I can't see forest in certain chunks of my custom map

I am currently working on my map but I ran into a big issue, I cant see the forest in certain chunks of my map here is a screenshot.
I don't know what caused this but It's a giant issue that will prevent me from finishing map if I can't fix it.

 

Try placing them down separate? I dont know, but that map looks giant. dont know if i can play that. LOL

 

Map looks big cause those are bushs put them there to out line the area

 

Oh the open area is the map. Makes sense.

 

I really need help with this issue