Question

Read the following passage and answer the question below.

For decades, the origin of the barren, circular patches of land known as "fairy circles" in the Namib Desert remained a subject of intense scientific debate. Two competing theories dominated the literature: one attributing the circles to subterranean termites clearing vegetation, and the other pointing to self-organizing plant competition for water. Recent field studies, however, have clarified the precise ecological mechanisms at play.

Termite activity, specifically by the sand termite *Psammotermes allocerus*, indeed initiates the creation of the circles. As these termites consume the roots of short-lived annual grasses, they create a local void in the vegetation. Because there are no longer plants to transpire water back into the atmosphere in these cleared circles, the soil moisture within the patch rises significantly. This elevated soil moisture acts as a crucial buffer, allowing the termites to survive the desert’s extreme droughts.

Crucially, the accumulation of water in the cleared soil triggers a secondary effect. Perennial grasses surrounding the circle detect the increased moisture gradient and grow exceptionally long, robust roots to tap into this reservoir. This peripheral root growth creates a highly competitive zone around the circle’s perimeter. Consequently, any new grass seeds attempting to germinate inside the circle are immediately deprived of water by the surrounding perennials, which permanently prevents vegetation from recolonizing the circle. Thus, while termites initiate the circle, it is this water deprivation by peripheral plants that maintains the barren state of the circle's interior.

Based on the passage, the increase in soil moisture within a newly formed fairy circle is directly caused by which of the following?