Why do the brown barbaloots depend on truffula trees?

The brown barbaloots depend on truffula trees because they rely on the trees' fruit, the truffula fruit, as a primary food source. The trees provide not only sustenance but also habitat and shelter for the barbaloots. The health of their population is directly linked to the availability of truffula trees, making them vital for their survival. When the trees are cut down, the barbaloots face food scarcity and habitat loss.