLA/XETE = Abies lasiocarpa/Xerophyllum tenax 

 PSME/SYAL = Pseudotsuga menziesii/Symphoricarpos albus 

 FESC-FEID = Festuca scabrella—F. idahoensis. 



28 



