Answer:
The dialogue is ironic because it presents a situation where the character Ulrich von Gradwitz is trapped in his stolen forest, and the speaker finds this to be a just punishment. However, the irony lies in the fact that the forest was originally owned by Ulrich's family, but it was taken away from them by the speaker's family. So, in reality, Ulrich is not the one who stole the forest, but his ancestors were the ones who lost it.
Furthermore, the fact that the speaker finds justice in Ulrich's predicament is also ironic because it is a reflection of the ongoing feud between the two families, where both sides believe that they are in the right and the other side is in the wrong. This demonstrates the absurdity of the situation and highlights the futility of holding onto grudges and seeking revenge, which ultimately lead to tragic consequences for both parties.