Fortune serves a role in the play in as much as desire for fortune drives the plot forward; however, once the characters are in the Forest of Arden, fortune ceases to be of significance.
The desire for fortune especially moves the plot forward by being the driving force that sends the characters into exile in the Forest of Arden. Duke Senior is driven into exile because his brother Frederick is jealous of both his fortune and his power as duke. In addition, Orlando is also driven into exile in the forest because he was rightly jealous of the fortune his own brother Oliver had that should have been distributed to Orlando based on their father's will. Rightfully wanting what should be his, Orlando confronts Oliver who happens to be denying Orlando his inheritance out of jealousy of his brother's qualities. However, confronting Oliver only makes him angrier, angry to the point that he threatens Orlando's life twice, driving him into the woods. Hence, in both situations, the desire for fortune drives the plot forward by sending both Duke Senior and Orlando into the woods.
However, the desire for fortune ceases to be an issue once in the woods. For example, Duke Senior claims to be happier in the woods than he was at court. Orlando even proclaims his love for Rosalind once in the woods, and never does his lack of fortune come up as an impediment to his ability to marry her. In addition, when Oliver becomes a changed man while in the woods and falls in love with Celia as Aliena, Oliver says to Orlando that her apparent "poverty" is not an issue (V.ii.6). But more interestingly, Oliver even asks for Orlando's permission to marry her, promising that if Orlando gives his consent, then Oliver will bequeath the whole of their father's estate and fortune to Orlando, while Oliver remains with Aliena in the woods, living in poverty as a shepherd in the woods, as we see in his lines:
[C]onsent with both that we may enjoy each other: it shall be to your good; for my father's house and all the revenue that was old Sir Rowland's will I estate upon you, and here live and die a shepherd. (V.ii.9-12)
Hence, we see that even for previously jealous and greedy Oliver, fortune is no longer an issue once in the forest, showing us that while fortune, or jealousy of fortune, helped to develop the plot, fortune ceases to be important once in the forest.