Table 12 — Summary indicators of resistance and tolerance for four vegetation types in Colorado's Rocky Mountains 



Vegetation type 



Trifolium Kobresia Vaccinium Geranium 



Resistance indicators^ 



Relative cover (percent) 



57 



63 



49 



23 



Relative height (percent) 



55 



45 



51 



11 



Species richness (number of passes) 



500 



75 



500 



75 



Species composition (number of passes) 



>500 



500 



200 



25 



Evident path (number of passes) 



500 



500 



200 



75 



olerance indicators^ 











Relative cover (percent) 



100 



85 



38 



88 



Relative height (percent) 



95 



62 



39 



76 



Species richness (number of passes) 



>500 



500 



>500 



>500 



Species composition (number of passes) 



>500 



>700 



200 



>500 



Evident path (number of passes) 



>500 



700 



200 



>500 



^Resistance indicators refer to immediate responses to trampling. They include mean relative cover and relative height, after tram- 



pling, for to 500 passes, as well as the minimum number of passes that causes a significant reduction in species richness or floristic 

 similarity, or that results in an evident path. The relative cover and relative height values are the durability indices described in the 

 data analysis section. 

 ^Tolerance indicators refer to conditions 1 year after trampling. 



levels of change after trampling. Height reduction was 

 unusually low. However, over the year after trampling, 

 cover and height continued to decline. Changes in spe- 

 cies composition and the visual evidence of impact in- 

 creased. The only sign of recovery was the regrowth 

 or colonization of species that had been eliminated by 

 trampling. Species richness returned to the original 

 levels on all lanes. 



Individual Species Responses 



Relative cover could be calculated for 16 species 

 (fig. 15). The responses ranged vndely. Relative cover 

 of Carex rossii (Ross' sedge) was 76 percent after 500 

 passes, while Thermopsis divaricarpa (pine golden- 

 pea) and Viola canadensis (Canada violet) were elimi- 

 nated after 200 passes. Most species recovered over 

 the year after trampling, but Vaccinium scoparium 

 decreased in cover over the year. Some species, such 

 as Thermopsis divaricarpa, recovered greatly, while 

 others, such as Kobresia myosuroides, made more 

 modest recoveries. 



A plot of response to light and heavy trampling illus- 

 trates how resistance to trampUng varied between spe- 

 cies (fig. 16). On the left side of the graph are species 

 that did not resist heavy trampling. They range fi"om 

 Thermopsis divaricarpa, which could not resist even 

 light trampling, to Erigeron melanocephalus (black- 

 headed fleabane), which could. Across the top of the 

 graph are species that resisted light trampling. They 

 range from Erigeron melanocephalus, which did not 

 resist heavy trampling, to Carex rossii, which did. 



A similar plot of relative cover after the year of re- 

 covery provides a more hnear distribution of points, 

 ranging from Trifolium parryi, tolerant of both light 



and heavy trampling, to Viola canadensis, only mod- 

 erately tolerant of light or heavy trampling (fig. 17). 

 The primary exception is Vaccinium scoparium, which 

 tolerated light trampling, but was not at all tolerant 

 of heavy trampling. The response of Thermopsis 

 divaricarpa is difficult to explain. It recovered after 

 heavy trampling, but not after light trampling. 



A plot of resistance and tolerance indices depicts a 

 broad range of responses (fig. 18). At one extreme was 

 the caespitose graminoid, Carex rossii, both highly 

 resistant and tolerant. The erect, caulescent (leafy- 

 stemmed) forbs. Aster laevis (smooth aster), Achillea 

 lanulosa (western yarrow), Thermopsis divaricarpa, 

 Geranium richardsonii, and Viola canadensis all ex- 

 hibited low resistance and relatively high resilience. 

 Consequently, their tolerance was moderate to high. 

 Intermediate between the erect forbs and Carex rossii 

 were a variety of other caespitose graminoids and 

 reptant (creeping) or rosette (leaves like the spokes 

 of a wheel at the plant's base) forbs. The dwarf shrub, 

 Vaccinium scoparium, was characterized by very low 

 resilience. Its resistance was moderate, but its toler- 

 ance was very low, due to its inability to recover dur- 

 ing the year following trampling. 



Table 13 classifies the responses of less common 

 species as low, moderate, or high. The table reinforces 

 the pattern of responses established by the more de- 

 tailed analysis of common species. The graminoids 

 were generally more resistant than the forbs. Among 

 the forbs, the most resistant species were short, creep)- 

 ing plants with tough leaves, or without leafy stems. 

 Mosses were resistant, but hchens were not. The one 

 shrub species had low resilience. Resihence was moder- 

 ate to high in graminoids, low to high in forbs, low to 

 moderate in hchens, and moderate to high in mosses. 



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