Table /. — 



Mean percentage species loss after various amounts of trampling for 

 eacfi fiabitat type and for all habitat types combined^ 



Number 







Habitat type^ 







All 



of 



passes 



ABLA/ 

 XETE 



FESC- 

 FEID 



ARI A/n IINI- 

 VACA phase 



ABLA/ 

 VACA 



PSME/ 

 SYAL 



ABLA/ 

 CLUN 



habitat 

 types 



5 



Oa 



5a 



7a 



9a 



10a 



7a 



6 



15 



8a 



23a 



2a 



17a 



20a 



8a 



15 



25 



8a 



20a 



8a 



18a 



22a 



20a 



16 



40 



10a 



11a 



7a 



17a 



33b 



10a 



16 



75 



19a 



17a 



16a 



35a 



26a 



38a 



25 



80 



23abc 



14a 



16ab 



35c 



33bc 



24abc 



25 



100 



14a 



24ab 



27ab 



35b 



38b 



21ab 



27 



200 



37a 



28a 



32a 



42a 



39a 



50a 



37 



300 



29ab 



24a 



40abc 



46c 



42bc 



64d 



39 



400 



44a 



47a 



53a 



55a 



54a 



56a 



51 



600 



53a 



58a 



63a 



51a 



51a 



61a 



55 



800 



38a 



45ab 



51abc 



66c 



61c 



59bc 



53 



900 



56 b 



40a 



64bc 



65bc 



59b 



79c 



58 



1,200 



58a b 



43a 



46ab 



66bc 



58ab 



81c 



58 



1,600 



57a 



58a 



65a 



58a 



69a 



79a 



63 



All 

 amounts 



28a 



29a 



31a 



39b 



40b 



42b 



35 



'Any two mean percentage species loss values in tine same row followed by the same letter 

 are not significantly different (Duncan's multiple range test, « = 0.05), 

 ^Habitat types are: 



ABLA/XETE = Abies lasiocarpa/Xerophyllum tenax 

 FESC-FEID = Festuca scabrella-F. idahoensis 



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

 ABLA/VACA = Abies lasiocarpa/Vaccinium caespitosum 

 PSME/SYAL = Pseudotsuga menziesii/Symphoricarpos aibus 

 ABLA/CLUN = Abies lasiocarpa/Clintonia unifiora. 



after which 64 percent of the species were lost. This type 

 eventually lost about 80 percent of its species at tram- 

 pling levels of 900, 1,200, and 1,600 passes. 



The relative resistance of these types is displayed in 

 table 7. Over the entire range of trampling intensity, 

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

 more prone to species loss than ABLA/XETE, FESC- 

 FEID, and ABLA/CLUN-VACA; however, differences 

 were not as pronounced as for resistance to cover loss. 



RESPONSE OF INDIVIDUAL SPECIES 

 TO TRAMPLING 



We were able to calculate relative cover and to graph 

 response to trampling for species abundant on control 

 lanes and most treated lanes (fig. 14). Cover loss for 

 individual species is generally more rapid than for total 



cover. The rate for individual species is actually a more 

 accurate reflection of how rapidly vegetation is lost, 

 because pretreatment total cover measures are underesti- 

 mated on account of multitiered vegetation cover. Median 

 relative cover for the 19 species fell below 50 percent 

 after 40 to 75 passes and below 30 percent after 100 

 passes. It dechned more slowly to 6 to 7 percent after 

 400 passes and then even more slowly to 1 to 2 percent 

 after 1,600 passes. 



The most sensitive species, Thalictrum occidentale, 

 Osmorhiza chilensis, and Melampyrum lineare, all lost 

 most of their cover after 15 passes and were aU but 

 eliminated— at least for the season— after 40 passes. 

 They are all forbs adapted to tolerate low sunUght condi- 

 tions. Such adaptations— thin cuticles, cell walls, and 

 stems, and a large amount of supportive and conductive 

 tissue— make them susceptible to breakage (Cole 1979). 



21 



