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Harvard Forest Symposium Abstract 2012

• Title: A centennial time-scale analysis of the effects of the hemlock woolly adelgid on the carbon balance of northeastern temperate forests
• Primary Author: Poliana Lemos (Boston University)
• Additional Authors: Adrien Finzi (Boston University)
• Abstract:

  By virtue of its structural and functional attributes, foundation species create and define an entire ecological community or ecosystem (Ellison et al. 2005). The eastern hemlock (Tsuga canadensis), a foundation species of temperate forests, is being severely infested by the hemlock woolly adelgid (Adelgis tsugae), a high impact invasive pest introduced in the northeast in the 1980s. Little is still known about the centennial, ecosystem-level consequences of this change, especially in relation to C storage and flux. We focused on an empirical comparative analysis measuring C in (1) primary-growth hemlock stands representing a scenario of non-infestation; (2) second-growth hemlock stands representing the starting point of HWA infestation for most hemlock forests in this region; (3) girdled hemlock stands representing an early stage (5 years) following hemlock death; (4) infested hemlock stands representing a later stage (ca. 18 years) following hemlock death, with substantial re-growth of other tree species; and (5) mature black birch stands representing the successional end-point a century after hemlock death. The first three stands were located at the Harvard Forest (Prospect Hill and Simes Tract), the fourth (infested) in the Connecticut River Valley and the fifth in Harvard, MA. C pool in above- and belowground live biomass, soil (O horizon to 45cm depth) and woody debris were measured, as well as changes in C input (dendrochronology and annual litterfall) and output (soil respiration). C density (kg C m-2) was highest in the primary-growth hemlock stands and recovery of C stocks in regrowing black birch stands was a slow process. Net primary production (NPP) increased 2.5-fold in the first five years following infestation (girdled stands), and black birch saplings contributed to 40% of the NPP in the infested stands. Despite high rates of NPP, the two stands representing up to twenty years following infestation resulted in a period of net carbon source of ~340 gC m-2 yr-1. We estimate that it takes ~74 years for C to accumulate to the levels of second-growth hemlock stands at the time they were infested and that by 135 years of stand development, the C density of black birch stands was equivalent to that of primary-growth hemlock stands.

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