68 NATURAL REGENERATION 



Scotch pine absolutely prevents reproduction. Jolyet holds that "the 

 depth of a soil from the rock base will be always greater in the forest 

 than on bare ground. This is due to the greater rapidity of decomposi- 

 tion, owing to the effect of water infiltration which is charged with car- 

 bonic acid by percolating the litter." Forest soil is deepened not only by 

 decomposition from the underlying rock, but also by the accumulation of 

 humus from above. 



Every forester should study the depth 3 and character of soils. A deep- 

 rooting tree on a shallow soil cannot develop its root system properly and 

 normally, but on a shallow soil with an outcropping rock such trees as 

 aleppo, mountain, or Austrian pine possess root systems that penetrate 

 the rock fissures and make the most of a sterile soil. A soil covered with 

 tree growth is always more porous than the same soil denuded. It is 

 not enough for a soil to receive the water necessary for tree growth; water 

 must be stored or retained in such form i nat it is available for use when 

 required by the tree during the vegetative period. On a bare though 

 porous soil the run-off is excessive. 



Soil Preparation. Soil preparation is often necessary in any kind of 

 cutting, yet in France the sentiment is everywhere in favor of natural 

 regeneration, preferably without the additional expense of artificial soil 

 preparation. But the more the system departs from nature's method, 

 the more the soil must be worked. With the shelterwood system there 

 must be more soil preparation than with the selection method. The suc- 

 cess of natural regeneration depends on the proper number and location 

 of trees bearing seed, the right amount of light or shade for the develop- 

 ment and existence of the young seedling, as well as upon proper texture 

 of the ground free from weed cover. But it is only under the most favor- 

 able conditions that some kind of soil preparation is not necessary for the 

 successful regeneration of a species like spruce. In theory, the forest 

 could wait until natural regeneration came in without assistance. In 

 practice, the regeneration would often be incomplete; it would come in 

 slowly and seed trees valuable for timber of the highest quality would 

 decrease in value and become firewood. Even with very full seed crops 

 some kind of. assistance may have to be given natural regeneration usually 

 for three reasons: (1) Because of a dense vegetable cover which prevents 

 the seed coming in contact with the mineral soil; (2) because of an exces- 

 sive cover of undecomposed dead needles, or (3) because the surface of the 

 soil itself is too compact. 



The vegetable cover is often too thick because, unfortunately, as trees 

 mature their cover is less dense especially with species like oak or 



3 Very shallow soil, less than 6 inches deep; shallow soil, less than 12 inches deep; 

 slightly deep soil, less than 24 inches deep; deep soil, less than 3.28 feet deep; very deep 

 soil, over 3.28 feet deep, according to French classification. 



