heart-wood rot

例句：

1. 1. The old tree's heartwood is rotting away due to age.
   由于年久失修，这棵老树的心材正在腐烂。
2. 2.The wood from the old tree was rotten and had to be replaced.
   那棵老树的木材已经腐烂了，不得不更换。
3. 3. The forestry department is investigating the cause of the heartwood rot in the area.
   林业部门正在调查该地区心材腐烂的原因。