I am a bit confused whether we need verbs in the second part of the comparison.

One of the questions in the problem set for comparisons:
Julia was able to climb the tree as fast as her brothers did.

So we have the verb 'did' in the second part of the comparisons.

Here's an example from the OG.

Land values in most parts of the pinelands rose almost as fast as those outside the pinelands.

Notice that 'did' is missing in the second part.

So is the verb in the second part optional.

thanks.

This can definitely get confusing. You need to repeat the verb when what you're comparing is an action. You don't need to repeat the verb when you are not comparing actions.

The first sentence compares Julia's ability to climb to her brothers' ability to climb (actions), so we need to use that "did."

The second sentence compares land values in one area to land values in another area.

Sorry for bumping up the thread. I still share the same doubt as the second sentence, IMO, is also comparing actions - how fast are the land values increasing compared to others?. Correct? Please clarify.

here's a better, and less hair-splitting, rule to follow:
if there's any ambiguity in the version that doesn't feature a verb, then throw the verb in there to resolve the ambiguity (even if one of the 2 ambiguous meanings is a bit farfetched - remember that ambiguity is ambiguity, and that we aren't supposed to use 'common sense' to resolve meanings). so, in the sentence about julia WITHOUT the 'did', we could read the sentence as meaning that julia climbed the tree as fast as she climbed up her brothers' backs. a bit strange, but not meaningless or ungrammatical, so we must consider it a genuine ambiguity. therefore, we need the verb.

in the sentence about land values, there is no possible ambiguous reading that doesn't violate some rule of grammar or parallelism, so the verb is not necessary.

how 'bout that?

Will you please clarify the same thing in the following senetence (this sentence is fabricated by me)

Because my little son do not perceive the things systematically, as I, he may notice details that I ignore.

or

Because my little son do not perceive the things systematically, as I do, he may notice details that I ignore.

Which is better?

Will you please clarify the same thing in the following senetence (this sentence is fabricated by me)

Because my little son does not perceive the things systematically, as I, he may notice details that I ignore.

or

Because my little son does not perceive the things systematically, as I do, he may notice details that I ignore.

Which is better?

Here, you're comparing your ability to perceive to your son's ability to perceive - since what you're comparing is a verb you should repeat the verb (that is, use "do" in this case).