I read this novel about 30 years ago and have been trying to hunt it down ever since. It was about a man (spaceman?) who fell to a jungle planet. This spaceman was in a capsule and the first part of the novel was about him getting out of the capsule and interacting with the jungle and the animals/locals.
I remember this spaceman interacting with the jungle indigenous people and learning that there was a "black" death coming through the jungle (I think from memory if was a mass critter invasion in the jungle eating everything). The spaceman tries to help the locals "escape" the jungle to the "floating" metal city that sits above the jungle (in the jungle canopy). The locals in the jungle and the spaceman fight the "death critters" and they end up trying to get into the metal floating city before all is lost on the jungle floor
I recall the cover having a "jungle" ish type cover-art on it (greenish and black with colouring). The novel was a paperback of normal size and was not overly thick.