Why de and not da? "The line of trees" seems like more like a quantity of trees than a quality the trees possess
It's certainly a quality. A line of trees, in contrast to a circle of trees, a triangle of trees, ... .
The row, line, whatever, doesn't contain the trees it's just our perception of how they are situated in the countryside.
(Dominoes, for those who have never seen the word before)
Why "vico" and not "linio"? "Vico" also seems to mean one's turn, as in a queue. I would interpret this sentence's use of "line" more as "linio" than "vico", based on the geometric line, rather than a queue.
Vico is used whenever a queue, or line, of individual objects is involved. I don't know why, but this has always made perfect sense to me. (despite Ĵetkubo's comment elsewhere on this page)
In Butler's Dictionary (Esperanto -> English; highly recommended) vico is defined as: Line, rank, turn; file, row, succession, suite (side by side, or one after another). Whereas linio is: Line (geometry); Long narrow mark, fold, furrow, seam, ktp.
Since a row of trees (probably a better translation than Duo's, IMHO) is not a mark or furrow that leaves us with vico, ĉeno (chain) or serio (series).
Now I'm trying to imagine a chain of trees…
Not an english native speaker so may I ask what's wrong with: "The row of trees fell down"?
Per MY studies, nothing. Go ahead and report it.
In fact, in many instances, it would be better English.
(Ref my earlier comment to Benja_Zouras)
What would the Esperanto be for "The line of fallen trees." as that's how I first read it.
Falintaj. "Fali" isn't a transitive verb, so it cannot have a passive form ("falita arbo" would mean "a tree fallen by someone", "a tree that someone fell" - so it doesn't make sense. Faligi, "to make something fall", can have a passive form: faligita arbo = a tree that someone made fall).
You could, but the Owl's database wouldn't recognize it. And it would be Arbovico the middle j is unnecessary.