Pennsylvania boreal conifer forests and their bird communities: past, present, and potential
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Pennsylvania spruce (Picea spp.)- and eastern hemlock (Tsuga canadensis)-dominated forests, found primarily on glaciated parts of the Allegheny Plateau, are relicts of boreal forest that covered the region following glacial retreat. The timber era of the late 1800s and early 1900s (as late as 1942) destroyed most of the boreal forest on a large scale, but there has been some recovery of vegetation and delayed recovery of the accompanying avian communities. Important locally from a biodiversity standpoint, these forests support the most southerly extent of the current breeding range of yellow-bellied flycatcher and blackpoll warbler. Now persistent at a few sites, yellow-bellied flycatcher was documented nesting in the 1980s after 50 years of being absent or overlooked. Blackpoll warblers were not documented as a breeding species in Pennsylvania until 1993 but have been confirmed nesting most years since. These boreal forest relicts also host numerous other species of more northerly distribution, sometimes in high densities.