I'm using this in conjunction with many other mods (most notably oh the biomes you'll go and yung's caves) and I seem to get increasingly low FPS the more chunks I load. I've done testing using the same seed and same chunks loaded and without subwild enabled I get around 100, and when I first load the world with subwild I get around 80-90, but the more chunks I load it drops drastically, eventually ending up at around 3. My allocated RAM isn't being used up (sits around 50-70% usage in game), so I'm not sure what the problem is. Let me know any and all testing I can do for you, I know there will be more information you need from me but I'm not sure what that is yet. Thank you!

I think these FPS issues come from the huge lush caves at the bottom parts of the world getting burnt away by YOUNG's Caves special lava-filled cavern caves.

Very good observation! I'll see if I can come up with a fix. Can you send some screenshots of said burning vines?

I meam, not that difficult to find. Just install both mods & you'll find plenty pretty quickly.