Afforestatioin and root system growth characteristics of {\sl Casuarina equisetifolia} clones grown on the sandy land in the draught in the coastal zone

The study showed that the mechanism of the planting survival on the dry sandy land in the draught was the physiology and morphological characteristics of forest trees forming the enormous and developed root system network so as to be suitable for the dry habitat and to guarantee the planting survival. The experimental results of different planting modes showed that the planting modes of clump, mass, etc. may raise the preserving rate by about 10%,, thus possess the extensive popularization and application value in the productive practice.