The Effects of Burning on the Heat and Water Regimes of Lichen-Dominated Subarctic Surfaces

Abstract

Areas of ground lichen in the subarctic are particularly susceptible to fire either by man's activity or by natural causes. Experimental evidence from the Hudson Bay lowlands gathered in the summer of 1970 indicates that the burning of lichen has a pronounced effect on the ground water regime. Soil moisture measurements made in a mature lichen woodland with thinly spaced trees, and in areas of recent and older burning indicate that the soil moisture under the lichen-dominated surface was at least 40% greater than in either of the burned areas. This suggests that a mature lichen cover offers a high resistance to the evaporation of soil moisture. The nature of the evaporation regime was determined using the energy budget (Bowen Ratio) approach over each surface. These data were augmented by measurements of the moisture content of the lichen made at three levels with the canopy. The evidence indicates that lichen dominated surfaces act as an effective mulch in preventing evaporation from the subsurface zone whereas the burned areas which are able to evaporate more water into the atmosphere when moist, also develop strong resistances to evaporation as the soil surface layers become drier. The role of ground lichen in the water budget of northern lands is significant because of its extensive cover and its destruction by fire must exert an important influence on the hydrologic and atmosphere water regimes.