Limits...
Experiments Testing the Causes of Namibian Fairy Circles.

Tschinkel WR - PLoS ONE (2015)

Bottom Line: Limitation of plant growth due to micronutrient depletion within fairy circles was tested by supplementing circles with a micronutrient mixture, but did not result in differences in plant seedling density and growth.These four experiments provided evidence that fairy circles were not caused by subterranean vapors, that fairy circle soil per se did not inhibit plant growth, and that the circles were not caused by micronutrient deficiency.Landscape-scale vegetative self-organization is discussed as a more likely cause of fairy circles.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Science, Florida State University, Tallahassee, Florida, United States of America.

ABSTRACT
The grasslands on the sandy soils of the eastern edge of the Namib Desert of Namibia are strikingly punctuated by millions of mostly regularly-spaced circular bare spots 2 to 10 m or more in diameter, generally with a margin of taller grasses. The causes of these so called fairy circles are unknown, but several hypotheses have been advanced. In October 2009, we set up experiments that specifically tested four hypothesized causes, and monitored these 5 times between 2009 and 2015. Grass exclusion in circles due to seepage of subterranean vapors or gases was tested by burying an impermeable barrier beneath fairy circles, but seedling density and growth did not differ from barrier-less controls. Plant germination and growth inhibition by allelochemicals or nutrient deficiencies in fairy circle soils were tested by transferring fairy circle soil to artificially cleared circles in the grassy matrix, and matrix soil to fairy circles (along with circle to circle and matrix to matrix controls). None of the transfers changed the seedling density and growth from the control reference conditions. Limitation of plant growth due to micronutrient depletion within fairy circles was tested by supplementing circles with a micronutrient mixture, but did not result in differences in plant seedling density and growth. Short-range vegetation competitive feedbacks were tested by creating artificially-cleared circles of 2 or 4 m diameter located 2 or 6 m from a natural fairy circle. The natural circles remained bare and the artificial circles revegetated. These four experiments provided evidence that fairy circles were not caused by subterranean vapors, that fairy circle soil per se did not inhibit plant growth, and that the circles were not caused by micronutrient deficiency. There was also no evidence that vegetative feedbacks affected fairy circles on a 2 to 10 m scale. Landscape-scale vegetative self-organization is discussed as a more likely cause of fairy circles.

No MeSH data available.


Related in: MedlinePlus

Location of the five replicate sets of experimental manipulations, showing the labeled detail of one of the replicate sets.The barrier treatments and controls were located only at Replicates 1 and 2. S = soil transfer experiment; A = artificial neighborhood experiment; M = micronutrient experiment. The experimental area is an undulating sandy plain sloping to the east, with scattered small dunes. Reprinted and modified from satellite image Namibia WV3 08DEC15 1010010008EC6A08 under a CCBY license, with permission from Digital Globe, Inc., original copyright 2008.
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pone.0140099.g001: Location of the five replicate sets of experimental manipulations, showing the labeled detail of one of the replicate sets.The barrier treatments and controls were located only at Replicates 1 and 2. S = soil transfer experiment; A = artificial neighborhood experiment; M = micronutrient experiment. The experimental area is an undulating sandy plain sloping to the east, with scattered small dunes. Reprinted and modified from satellite image Namibia WV3 08DEC15 1010010008EC6A08 under a CCBY license, with permission from Digital Globe, Inc., original copyright 2008.

Mentions: Four experiments each with five replicates were set up along a track that traversed a rolling sandy plain that rose gradually over 6 km from a pan at 960 m elevation in the east to the margin of a rocky outcrop (Jagkop) at 1100 m elevation in the west. Fig 1 shows the locations of the 5 replicate sets, each of which contains one replicate of each of the 4 experiments (except for the Barrier Experiment, of which there are only 2 replicates. Rain gauges have been set up and monitored by the reserve staff. Locations and treatments of all plots can be found in S1 Table.


Experiments Testing the Causes of Namibian Fairy Circles.

Tschinkel WR - PLoS ONE (2015)

Location of the five replicate sets of experimental manipulations, showing the labeled detail of one of the replicate sets.The barrier treatments and controls were located only at Replicates 1 and 2. S = soil transfer experiment; A = artificial neighborhood experiment; M = micronutrient experiment. The experimental area is an undulating sandy plain sloping to the east, with scattered small dunes. Reprinted and modified from satellite image Namibia WV3 08DEC15 1010010008EC6A08 under a CCBY license, with permission from Digital Globe, Inc., original copyright 2008.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4625006&req=5

pone.0140099.g001: Location of the five replicate sets of experimental manipulations, showing the labeled detail of one of the replicate sets.The barrier treatments and controls were located only at Replicates 1 and 2. S = soil transfer experiment; A = artificial neighborhood experiment; M = micronutrient experiment. The experimental area is an undulating sandy plain sloping to the east, with scattered small dunes. Reprinted and modified from satellite image Namibia WV3 08DEC15 1010010008EC6A08 under a CCBY license, with permission from Digital Globe, Inc., original copyright 2008.
Mentions: Four experiments each with five replicates were set up along a track that traversed a rolling sandy plain that rose gradually over 6 km from a pan at 960 m elevation in the east to the margin of a rocky outcrop (Jagkop) at 1100 m elevation in the west. Fig 1 shows the locations of the 5 replicate sets, each of which contains one replicate of each of the 4 experiments (except for the Barrier Experiment, of which there are only 2 replicates. Rain gauges have been set up and monitored by the reserve staff. Locations and treatments of all plots can be found in S1 Table.

Bottom Line: Limitation of plant growth due to micronutrient depletion within fairy circles was tested by supplementing circles with a micronutrient mixture, but did not result in differences in plant seedling density and growth.These four experiments provided evidence that fairy circles were not caused by subterranean vapors, that fairy circle soil per se did not inhibit plant growth, and that the circles were not caused by micronutrient deficiency.Landscape-scale vegetative self-organization is discussed as a more likely cause of fairy circles.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Science, Florida State University, Tallahassee, Florida, United States of America.

ABSTRACT
The grasslands on the sandy soils of the eastern edge of the Namib Desert of Namibia are strikingly punctuated by millions of mostly regularly-spaced circular bare spots 2 to 10 m or more in diameter, generally with a margin of taller grasses. The causes of these so called fairy circles are unknown, but several hypotheses have been advanced. In October 2009, we set up experiments that specifically tested four hypothesized causes, and monitored these 5 times between 2009 and 2015. Grass exclusion in circles due to seepage of subterranean vapors or gases was tested by burying an impermeable barrier beneath fairy circles, but seedling density and growth did not differ from barrier-less controls. Plant germination and growth inhibition by allelochemicals or nutrient deficiencies in fairy circle soils were tested by transferring fairy circle soil to artificially cleared circles in the grassy matrix, and matrix soil to fairy circles (along with circle to circle and matrix to matrix controls). None of the transfers changed the seedling density and growth from the control reference conditions. Limitation of plant growth due to micronutrient depletion within fairy circles was tested by supplementing circles with a micronutrient mixture, but did not result in differences in plant seedling density and growth. Short-range vegetation competitive feedbacks were tested by creating artificially-cleared circles of 2 or 4 m diameter located 2 or 6 m from a natural fairy circle. The natural circles remained bare and the artificial circles revegetated. These four experiments provided evidence that fairy circles were not caused by subterranean vapors, that fairy circle soil per se did not inhibit plant growth, and that the circles were not caused by micronutrient deficiency. There was also no evidence that vegetative feedbacks affected fairy circles on a 2 to 10 m scale. Landscape-scale vegetative self-organization is discussed as a more likely cause of fairy circles.

No MeSH data available.


Related in: MedlinePlus