What are the most dramatic environmental watersheds in the history of Canada to 1867?

What are the most dramatic environmental watersheds in the history of Canada to 1867?

Whether one looks at resource extraction (including fur trading, fisheries, and hunting), land use (like farming or logging), or biological change (for example, disease), Canadian history after 1608 is punctuated by important environmental events. What are the most dramatic environmental watersheds in the history of Canada to 1867? Assess their impact on the rise to power of Euro-Canadian forces.