PLANT SUCCESSIONS OF MT. ROBSON 215 



Below this fine stretch of forest the country has been burned 

 over for many miles, but relicts show that the original vege- 

 tation was like that described, doubtless becoming even more 

 luxuriant down-riverward. Above, along the northeast shore 

 of Lake Ivinney, and upon the oldest parts of the shingle flat 

 at its head, are areas of very similar forest, differing mainly 

 in that the trees do not attain so large a size. The valley just 

 above the shingle fiat is interrupted by a "step" cliff, and be- 

 yond and above this the forest becomes that of the Subalpine 

 Zone. 



The Montane Zone is unfavorable for the study of successions, 

 because of the almost total destruction of the primitive habitats, 

 rock surfaces and moraines. The bulk of the territory is now 

 divided between rocky and talus covered slopes and shingle 

 flats. Vegetational development is correspondingly advanced. 

 The climax forest makes an almost continuous cover upon the 

 slopes, except where it has been destroyed by avalanche or fire, 

 and successional stages are hard to find. On the shingle flats 

 too there are tracts of mature climax forest, but areas in all 

 stages of the succession are common here because of the con- 

 tinual erosional and depositional activity of the rivers. Bare 

 rock surfaces are uncommon, and the moraines which formerly 

 existed have been almost entirely destroyed. The successional 

 stages related to these habitats are correspondingly incomplete 

 in representation and difficult of observation. 



The Climax Forest of the Subalpine Zone is poorer in number 

 of species than that of the Montane, and two of its three species 

 occur in the latter also. Picea Engelmanni, one of these two, 

 which is of moderate importance in the lower forest, is greatly 

 predominant here. Abies lasiocarpa is next in abundance, and 

 Pinus albicaulis Engelm., absent in the Montane Zone, is pres- 

 ent here, but was found nowhere in great abundance. The 

 first species mentioned ordinarily makes perhaps nine tenths of 

 the mature stand. Young growth is mostly Abies, which layers 

 abundantly. 1 The following list of plants is sadly incomplete: 



' Bot. Gaz. 52: 369-379; 1911. 



