Statistical Inference 



The significance of differences between vegetation 

 types and between trampling treatments was tested 

 with analysis of variance. Because variances were 

 heterogeneous, we used a nonparametric procedure, 

 based on ranks rather than original values. Data 

 fi-om 700-pass lanes were excluded from this analysis. 

 Scheffe's test for multiple comparisons was used to 

 identify significantly different treatments and veg- 

 etation types. Alpha was set at 0.05. 



EFFECTS OF TRAMPLING IN THE 

 CASCADE MOUNTAINS 



The study sites in the Northwest were located in the 

 OkanogEin National Forest in northern Washington, 

 along or east of the crest of the Cascade Mountains. 

 One site was located at the relatively low elevation of 

 760 m along the upper Methow River in a Douglas-fir 

 forest {Pseudotsuga menziesii). The moderately dense 

 tree canopy (65 percent cover) consisted almost entirely 

 oi Pseudotsuga menziesii. The ground cover was only 



moderately dense. The primary species was the 

 medium-sized shrub, Pachistima myrsinites (moun- 

 tain boxwood). Species diversity was low (fig. lA). 

 This vegetation type is an example of the Pseudotsuga 

 Tnenziesii/Pachistima myrsinites association, as defined 

 by Williams and Lillybridge (1983) and Agee and 

 Kertis (1987). 



The other vegetation types were located at higher 

 elevations near Harts Pass and Slate Peak. Two 

 types were intermixed with each other in a mosaic 

 of subalpine forest and meadow, at an elevation of 

 about 1,750 m. One type was a lush subalpine herb- 

 land, dominated by forbs such as Valeriana sitchensis 

 (valerian) and Trollius laxus (globeflower) (fig. IB). 

 It occurred under an open canopy (30 percent cover) 

 of Abies lasiocarpa (subalpine fir) and Picea engel- 

 mannii (Engelmann spruce), as well as in the open. 

 Groiind cover was extremely dense, with a number 

 of different layers. Species diversity was high. For- 

 ests with similar ground cover vegetation have been 

 termed the A6ies lasiocarpa/Valeriana sitchensis 

 association by Hemstrom (1982). A variety of lush 

 subalpine herblands, with abundant quantities of 



Figure 1 — Vegetation types in Washington's Cascade Mountains are (A) Pachistima, (B) Valeriana, 

 (C) Phyllodoce, and (D) Carex. 



4 



