elm bark

例句：

1. 1.The elm tree is in the park, and its bark is very hard.
   这棵榆树在公园里，它的树皮很硬。
2. 2. The elm tree's bark is used to make a natural wood substitute for furniture.
   榆树的树皮被用来制作家具的自然替代品。
3. 3. The bark of the elm tree is rich in tannins, which makes it useful for tanning leather.
   榆树的树皮富含单宁，这使得它对鞣制皮革很有用。