There are shown to be lots of unnatural happenings after Duncan's death due to the disruption of the Great Chain of Being, and therefore the disruption of natural order

darkness does the face of Earth entomb / when living light should kiss it

a falcon, tow'ring in her pride of place / was by a mousing owl hawk'd at and kill'd

Lots of imagery about animals eating each other - links to how Macbeth has usurped Duncan's throne

Duncan and Malcolm use natural imagery to describe kingship and reigning, and when referring to Macbeth

I have begun to plant thee, and will labour / to make thee full of growing - shows that if Macbeth had stuck with Duncan, which was the natural thing to do, it would have been better for him in the long run

The witches are shown to be an example of unnatural things

you should be women / and yet your beards forbid me to interpret / that you are so

look not like th'inhabitants o' th' Earth, / and yet are on't

They are unnatural and also evil - unnatural things are evil

Each new morn / new widows howl, new orphans cry - shows the state of Scotland after Macbeth is King

Malcolm echoes his father's metaphor in the final soliloquy: What's more to do / which would be planted newly with the time