Invasive woolly adelgid appears to drive seasonal hemlock and carcass inputs to a detritus-based stream.
Abstract:
Ecosystems are experiencing rapid ecological changes due to
human-driven alterations in climate, land-use, nutrient availability,
and introduction of pests and pathogens. Many of these environmental
changes are predicted to result in non-random loss of species that will
alter community composition (VITOUSEK et al. 1997, LOREAU et al. 2001,
ELLISON et al. 2005). For example, in eastern U.S. forests, current
declines in eastern hemlock (Tsuga canadensis) resulting from
infestation of the woolly adelgid (Adelges tsugae) are altering
riparian tree community composition (ORWIG et al. 2002). Declines in
eastern hemlock in southern Appalachian forests are projected to result
in long-term increases in tulip poplar (Liriodendron tulipifera) or
rhododendron (Rhododendron maximum; ELLISON et al. 2005), but
short-term seasonal effects of woolly adelgid infestation on
allochthonous inputs to streams have not been studied.
The life cycle of the woolly adelgid contains 2 generations. Overwintering adult woolly adelgids deposit eggs in ovisacs from February to late March, and larvae emerge in early April (McCLURE 1989,1991, McCLURE & CHEAH 1999). These larvae develop into the adult stage and deposit a second generation of eggs in June. Emergent larvae remain inactive until October, when feeding resumes (McCLURE 1989, 1991, McCLURE & CHEAH 1999). Larvae feed on sap from the base of hemlock needles (McCLURE 1987), which causes the needles to fall off. Needle inputs from infested riparian hemlock trees may serve as an important resource to stream ecosystems.
Terrestrial litter subsidies are important organic matter and energy resources for recipient stream ecosystems (FISHER & LIKENS 1973, VANNOTE et al. 1980, HALL et al. 2001), and the chemical quality of litter can be altered by terrestrial herbivores (HUTCHENS & BENFIELD 2000, CHAPMAN et al. 2003, 2006). Herbivory on evergreens results in higher litter quality and accelerated decomposition and nutrient cycling in terrestrial environments compared to herbivory on deciduous trees (CHAPMAN et al. 2003, 2006) and eastern hemlock litter from infested trees has been reported to contain higher nitrogen concentrations than litter from uninfested trees (STRADLER et al. 2006).
Here we present data from a 2-year litter trap study, conducted during the early stages of woolly adelgid infestation and hemlock decline. We assess the contribution of eastern hemlock to direct litterfall and lateral inputs to streams as well as entrainment of woolly adelgid carcasses by leaf packs in a second-order reach of Ball Creek, a headwater stream located at Coweeta Hydrologic Laboratory (Coweeta), Macon County, North Carolina, U. S. (35˚00'N; 83˚30'W).
The life cycle of the woolly adelgid contains 2 generations. Overwintering adult woolly adelgids deposit eggs in ovisacs from February to late March, and larvae emerge in early April (McCLURE 1989,1991, McCLURE & CHEAH 1999). These larvae develop into the adult stage and deposit a second generation of eggs in June. Emergent larvae remain inactive until October, when feeding resumes (McCLURE 1989, 1991, McCLURE & CHEAH 1999). Larvae feed on sap from the base of hemlock needles (McCLURE 1987), which causes the needles to fall off. Needle inputs from infested riparian hemlock trees may serve as an important resource to stream ecosystems.
Terrestrial litter subsidies are important organic matter and energy resources for recipient stream ecosystems (FISHER & LIKENS 1973, VANNOTE et al. 1980, HALL et al. 2001), and the chemical quality of litter can be altered by terrestrial herbivores (HUTCHENS & BENFIELD 2000, CHAPMAN et al. 2003, 2006). Herbivory on evergreens results in higher litter quality and accelerated decomposition and nutrient cycling in terrestrial environments compared to herbivory on deciduous trees (CHAPMAN et al. 2003, 2006) and eastern hemlock litter from infested trees has been reported to contain higher nitrogen concentrations than litter from uninfested trees (STRADLER et al. 2006).
Here we present data from a 2-year litter trap study, conducted during the early stages of woolly adelgid infestation and hemlock decline. We assess the contribution of eastern hemlock to direct litterfall and lateral inputs to streams as well as entrainment of woolly adelgid carcasses by leaf packs in a second-order reach of Ball Creek, a headwater stream located at Coweeta Hydrologic Laboratory (Coweeta), Macon County, North Carolina, U. S. (35˚00'N; 83˚30'W).
Kominoski, J., C. M. Pringle, and B. A. Ball. 2008. Invasive woolly adelgid appears to drive seasonal hemlock and carcass inputs to a detritus-based stream. Verhandlungen Internationale Verein. Limnol. 30: xx-xx.
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