Boreolenta dendron
When the tree Megaplortatus sustensa entered Zone B, it almost immediately transferred it into a forest, blocking light for the other two plants and bringing in organisms to prey on these now weakened polyphs. This also gave Boreolonta hydraherbensis a new potential host, also!
Boreolenta hydraherbensis originally parasitized the roots of the tree, which while less caloric were very large and plentiful. Large enough, even, to allow easy access inside the tree. Sometimes they accidentally went inside, and traveled in the circulating water and nutrients. This water eventually made its way to the leaves, which was very high in calories due to being where all the energy was created. This caused the cells to flourish, which gave them incentive to purposely go through the roots and up to the leaves. This, however, took a long time and required alot of energy and very little breaks. So they decided to climb the trunk from the leaves, giving more availability for breaks and conserving energy.
Boreolenta dendron is a weaker swimmer due to primarily living outside of water, so it does not enter from the roots. Instead, it enters from the leaves or trunk of another tree next to it, climbing up and down the trunk with its flagella, which are stiffer with spiked ends to allow for better climbing. So remember the fact that leaves are filled with calories? This extra energy allowed them to multiply faster, causing individual leaves to have failed in a few weeks and it typically killed the tree between two to two and a half months. This caused a massive forest collapse, with the only trees surviving being seperated and isolated from eachother. This lack of trees caused B. dendron to significantly slow down its digestion, but it still caused Zone B to become a savannah, as any trees next to eachother would almost certainly die.