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Harvard Forest Symposium Abstract 2010

  • Title: Changes in carbon pools in northeastern temperate forests as a consequence of the hemlock woolly adelgid
  • Primary Author: Poliana Lemos (Boston University)
  • Additional Authors: Adrien Finzi (Boston University)
  • Abstract:

    A legitimate concern in ecological studies has been the recent and rapid increase of invasive pests in forests around the world. In northeastern US forests, hemlock (Tsuga canadensis) is considered a foundation species. The loss of hemlock as a result of the hemlock woolly adelgid (HWA, Adelgis tsugae) and its replacement by black birch (Betula lenta) raises fundamental questions about the C balance of forests in this transition. We are using a chronosequence approach to better understand this issue. Five sites – old-growth and secondary hemlock forests, forests at an early and advanced stages of infestation, and secondary black birch forest – are being studied. So far, it has been found that black birch forests are capable of rapidly recovering its belowground biomass, with live fine root biomass almost as high as that found in old-growth hemlock forest. The difference consists in the C:N ratio of these fine roots, which linearly decreased along the chronosequence. The secondary hemlock forest and the forest in early stage of infestation had similar fine root biomass, while the late stage of infestation had the lowest value. An abrupt 5-fold increase in the volume of coarse woody debris (CWD) was found during the five years that separate the secondary hemlock forest and the early stage of infestation. The form at which CWD is found relates to the different ways it contributes to the C balance of that forest. Snags were switched to stumps in a 10-year period of infestation. An increase in the diversity and abundance of fungal fruiting body between the secondary hemlock forest and the forest in a later stage of infestation reinforces the idea of a relevant increase in the decomposition rate of these dead trees, as they become in close contact with the soil. The mass of hemlock litter decreases until the early stage of infestation. Litter mass of black birch as well as other hardwood species increase exponentially with an input of litter mass in secondary black birch forests approximately twice as that found for hemlock litter in old-growth hemlock forests. Concurrently, the organic horizon mass decreases along this transition, suggesting that the slow decomposition of organic matter in hemlock forests is not offset by the lower input of litter.

  • Research Category: Invasive Plants, Pests & Pathogens
    Soil Carbon and Nitrogen Dynamics