24 BULLETIN 1423, U. S. DEPARTMENT OF AGRICULTURE 



Some species of lichens form leaf-like expansions (foliaceous) , 

 some are cup shaped, some closely encrust the surface on Avhich they 

 gi'ow (crustaceous), and others are shrublike (fruticose), the 

 branches in this case beinj; either cylindrical or flattened. Their 

 colors vary from almost white to greenish gray, j^ellow, orange, 

 brown, or a purplish black. Changes in color are greatly influenced 

 by degrees of light and moisture or the nature of the habitat. In 

 Alaska the fruticose lichens form the bulk of the winter forage. 

 (Pis. 14-17.) 



For their growth lichens require moisture, light, and heat, and 

 probably derive some inorganic substances from the base upon 

 which they grow, but most lichens probably take a smaller propor- 

 tion of their food from the substratum and a larger proportion 

 from the air than do the higher vascular plants. They take carbon 

 dioxide from the air in the processes of nutrition, build up lichenin, 

 a substance similar to starch, and return free oxygen to the atmos- 

 j)here. When wet and in a partially decomposed condition, some 

 lichens are often of a gelatinous consistency. The thallus of some 

 s])ecies contains a bitter principle, which in a few instances may 

 make the plant unjDalatable to stock. 



LICHEN OCCUKEENCE AND DISTRIBtTTION 



On Alaskan coast ranges the best lichen growth is often found on 

 west and north exposures. In thick stands of forest or brush very 

 little of it occurs, but at the edges or in openings in the forest, or in 

 scattering tree growth, a luxuriant lichen cover may usually be 

 found (pi. 12, fig. 1). On moist tundra flats of favorable soil and 

 atmospheric conditions, as on Nunivak Island, lichen growth may be 

 abundant, both in volume and density (pL 12, fig. 2). On the 

 average summer tundra range of the coast, however, the herbaceous 

 and shrub vegetation competes predominantly with the lichens. On 

 the more rugged inland country the competition is retluced and the 

 lichens often become the predominant vegetation. Here the best 

 liclicn cover of value for grazing is on the lower slopes, in coves, and 

 hollows, and at the heads of creeks. The best individual growth 

 occurs particularly in depressions on slopes and in swales and is 

 most luxuriant in hollows between and at the bases and sides of 

 hummocks. Certain valuable species, however, of comparatively 

 short height often occur abundantly on the tops of hummocks in 

 favorable situations and under minimum competition. On rocky 

 up])er slopes and tops of ridges the lichen cover becomes scattering 

 and is usually small or dwaifed. 



Even among the best of lichen types a pure stand does not occur, 

 either with reference to class of vegetation or to individual species. 

 Generally an admixture of lichens with other vegetation is found, 

 as species of browse, mosses, and sedge. Often in the lichen stand 

 tliere may occur a considerable ])()i-tion of such mosses as SpJiaf/iium 

 and Pol i/trichum. On most of the winter ranges the lichens aver- 

 age .■)() per cent of the cover, although some forage types occur that 

 may contain as much as {)() ])er cent lichen vegetation. 



Within the stand the lichens gi'ow more or less intermingled in 

 a solid mat, with species intermixed generally, but often by indi- 



