We spent much of the morning looking at our experiment treatment sites that Nichole Barger, Mike Cramer, and Walter Tschinkel originally set up in 2015. The experiment tests a few of the hypotheses (see post 1) for why fairy circles might form. We test these multiple competing hypotheses by trying to do the opposite of creating fairy circles— in other words, we are trying to “kill” them. The idea is to apply different treatments and see which ones allow fairy circles to fill in with new recruits (thus killing the fairy circles as they fill with grass, removing any spatial patterning).
A Little Background
In a fenced in area that was initially created to keep the animals from ruining any equipment, Nichole, Mike, and Walter applied a treatment of water or water + fertilizer to some of the circles. Others were left alone as controls. And still others were treated with an insecticide to kill the termites within the circles.
Outside of the fence, we have additional control sites that received no treatments and are accessible to herbivores (mainly Gemsbok Oryx, Springbox Oryx and zebra here).
The site was set-up approximately a year into the drought. Since then, it hasn’t received any measurable rainfall until just a month ago or so—the reason for this trip.
The Current Story
After getting the lay-of-the-land, we were excited to return to the sites and scope them out. While the next several days are devoted to more detailed measurements, we wanted to stop by right away and just get a sense for what had happened to the circles. Our first circle looked similar to back in 2015…but as we walked around, it became clear about 2/3 of the circles within the fence have started filling in. Some have a few young recruits in the center, while others have many, many recruits!
Surprisingly, we didn’t notice a strong signal of any of the treatments within the fence, though maybe one for the watering + nutrient treatment.
The striking pattern is that herbivores seem to play a critical role in maintaining fairy circles. None of the circles outside of the fence have recruits within them, but many of those inside the fence are filling in—even in the controls! Herbivores indeed seem to be playing a critical—and perhaps overlooked—role in this system. While they likely don’t create fairy circles, our first stop at the site seems to say that they definitely do help promote the long lifespan of fairy circles. We are heading back to the site tomorrow to begin collecting more detailed measurements.