Abstract:

Pinus tabulaeformis forest mixed with deciduous oak species such as Quercus mongolica and Q.liaotungensis is the zonal native vegetation in Western Liaoning Province. However, the present artificial vegetation dominated in Western Liaoning Province is monocultures of P.tabulaeformis. It is of great significance to introduce oak species into the pure P.tabulaeformis plantations to promote the restoration of P.tabulaeformis forest mixed with oak species and the sustainable management of the pure P.tabulaeformis plantations. The objective of this study was to investigate the afforestation techniques for Q.mongolica, Q.liaotungensis and Q.acutissima under the semiarid conditions in Western Liaoning Province. In view of the natural conditions in Western Liaoning Province, a series of direct seeding and planting experiments for oak species under different shading conditions such as in the cutting strip of P.tabulaeformis stand, under the canopy of P.tabulaeformis stand and in the open stand of P.tabulaeformis were carried out. The results showed that oak growth was characterized by growth of root system during the first 3～4 years after seeding or planting. However, it was dominated by the elongation of the taproot while the absorptive root was too less to maintain balance of water contents between the above and below ground parts of the oak seedlings and saplings. This was the main reason for the failure of oak afforestation in wild land in Western Liaoning Province. Under shading conditions, transpiration rate of oak seedlings decreased greatly because of the drastic reduction of light intensity, which reduced the waste of water in summer, while in winter and at the end of winter and at the beginning of spring, seedling death rate resulted from top_drying or withered stem after physiological drought was greatly reduced. Both situations contributed to the high survival rate and satisfactory growth of oak seedlings and saplings. The survival rate could be as high as 100% in the first few years when afforestation was done under closed canopy of P.tabulaeformis stand, but the growth increment of height and diameter was less. This phenomenon became more obvious with increase of age of the seedlings. The survival rate of oak saplings at the age of 6 years was more than 90%; the average basal diameter of trees ranged from 0.45 to 0.95 cm; the average tree height from 19.5 to 32.3 cm; the root system reached a depth of 70.5 cm, the width in diameter was 1.728 cm, and the width in diameter where the root was broken was 0.344 cm. With the increase in number of lateral and fibrous roots and the enhancement of their adsorptive capability, the oak saplings was at a stage of stable growth from 6～7 years onwards. Based on this study, it was concluded that the following set of techniques should be followed to guarantee the success of artificial oak afforestation in Western Liaoning Province:(1)Afforestation under shelter such as in the cutting strip of P.tabulaeformis stand, under the canopy of P.tabulaeformis stand and in the open stand of P.tabulaeformis, but afforestation under closed canopy of P.tabulaeformis stand should be avoided; (2) Direct seeding in autumn with careful site preparation, seed screening and classification before seeding, and a favorable mulching soil layer depth of 5～8 cm, but places where were heavily damaged by mouse or hare should be avoided; (3)Selection of site with a thick soil layer depth; and (4) Careful tending, particularly stumping of saplings.

Key words: Semiarid areas, Quercus mongolica, Q.liaotungensis, Q.acutissima, Afforestation techniques