LODGEPOLE-PINE FORESTS OF BOULDER PARK 271 



ence of aspens. The sink holes are likely to be filled with water for 

 periods during rainy weather, and this standing water would kill 

 coniferous trees. 



A few willows {Salix brachycarpa Nutt., Salix chlorophylla Anders.) 

 are found sparingly among the herbs and shrubs in the open forma- 

 tion. 



Shrubs of the Forest Floor. — The occurrence of shrubs on the 

 forest floor has already been mentioned. Close-growing species 

 are Vaccinum erythrococcum Rydb., Vaccinium oreophilum Rydb., 

 Arctostaphylos uva-ursi (L.) Spreng. Linnaea americana Forbes 

 forms mats in shady places at the bases of trees and under fallen 

 logs, and is found in parts of the forest where spruces and firs are 

 more numerous. Other shrubs are Samhucus microhotrys Rydb., 

 Rosa sayi Schweinitz., Berberis aquifolium Pursh, Dasiphora fruticosa 

 Rydb., Juniperus siherica Burgsd., Lepargyraea canadensis (L.) 

 Greene and Lonicera involucrata Banks. The species of Vaccinium 

 are the commonest and most widely distributed of all the shrubs. 



Herbs of the Forest Floor. — The number of flowering herbs on 

 the forest floor is large, 62 species being noted, and this certainly 

 does not include all. A succession of various plant associations 

 follows the seasons. The appearance of the forest floor changes 

 from week to week depending on the flowering of the more conspicuous 

 species. An area may be covered by one society (Thermopsis, 

 Chamaenerion) or by several smaller societies. Some of the most 

 conspicuous changes in the aspect of the forest floor will be noted. 



1. About April 15, Pulsatilla hirsutissima and Thlaspi color adense 

 appear, forming the chief part of the pre-vernal flora. These plants 

 occur only on the edges of the forest and in open places. 



2. Somewhat later, in May or early June, Thermopsis divaricarpa 

 follows, producing large yellow patches among the trees. About 

 the same time Anemone cylindrica and Erysimum wheeleri become 

 conspicuous. In shady places at the bases of pine trees Arnica 

 societies may be seen. The above named may be said to belong to 

 the vernal flora, the first flowers appearing about May 15. 



3. The appearance of the loco weed, Aragallus lambertii, marks 



