The most common and most likely answer to this crossword clue is the 4 plus 4 letter word TREE LINE
I've seen this crossword clue in Financial Times
T
R
E
E
L
I
N
E
More clues leading to the result TREE LINE
Buddy explains!

The straight part
We know that "an alpine feature?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case an alpine feature? = tree line.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does TREE LINE mean?
TREE LINE noun- The edge of the habitat at which trees are capable of growing; the timberline.