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Paleofloods in the Red River Basin

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Flooded Red River Basin
 

 

Dendrochronology

Trees growing on the banks of the Red River can provide a detailed record of past flooding and environmental change.

Dendrochronology LaboratoryIn July 1999, the GSC and MGS established a joint dendrochronology laboratory at the MGS office in Winnipeg. Funding was provided by the GSC, MGS and the Manitoba Hydro Forest Enhancement Program. Dendrochronology uses the information recorded in the structure of annual rings of trees to answer environmental and historical questions. The power of tree-ring analysis lies in their annual, absolutely-dated record, which is unparalleled in geology. Unlike radiocarbon methods, tree-rings provide real calendrical dates, without any associated errors.

Although oak trees in Manitoba can live for up to 300 years, most trees in the Red River valley are only about 100-120 years old. During the middle of the 19th century, woodcutting was a major industry in the Red River valley that supplied construction material and fuel. The current riparian forest in the valley reflects this historical clear-cutting so it is very rare to find trees that are older than 150 years.

 

The Forks in Winnipeg: former deforestation

The Forks, Winnipeg, Manitoba, 1875

1875

The Forks, Winnipeg, Manitoba, 2001

2001

Principles of Crossdating larger image

How do we get long tree-ring records when living trees are usually not more than 100 years old? The answer lies in the buildings around you and in the alluvial mud of the Red River itself. Our oak record includes tree-ring samples from several stands of trees between Winnipeg and Emerson but also has specimens taken from 19th century buildings like Fort Dufferin and from subfossil logs preserved in river alluvium. Pattern matching (called crossdating) compares sequences of wide and narrow rings so that older, dead trees can be dated and included in our record.

 

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