Trees:
* Grove: A small group of trees.
* Forest: A large area of trees.
* Wood: A small area of trees.
* Stand: A grouping of trees of the same species.
* Thicket: A dense group of trees, often tangled.
Whales:
* Pod: A group of whales.
* School: A group of whales, especially if they are feeding together.
* Herd: Can be used for whales, but less common.
Why no single collective noun:
* Different Species: Trees and whales are very different species. They have different behaviors and social structures, which makes a single word for their groups unlikely.
* Context Matters: The best collective noun depends on the specific type of trees or whales and the situation you are describing.
Examples:
* "A grove of ancient oak trees stood at the edge of the meadow."
* "A pod of humpback whales breached the surface of the water."
* "A stand of towering redwood trees lined the path."
Ultimately, the best collective noun will be the one that best captures the specific situation you are describing.