it's an adverbial modifier that modifies the action of the clause with which it's associated. technically, that action is encapsulated by "is (able)", although it's probably easier to think of it as "modifying the entire clause".

with modifiers that serve as adjectives (such as "..., which ..."), it's crucial that you isolate the single noun modified by the modifier.
on the other hand, with adverbial modifiers, it's unimportant to isolate the single word being modified, because the placement of the modifier isn't restricted anywhere near as severely as with adjective-type modifiers.

Ron,
First of all, thanks for all your excellent explanations. It helped me a lot.

I'm really confused about usage of adverbial phrase. Is it possible that adverbial phrase can modify verb or a clause that comes after adv phrase?

According to your explanation in one of the threads, subject: "modifiers using -ing", you have mentioned
"do notice that if the -ing modifier follows the noun immediately, as in 'the car speeding down the hill', then it cannot be an adverbial modifier, as there's no verb to modify."

If I understood your explanation correctly, then how come in this question participle "depending.." can modify "a single tree is able to produce..." or "is" verb?

hey.

when i said that the -ing modifier follows the noun IMMEDIATELY, i meant IMMEDIATELY - as in "there's not even a comma between the noun and the modifier". if the -ing modifier is DIRECTLY after the noun, without so much as even a comma in the interim, then it's an adjective style modifier that modifies the noun.

in this problem, "depending" is set off by commas, so it doesn't fall into that category.

I think didn't ask my question properly

I understand noun modifiers, i.e. without comma. But my question is only for adverbial modifiers.

Here "is able to produce enough berries..." comes after "depending.." phrase
So can adverbial modifiers modify part of sentence that comes after it?

sure, there are different orders in which you can arrange such components of a sentence. for instance:
coming home from school, i was blown off my bike by the wind.
or
james, coming home from school, was blown off his bike by the wind.
same sort of deal there.

--

and let's not forget the ultimate rule:
if the gmat does it in a correct answer choice, then it's allowed.
(this is not meant to be facetious at all; in fact, this is the absolute #1 rule you should follow. if you see a construction in a correct answer choice, then you're allowed to use that construction, period.)