Clearly, in some cases an isolated list cannot be a sentence. For example,
Apples, oranges, and bananas.
is not a sentence. But what about a list of independent clauses following a declarative sentence? Consider the following:
Autumn is an excellent time to enjoy the outdoors. The weather is warm, campsites are abundant, and insects are scarce.
Is it acceptable to let the second sentence above stand alone as such? Or must it always be joined to the first sentence with a semicolon? Other alternatives would be to append "...for several reasons" to the first sentence, or prepend "The reasons for this are that..." to the second sentence.
EDIT: The original version of this question incorrectly identified certain clauses as "adjective phrases".
As EdwinAshworth pointed out, I am claiming that the first example above is not a sentence because it does not have a complete subject and a complete predicate.