If a land is animated into a creature and then loses its creature type does it still count as a land?

This question hinges on an important distinction: card types (like Land, Creature, Enchantment) are separate from subtypes (like creature types such as Elemental, or land types such as Forest). Losing a creature type does not remove the Land card type. These are governed by CR 205.1 and CR 205.2.

When a land is animated — for example by an effect like Nissa, Who Shakes the World making a Forest into a 3/3 Elemental creature — it gains the Creature card type in addition to the Land card type. It now has multiple card types simultaneously (CR 205.1a). It is both a land and a creature at the same time.

If that creature then loses its creature subtype (e.g., it loses the 'Elemental' type), it still retains the Land card type and any land subtypes it had. Losing a subtype never strips away a card type. The permanent would still be a land and could still be used to produce mana, and it still counts as a land for any game-rule or spell purposes (CR 305.1).

Concrete example: Your Forest is animated into a 3/3 green Forest Elemental land creature. An effect then causes it to lose all creature types, so it's no longer an Elemental. It is still a land (Forest), still taps for green mana, and still counts as a land for cards like 'destroy target land.' It just has no creature subtype now.

In short: card types and subtypes are tracked independently. Removing a creature type (subtype) never removes the Land card type (CR 205.1, 205.2, 305.1).