1'-^ JOIKNAI, dl" 1•()KI•;STR^■ 



After the seed germinates the greatest deleterious effect that the 

 chajjarral exerts on the young tree is the root competition for soil 

 moisture, which in jjcriods of drought is exceedingly harmful. Chap- 

 arral plants as a rule have a douhle root system, (^ne of these lies 

 close to the surface, where there is a mass of very fibrous roots, while 

 a much deeper system, of which we know very little, grows to a dei)th 

 of 30 feet and over. The roots nearest the surface are believed to 

 become dormant as soon as the soil moisture is reduced to a point at 

 which they can no longer function, and all water required by the i)lant 

 is then furnished 1)\- the deeper roots. 



With such an established root system the young tree is at a decided 

 disadvantage, for it must reach that level from which it is able to 

 secure enough water to sustain life throughout the long, dry season. 



A study was made of the rate of growth of the Jeffrey pine under 

 tree cover where the influence of shale on height growth was greater 

 than that of root competition, and of trees growing in the chaparral, 

 where measurements revealed the light to be less than under a tree 

 cover but where the root competition was much greater. The results 

 show to' what extent the root competition affects the rate of growth, 

 there being seven years difference in the between trees growing in the 

 chaparral to a height of seven feet and those grow ing under tree cover. 

 This difference can be explained only on the basis of root competition. 

 After Jeft'rey pine had attained the height of the chaparral it was found 

 that the height growth was reduced 2^4 inches annually for a period of 

 16 years, and the height grow^th of the Coulter pine was reduced 1.7 

 inches annually for a period of nine years. 



In plantations of the Jeft'rey pine in chaparral on the same site and 

 under the same conditions of soil, density of brush and species, it was 

 found that where the chaparral roots were eliminated to a depth of 

 30 inches the height growth of the trees averaged 1.3 inches greater 

 the first year after planting and i.S inches greater the second year 

 than trees of the same stock planted in direct competition with the 

 brush. Soil moisture determinations give a very good reason for this 

 difference, as the chart evidences, being especially marked at the time 

 when growth first begins. 



The root systems of the brush are of great value in furnishing a 

 most effective preventative against erosion and landslides. 'Phe roots 

 which lie near the surface form a closely woven mat, which so binds 

 the soil that there is little displacement during heavy storms, no matter 

 what its character. Surface erosion, or sheet erosion, is therefore of 



