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Hi Steve & All, Oct 11, 2013
Those so called fairy rings of the desert were mentioned in the Sept =
2013 issue of National Geographic (un-numbered pp 24&25); location not =
specified beyond southern Africa but Juergens is mentioned. It confuses =
the issue to use the term fairy ring for a simple case of water =
conservation, but anything goes I suppose to hype the hype and keep =
those grants coming.=20
=20
The mechanism is similar to the use of rock mulch; e.g. flat rocks =
to cover the soil between depressed rows in ancient Persia and washed =
round rocks to cover the soil of watermelon (and other similar crop) =
fields in some arid regions of China. When visiting Death Valley once =
(USA not Biblical) the only green showing was a narrow band on both =
sides of the paved road.=20
They are a curious negative of the circular rock walls that used to =
be built around Olive trees in the Middle East; the walls cool off more =
rapidly than the soil so all potential dew is captured by the walls as =
cool night air flows down the valleys and the Olive tree roots below the =
ring are watered by 'drip irrigation'. -- continued below--
=20
----- Original Message -----=20
From: "Stephen R. Shaw" <srshaw@Dal.Ca>
To: <naturens@chebucto.ns.ca>
Sent: Friday, October 11, 2013 1:49 PM
Subject: [NatureNS] More on Fairy Rings
> Still interested in the origin of the 'Sensitive Fern' rings on the Mt =
=20
> Uniacke estate, on a recent visit to UK I mentioned this to a =20
> colleague. He had been in S. Africa with a biologist there, who in =20
> turn had had some involvement with the Namibian fairy ring phenomenon. =
=20
> In a low rainfall zone in a remote Namibian desert, there are =20
> thousands of these circular depressions of bare sand up to 30 feet =20
> across in 'colonies', each surrounded by a fringing ring of desert =20
> grass that is more luxuriant than that in the clumps lying between the =
=20
> rings. Ring origin is uncertain but one recent research suggestion is =
=20
> that certain sand termites eat the grass from the middle of the ring =20
> outwards and kill it, so the centre retains no grass at all. The =20
> centre therefore is able to collect and retain precious rainfall water =
=20
> just below the surface for use by the termites, water that elsewhere =20
> gets taken up rapidly by root systems of the grasses. The grass at =20
> the edge of the circle has partial access to this reservoir so becomes =
=20
> lusher and available as termite food. The rings can last for up to 75 =
=20
> years but eventually each disappears, individually. If you?re not =20
> aware of these fascinatingly bizarre structures (I wasn?t), type =20
> ?Namibian fairy rings? into Wikipedia or Google. These particular =20
> termites are stylized by researcher Juergens as even more effective =20
> water engineers than beavers, which might raise a few eyebrows here.
>=20
> The S. African biologist e-mailed back that he did not know about =20
> fairy rings involving ferns, but had turned up a reference to a N. =20
> American fern that I?d missed:
>=20
> http://www.blueplanetbiomes.org/lady_fern.htm
>=20
> This site refers to the Northern Lady Fern (Athyrium filix-femina), a =
> common native species and ornamental, which according to this site =20
> often forms fern rings, though no further reference for this is cited. =
=20
> Trying to pursue this on Google turned up several interesting =20
> medicinal uses by native peoples, but failed to reveal any other =20
> citations of Athyrium ring formation or speculation about the =20
> mechanism. Have any of the botanists on this list run across any more =
=20
> information, for Athyrium, or for Osmunda mentioned below?
>=20
> Somehow this led to the Interrupted Fern (Osmunda claytoniana). In =20
> Wikipedia, it is said to form small, dense colonies, each spreading =20
> locally through a very large rhizome, and it is said also to often =20
> form fairy rings. So at least in this case, there is some possibility =
=20
> of a mechanism, in that an extended rhizome might use up essential =20
> resources (nitrogen?) at its centre. It might then give rise to =20
> above-ground fronds in a ring but only at the still-resourced edge of =
> the rhizome, as I think Dave Webster originally suggested. =20
You may by thinking of my comments of July 25 with reference to true =
(i.e. fungal) fairy rings but these would not apply to ferns in the =
absence of some fungal association.
Many plants that grow from the perimeter, by rhizome branching and =
extension or by vert space vegetative branching, and die from the origin =
can tend to form roughly ring like growths, in the absence of disrupting =
features. Some Lichen growths on the surface of trees or rocks are good =
examples. Some Mosses and Liverworts may also form roughly circular =
growths with dead or weak centers But in most cases the rings are =
irregular, broad and not sharply deliniated; an area in the middle with =
no, weak or dead shoots and a broad diffuse halo of plants with the most =
vigorous tending to be near or at the perimeter. A gradual buildup of =
nematodes, root fungi and other like weakening agents in the older parts =
of a patch may sometimes be involved.
But the mechanism in all these cases is essentially outward =
extension of new vigorous growth by repeated branching into 'virgin' =
soil; entirely distinct from the green rings in uniform grass that are =
of fungal origin. Calling such vaguely ring-like growths fairy rings is =
an unfortunate consequence of internet enthusiasm. =20
On the other hand your ring is huge in diameter and very narrow in =
width. I find it hard to believe that only rhizome extension is at work =
here.=20
Yt, DW
=20
If this is =20
> correct, the consequence would be that each fern ring actually is a =20
> clone of genetically identical individuals. Apparently this is true =20
> for other ferns with rhizomes, and for some plants like goldenrod that =
=20
> also spread through rhizome colonization. Perhaps everyone but me knew =
=20
> this already.
>=20
> Steve (Halifax)
>=20
>=20
>=20
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<DIV>Hi Steve &=20
All,&a