All other species were too sparse or irregularly distrib- 

 uted for reliable estimates. The responses of individual 

 species were more diverse than the responses of vegeta- 

 tion types. For example, the relative cover of Carex 

 nigricans exceeded 50 percent after trampling, even 

 on the 700-pass lanes, while the relative cover of 

 Senecio triangularis (arrowleaf groundsel) was only 

 1 percent on the 200-pass lanes. Recovery also varied 

 greatly. Pachistima and Phyllodoce both lost cover 

 over the year followdng trampling, while mosses re- 

 covered so dramatically that relative cover exceeded 

 100 percent, even on the 500-pass lanes. 



A plot of the initial response to light trampling (25 

 passes) on one axis and the response to heavy tram- 

 pling (500 passes) on the other suggests three levels 

 of resistance (fig. 7). Carex nigricans and Pachistima 

 myrsinites were generally resistant to trampling, even 

 when intensities were as high as 500 passes. Senecio 

 triangularis, Vaccinium membranaceum (big huckle- 

 berry), Phyllodoce empetriformis, and mosses resisted 

 light trampling, but were susceptible to heavy tram- 

 pling. The other species — Trollius laxus (globeflower), 

 Valeriana sitchensis, Potentilla flabellifolia (fan-leaf 

 cinquefoil), and Mitella breweri (Brewer's mitrewort) — 

 were susceptible even to light trampling. 



In a similar plot of relative cover after the year of 

 recovery, species groupings are less obvious, and re- 

 sponses to Hght and heavy trampling are more similar 

 (fig. 8). Species tended to be tolerant of trampling, re- 

 gardless of its intensity, or intolerant. At one extreme 



(0 



o 



(0 

 (0 

 (0 

 Q. 



in 



Csl 



Phyllodoce 



Mosses 



\ i,"*^ Vaccinium 

 80 - Senecio 



1. 60 



0) 

 < 



> 

 o 

 o 



> 



C3 

 O 



40- 



20 



^Pachistima 



X Carex 



» Mitella 

 >. 



Potentilla 

 Valeriana 



/ 



Trollius 



1 1 \ 1 1 



20 40 60 80 100 



Relative Cover After 500 Passes 



Figure 7 — Relative cover after light and heavy 

 trampling for abundant species in four vegeta- 

 tion types in Washington's Cascade Mountains. 



(0 

 0) 

 (0 

 (0 

 (0 

 Q. 



in 



CM 



o 



< 



> 

 O 



o 



> 



160-1 

 140 - 

 120 - 

 100- 

 80- 

 60 - 

 40- 



(0 



O 20 H 

 QC 



Mosses 



Phyllodoce 



J • Senecio 



Mitella 

 • • Carex 



Valeriana 



• Potentilla 

 • Trollius 



Pachistima Vaccinium 



-1 — T r- 



40 60 80 100 



Relative Cover After 500 Passes 



20 



~l 1 1 



120 140 160 



Figure 8 — Relative cover 1 year after light and 

 heavy trampling for abundant species in four 

 vegetation types in Washington's Cascade 

 Mountains. 



were the highly tolerant mosses and Carex nigricans. 

 Relative cover exceeded 100 percent, regardless of how 

 heavily they were trampled. At the other extreme were 

 the three shrub species, which had relative cover val- 

 ues less than 100 percent at all levels of trampling 

 and less than 40 percent on the 500-pass lanes. The 

 response of the forbs was intermediate. 



It is possible to plot both the resistance index (mean 

 relative cover immediately after to 500 passes) and 

 the tolerance index (mean relative cover 1 year after 

 to 500 passes) for these species. This depicts the rela- 

 tive resistance and tolerance of each species (fig. 9). 

 Resilience is the perpendicular distance fi"om the line 

 of equal resistance and tolerance. At one extreme was 

 the turf-forming graminoid, Carex nigricans, which 

 was highly resistant, resilient, and tolerant. The forbs, 

 Mitella breweri, Potentilla flabellifolia, Senecio trian- 

 gularis, Valeriana sitchensis, and Trollius laxus, exhib- 

 ited low resistance and relatively high resilience. Con- 

 sequently, they were moderately to highly tolerant. 

 The woody shrubs, Pachistima myrsinites and Phyllo- 

 doce empetriformis, were moderately resistant, but 

 had low resilience. Therefore, they had low tolerance. 

 Vaccinium membranaceum was substantially less 

 resistant and more resilient than the two other shrub 

 species, making its response intermediate between 

 the forbs and other shrubs. Its deciduous leaves may 

 contribute to this response, since deciduous leaves are 

 not likely to be as tough as evergreen leaves, but are 



13 



