DISTRIBUTIONAL CHARACTERISTICS ON BIOMASS AND NUTRIENT ELEMENTS OF PINE-OAK FOREST BELT IN MT.QINLING Photosynthesis Inhibition of Two Varieties of Quercus aliena in Salt Stress Photosynthetic Characteristics of Six Plant Species in Quercus aliena var. acuteserrata Community at Huoditang Forest Region of Qinling Mountains Spatial Structure Characteristics of Quercus aliena var.acuteserrata Secondary Forest on South Slope of Qinling Mountains A QUANTITATION STUDY OF THE INTESPECIFIC ASSOCIATION OF QUERCUS ALIENA VAR. ACUTESERRATA COMMUNITY IN XIAOLONGSHAN MOUNTAIN OF TIANSHUI