Why are people afraid of the Greeny Jungle in the novel, Zahrah the Windseeker?

The Greeny Jungle is untamed land that lies beyond the farmlands of Kirki. It is a massive, mostly unknown place filled with strange monsters, vicious plants, and unusual fruit. However, the people of Kirki (and likely most of the Ooni Kingdom) avoid the Greeny Jungle and tell stories of those who have entered and never came back. There is a single guidebook on this jungle, but looking at it is frowned upon. By the end of the novel after Zahrah returns from retrieving the elgort egg, some researchers begin exploring the Greeny Jungle again, but progress is slow and many are still anxious about it.