I have revised myself a lot, and I'm very critical to make as little mistakes as possible, so take my guidelines however you want.
'..now there are the dead skeletal remains of trunks and branches.'
'Dead skeletal remains' is making the same statement more than once, which is something to watch out for in writing. It would be better to use 'remains', 'skeletal remains', or 'dead remains'.
'Fifty years ago this was rural farmland in what used to be known as the state of Tennessee. Now it's a desolate wasteland.'
Its best to stay in one tense, preferably past tense. You could still use 'Now' it would just be 'Now it had become a desolate wasteland.'
'"I'm not about to walk away from this house, it will be dark soon and I need it for protection. It looks like the zombie will have to move out the hard way." Red made up her mind to take over the house by force.'
This is tricky, it sounds like you would rather have your character thinking. If so, there's different ways to do that, but quotes should be kept specific to talking. The above segment is also a double statement, you want to keep either the dialogue or the sentence afterwards, and then keep arrest of this paragraph.
Hope you found this helpful. Keep writing!