"To be continued…"
After re-imprisoning Ahriman, you will be carrying Elika. Carry her out of the temple and place her on the altar. You will see 4 pillars of light in the desert. go to each of these, and press X to cut the trees. Once all 4 have been cut, return to the temple and enter. In the centre of the temple is the fifth and last tree. Cut this and you will get a Light Seed. Take this back to the Altar Elika is laying on.