Photosynthetic mechanisms of northern boundary formation of Quercus wutaishanica forest in Loess Plateau of northern Shaanxi Province. PRELIMINARY STUDIES ON THE STRUCTURE AND DYNAMICS OF PLATYCLADUS ORIENTALIS POPULATION AT THE FOREST AREA IN LOESS PLATEAU OF NORTHERN SHAANXI PROVINCE THE RELATION AMONG ECOLOGICAL FACTORS AND DIAMETER GROWTH OF PLATYCLADUS ORIENTALIS IN THE SOUTH OF NORTHERN SHAANXI PROVINCE Study on the Cenozoic Flora and Flora Evolution of the Loess Plateau of Northern Shaanxi Province