La Mauricie National Park of Canada
Megafossils in the Lakes of La Mauricie National Park
They are long, weigh almost a ton, and populated the forest of La Mauricie National Park a few hundred years ago. And they are now being studied by a Université Laval researcher, who saw in the park’s aquatic environment restoration program a golden opportunity to deepen our understanding of the forest’s history. The trees, of course, are considered to be ligneous fossils by dendrochronology specialists, who use growth rings on trees to grasp the ecology of old-growth forests and disturbances to forest ecosystems over the last few centuries (fire, logging, climate change, etc.).
Logs removed from Isaïe Lake
©Parks Canada/Philippe Henry
Isaïe Lake Spills its Secrets
Restoration work was begun at Isaïe Lake. More than 11 000 logs later and after slightly lowering the water level, the new face of the lake is already becoming visible. The purpose of From Log to Canoe is to mitigate the effects of the past on the natural environment, while also preserving the possibility of studying the park’s history and passing this knowledge on to future generations.
The Université Laval dendrochronology laboratory team had the chance to study more than 400 samples from the logs taken out of Isaïe Lake. The results show that the Tsuga canadensis, better known as eastern hemlock, is the dominant species. Hemlock bark, which contains many tannins, was widely used in tanneries to make leather from hides. Though classified as a softwood, hemlock was used in railway ties, framing timber and bridge construction. Hemlock was heavily harvested in the 19th century, such that it is much less abundant in the park’s forests today.
Université Laval's dendrochronology laboratory
©Parks Canada/Louise Filion
The dendrochronology series developed based on the 37 hemlock logs from the lake was linked to the series of 37 living hemlocks growing on top of a rocky slope overlooking Isaïe Lake. The oldest recorded living tree in the park is 328 years old and the oldest sample retrieved at the bottom of the lake is from a tree that was 384 years of age. In other words, this particular tree was growing on present-day park lands before Jacques Cartier landed at Québec City in 1535! It is thought to have been felled around 1902.
The hemlock is a slow-growing tree, but has a long life expectancy. Under the right conditions, it can live 500 to 600 years. More than 50 of the 400 samples have at least 200 annual growth rings.
The dendrochronology data also shows that the hemlocks were felled between 1896 and 1907. Judging by the stamped markings and the letters ‘LP’ found on some of the logs, it would appear that the trees were harvested by the Laurentide Paper Co. These findings have been corroborated by historical data pertaining to this company’s operations in La Mauricie that date to the late 1880s.
Pressed markings of the Laurentide Paper Co.
©Parks Canada/Jacques Pleau
The discovery of logs partially buried in sediments will allow researchers to pinpoint the exact year the trees were felled. Over time, the buried sections of the logs were protected from certain decomposer organisms. As the circumferences of the logs have remained unaltered, the last growth rings – those of the year they were cut down ‑ are still visible.
Log that was driven vertically into the bottom of Isaïe Lake
©Parks Canada/Véronique Nadeau
For Logs, a Second Life
The resource will not go wasted, for each log is useful. Quality logs are turned into saw timber and low value logs into firewood. Logs have even been transformed into works of art in the hands of sculptors!
Works of art
©Parks Canada/Jacques Pleau