"Because" is a conjunction; it is used to indroduce a clause.Originally Posted by Atesttaker
"Because of" is a preposition; it introduces a prepsotional phrase.
Let's look at what is being introduced:
the time and area involved in the cultivation of a forest
article-noun-conjunction-noun-verbal past participle (acting as an adjective and introducing an adjectival participial phrase)-preposition-article-noun-preposition-article-noun
There is no verb, so the phrase cannot be a clause. The verbal "involved" is an adjective. It is modified by the prepositional phrase "in the cultivation"; in turn, the next prepositional phrase modifies "cultivation".
Because there is no verb and no clause, "because of" is the correct answer to your question.