Comparison of the three linear models applied for studying of the correlation of site-indexes between Cunninghamia lanceolata and Pinus massoniana stands ESTABLISHMENT OF SITE-INDEX TABLE FOR POPLAR IN LINYI REGION,SHANGDONG PROVINCE ESTABLISHMENT OF THE SITE-INDEX TABLE FOR PINUS TABULAEFORMIS PLANTATION AND THE RELATIONS BETWEEN THE GROWTH OF P.TABULAEFORMIS STANDS AND THEIR SITE FACTORS IN JIULONG MOUNTAIN AREA, BEIJING