There is also the problem that we are talking about certain subsets of badgers and squirrels. Consider that many of the badgers that originally grew the forest that they now enjoy only did so because they were shunned not just by the squirrels, but by many other badgers. Look closely and you'll notice that some of these badgers, or those of the same subgroup, are resistant to both squirrels and other badgers coming into the forest. It isn't due to some sense of greed or superiority, but from a trained desire of self preservation.

And then you have the issue that in this forest, the job of maintaining the forest and the hobby of playing in the forest merge together, so groups that formed by badgers who play together carry over their group behaviors, including the exclusion of outsiders, into their work of maintaining and growing the forest. They likely don't even mean to do this most of the time.