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Harvard Forest Symposium Abstract 2009

  • Title: Hemlock woolly adelgid in New England forests and its impact on carbon sequestration: preliminary results on belowground pools of carbon
  • Primary Author: Poliana Lemos (Boston University)
  • Additional Authors: Adrien Finzi (Boston University)
  • Abstract:

    The hemlock wooly adelgid (Adelgis tsugae, or HWA) is transforming the southern New England landscape, converting late-successional hemlock (Tsuga canadensis) stands into early successional hardwood stands composed primarily of black birch (Betula lenta). Hemlock forests store a large quantity of carbon, particularly in the soil, as a result of a thick accumulation of partially decomposed organic matter on the forest floor. The work presented here is part of a larger study that will be quantifying the change in carbon storage and uptake associated with the loss of hemlock and its substitution by black birch. We are using a chronosequence approach to document the change of carbon starting from primary-growth hemlock stands to second-growth black birch stands. Phase two of the research includes estimates of net primary production at each of the chronosequence sites. Phase three of the research uses geographical information system (GIS) and remote sensing to better understand the spatial distribution of this transition.

    The work presented here focuses on changes in soil carbon and fine root biomass. We hypothesized that the mass of the surface organic horizon and fine root biomass would be highest in the primary-growth hemlock stands, lowest in the stands attacted by the HWA 5-10 years ago, and that recovery would be observed in older black birch stands, but not to the extent observed in second-growth hemlock forests. Fine root biomass, organic horizon mass and soil bulk density were collected and analyzed from old-growth hemlock stands (>250 years old), second-growth hemlock stands (60-80 years old, Simes Tract), girdled hemlock stands (Simes Tract), HWA affected stands from the 1990ís with 13 year old black birch saplings (Connecticut River Valley) and second-growth black birch stands (~60 years old, Harvard, MA). Consistent with our hypothesis, we found a large reduction in organic horizon mass and fine root biomass when comparing primary hemlock forest with the 13 year old black birch stand. There was however a substantial recovery of fine root biomass. Fine root biomass in the ~60 year old black birch stand was the same as that in the second growth hemlock stand, although organic horizon mass remained lower in the black birch stand. The ecosystem-level effects on C storage (including live biomass, coarse wood debris and soil carbon stocks) have not yet been quantified, but the data are in hand, so these effects will be known very soon.

  • Research Category: Soil Carbon and Nitrogen Dynamics