有时他们不得不砍倒一棵树来做木柴。

Sometimes they have to chop down a tree for firewood.

《柯林斯英汉双解大词典》

另外，请记住，有时有必要砍倒一棵树。

Also, remember that sometimes it's necessary to cut down a tree.

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每砍倒一棵树就要种上三四棵树。

For every tree cut down, three or four new ones are planted.

《新英汉大辞典》