There's definitely a single word that is used to describe, when seen from a distance, a single row of trees on a hilltop. I searched quite a bit but am unable to find the word.
Great answer from Silenus (collonade is particularly appropriate) but here is one more you could consider:
A cluster of trees; a tuft of trees or shrubs’ (Johnson); now also, a compact mass or patch of any growing plant, e.g. a clump of lily of the valley. OED
(I know from personal experience that these are most commonly on a hilltop and are therefore visible from miles around.)
Patch is also a close synonym.
...dense 'copse' of trees.
...thin copses of trees that scattered sporadically along the distant hills.
protected by MetaEd♦ Nov 18 '18 at 20:29
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