That looks like tributaries draining to a river. That's like what kept them from being cut down for farmland

interesting

You have it backwards.

What? You mean farmland looks like patches on the bit of nature there is left

That's creeks/rivers with vegetation growing alongside.

I think you misspelled farms as forest.

The Forrest is the part that isn’t diseased.

you have an artists mind

Even without people there'd still be more trees along the water channels which is what this looks likes

Lungs spreading through the disease