Mr.Eko has took up episode time twice marking and chopping down trees, the first time he was only marking the trees that he "liked". Charlie burned that area down, and Dko looked like he was holding back a tear

. So during "Maternity Leave" we see him chopping down trees, the tree he cuts down has an "X" on it aswell.
So what do you think Mr.Eko is doing with these trees that he "likes"?
And before you say it I will, no he in not just getting firewood.

The writers write things in to episodes twice for a better reason then starting small fires every night.