These are, in most cases, diagnostic of the three communities as recognized above because 

 major changes in status along the transect correspond with changes in importance of trees. For 

 example, alder has, on the average, low cover-abundance (C-A) values in the birch community and 

 high values in the transition and spruce communities. Rosa acicularis C-A values are relatively 

 high in the birch community, somewhat lower in the transition community, and low in the spruce 

 community. WiUow (Salix spp.) has its highest importance only in the latter community. 



The ericaceous shrubs. Ledum groenlandicum and Vaccinium vitis-idaea ssp. minus are impor- 

 tant primarily in the spruce community. The prominent peak in the Ledum curve and accompanying 

 lesser peaks in the Vaccinium curve in quadrats 8 - 10 (Fig. 41), correspond to moderately high 

 values of black spruce (Fig. 39). This combination of species probably reflects a local topographic 

 swale where drainage is somewhat inhibited and soil pH is higher than in the adjacent birch 

 community. 



Figure 42 shows the relative importance along the transect of the six most abundant herbaceous 

 species. Equisetum arvense and Equisetum pratense show high to very high stem counts in quadrats 

 1 - 40. These quadrats are located along that segment o( the transect which lies within the birch 

 community. An abundance of these two species of Equisetum appears, therefore, to be diagnostic 

 of this community. Moehringia lateriflora is also diagnostic, as stem counts were much higher in 

 the birch community than in the others. The occurrence of Calamagrostis canadensis in moderately 

 high numbers in both the birch and transition communities helps to distinguish these from the 

 spruce community, although this species is still of significant occurrence in the latter. The 

 Geocaulon lividum curve in Figure 42 is high in the spruce community segment of the transect. In 

 contrast, this species appears to be rare in the transition community, and it was not encountered 

 at all in the birch community. Interestingly, Comus canadensis is fairly important in both the 

 birch and spruce communities but is nearly absent in the transition community. This is an excep- 

 tion to the rule, in that most species tend to show trends of increasing or decrea:sing importance 

 along the transect. Tables XXXIX and XL contain four other species and groupings {Calamagrostis 

 canadensis, Rubus arcticus, other mosses, and other ground lichens) which do not show such 

 trends. Here, however, the differences in importance between communities are not significant as 

 compared with those for Comus canadensis. 



40 60 



QUADRAT NO. 



Figure 42. Stem counts of six major herbaceous species in 105 l-m^ quadrats 

 along the hot-pipe vegetation survey transect. Values shown are moving aver- 

 ages of 10 quadrats each, calculated at 5-quadrat intervals. 



104 



