Ground plane on homemade boart

Dear all,
I use an Arduino Mega 2560 and an Ethernet shield. In the case of a project, I have to make a board that will interpose between the Mega and the Ethernet shield.

I would like to know if a ground plane on my board will not bring disturbances between the two cards?

Thank you in advance,

No, it will even shield them from each other a bit, but that's not necessary since each already has a
groundplane and is designed sensibly.