Fires
Fires feed the forest.
Thousands of square kilometres of boreal forest burn every summer in the Yukon, Alaska and Siberia. Yukon forests burn naturally every 50 to 200 years releasing nutrients into the soil and creating open spaces for new growth. Pine, aspen and willow can only grow in full sun, so they are the first to colonize freshly burned areas. Spruce can grow up through a shaded forest to become the dominant tree in an "old forest." Since there are no fire scars on the old spruce in this forest, it was probably human disturbance, and not fire, that opened these woods to aspen and pine.
Forest fires burned during the last glacial age.
Burnt spruce and birch stumps, approximately 125,000 years old, have been found near Fairbanks, Alaska. During the warmer interglacials, when there were forests in Beringia, widespread and repeated fires probably renewed the forests just as they do today.
Fireweed growing in burnt aspen stand, one month after the fire, Yukon. Photo:
Indian and Northern Affairs Canada
New plants move in after a fire.
Fires also played a role in the spread of plant species north during warming
periods. In a changing climate, well-established plants can survive a long time
in areas that have become too warm or too wet. Fires burn out the old growth,
allowing different plant species that are adapted to the new climatic conditions
to move in.
Aspen saplings overtaking fireweed in a four year-old burn of an aspen stand,
Burwash Landing, Yukon. Photo: John Meikle, Government of Yukon
Inset: Yukon fire. Photo: Indian and Northern Affairs Canada
In a warmer Yukon, will we see increased fires due to drier conditions, or will increasing temperatures mean more rain and fewer fires? Do both situations threaten Yukon ecosystems equally?