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Abstract: Plants balance resource allocation to growth with antiherbivore
defenses for survival. Sometimes, these defenses fail and insect herbivores outbreak.
Because they lack a recent coevolutionary history, exotic herbivores often overcome plant
defenses, becoming invasive in impacted ecosystems. I examine the effect of two invasive
sap-feeding insects, hemlock woolly adelgid (HWA, Adelges
... read more tsugae) and elongate hemlock scale (EHS, Fiorinia
externa) on Eastern hemlock (Tsuga canadensis).
While extensive changes associated with hemlock stress and population decline are apparent
in affected forests, I elucidate the plant-level effects of these herbivores through two
studies. To understand increased litterfall in infested stands, I studied the effect of HWA
on biomechanics of needles, twigs, and branches. To understand decreased growth in infested
trees, I studied the effects of HWA and EHS on carbon resource allocation. I found evidence
of stress in both the biomechanics and chemistry of infested trees, with implications for
Thesis (M.S.)--Tufts University, 2013.
Submitted to the Dept. of Biology.
Advisor: Colin Orians.
Committee: Philip Starks, and George Ellmore.
Keywords: Plant biology, Biomechanics, and Ecology.read less