100 



(a) ABLA/CLUN 



DC 

 UJ 

 > 

 O 



o 



UJ 



> 



O 



o 



100 400 800 1200 



NUMBER OF PASSES 



1600 



(b) ABLA/CLUN 

 VACA PHASE 



(d) ABLA/ XETE 



(f) FESC - FEID 



100 



400 800 1200 



NUMBER OF PASSES 



1 



160 



Figure 10. — The relationship between number of passes and relative vegeta- 

 tion cover (percentage of original cdver that survives, adjusted for changes on 

 control lanes). Lines at the right of each graph connect values that are not 

 significantly different (Duncan's multiple range test, a = 0.05). 



At the other extreme, the most fragile of the forested 

 types was the lush forb-rich ABLA/CLUN type. Here 

 just 15 passes caused a significant loss of cover (fig. 11a, 

 b), and cover loss grew rapidly with increased trampling. 

 Seventy-five passes was sufficient to reduce relative 

 cover to only 35 percent (fig. 11c). Cover was less than 

 10 percent after 300 passes (fig. lid), and further in- 

 creases in tram.pling caused no significant further reduc- 

 tions in cover (fig. lie). 



In dramatic contrast to the forested types, the FESC- 

 FEID grassland tolerated 1,200 tramples without signifi- 

 cant cover loss. Biomass was lost and plants were 

 damaged, but nearly total cover remained. Cover was 

 reduced to 72 percent after 1,600 passes. It is not possi- 

 ble to conclude whether or not the shape of the curve of 

 cover loss beyond the 1,200-pass threshold will also 

 approximate a logarithmic curve as the forested types do. 



14 



