25 n 



20- 



0> 



E 



15- 



10- 



5 - 



0) 



c 



(0 



-J 



w 

 o 



o 

 o 



Q. 



O 25 



(A) Trifolium parryi 



□ Before trampling 

 ■ After trampling 

 H After 1 y^ar 



(B) Kobresia myosuroides 



25 75 200 



_, (C) Vaccinium scoparium 



20 - 



15 - 



10 - 



5 - 



75 200 500 



(D) Geranium richardsonii 



I 



25 



Number of Passes 



Figure 13 — Species richness before and after trampling and after 1 year of 

 recovery in four vegetation types in Colorado's Rocky Mountains. Vertical 

 bars represent 1 standard error above the mean. 



700 



Trifolium, the number of species declined signifi- 

 cantly on all lanes, including the control lanes that 

 weren't trampled at all. This reflected both seasonal 

 dieback of plants and gopher activity. Accounting for 

 changes on the control, trampling's only significant 

 effect was on the 500-pass lanes. One year after trgim- 

 pling, species richness approached or exceeded the 

 original levels on nearly all lanes and types. The 

 chief exceptions were the 500- and 700-pass lanes in 

 Kobresia, where species richness remained depressed. 



Species composition did not change as a result of 

 tramphng on any of the Trifolium lanes (fig. 14). Simi- 

 larity values for 500-pass lanes were 80 percent com- 

 pared v^dth 89 percent for controls. In contrast, just 

 25 passes significantly changed species composition 

 in the Geranium type. Significsmt changes occurred 

 after 200 passes in Vaccinium and after 500 passes 

 in Kobresia. Similarity values for 500-pass lanes were 

 78 percent in Kobresia, 58 percent in Vaccinium, and 

 52 percent in Geranium. After the year of recovery, 

 mean similarity values for treated lanes were similar 

 to those for controls in three of the four types. Shifts 

 in species composition actually increased over the 



year in the Vaccinium type. One year aft«r trampling, 

 the mean similarity value for the 500-pass lanes was 

 33 percent (compared to 94 percent for controls). This 

 reflects the continued decline of the dominant spe- 

 cies, Vaccinium scoparium, over the year following 

 trampling. 



General Appearance 



Visually obvious changes occurred most rapidly in 

 the Geranium type, dominated by erect forbs. After 

 75 passes many of the plants were flattened and a path 

 of broken vegetation was apparent. After 200 passes, 

 most of the vegetation had been eliminated. In the 

 Vaccinium type, a path was evident only on lanes 

 trampled at least 200 times. In the Trifolium and 

 Kobresia types, some obvious flattening occurred after 

 200 passes, but a path was not obvious until lanes had 

 been trampled at least 500 times. One year after tram- 

 pling, paths were evident only in the Vaccinium type, 

 and only on lanes trampled at least 200 times. In the 

 three other types, the visual evidence of trampling 

 was minimal. 



21 



