Introduction Pennsylvania Boreal Conifer Forests And
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PENNSYLVANIA BOREAL CONIFER FORESTS AND THEIR BIRD COMMUNITIES: PAST, PRESENT, AND POTENTIAL Douglas A. Gross1 Abstract.—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. Historically, olive-sided flycatcher was widespread and locally common in the high elevations as late as the 1890s, but has not been documented nesting since the 1930s. Many of these boreal bird species such as the yellow-bellied flycatcher and red crossbill are not easily detected and need specialized surveys for adequate monitoring. Diversity of habitat and plant species structure are important elements of locations that support the rarest and most diverse species assemblage. Populations of some species seem to be increasing over time, but problems with wintering grounds or migration stopover sites may be limiting some species as much as nesting habitat. The best boreal conifer sites have some level of protection, but their isolation and a general lack of appreciation present challenges for conservation of this ecosystem. On North Mountain the forest is truly primeval; the Hemlock, the Yellow Birch, and the Maple are the characteristic trees and attain great size. The Hemlocks are scattered in considerable numbers through the forest and tower above it, their huge trunks often four or five feet in diameter marking them out as giants among their lesser brethren. The underbrush is often dense and everywhere great logs, covered with green moss, lie moldering. Here and there you hear clear cold brooks that seem to imitate the song of the Winter Wren that is almost constantly heard along them. The drawling song of the Black-throated Blue Warbler is heard on every hand. High up in the Hemlocks the drowsy sound of the Black-throated Green Warbler is heard, and the lively chatter of the Blackburnian Warbler catch the ear. Is not this a bit of northern Maine? Here it was that for the first time I heard the Wood Thrush, the Hermit, and the Olive-backed all singing at the same time. The three species were abundant and the music at sundown was a concert which for sweetness would be hard to excel. Jonathan Dwight, writing of North Mountain in 1892 (Dwight 1892). INTRODUCTION the state lies within the Appalachian Mountain Bird Size and geographical position give Pennsylvania an important Conservation Region. Although most of the state’s forests role in the Appalachian Mountain forest ecosystems. Most of are deciduous or mixed deciduous–conifer, some areas in the state contain boreal or conifer forests. Extant boreal conifer forests are found primarily on glaciated parts of the 1 Pennsylvania Game Commission Endangered Birds Specialist, 144 Winters Road, Orangeville, PA 17859. To contact, email at Allegheny Plateau and are relicts of former boreal forests [email protected]. that were once more extensive. Most are associated with 48 Proceedings from the Conference on the Ecology and Management of High-Elevation Forests GTR-NRS-P-64 in the Central and Southern Appalachian Mountains forested wetlands/peatlands or are part of wetland complexes Mountains (Rhoads and Klein 1993). Bear Meadows Natural at headwaters of high-quality cold water streams (Gross Area of Rothrock State Forest is an outlying location for 2002a). Much of the current spruce (Picea spp.) forest areas balsam fir and several other boreal conifers (Rhoads and Klein are located in northeastern counties, but some stands also 1993, Abrams et al. 2001). Black spruce (Picea marina) is less are found in northern Pennsylvania as far west as the Ohio common than red spruce and confined solely to wetlands, border, along with a few stands south of the State College especially sphagnum bogs and peatlands with American larch area in the central portion of the state (Fig. 1). or tamarack (Larix laricina) (Donahoe 1954; Rhoads and Block 2000, 2005). Eastern white pine (Pinus strobus) also is a The map of current distribution of possible spruce forest is component of boreal conifer swamps. Even when spruces are estimated and subject to further research (Fig. 1). In dominant, large black gums (Nyssa sylvatica) are often a particular, the Pocono Mountains, especially the High prominent feature of the forested wetlands where some of the Poconos near Blakeslee in the northeast; North Mountain, birds featured in this report are found. the eastern part of the Allegheny Plateau in the northwest; and the Northcentral Highlands all have tracts of conifer History and Extent of Pennsylvania forests that sustain populations of birds generally associated Boreal Forests with northern forests. These conifer swamps and bogs were Pre-settlement Pennsylvania was approximately 90- to 95- formed from glacial kettle lakes and filled in with peat from percent forested (DeCoster 1995). Glaciation and European accumulation of organic matter (Johnson 1985; Davis et al. settlement have created a more patchy forest in the state 1991; Davis et al. 1995a, 1995b, 2002). In older texts, these with fewer old forests. Most Pennsylvania forests are now in areas would have been considered to be in the “Canadian” age classes between 60 and 120 years, with the largest 10- life zone (Merrium 1894, Poole 1964). year classes in the 81- to 100-year range (Jenkins et al. 2004). The forests of the Allegheny Plateau once comprised In these conifer forests, eastern hemlock (Tsuga canadensis) a much larger percentage of hemlock. Many bird species are often is dominant or is a cohort associate with red spruce associated with hemlocks in the Northeast and the (Picea rubens). Balsam fir (Abies balsamea) is much rarer than Appalachians. On a general basis, Acadian flycatcher red spruce and also is scattered across the highlands of (Empidonax virescens), blue-headed vireo (Vireo solitarius), Pennsylvania, but occurs most commonly in the Pocono magnolia warbler (Dendroica magnolia), Blackburnian Figure 1.—Red and black spruce community distribution in Pennsylvania (red circles), PA Natural Heritage Program with The Digital Base Map of Pennsylvania and Delaware Valley Regional Planning Commission imagery as backdrop. GTR-NRS-P-64 Proceedings from the Conference on the Ecology and Management of High-Elevation Forests 49 in the Central and Southern Appalachian Mountains warbler (D. fusca), and black-throated green warbler (D. McWilliams and Brauning 2000). Some of the characteristic virens), are often associated with hemlock forests (Haney birds of this diminished boreal conifer forest will be 1999, Ross et al. 2004, Allen et al. 2009). Conifer forests emphasized herein. One of the objectives of my paper is to extend across Pennsylvania, and some of the most extensive share surveys and research conducted in Pennsylvania that and oldest are in the northwestern counties, especially in the are unpublished or have been reported in obscure reports. Allegheny National Forest and in Cook Forest State Park Findings may be relevant to similar bird conservation and some public lands nearby (Haney 1999). The forests of concerns in the Appalachians south of Pennsylvania. northwestern Pennsylvania formerly had a higher component of hemlock than in present times (Lutz 1930, The timbering era left a lasting mark on the vegetation of Whitney 1990). Only a few old-growth forests remain in Pennsylvania and much of the Appalachian Mountain the state, and most of these are dominated by conifers, region. Much of the Pocono Mountain region where many particularly eastern hemlock and eastern white pine. Several of the red spruce forests occurred, was logged fairly early bird species are broadly associated with more mature conifer compared to the rest of northern Pennsylvania because of its forests, including red-breasted nuthatch (Sitta canadensis), proximity to urban areas, coal mines, and large rivers brown creeper (Certhia americanus), winter wren (Troglodytes (Oplinger and Halma 1988). This region was accessible to troglodytes), and golden-crowned kinglet (Regulus satrapa), as transportation corridors, first canals and later railroads, well as the Empidonax flycatcher, vireo, and Dendroica through Stroudsburg along the Delaware River, Mauch warblers just mentioned, and the hairy woodpecker (Picoides Chunk (later Jim Thorpe) along the Lehigh River, and villosus), Swainson’s thrush (Catharus swainsoni), and Wilkes-Barre along the Susquehanna River to New York, magnolia warbler (Dendroica magnolia) (Haney and Schaadt Philadelphia, and Baltimore (Oplinger and Halma 1988, 1996, Haney 1999). Dando 1996). Large rafts of pine were floated down the Susquehanna from southern New York and northern The loss of avifaunal elements of the “Canadian” life zone Pennsylvania to Baltimore as early as 1794 (Harvey and was documented and lamented by many ornithologists and Smith 1927). ecologists in Pennsylvania (Todd 1940; Poole 1964 unpublished; Conant 1989a, b; Mellon 1989). Similar The tanning industry started as early as 1822 in declines have been documented in West Virginia in more Stroudsburg and grew to a million-dollar industry by the recent times as a result of natural forest changes (Hall 1985). 1860s. Timbering was extensive during the Civil War in the The size and extent of the former boreal conifer element in lowlands of the Poconos and culminated in the higher Pennsylvania is often underestimated.