2007 Harvard Forest REU Student Symposium Abstracts
Haley Smith - Oklahoma State University - Main Campus
Impacts of invasive insects on eastern hemlock physiological performance
Impacts of invasive insects on eastern hemlock physiological performance.
Eastern hemlock (Tsuga canadensis) stands throughout southern New England are being decimated by the hemlock woolly adelgid (HWA, Adelges tsugae) and the lesser known elongate hemlock scale (EHS, Fiorinia externa), invasive pests from Asia. Recent sampling efforts suggest that these 2 pests have continued to migrate across the landscape. However, virtually nothing is known about how these pests impact hemlock physiology. Hemlock trees from northern CT and south-central MA with the following four infestation ‘treatments’ were examined in this study: Uninfested control, infested with HWA, infested with EHS, and infested with HWA and EHS. Leaf-level gas exchange and foliar chemical content was examined in one-year old foliage from 12 to 25 trees of each treatment. Compared to uninfested foliage (5.9 µmols CO2 m-2 s-1), hemlock woolly adelgid and elongate hemlock scale alone had lower photosynthetic rates (5.1 and 4.8 µmols CO2 m-2 s-1, respectively)(figure 1). Foliage infested with both insects had even lower rates, averaging 4.4 µmols CO2 m-2 s-1. Density of EHS had no impact on photosynthetic rates, while HWA density was weakly correlated with photosynthetic rates, perhaps due to a defensive response. Leaves with HWA (both alone and with EHS) had higher foliar nitrogen than both EHS infested and non-infested foliage. Future work that takes into account infestation history and duration and minimizes site to site variability in samples will help clarify the long-term impacts of these invasive pests on physiological performance.