When does the effect of hedge shroud end?

While defending within range 1-GreenRunes of overgrown terrain, you may exhaust this card to treat your defense as GreenRunes.

In contrast, shield wall and visored helms stipulate "for this attack".

-Matt

I assume it is the same timing, but I could see a strict interpretation of the text as written saying that your defense is now equal to natural energy until something else changes the defense.

83.6 A “while” effect is in effect for the entire duration of the specified event

I could see the argument that that only applies to the window to trigger the ability and not the ability itself, but it seems a safe bet that it will only last for the one attack.