INDICATOR SIGNIFICANCE OF NATIVE VEGETATION 273 



fir and western yellow pine {Pinus ponder osa) types at an 

 elevation of 8700 feet on the San Francisco Mountains in north- 

 ern Arizona. Both sites had the same exposure but one was 

 aspen-covered and the other was in the open. After making 

 detailed studies of the physical factors of the two adjacent sites, 

 the survival and development of Douglas fir planted on both 

 sites and the correlation of the native vegetation occmTing on 

 the sites the conclusion was drawn that the open sites, due to 

 their greater severity, should doubtless be reforested with west- 

 ern yellow pine {Pinus ponderosa) while the aspen-covered 

 areas should be planted with Douglas fir. The aspen thickets 

 supported a luxuriant growth of broad-leaved mesophytic herba- 

 ceous plants, such as Frasera scabra, Pteridium aquilinum and 

 Verbasciim thapsus, while grasses {Muhlenbergia gracilis, Festuca 

 arizonica, Festuca pseudovina, and Bromus polyanthus) pre- 

 dominated in the openings. The growth of all herbaceous plants 

 was invariably more luxuriant under the aspen than in the 

 open. 



Shreve^^ reports a rather marked variation in the distribution 

 of the vegetation occurring in a forest of Pinus arizonica on the 

 Santa CataHna Mountains in southern Arizona. Throughout 

 the pine forest are to be found a large number of herbaceous 

 perennials, the greater majority of which accompany the closed 

 stands of pine. The occurrence of another large group of plants 

 is confined to the near proximity of streams and stream-courses. 

 In the dense shade of the evergreen-oak woodland Pteris aquilina 

 is reported as being common, and it again becomes common in 

 the pine forest above 7500 feet, but is infrequent in the lower 

 portion of the forest region. Alnus acuminata, Acer interius, 

 and Quercus submollis become frequent along streams at about 

 6800 feet. Herbaceous plants are reported as being found in 

 increasing numbers at or near the banks of streams between 

 6000 and 7400 feet, among which may be mentioned J uncus 

 arizonicus, Aquilegia chrysantha, Thalictrum fendleri var. wrightii, 

 Scrophidaria sp., Trifolium pinetorum, Fragaria ovalis, Poten- 



11 Shreve, Forrest. The Vegetation of a Desert Mountain Range as Condi- 

 tioned by Climatic Factors, Pub. 217, Carnegie Inst. Wash. 112 pp. 1915. 





;^ILIBRARY 



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