Forest rings are large, circular patterns of low tree density in the

boreal forests Taiga or tayga ( ; , ), also known as boreal forest or snow forest, is a biome characterized by coniferous forests consisting mostly of pines, spruces, and larches. The taiga, or boreal forest, is the world's largest land biome. In North Ame ...

of northern

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

. These rings can range from to nearly in diameter, with rims about in thickness. The origin of forest rings is not known, despite several mechanisms for their creation having been proposed. Such hypotheses include radially growing fungus, buried kimberlite pipes, trapped gas pockets, and meteorite impact craters.

History

Because of their large scale, forest rings are not apparent from the ground, and it was not until aerial photography became a common surveying tool in the 1950s that geologists began to notice them. The term "forest ring" was coined by The Ontario Geological Survey to differentiate the phenomenon from

fairy ring A fairy ring, also known as fairy circle, elf circle, elf ring or pixie ring, is a naturally occurring ring or arc of mushrooms. They are found mainly in forested areas, but also appear in grasslands or rangelands. Fairy rings are detectable by ...

Geobacter ''Geobacter'' is a genus of bacteria. ''Geobacter'' species use anaerobic respiration to alter the redox state of minerals and many pollutants, a trait that makes them useful in bioremediation. ''Geobacter'' was the first organism described wit ...

spp. and

methanotroph Methanotrophs (sometimes called methanophiles) are prokaryotes that metabolize methane as their source of carbon and chemical energy. They are bacteria or archaea, can grow aerobically or anaerobically, and require single-carbon compounds to ...

s, such as Candidatus Methylomirabilis and Methylobacter, were highly abundant in samples from the 'Bean' and the 'Thorn North' ring, in Ontario, Canada.

Hypothesis

Forest rings were originally thought to be caused by the radial growth of fungi within the root system of

black spruce ''Picea mariana'', the black spruce, is a North American species of spruce tree in the pine family. It is widespread across Canada, found in all 10 provinces and all 3 territories. It is the official tree of Newfoundland and Labrador and is tha ...

(''Picea mariana''), possibly the fungus ''

Armillaria ostoyae ''Armillaria'' is a genus of fungi that includes the ''Armillaria mellea, A. mellea'' species ('honey fungus') that live on trees and woody shrubs. It includes about 10 species formerly categorized summarily as ''A. mellea''. ''Armillaria'' ...

''. A ring would begin as a single point of infection and grow outward in all directions. Affected trees would die in the interior of the circle, and eventually new trees would grow in their place. The fungal mat would become ring-shaped and visible from above as a circular ring of stunted trees. The fungal hypothesis is no longer favoured as there is little compelling evidence to support it. Observations of forest rings in the Abitibi region of Quebec have found no evidence of mass tree mortality by a pathogen. It was further hypothesized that bacteria, such as ''

'', might be contributing to the ring formation. Their capability to form conducting nanowires or pili and to perform directional electron transport might contribute to a circular charge transfer from the electron-rich center of the ring towards the ring edges. The so-catalyzed oxidation processes increase

acidity An acid is a molecule or ion capable of either donating a proton (i.e. hydrogen cation, H+), known as a Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis acid. The first category of acids are the ...

and dissolve carbonates, thus creating a depression, and, accordingly, the ring edge. Recent microbiological investigations indeed show a high abundance of ''

'' at the ring edge.

Outside of Canada

Forest rings have also been reported in

Russia Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...

and

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

References

{{reflist, 30em, refs= {{cite journal , title=The enigmatic rings of the James Bay Lowland: a probable geological origin , journal=Geological Survey of Canada, Open File , year=1999 , last1=Veillette , first1=J.J. , last2=Giroux , first2=J-F. , issue=3708 , doi=10.4095/210206 , url=http://geoscan.nrcan.gc.ca/starweb/geoscan/servlet.starweb?path=geoscan/fulle.web&search1=R=210206 , accessdate=2017-02-24 , doi-access=free {{cite web , url=http://epod.usra.edu/blog/2007/04/boreal-forest-rings.html , title=Boreal Forest Rings , last=Murphy , first=Ray , work=EPOD , date=2007-04-26 , accessdate=2016-12-09 {{cite news , last=Andra-Warner , first=Elle , url=http://www.cbc.ca/news2/background/tech/science/forest-rings.html , title=The mysterious forest rings of northern Ontario , work=

CBC News CBC News is the division of the Canadian Broadcasting Corporation responsible for the news gathering and production of news programs on the corporation's English-language operations, namely CBC Television, CBC Radio, CBC News Network, and CBC ...

, publisher=

Canadian Broadcasting Corporation The Canadian Broadcasting Corporation (), branded as CBC/Radio-Canada, is the Canadian Public broadcasting, public broadcaster for both radio and television. It is a Crown corporation that serves as the national public broadcaster, with its E ...

, date=2008-05-21 , accessdate=2016-12-08 {{cite journal, last1=Hamilton, first1=S.M., last2=Cranston, first2=D.R., title=Thick Overburden Geochemistry – Methods and Case Studies, publisher=Ontario Ministry of Northern Development and Mines, Ontario Geological Survey, periodical=Ontario Geological Survey Open File Report, Summary of Field Work and Other Activities 2000, volume=6032, year=2000, pages=10–17, url=http://www.geologyontario.mndm.gov.on.ca/{{cite journal, last1=Brauneder, first1=Kerstin, last2=Hamilton, first2=Stewart M., last3=Hattori, first3=Keiko, title=Geochemical processes in the formation of 'forest rings': examples of reduced chimney formation in the absence of mineral deposits, journal=Geochemistry: Exploration, Environment, Analysis, volume=16, issue=1, year=2016, pages=85–99, issn=1467-7873, doi=10.1144/geochem2015-360, bibcode=2016GEEA...16...85B , s2cid=131060951 {{cite journal, last1=Giroux, first1=Jean-François, last2=Bergeron, first2=Yves, last3=Veillette, first3=Jean J, title=Dynamics and morphology of giant circular patterns of low tree density in black spruce stands in northern Quebec, journal=Canadian Journal of Botany, volume=79, issue=4, year=2001, pages=420–428, issn=0008-4026, doi=10.1139/b01-022 {{cite journal , last1=Hamilton , first1=Stewart M. , last2=Hattori , first2=Keiko H. , title=Spontaneous potential and redox responses over a forest ring , journal=Geophysics , date=May 2008 , volume=73 , issue=3 , pages=B67–B75 , doi=10.1190/1.2890287, bibcode=2008Geop...73...67H {{cite journal , last1=Hamilton , first1=S.M. , last2=Govett , first2=G.J.S. , title=Vertical Dispersion of Elements in Thick Transported Cover Above the Thalanga Zn-Pb-Cu Deposit, Queensland, Australia: Evidence of Redox-Induced Electromigration , journal=Special Publication , publisher=Society of Economic Geologists , date=2010 , volume=2 , issue=15 , pages=391–398 {{cite journal , last1=Reguera , first1=Gemma , last2=McCarthy , first2=Kevin D. , last3=Mehta , first3=Teena , last4=Nicoll , first4=Julie S. , last5=Tuominen , first5=Mark T. , last6=Lovley , first6=Derek R. , title=Extracellular electron transfer via microbial nanowires , journal=Nature , date=23 June 2005 , volume=435 , issue=7045 , pages=1098–1101 , doi=10.1038/nature03661, pmid=15973408 , bibcode=2005Natur.435.1098R , s2cid=4425287 {{cite journal , last1=von Gunten , first1=Konstantin , last2=Hamilton , first2=Stewart M. , last3=Zhong , first3=Cheng , last4=Nesbø , first4=Camilla , last5=Li , first5=Jiaying , last6=Muehlenbachs , first6=Karlis , last7=Konhauser , first7=Kurt O. , last8=Alessi , first8=Daniel S. , title=Electron donor-driven bacterial and archaeal community patterns along forest ring edges in Ontario, Canada: Electron donor-driven microbial community patterns along forest ring edges , journal=Environmental Microbiology Reports , date=December 2018 , volume=10 , issue=6 , pages=663–672 , doi=10.1111/1758-2229.12678 , pmid=30014579 , s2cid=51650191 Geography of Canada Forests of Canada

History

Hypothesis

Outside of Canada

See also

References