Very nice animation!
I like the lighting and the shots nearby trees. Also the last shot was very nice with that tilted camera, rows of grasses and great atmosphere
The artefacts are probably because of the lowish detail setting of 0.4.
For animations a detail setting of 0.6-0.7 is often desirable to avoid geometry popping, the artefact which you can see in this animation.
Further you have shadow flickering because of too low GI samples and too low GI blur.
Thing is, improving these will make it render lots longer
What are your machine specs?
Cheers,
Martin