EFFECT OF TRAMPLING ON 

 NUMBER OF PLANT SPECIES 



Loss of species after trampling was assessed by 

 calculating 



Species 



I : • 



number of species before trampling — number after trampling 

 X 100% 



number of species before trampling. 



This loss of species varies significantly both with num- 

 ber of passes and between habitat types; interaction be- 

 tween these two major effects is also significant (two- 

 way analysis of variance; p < 0.001). 



The graphs in figure 13 show that as number of passes 

 increased from zero to 1,600, loss of species was initially 

 rapid and then leveled off. Most habitat types lost the 

 first quarter of their species by 75 to 100 passes and the 

 second quarter by 400 passes; a further increase in tram- 

 pling to 1,600 passes caused an additional loss of only 

 10 to 15 percent. 



Initial loss of species was most rapid in the ABLA/ 

 VACA (fig. 13c) and PSME/SYAL (fig. 13e) types; it was 

 least rapid in the FESC-FEID (fig. 13f) and ABLA/XETE 

 (fig. 13d) types. Generally, the initial rapid loss of spe- 

 cies began to abate after 25 passes, increasing more 

 slowly to 400 passes. In the ABLA/CLUN type (fig. 13a), 

 the initial rapid loss continued unabated to 300 passes, 



100 r- 



W 

 <0 

 O 

 -I 



(/) 

 UJ 



O 

 u 



0. 



100 r 



(A 

 o 



w 



UJ 



o 

 lit 

 a 



CO 



100 



(b) ABLA/CLUN 

 VACA PHASE 



100 



400 



800 



1200 



1600 



100 



NUMBER OF PASSES 



400 800 1200 



NUMBER OF PASSES 



1600 



Figure 13. — The relationship between number of passes and species loss (per- 

 centage of species originally present that were absent after trampling). Lines 

 at the right of each graph connect values that are not significantly different 

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



20 



