Abstract: The arbor stratum of Quercus aliena var．acuteserrata stands included two substratums．P妇nerophyta synusium was in first position．and hemicryptophyta was inferior to it The DBH structures of Quercu5 aliena var．acuteserrata and Pinus armandii were sinister normal school，which could finish self—regeneration under the natural conditions．The small DBH class individuals of Pinus tabulaeJbrmis were dominant，their DBH classes being distributed irregularly and absent very much．The large DBH classes of Toxicodendron verniciflUUDI took biggish proportion，belonging to declining population．Young trees were the principal individuals of Castanea mollissima，and in transitional age stage from the young to the middle Populus davidiana was in the transitional stage from progressive to stable and young—middie age stands．The stands DBH structure was mainly influenced by the DBH variety of Quercus aliena var．acuteserrata population．Quantitative classification (ward’s method ward)  and ordination(PCA)were used to study the community types of sharp to th oak．The results showed that the community could be divided into 6 types：①Ass Smilax stans + Rosa multiflora—QueFcus variabilis + Ul+ THUS glaucescens—Quercus aliena var．acuteserrata；②Ass．Smilax stans+ Lespedeza bicolor—Castanea mollissima—Q．aliena var．acuteserrata；③Ass．Co rJus mandshurica—Populus davidiana +Dendrobenthamia angustata—Q．aliena var．acuteserrata；④ Ass．Prunus pseudoccrasus + Co rvlus mandshurica —Toxicodendron vernicifluum —Q．aliena var．acuteserrata；⑤ Ass．Co rylus mandshurica + Rosa multiflora—Pinus ar．mandii—Q ．aliena var．acuteserrata；and ⑥ Ass．S ，znr“，z ，znr n nitida．Pinus armandii + Pinus tabulae．rmis．Q ．aliena var．acuteserrata．Ward’s method ward was better for classifying community types than the other clustering analyses in Qinling Mountains．The PCA results were consistent with the clustering，and demonstrated that the sharp．to th oak stands were influenced by the altitude．site gradient and soil mainly

Key words: Quercus variabilis, increased CO₂, N supply, eco-physiological response.