Boreal forest of Canada

In the boreal forest of Canada, wildfires are important disturbance factors. A single wild fire seldom burns the whole forest. Instead it burns large patches or stands and leaves others untouched. Following a wildfire in a black spruce forest, there is usually a predictable regrowth of the vegetation, starting with ground lichens and small spruce seedlings. As the spruce trees grow and form a closed-crown canopy, feather mosses (Bryophytes) are found in an increasing proportion on the forest floor. In some cases, the peat moss Sphagnum outcompetes the feather mosses and eventually dominates the ground cover. Because wildfires occur naturally about every 10 years, a forest stand can sometimes burn before Sphagnum dominance is reached, and the whole process repeats.

a. Graph “Tree Biomass vs. Time” over a 100-year period:

i. at the stand scale (the stand is a particular part of the forest that burned) and
ii. at the landscape scale (composed of many forest stands).

• Assume, at the stand scale, that when a stand burns, all trees in that stand die.
• Assume, at the landscape scale, that there is one fire every 10 years, and that each fire burns a different stand.

b. Explain how (and why) the graphs differ.