祁连山南坡东段还保存着面积较大的天然云杉林,云杉杨桦混交林。云杉林主要分布在大通河中游的南岸和大小峡谷的北、东北、西北三个坡向,有些阳坡则残留着小块的桧柏林。由于大通河谷下切很深,两岸山坡异常陡峻,土层浅薄,在没有森林复被的某些地段,已经形成石质荒漠。所以这里的林区的天然林起着极重要的水源涵养作用。但是,天然林经过解放前的滥伐滥牧和严重 In the eastern section of the southern slope of Qilian Mountains, there are also preserved natural spruce forest and spruce birch mixed forest. The spruce forest is mainly distributed in the north, northeast and northwest of the south bank and the size canyon in the middle reaches of the Datong River, while some sunny slopes are remaining with small cypress trees. Due to the deep undercut of the Chase Valley, the steep hillsides on both sides of the Strait and the shallow soil layers have led to the formation of stony deserts in certain areas where there is no forest reappearance. Therefore, the natural forest in the forest here plays a very important water conservation role. However, natural forests were overbreddough and severely deforested