Studies on lichen-dominated systems. XIX. The postfire recovery sequence of black spruce – lichen woodland in the Abitau Lake Region, N.W.T.

The postfire recovery sequence in spruce woodland growing on drumlins in the Abitau–Dunvegan Lakes area of the Northwest Territories is described. Four phases are recognized: year 1 to year 20, the Polytrichum phase dominated by P. piliferum, with Lecidea granulosa and L. uliginosa as associated species; year 21 to about year 60, the Cladonia phase dominated by Cladonia stellaris and C. uncialis; year 61 to about year 130, the spruce–Stereocaulon phase with Stereocaulon paschale forming an almost pure lichen ground cover; after year 130, the canopy closes and the lichen cover disappears and is replaced by a moss cover forming the final phase, spruce–moss woodland. These phases are confirmed by component analysis.The existence of spruce–Stereocaulon woodland in the area is thus dependent on cyclic burning. In the absence of fire the spruce canopy would close and the lichen cover would largely disappear. This event is rare in the area with a rebum cycle of about 100 years. Fire is thus an important vector in the maintenance of this extensive barren-ground caribou winter range.