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Conserving Boreal Songbirds Using Variable Retention Forest Management
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- Author / Creator
- Odsen, Sonya G.
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The Canadian boreal forest is vital breeding habitat for North American songbirds. Extensive anthropogenic disturbances within this biome are therefore of conservation concern. Using unharvested stands as controls, I examined the effects of variable retention management (VRM) relative to clear-cuts on songbird assemblages and individual species in a boreal mixedwood forest. Breeding season point count surveys were performed in 10-ha cutblocks applied across four dominant forest types (deciduous dominated, deciduous with spruce understory, mixedwood, and coniferous dominated), and harvested in winter 1998/99 to five retention levels (clear-cut (2%), 10%, 20%, 50%, and 75%), plus unharvested controls. Surveys were conducted prior to harvest in 1998, and subsequent to harvest in 1999, 2000, 2005, 2006, 2012, and 2013 at the Ecosystem Management by Emulating Natural Disturbance (EMEND) experiment in northwestern Alberta. In the first two post-harvest years, songbird assemblages in stands with less than 75% retention differed significantly from those in unharvested stands. After 14-15 years, assemblages in stands with 20% retention or higher no longer differed significantly from the controls, suggesting accelerated recovery within high retention stands. In the controls, however, species richness increased after 7-8 years, and species composition changed after 14-15 years, suggesting that c. 10-ha unharvested stands were too small to maintain unchanged songbird assemblages of undisturbed forest. Closer examination of six old forest-associated species – brown creeper (Certhia americana), winter wren (Troglodytes hiemalis), ovenbird (Seiurus aurocapilla), black-throated green warbler (Setophaga virens), Canada warbler (Cardellina canadensis), and western tanager (Piranga ludoviciana) - revealed that 20-75% retention prevented significant declines of all six species, and five of the six species increased significantly after 14-15 years. This suggests that variable retention management can be useful for conservation of songbird assemblages and species typical of unharvested forest. However, spatial trade-offs, lagged recovery in harvested stands, and assemblage changes in unharvested stands reinforce the importance of larger (> 10 ha) forest reserves in harvest planning.
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- Graduation date
- Fall 2015
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- Type of Item
- Thesis
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- Degree
- Master of Science
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- License
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.