### Clue: Tree found after top of altitude line? (6)
### Answer: ALPINE 
 ### Explanation: Definition: found after top of altitude line
 PINE(the coniferous tree) **placed after**(found after, in an across clue) [ **the 1st letter of**(top of) "altitude " + L(abbrev. for "line ") ].
Defn: Descriptive of growth, usually plants, found above;after top of the timber line, the altitude above which there is no tree growth. A WIWD (wordplay intertwined with definition) clue.