How might the acacia's adaptations contribute to the sustainability of its browser population?

The browser population is going to start decreasing.

Explanation:

This is because acacias are plants that have a defense mechanism which prevents herbivores from eating them. This mechanism involves the browsing stimulating the acacia to produce toxic alkaloids. These alkaloids have a disgusting flavor which stops animals from eating them.

When this happens the browsing animals become starved of food and thereby results in death and a decrease in their population.