Ecography ECOG-02461Cramer, M. D., Barger, N. N. and Tschinkel, W. R. 2016. Edaphic properties enable facilitative and competitive interactions resulting in fairy circle formation. – Ecography doi: 10.1111/ecog.02461

Supplementary material

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Supplementary material

Cramer, M.D., Barger, N.N. and Tschinkel, W.R. 20XX. Edaphic properties enable facilitative

and competitive interactions resulting in fairy circle formation. – Ecography 000: 000–000.

Appendix 1

Figure A1 Hypothetical relationship between feedback strengths in fairy circles in a shorter-

grass matrix.

Figure A2 Aerial image image showing fairy circles with hand-drawn polygons around each.

Figure A3 Proportion of the soil volume comprising different particle sizes between sites used

for infiltration measurements.

Table A1 Comparison of the proportion of the soil volume (%) comprising different particle

fractions between sites used for infiltration measurements.

Figure A4 Variation in water infiltration rates with soil texture (proportion of sand, silt and clay).

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Figure A1. Hypothetical relationship between positive (+) and negative (-) feedback strengths (y-

axis, blue line) portrayed in the context of fairy circles (FC) in a shorter-grass matrix. The

nominal range over which positive and negative feedbacks operate is shown. Peripheral grasses

between fairy circle and matrix are shown to be larger than those in the matrix. Blue arrows

indicate possible resources fluxes (i.e. water and nutrients) in the soil. The average distance

between fairy circle peripheries at our study site is shown for reference. Peripheral grasses are

shown to have short-range positive feedbacks due to focussing of resources and longer-range

negative feedbacks due to competitive resource depletion.

Feed

backstrength

+

-

Short-rangeposi5vefeedback

Long-rangenega5vefeedback

FC Matrix FC

5.7m

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Figure A2. A Google earth image showing fairy circles (24.9638°S, 15.9735°E) with hand-

drawn polygons around each. A vehicle track through the site that is more than a decade old has

not eliminated fairy circles that it intersects. Faint game tracks are also visible.

50m

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Figure A3. Comparison of the proportion of the soil volume (%) comprising different particle

sizes (log scale) between sites used for infiltration measurements (Fig. 1) that either had fairy

circles (FC) present or in which there were no fairy circles present (No FC) within 75 m of the

soil sampling point. The grey ribbons represent the 95% confidence bands.

0

2

4

6

-1 0 1 2 3Particle size (Log, μm)

Volu

me

(% p

er s

ize

clas

s)

FCNo FC

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Table A1 Comparison of the proportion of the soil volume (%) comprising different particle

sizes (upper limit of each class in µm: clay <4, silt <62, very fine sand <125, fine sand <250,

medium sand <500, coarse sand <1000, very coarse sand <2000) between sites used for

infiltration measurements (Fig. 1) that either had fairy circles (FC) present or in which there were

no fairy circles present (No FC) within 75 m of the soil sampling point. The P values were

determined using Student’s t- tests (n = 35).

Component No FC FC P

Clay 4.7 ± 1.3 2.4 ± 0.3 0.015

Silt 12 ± 2 7.1 ± 0.6 0.016

Sand 84 ± 4 90 ± 1 0.014

Very fine sand 22 ± 2 19 ± 1 0.248

Fine sand 32 ± 5 30 ± 2 0.603

Medium sand 20 ± 2 22 ± 1 0.329

Coarse sand 9 ± 3 17 ± 2 0.116

Very coarse sand 0.3±0.2 2.9±0.6 0.079

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Figure A4. Variation in water infiltration rates, represented by the colour of the points, with soil

texture (proportion of sand, silt and clay). The blue line represents the linear model for variation

in texture with the 95% confidence interval shown by the grey ribbon. The size of the points

indicates the variation in fairy circle perimeter lengths from the absence of fairy circles (0 m) to

a maximum average of 29 m per fairy circle in a site.

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Infiltration rate (mm h−1)