I 



HEtEODtTCrrOK OF WESTERN YElLOW PINE. 41 



being equal, germination is favored by loosening the soil, but that 

 removal of ground cover or litter is detrimental. The explanation 

 is simple, once the facts are clearly in mind. Cultivation, in the first 

 place, tends to bring to the surface the clayey subsoil. It not only 

 removes the vegetation which shades the soil and young seedlings, 

 but also destroys the accumulation of leaf mold and litter resulting 

 from fallen stems and leaves. The mold seems to be especially 

 important, as it gives a loamy texture to the surface of an other- 

 wise heavy soil. Observations show that where the grass is undis- 

 turbed for a number of years, a considerable amount of mold ac- 

 cumulates. Seeds bury themselves readily in this material; favor- 

 able conditions of soil moisture are preserved, at least during the 

 rainy period; and the young seedlings are screened from the wind 

 and hot sun by the taller herbage. ^\'Tiere the ground is shaded 

 through the hot portion of the day, seeds germinate during the 

 rainy season without being covered by soil. In the vicinity of trees 

 the ground is usually littered with needles, which aid in keeping the 

 surface moist. On the uncultivated plots, this litter was often too 

 deep for good germination; but on the cultivated plots the old ac- 

 cumulation was turned under, thus adding organic matter to the 

 soil and at the same time removing the excess of litter from the sur- 

 face. Shade and litter usually go together, and apparently, within 

 certain limits, the effects are silimar as far as germination is con- 

 cerned. On some of the plots herbaceous vegetation has already come 

 in to a considerable extent, but since the plants are of a different type 

 from those on natural plots, it is difficult to make comparisons. In a 

 few instances these plots have as many as or more seedlings than the 

 adjoining natural ones. 



Seedlings are in almost every case more numerous on the plots 

 within 25 feet of seed trees than on those more remote. This sub- 

 ject has been discussed under " Seed supply." The distinction is 

 made here primarily in order to place the shaded plots, all of which 

 are within 25 feet of the trees, on a comparable basis with unshaded 

 plots. Although distance from trees undoubtedly has an important 

 bearing on survival, other factors must be considered. 



Table 11 shows the percentage survival in various situations. In 

 considering ultimate survival the plots shaded by trees half or more 

 of the day may at once be eliminated, because it has been repeatedly 

 demonstrated that western yellow pine seedlings will not thrive in 

 such situations. Considering only the plots which are exposed 

 to direct sunlight more than half the day, we find no consistent dif- 

 ference in percentage of survival, although the natural plots main- 

 tain the lead over the cultivated ones in actual numbers: Many of 

 the natural plots are gradually losing their margin ; there are, how- 

 ever, too many exceptions to recognize a definite trend in that direc- 



