The Primaria Zone is the main area of The Gateway that I've focused on charting. It neatly contains all of my family's entrances to their realities (+1 stranger). This is the only area of The Gateway that I truly understand, it is coated in darkness through and through. By the look of it, areas beyond Primaria are no different. A strange dim light source seems to come from the ground itself, I don't know if it may come from the grass or the soil. The light source makes it possible to see as long as you put in the effort of peering through the darkness, I have yet to work out a good solution for seeing easily in the Gateway but given my current situation, it's not a priority. The dominant biome of Primaria (and possibly the entirety of The Gateway itself?) is what I call the Eternal Forest, because of how infinite it feels. Dark twisted trees make up and block up the majority of the zone, any areas without trees were made artificially, which I'll get into later. The only other naturally occurring biome that I have found is one that I do not yet dare to explore: The Darklands. From what I have somehow managed to see, it appears to be the same as the Eternal Forest, just with no light source whatsoever. Denver seems to be familiar with the Darklands in his time roaming the Gateway, but again, exploration is just not a priority at this time in life.  ~ Excerpt: Contingentplane Volume 1 by Cessa Somnium

From what I've observed, The Gateway is a marvel in its many tactical advantages. The entrances to the realities of Corydon Somnium, Spook Somnium and the anomalous fifth Dreamleaper are all placed closer in proximity to the entrance of Cirem's reality which has given me remarkable freedom in terms of my exploration and data collection. I feel as though I have sufficiently established myself as the dominant threat, the fear will make Somnium move sparingly in his own attempts at data collection and monitoring of his children's realities. The persistent foliage of the Gateway provides both myself and the enemy with cover when traveling through the majority of the realm. However, yet again I am advantaged from the tactical standpoint. There appears to be a lack of trees surrounding the entrance of Somnium's reality, leaving the entrance vulnerable to surveillance and attack. ~ Excerpt: Archives i by Tresn

Lore Relevant Map of The Primaria Zone:

The Primaria Zone is the only charted area of The Gateway by Cessa Somnium and Tresn within The Twisted Reality. The vast majority of the zone is taken up by the Eternal Forest, named by Cessa due to the fact that no end has been discovered. Smaller biomes (both artificial and natural) are The Darklands, The Flats and The Scorches (Both Major and Minor). The Primaria Zone includes the entrances to the realities of every living Dreamleaper at this point in time. The cover of the many trees is taken advantage of by Cessa and Tresn in their conflict against eachother, both sides sneaking from reality to reality, collecting information and plotting against eachother.

Cessa Somnium's Map of The Primaria Zone:

On the topic of artificial biomes and areas of Primaria, there are two which are similar in their lack of foliage, just for different reasons. I’ll start off with The Flats, since I know more about them than I do about The Scorches. The Flats were gradually pressed into place over a few decades by Denver, back before I had him repurposed. All of the trees and grass within The Flats were flattened down into a spongy mess of dried mush. Because of his limitations (needing the moonlight from my reality specifically in order to survive) he hasn’t been able to go very far, and really there was no reason for him to want to. His purpose back in those days was to kill, so my reality would of course be the optimal hunting ground. While the area’s creation is understandable and ultimately unavoidable, it leaves me with a huge disadvantage towards Rem’s monsters. Exit from my reality is always an enormous risk, only Bringer and Scythe are fast enough to leave without risk as far as I know. I had to stop sending Wrath out there long ago, it was stupid of me to do so in the first place.  ~ Excerpt: Contingentplane Volume 1 by Cessa Somnium

As for The Scorches, by my understanding the creation of those two patches of charred trees took place during two different events. Both were burned into place by Tentoria, the colossal jellyfish monster. I was not witness to the events that made the minor area of the scorches but I have a theory. In an escape from the reality it originated from, Tentoria squeezed it’s way through the exit of the reality which was so close to the ground that it seared all of the trees and grass outside of it. As for the major portion, it was created long after the minor portion. It happened during a campaign by Rem’s monster in order to have control over Tentoria. I only witnessed the end of the fight, when it was tugged downward and captured by the monster, so close to the ground that once again, all of the wildlife was burnt to a crisp. 
~ Excerpt: Contingentplane Volume 1 by Cessa Somnium