Features of Quercus variabilis Stump Sprouting and Its Contribution to Population Regeneration in Different Habitats Sprouting and Growth Characteristics of Quercus variabilis Stump after Cutting in Different Habitats of the Southern Slope of the Qinling Mountains STUDY OF FRAXINUS MANDSHURICA ASEXUAL REGENERATION IN THE HILLS AREA OF SANJIANG PLAIN Regeneration and Development of Stump Sprouts of Quercus wutaishanica