Boreal woodpecker assemblages in recently burned forested landscapes in Alberta, Canada: effects of post-fire harvesting and burn severity.

摘要

Canadian boreal forests are increasingly modified by post-fire removal of trees (salvage logging), yet the ecological consequences of this practice are little studied. As mixed-wood forests have recently become accessible for salvage operations, we studied woodpeckers in mixed-wood (trembling aspen Populus tremuloides and white spruce Picea glauca) and adjacent coniferous (black spruce Picea mariana and jack pine Pinus banksiana) areas in Alberta, Canada, to examine the effects of salvage logging and burn severity on these species. During 2003-2004 we carried out transect counts in 24 landscape units (625 ha each) that varied in pre-fire amount of merchantable mixed-wood (low=7-15% and high=25-35% of the unit area), salvage logging intensity (from control=no salvaging to high=60-70% of merchantable mixed-wood harvested) and burn severity (estimates based on tree survival after fire). Six main findings are presented: (1) in mixed-wood areas subjected to salvage, total woodpecker abundance and woodpeckers of the genus Picoides (most notably black-backed woodpecker Picoides arcticus) responded negatively to increasing salvage logging intensity; (2) northern flicker (Colaptes auratus) showed a marginally significant positive response to salvage in the mixed-wood areas; (3) the salvage response of the black-backed woodpecker was season dependent (first post-fire summer, winter and second post-fire summer compared); (4) in coniferous but not in mixed-wood areas, black-backed woodpecker responded positively to increasing burn severity. Moreover, the response in coniferous habitat was stronger in the first post-fire summer, compared to the subsequent winter and the second post-fire summer. In the retained mixed-wood areas, northern flicker responded positively to increasing burn severity; (5) the majority of the detected 73 woodpecker nests with chicks were in trembling aspen trees or in mixed-wood stands; (6) among coniferous tree species, dead standing jack pine and white spruce trees had much greater evidence of woodpecker foraging than had black spruce (~65-75% versus 15% of trees). These results indicate the crucial influence of salvage logging, the amount of retained mixed-wood forests and burn severity on woodpecker abundance. Hence, we recommend retention of large, burned mixed-wood areas during salvage harvesting to support these dead-wood dependent birds..