Alpine plants must be capable of tolerating harsh and 

 abrasive conditions, such as high winds and blowing 

 snow and ice. Therefore, most of the plant biomass is 

 below the ground. The aboveground tissues are gen- 

 erally tough and grow low to the ground. These char- 

 acteristics also make a plant resistant to trampling. 

 All three of the alpine vegetation types were dominated 

 by turf-forming graminoids, the most resistant growth 

 forms (as suggested by their use on football fields and 

 lawns). Other alpine vegetation types are likely to be 

 less resistant (Bell and Bliss 1973). 



The resilience of alpine vegetation was unexpected. 

 I suspect that resilience would be low following either 

 high-intensity or long-duration tramphng. This study's 

 results apply only to the low-intensity, short-duration 

 use these experiments simulated. Even above timber- 

 line, the capacity for recovery from this type of use is 

 high. 



The subalpine zone is characterized by tremendous 

 variation in response. The most tolerant type {Trifo- 

 lium), two intermediate types (Valeriana and Dryop- 

 teris), and the three least tolerant types {Vaccinium, 

 Phyllodoce, and Lycopodium) were all in the subalpine 

 zone. In subalpine basins, it is not imcommon for four 

 or five different vegetation types within a few hundred 

 meters of each other to vary in response from highly 

 tolerant to highly intolerant. Attention to the dura- 

 bility of vegetation is particularly important in the 

 subalpine zone. This conclusion is fiirther underscored 

 by the attractiveness of the subalpine zone, usually 

 the primary destination of most wilderness visitors, 

 particularly in the West. 



Canopy Density — ^A nimiber of impact studies have 

 found that vegetation types found in open areas tend 

 to be less severely impacted than those found in closed 

 forests (Cole 1979; Marion and Merriam 1985; Schreiner 

 and Moorhead 1979). Direct sunlight does not confer 

 greater durability; rather, the growth forms of plants 

 adapted to shade tend to make them susceptible to 

 damage from trampling (Cole 1979). 



Of the 16 vegetation types in this study, the four 

 types found in open areas were significantly more re- 

 sistant than those found in partially and completely 

 forested areas (fig. 40). The four types found in open 

 areas were among the five most resistant vegetation 

 types. They also were more tolerant; however, resil- 

 ience did not vary with canopy density. This confirms 

 the conclusion that vegetation types in open areas are 

 generally more tolerant of trampling impact than 

 ground cover vegetation in forests. 



Plant Morphology — Many studies have related 

 observed differences in impact to differences in the 

 morphology of the species involved (Kuss 1986; Liddle 

 1991). Tolerant plants are generally short rather than 

 tall, with a tufted or prostrate rather than an erect 



forested 



Relative Cover After Trampling (percent) 

 Resistance Index 



Figure 40 — Resistance, tolerance, 

 and resilience of vegetation types 

 with varying degrees of canopy clo- 

 sure. Resilience is indicated by the 

 perpendicular distance from the di- 

 agonal line of equal resistance and 

 tolerance. Refer to figure 37 for 

 names of each vegetation type. 



grovd;h form. Two alternative classifications of life 

 forms have also been used to assess durability. One 

 classification distinguishes between shrubs and her- 

 baceous vegetation, subdividing herbs into graminoids 

 and forbs. Using this classification, graminoids have 

 fi"equently been found to be resistant (Holmes and 

 Dobson 1976). Life forms also have been classified on 

 the basis of the location of growing points (perennat- 

 ing tissues such as buds) (Raunkiaer 1934). Chamae- 

 phytes (plants with perennating buds above the soil 

 surface) have generally been found to be less durable 

 than hemicryptophytes and cryptophytes (plants with 

 perennating buds at or below the soil surface, respec- 

 tively). Most of these generahzations were made after 

 comparing the vegetation in trampled and imtrampled 

 areas. This makes any conclusions about cause and 

 effect risky. Moreover, any single study is likely to 

 have assessed impacts only in a few vegetation types. 



This experimental study of 16 different vegetation 

 types avoids these drawbacks, allowing comparisons 

 between (1) tall, erect growth forms and short growth 

 forms that are not erect, (2) shrubs, graminoids, and 

 forbs, and (3) chamaephytes, hemicryptophytes, and 

 cryptophytes. Vegetation types dominated by erect 

 plants were significantly less resistant than those 

 dominated by caespitose or matted plants (fig. 41). 

 However, erectness had no effect on resilience or tol- 

 erance. Regression analysis also showed a significant 

 negative relationship between plant height and resis- 

 tance (p = 0.005, = 0.14). Plant height was not sig- 

 nificantly related to resilience or tolerance. 



50 



