Silene

Waldgeists act as avatars of nature that seek vengeance for environmental abuse, such as pollution and deforestation. These undead spirits of destroyed trees form at the site of their destruction or in a nearby woodland, if the original location was entirely razed. They become guardians of the forest, possessing power over the plants within its boundaries. Waldgeists show no mercy to anyone caught damaging their bonded woodland, attacking loggers, fey, travelers, and invasive species with equal prejudice.

When disaster befalls the natural world, a different kind of undead may rise, entirely unlike risen humanoids. Most plants, fish, insects, and other animals don't possess a psychology complex enough to experience the emotional catharsis required to return as undead without intervention from an outside force. Mass extinction can serve as that outside force.

Humanoids clear-cutting an entire forest or a seaside community wiping out a species critical to their ecosystem can spawn a verdorite. The collective spiritual energy and emotional distress of a dying biome powers these undead, formed as conglomerates or representatives.