30 BULLETIN 1105, U. S. DEPARTMENT OF AGRICULTURE. 



RELATION BETWEEN REPRODUCTION AND CHARACTER OF SOIL. 



Observations throughout the yellow-pine type in Arizona and 

 New Mexico indicate that yellow pine reproduction is uniformly 

 better on the coarser, sandy, gravelly, or stony soils than on the 

 finer soils, regardless of geologic origin. Since the finer materials 

 are deposited in the valleys and flats, reproduction is usually 

 poorer in such situations than on the slopes. On table-lands, where 

 the soil is mainly residual, the best reproduction is always asso- 

 ciated with the presence of stones or gravel. Often the soils on 

 which seedlings are most numerous are too shallow or too stony 

 to support a good stand of timber, whereas the deepest and most 

 fertile soils, which produce the heaviest stands once they are well 

 stocked, are often stocked below their capacity because they are 

 unfavorable to the establishment of seedlings. 



son- SUEA^YS. 



The above observations are confirmed by detailed studies of a 

 number of areas on which the soil types were mapped by J. O. 



Sample pJors 3 Aand 3 B J9E0 



■f 



Fig. 3. — Number of seedlings per acre on various soils. 



Yeatch, of the U. S. Bureau of Soils. Special attention was given 

 to sample plots 3a and 3b previously mentioned, because these 

 plots are typical of extensive areas which are restocking unsatis- 

 factorily. Table 10 and Figure 3 give the results of seedling counts 

 in the most prevalent types of soil on these two plots. All seed- 

 lings over 2 years old (omitting the 1919 crop) were counted by 

 1-chain squares (Fig. 1). In order to avoid transition zones be- 

 tween types, and to simplify computation of area, counts were 

 made, with a few exceptions, only on squares which fall entirely 

 within a single soil type as indicated by the map. 



Description of soils. — The following soil descriptions were pre- 

 pared by J. O. Veatch, of the Bureau of Soils, and based upon 

 field examinations made by him in 1919. 



PLOT 3a,. 



The soils belong in the upper part of tlie Coloradan soil zone, to tlie Tusayan 

 types and geologically to the basalt group. The mineral base of the various soil 



