4 Oct 2004
The ability is not optional.
4 Oct 2004
This ability does not trigger at all if there are not seven lands on the battlefield at the beginning of upkeep. It checks this number again when it is going to resolve and does not do anything if the land count is below 7.
15 Jun 2010
If this card is not on the battlefield at the times its ability resolves, then you can’t sacrifice it. However, you still destroy all lands.