The Effect of Shrub and Herb on the Population Regeneration and Density of Sterculia lychnophora Saplings and Seedling

The purpose of this research is to study the effect of height and cover degree of shrub and herb cover degree on the regenerative density of Sterculia lychnophora (SL) saplings and seedling of broadleaved and semideciduous forests at Dongnai Natural and Cultural Reserve in Vietnam, and discuss the population regeneration and sustainable development of SL saplings in shrub and herb. The results showed that: The regenerative density of SL is significantly correlated with shrub cover, which can be reflected in the three dominant levels of forests that when shrub cover degree gradually increases, the regenerative density of SL monotonically decreases, and the conform model for the relation between regenerative density of SL and shrub height is y=a + bx + cx2; Different cover degrees and height levels of shrub is significantly related with the regenerative density of SL. In the first and second dominant levels of forests, when the shrub height is 300-400cm and the cover degree is less than 40%, the density of SL is 2500-3000plants/hm2; when the cover degree is least 70% and the height is less than 200cm, the density is 500-1000plants/hm2. In the third dominant level of forest, when the height is 300-400cm and the cover degree is less than 40%, the density is 3000-4000plants/hm2; The density of SL gradually decreases along with the increase of herb cover degree. In the three dominant levels of forests, the related model between the density of SL saplings and herb cover degree is y=a × exp (-bx); The herb cover degree and shrub cover degree have combined effect on the regenerative density of SL, for which the model is y=a + b1x1 + b2x2 + c1x21 + c2x22 + dx1x2. When the low levels of shrub cover degree and herb cover degree is less than 30%, the highest density is 2500-3000plants/hm2; when the shrub cover degree increases to and herb cover degree reaches to above 80%, the density is 500plants/hm2 or less. Increasing shrub and herb cover degree and decreasing shrub height are unsuitable for the regeneration of Sterculia lychnophora. Therefore, in the natural regeneration of Sterculia lychnophora or plantation management, shrub and herb should be cleared in an appropriate way so as to provide a suitable environment for the regeneration and growth of Sterculia lychnophora.