16 CONCEPT AND HISTORY. 



moisture requirements and greater demands for light, will probably prove 

 more suitable than Douglas fir for openings within the natural range of the 

 former. A later study has dealt with the correlation of height-growth with 

 precipitation, but this is considered under growth-forms in Chapter II. 



Zon, 1915. — At the suggestion of the writer, a conference was held at 

 the Utah Forest Experiment Station in 1915 to discuss the feasibility of a 

 system of indicators for silvics and grazing, and especially the indicator value 

 of shrubby and herbaceous species and communities, with particular reference 

 to succession. The conference consisted of Mr. Zon, chief of silvics, Mr. 

 Jardine, inspector of grazing, Dr. Sampson, director of the station, Dr. E. S. 

 Clements, and the writer. There was general agreement upon the value of 

 indicators as a basis for the experimental regeneration of forest and grassland. 

 As an outcome, Mr. Zon drew up a preliminary outline of the indicator sig- 

 nificance of the important dominants of the various zones and represented 

 this graphically in a schematic transect (fig. 25). This appears to have been 

 the first definite organization of the indicator experience of the Forest Service 

 in silvical work. Its proposals as to indicators are considered in Chapter VII. 



A similar conference on indicators and succession was held at the station in 

 1917. It was attended by Professor Tourney, Professor Pool, Dr. E. S. 

 Clements, Dr. Sampson, Mr. Korstian, Mr. Baker, Mr. Weil, and other mem- 

 bers of the staff, together with the writer. Particular attention was given to 

 serai indicators of grazing burns, erosion and slides, as well as to climatic 

 indicators in the chaparral belt. Some of the conclusions are to be found in 

 the discussion of indicator papers in Chapter VII, as well as in the body of the 

 text itself. 



Hole and Singh, 1916. — In studying the reproduction of sal (Shorea robusta) 

 in the forests of India, Hole and Singh have made a quantitative study of the 

 water and light factors which control germination and ecesis. Their work is 

 especially noteworthy in that experimental quadrats have been employed for 

 the analysis of different sites (p. 48), and that a detailed study was made of 

 soil aeration as a critical factor. The general indicator results are given in 

 the following excerpts : 



"Broadly speaking three principal soil types may be distinguished in these 

 areas, and these are characterized by different types of vegetation, as follows : 



A. Containing a large percentage of sand and a relatively small percentage of the 



finer particles of silt. The soil is also frequently shallow, with gravel and 

 boulders below, and is therefore essentially dry. 

 Dry miscellaneous forest with Acacia catechu and Dalbergia sissoo prominent, or 

 grassland with Saccharum munja dominant. 



B. Sal forest or grassland, well aerated deep loam with Saccharum narenga (often 



mixed with Anthistiria gigantea arundinacea) dominant. 



C. Badly aerated deep loam. This differs from (B) either in containing more clay 



and silt, in being actually denser with less pore space per cubic foot, or in 

 having the water-table nearer the surface. 

 Moist miscellaneous forest with Butea frondosa, Stereospermum suaveolens, Ter- 

 minalia, Cedrela toona and others, or grassland with Erianthus ravennae 

 (often mixed with Anthistiria gigantea villosa) dominant. 



"One of these types is unsuitable for the growth of sal, inasmuch as the 

 water-content of the soil falls rapidly to the death-limit after the close of the 

 rainy season, while another type is unsuitable on account of bad soil-aeration 

 which leads to a low percentage of germination, a high percentage of deaths 



