Also I don't think there should be much more rare Nature cards, especially not specialised ones. It's already hard and resource-costing to summon rare natures in your hand and there's 25% chance the card will be Earthquake. By increasing the number of rare Nature cards around, you destabilise the strength, fairness and nature of the keyword I think. It's good to combine Nature with other keywords, such as the Beast keyword that was implemented recently, but this combination should be kept to uncommons and commons. Nature's strength is in its rares and they should be kept pure of specific keywords (such as Undead in this case). I.e. there's 1 rare that is destructive for both players and only used in extreme cases, there's one card that is averagely good (Volcano), there's a situational killer card (Forest Dragon) and there's a resource increasing card (Ancient Sage). They are not specific, other than requiring more Nature cards in hand, and can be averagely good even if there's not enough nature cards in hand. However the cards you created are not that good as rares and some of them are very specific.
EDIT: I don't mean to overwhelm you or anything, it's a good idea and I like it as a concept, but that's just how I feel for Nature keyword. Maybe we could look into it further