Status of Old-forest Birds

Old deciduous and mixedwood forests provide important habitat to a range of bird species ^{[1 ,2]} ; for example:

• these forests supply an abundance of nesting sites for cavity-nesting birds, like the Pileated Woodpecker and Red-breasted Nuthatch.
• the leaves of deciduous trees host numerous herbivorous insect species gleaned by canopy-foraging birds, like the Blue-headed Vireo.
• the complexity in the habitat structure of deciduous and mixedwood forests, including an abundance of shrubs and a mixture of deciduous trees of various sizes and decay states, allows more species to coexist.
• finally, old mixedwood stands with even a few White Spruce trees support species that are often found in coniferous forests, such as the Brown Creeper.

Overall, deciduous and mixedwood forests support a greater diversity of birds than younger stands or coniferous forests, although a range of stand types and forest age classes are important to support the full suite of bird species.

Intactness and sector effects are summarized for bird species associated with old deciduous and mixedwood forests in Norbord’s operating areas. Details for calculating intactness and sector effects can be found in the Methods.

• Habitat suitability for old-forest bird species, as indicated by intactness, is higher in the Northern Operating Area compared to in the Southern and Partner Operating Areas; this can be attributed to the lower amount of human footprint in the north.
• Although habitat suitability was slightly higher in the north compared to the south for old-forest birds, the same species consistently showed the largest deviation from intact reference conditions in all three operating areas, including: Brown Creeper, Black-throated Green Warbler, Winter Wren, Bay-breasted Warbler, and Western Tanager.
• Old-forest birds are disproportionately affected by human footprint because, as of 2018, 46% and 49% of human footprint had occurred in deciduous and mixedwood forest in the Northern and Southern Operating Areas. 

Local scale sector effects are used to understand what industrial sectors are most affecting the abundance of bird species associated with old deciduous/mixedwood forests in Norbord’s operating areas. Changes in species relative abundance are predicted within each sector’s footprint compared to the reference conditions with no human footprint.

• All types of human disturbances greatly decrease habitat suitability for most bird species associated with old deciduous/mixedwood forests in Norbord’s operating areas because these activities impact their preferred habitat.
• Within forestry footprint, the abundance of most old-forest bird species is predicted to be less abundant than expected compared to in the habitat it replaces, with half of the old-forest birds predicted to be more than 50% less abundant.
• Two species—Yellow-bellied Sapsucker and Philadelphia Vireo—while associated with old-forest habitat, also respond positively to harvest areas and are therefore more abundant than expected in forestry footprint.

Regional population effects reflect the total expected change for the population of each old forest bird species across Norbord’s operating areas due to each sector’s footprint. This incorporates the area of the footprint, the native habitats in the region where the footprint occurs, and the species response to a particular footprint. The calculation also incorporates the entire landbase of each operating area, large tracts of which have no human footprint.

• Regional effects are much less than local scale effects because a great deal of old forest bird habitat has not been disturbed by human footprint in the operating areas; regional effects are larger in the south because of higher footprint there.
• Regional population effects from energy, transportation, and urban/industrial footprint on birds associated with old deciduous/mixedwood forest were small—ranging from between -3.0% and +1.0% in both operating areas.
• Forestry footprint resulted in the largest predicted changes to suitable habitat for many old forest birds—on average -6.5% and -9.3% in the Northern and Southern Operating areas, respectively—because harvesting is the largest footprint type in both regions. Several species are predicted to decrease by at least 10% at the regional scale as a result of forestry footprint in each operating area, for example Brown Creeper and Black-throated Green Warbler.