A copse, as the name suggests, is a stand of trees that have been deliberately coppiced (ie, repeatedly cut near the base so that the rootstock remains alive and generates fresh branches at ground level).
One of the surnames on my mom's side of the family means "grove of trees near a bog" and comes from the same area as my best friend's surname that means "evil bog goblin"
I like to think that his family was evil bog spirits, and my family were good tree people, and he and I have mended the feud.
This has nothing to do with OP's question, I just thought of it when grove came up, and thought I'd share.
I agree with others saying copse, as being my first thought as well, but I'm really commenting to say I love the imagery the description, "a gathering of trees" produces.
The only reply which takes the "gathering" aspect into account. But wouldn't Ents tell you they are not trees? Still, we don't have to cede to their demands here.
Fun fact: when you see a copse of trees like that, there's a chance there's an old graveyard there. Not always, of course. Sometimes they are left as a windbreak, and other reasons.
"close-set growth of shrubs, bushes, trees, etc.; tangled coppice or grove," late Old English þiccet, from þicce in the sense of "dense, growing close together" (see thick (adj.)) + denominative suffix -et. Absent in Middle English, reappearing early 16c., perhaps a dialectal survival or a re-formation.
Spinney is a nice word for a smallish gathering of trees, alongside copse, coppice, etc. I'm not aware of a term for one specifically in an open field, though.
A fairy teleportation portal. It's the upgraded version of a circle of mushrooms.
To not be confused with a circle of 4-leaf clovers, which is the treasury entrance to a leprechaun's pot of gold.