[_ks3e]

Davis says the buried structure caused the drought-stricken plants above ground to ripen at different rates, because the earth was deeper in some places than in others. This created a green-and-brown pattern in the plants that corresponded to the buried ruins.

Can someone please explain why this is the case? Is it because plants try to grow their roots deeper during droughts in order to access water that can't be obtained at the surface?

[dnag]

Assuming the round circle was built of stones, plants growing over stones tend to develop stronger, more entangled roots. These plants become hardy than similar species of plants growing nearby over loose soil. Rock crevices also tend to accumulate water which these plants should be able to use when other adjoining plants are dying. I think this is the reason why the circle became apparent during this drought.

[masklinn]

Considering the wording, I'd expect the plants simply shoot their roots as deep and wide as they can, since those above stone can't sink theirs as far as the others they get less access to water and nutrient and thus mature slower for lack of resources. So they're still green while the others are already past that point.

[meritt]

If the markings were formerly large wooden posts, those would have decomposed over time and the enriched organic matter simply retains more moisture.

Separately, if they had dug trenches and lined with clay or something that retains water, it would still retain more water today. But as these markings are separated, I think it's more likely the first.

[NegativeLatency]

Even unlined trenches do this, because the underlying soil holds less moisture than to topsoil. Dig a trench, wait a long time, and smooth it out and you’ll end up with an area where the trench was with better soil.

[dvtv75]

This may help:

http://www.pastperfect.org.uk/archaeology/parchmarks.html