HISTORICAL. 15 



pioneers of the burn subsere, together with the mosses Bryum argenteum and 

 Funaria hygrometrica. Several other species are almost equally good indi- 

 cators of burns, especially when abundant. These are Rubus strigosus, Carex 

 rossii, Arnica cordifolia, Achillea lanulosa, and Anaphalis margaritacea. The 

 water and light factors for the six dominant trees were measured and the 

 successional sequence thus obtained exhibits the indicator value of each 

 species, (plate 3.) 



A successional study was made of the so-called natural parks of Colorado 

 in 1910 for the purpose of determining their indicator significance as to refor- 

 estation, both natural and artificial. The conclusion was reached that all 

 such grassland areas in forested regions are but serai stages leading to a forest 

 climax. The majority of them are due to repeated burns or the slow filling 

 of lakes, with the result that they persist as apparent climaxes for several 

 hundred years. Their origin is readily disclosed by the indicators in them, as 

 is also true of the rate of development. 



Pearson, 1913-1914. — In discussing the proper basis for the classification 

 of forest lands into types, Pearson (1913 : 79) has reached the following 

 conclusions: 



"The only scientific basis for such a classification is that of potential pro- 

 ductiveness, considering both agricultural and forest crops. The productive 

 value may be ascertained in two ways: The first measures directly, as far as 

 possible, all physical factors on the site and gauges the productive capacity by 

 the measure in which the sum of these factors meets the requirements of various 

 crops. The second method uses characteristic forms of vegetation on the 

 ground as an indicator of the physical conditions present, and upon this basis 

 ascertains the adaptability of the site for different crops. The obvious objec- 

 tion to the first method is the need of climatological data and soil analyses on 

 each site to be classified; and owing to the diversity of sites in our forest 

 regions, together with the almost complete absence of climatological records in 

 many sections, the collection of the needed data would involve an expense 

 which, at this stage of our advancement in forestry, would be almost pro- 

 hibitive. The second method requires a thorough preliminary investigation 

 in each region to be covered, in order to secure a working knowledge for the 

 actual land classification, and obviously reliable results can only be obtained 

 by the employment of trained men. This method is the simpler and probably 

 the more reliable of the two, and it is considered entirely applicable to the 

 needs of the forester." 



A general indicator relation is established between the five forest types and 

 the agricultural possibilities of the Coconino National Forest in northern 

 Arizona. The same author (1914 : 249) has employed seedlings of Douglas 

 fir as indicators of the conditions for planting in aspen and in open situa- 

 tions at 8,700 feet on the south slope of the San Francisco Mountains., 

 The seedlings were planted in two plots in the aspen and two in the opening 

 each spring of the 3-year period, and instrumental readings were made of 

 water-content, evaporation, wind, and temperature. The aspen uniformly 

 gave a larger survival of seedlings than the opening, the percentage varying 

 from 7 to 13. The critical factor in this was evaporation, which was 50 to 

 90 per cent higher in the open than under the aspen. The author further 

 points out that the results indicate that yellow pine, because of its lower 



