Impact of fire on Picea mariana and Pinus banksiana seedlings in subarctic lichen woodlands

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Abstract
The demography of Picea mariana (black spruce) and Pinus banksiana (jack pine) seedlings was monitored through five censuses over 13 months in four different seed bed types after fire of four severity levels in lichen woodland. Most seeds germinated just before early frost in late summer 1990 or immediately after snow thaw in early spring 1991; the germination rate subsequently decreased. For both species, germination rate decreased along a gradient of fire severity. The proportion of Pinus seeds that produced a seedling surviving 13 months after sowing was 4.3 % and 0.4 % respectively in the intact lichen mat and in the mineral soil seed bed type. For Picea these values are 3.2 % and 0.2 % respectively. The low germination rate in a severely burned seed bed type appeared to be associated with the formation of a water‐repellent crust at the soil surface following the fire. Seedlings were contagiously distributed and were more frequent in flat and hollow microsites, where there is probably more water available than on bumps or among pebbles. Properties of experimentally burned seed bed types may differ from those under natural fires where regeneration by seed generally occurs following dispersal. However, the high germination rate observed in the intact lichen mat suggests that scattered lichen woodland patches may respond to increased seed input by a higher frequency of seedling establishment.