Response of Avian Communities to Disturbance by an Exotic Insect in Spruce‐Fir Forests of the Southern Appalachians

Abstract

The avian community of montane coniferous forests changed substantially over 21 years in response to the introduction of the balsam woolly adelgid insect ( Adelges piceae ) and the resulting death of endemic Fraser fir trees ( Abies fraseri ). These relict forests are at the southern limit of their distribution on the highest ridges of the southern Appalachian Mountains. We combined a historical study at Mount Collins in the Great Smoky Mountains with a geographic comparison of sites within five southern Appalachian mountain ranges variably affected by the adelgid. At Mount Collins, fir was virtually eliminated and canopy cover reduced to half its previous level. Long-term data from Mount Collins showed that the combined density for all breeding birds also declined by half. Of the common territorial species present in 1974, 10 of 11 declined, 6 by more than 50%. Some species are near local extinction. Canopy-and subcanopy-foraging species declined more than near-ground and trunk-foraging species. In addition, invasions of birds characteristic of open and disturbed forests have diluted the boreal character of the avifauna. These changes are consistent with two other long-term studies and are not explained by regional population trends. In the other southern Appalachian mountain ranges, where habitat is not as extensive, the adelgid invasion resulted in greater declines in avian abundance, stronger effects on sensitive species, and more pronounced invasions by successional species. Sensitive species in the southern Appalachian studies were also strongly affected in other studies of forest disturbance by fire and logging. The extent of relatively pristine spruce-fir forest and the population pools in other forest types in the Great Smoky Mountains appear to have buffered the effects of forest decline on the bird community. Respuesta de Comunidades de Aves a Perturbaciones de un Insecto Exótico en Bosques de Abeto en el Sur de los Apalaches Resumen: La comunidad de aves de bosques coníferos de montaña cambió sustancialmente a lo largo de 21 años en respuesta a la introducción del insecto adélgido lanudo Aldeges piceae y a la resultante muerte de ár-boles de Abetos Fraser ( Abies fraseri ). Estos vestigios de bosques se encuentran al limite sureño de su distribución en las montañas mas altas de los Apalaches. Combinamos un estudio histórico del monte Collins en las montañas Great Smoky con una comparación geográfica de sitios entre cinco cordilleras de los Apalaches afectados en forma variable por el adélgido. En el monte Collins, los abetos fueron virtualmente eliminados y la covertura del dosel reducida a la mitad de su nivel previo. Datos de largo plazo del monte Collins mostraron que la densidad combinada para todas las especies de aves anidando también disminuyó a la mitad.De las especies comunes en el territorio en 1974, 10 de 11 disminuyeron, seis en mas de un 50%. Algunas especies se encuentran cerca de su extinción local. Especies forrajeras de dosel y sub-dosel disminuyeron mas que aquellas especies forrajer...

Direct and indirect effects of alien insect herbivores on ecological processes and interactions in forests of eastern North America

“…For example, hemlock decline and mortality caused by hemlock woolly adelgid increased canopy gaps and levels of light reaching the forest floor (Orwig and Foster 1998), which decreased soil moisture within 3 years (Orwig et al 2008). Such alterations in microhabitat conditions can alter understory vegetation dynamics (Orwig and Foster 1998;Rabenold et al 1998; see section ''Impacts on Native Understory Plants'').…”

“…Gap formation resulting from decline and mortality of oak and beech, resulting from gypsy moth defoliation (Davidson et al 1999;Jedlicka et al 2004) and beech bark disease (Houston 1975;Morin et al 2007;Runkle 2007), respectively, is particularly well documented. By inducing the decline and mortality of host trees, alien herbivorous insects cause the formation of canopy gaps (Rabenold et al 1998;Runkle 2005), with their size and frequency being dependent upon host dominance, density, distribution, and mortality levels. The ecological significance of gap formation for community structure and successional trajectory is especially important in eastern forests where wildfire frequency is naturally low and has been further suppressed by management activities (Runkle 1982(Runkle , 1990(Runkle , 1998(Runkle , 2000Shang et al 2007).…”

Impact of Phytophthora-dieback on birds in Banksia woodlands in south west Western Australia

“…Similarly, Rabenold et al (1998) found that canopy and sub-canopy bird species declined in spruce-fir forest following balsam woolly adelgid (Adelges piceae) attacks. Research on other types of disturbance that similarly alter vegetation, such as fire, forest clearing and subsequent regrowth, consistently indicate modified bird communities in response to the disturbance agent (Borges and Stouffer, 1999;Easton and Martin, 1998;Valentine et al, 2012a).…”

“…overstorey. No studies involving disease-induced loss of overstory are available for comparison, but similar studies on forest insect attack have indicated the importance of canopy, with canopy-dependent species declining due to the loss of habitat (Matsuoka et al, 2001;Rabenold et al, 1998;Tingley et al, 2002).…”

Breeding Birds of Mature Woodlands of Point Pelee National Park Prior to Infestation by Emerald Ash Borer, <em>Agrilus planipennis</em>

“…Hemlockdwelling species, e.g., Black-throated Green Warbler (Dendroica virens), Blackburnian Warbler (Dendroica fusca), Blue-headed Vireo (Vireo solitarius), and Acadian Flycatcher (Empidonax virescens), have declined in abundance, whereas species that inhabit deciduous forests, e.g., Eastern Wood-Pewee, Great Crested Flycatcher, Red-eyed Vireo, and Wood Thrush, or more fragmented forests, e.g., Brown-headed Cowbird, Tufted Titmouse (Baeolophus bicolor) and Whitebreasted Nuthatch (Sitta carolinensis), have benefited from the loss of hemlock trees (Tingley et al 2002;Ross et al 2004;Becker et al 2008) (scientific names of species recorded at PPNP are given in Table 1). In another study of high-elevation Red Spruce (Picea rubens)/Fraser Fir (Abies fraseri) forests in the Appalachian Mountains, the loss of conifers caused by the introduced Balsam Woolly Adelgid (Adelges piceae), subsequent windthrow, and air pollution changed avian communities in much the same way as fire or logging would (Rabenold et al 1998).…”