Initially, the Geranium type reacted most strongly 

 to trampling. It was dominated by erect herbs — mostly 

 forbs. The relative height decreased to 24 percent after 

 25 passes and to 8 percent after 200 passes (fig. 12). 

 The most resistant types were Trifolium and Vaccin- 

 ium, where relative height exceeded 80 percent after 

 25 passes and was still about 50 percent after 200 

 passes. The response of the Kobresia type was inter- 

 mediate, with a relative height of 39 percent after 

 200 passes. 



Three types of response are apparent during the 

 year after tramphng. In the Vaccinium type domi- 

 nated by dwarf shrubs, height continued to decline. 

 In the Kobresia type dominated by graminoids, height 

 increased somewhat, with the amount largely inde- 

 pendent of trampling intensity and relative height 

 immediately after trampling. In these two types, rela- 

 tive height 1 year after trampling varied with tram- 

 pling intensity. The relative height increased much 

 more during the year in the Geranium and Trifolium 

 types, often increasing more on the more heavily 

 trampled lanes. Consequently, relative height 1 year 

 after trampling was largely independent of trampling 

 intensity on these types. The significant interaction 



between trampling intensity and vegetation type, 

 apparent in the analysis of variance, reflects these 

 responses. One year after tramphng, relative height 

 approached 100 percent on aU lanes in the Trifolium 

 type. In the Geranium type relative height was 70 

 to 80 percent on aU lanes. 



The rate of height reduction and the rate of cover 

 loss were substantially different only in the Kobresia 

 and Geranium types. In both of these types, height 

 reduction occurred more rapidly than cover loss and 

 recovery after 1 year was less complete. For example, 

 in Kobresia,lb passes eliminated about 10 percent of 

 the cover, but it reduced height by about 35 percent. 



Species Richness and Composition 



Species richness declined as trampling increased on 

 aU foiu- vegetation types. The response was most rapid 

 on the Kobresia and Geranium types, where 75 passes 

 caused a significant reduction (fig. 13). In Geranium, 

 the mean number of species on the 500-pass lanes 

 was 12 before trampling and three after trampling. 

 In the Vaccinium type, the number of species was 

 significantly reduced only on the 500-pass lanes. In 



100 200 300 400 500 100 200 300 400 500 



Number of Passes 



Figure 12 — Relative vegetation height after trampling and after 1 year of recovery 

 in four vegetation types in Colorado's Rocky Mountains. Vertical bars represent 

 1 standard error above and below the mean. 



20 



