INDICATOR SIGNIFICANCE OF NATIVE VEGETATION 281 



It is true that crown form reflects the growing conditions as 

 determined by competition but competition cannot be regarded 

 as a site factor. 



The differences in the native vegetation on the two different 

 sites were so apparent that the writer immediately conceived 

 the idea that it could be correlated with increment and used as 

 an additional criterion in the determination of the productivity 

 of a given forest site. 



The vegetation on a number of 5 by 10-ioot quadrats was 

 listed in addition to that on the regular permanent reproduc- 

 tion plots of the same size, which were instituted with the pri- 

 mary object of studying the establishment of natural reproduc- 

 tion on the cut-over areas. Although the plots had been cut- 

 over in 1910, the logging operation which was conducted under 

 Forest Service regulations did not destroy the continuity of the 

 forest canopy sufficiently to noticeably interfere with the sta- 

 bilized climax vegetation since the virgin western yellow pine 

 forest was originally comparatively open and park-like. The 

 vegetation which was found on these list quadrats is systemati- 

 cally summarized in table 3, showing for the canon bottoms, the 

 north slopes, south slopes and ridge tops the percentage of the 

 quadrats on which each species was found. The arrangement 

 of the families is essentially an adaptation of Engler and Prantl's 

 "Die Naturlichen Pflanzenfamilien" as used in the United 

 States National Herbarium, which aims to indicate something 

 of the natural developmental relationships of the families by 

 proceeding from the simpler to the more complex. The writer 

 desires to express his indebtedness to Prof. J. J. Thornber of the 

 University of Arizona and Grazing Examiner R. R. Hill of the 

 United States Forest Service for determining numerous plants 

 and for verifying the list. A perusal of the list shows marked 

 differences in the individuality of the vegetation of the two sites. 

 Site I is shown to produce such typical mesophytes as Mnium 

 sp., Agrostis hiemalis, Bromus polyanthus, Muhknbergia wrightii, 

 Populus tremuloides, Arenaria confusa, Cerastium longipeduncu- 

 latum, Silene laciniata, Aquikgia chrysantha, Thalictrum wrightii, 

 Draba helleriana, Potentilla atrorubens, P. crinita, Rosa fendleri, 



