No. "String" is good (like "string of pearls"), but "stretch" wants something that is already continuous, like a stretch of desert or a stretch of road. You can have a stretch of forest but not a stretch of trees.
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messier42Ok thank you~ How do you describe many trees or taxis in one column, one and another?"Line" is a plain word for that. "Row" is plain, too. I'd go with a line of taxis and a row of trees, because the trees are farther apart than the taxis are.