Remember, Perez is also looking out for the Emperor's best interests. The Emperor doesn't want to punish Angenas, his wife's family, but is being forced to do so. Perez found the best solution for the Emperor. It's a seemingly light punishment for Angenas, but since Perez offered the solution, the Emperor won't be accused of being soft or showing favoritism. What the Emperor doesn't know is Angenas is desperate for resources, both timber and money.
The loss of money stings, but losing timber is worse. Since the North will no longer be logging for trade, there are currently two powers who have stocks of timber. Pellet Trading Company and Perez's (secret) company. Since Pellet Trading is donating their Timber to the North, Perez is now the sole supplier of timber on the market, meaning he can jack up the price as high as he wants. Perez can now drain all of Angenas wealth, and increase his own wealth.
Perez has put himself in an incredibly advantageous position with one move. He has gained the favor of the Emperor. Hurt Angenas wealth once with the fine and twice with his timber monopoly. Has gained his enemy's wealth as his own. Grandpa Lombardi is not aware of Perez's control of the timber market, but this move greatly helps Lombardi's (Tia's) end goal of completely destabilizing Angenas. That's five birds one stone.
With Perez also volunteering to supervise the North, he has gained the favor of the Nobles, lowered the first prince's position, improves his connections with the North, and he gets to see Tia again. Four more birds for another stone.
A grand total of 9 birds for 2 stones!