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Harvard Forest Symposium Abstract 2020

• Title: Soil carbon stocks and fluxes in a hemlock stand infested by the hemlock woolly adelgid
• Primary Author: Marc-Andre Giasson (Boston University)
• Additional Authors: Adrien Finzi (Boston University)
• Abstract:

  The introduction of the hemlock woolly adelgid (HWA) has resulted in widespread hemlock mortality. The impact of tree mortality on carbon fluxes remains poorly constrained. Exactly how much C is lost and how long it would take to recover those C stocks following succession is unknown. The HWA is now widespread at Harvard Forest and the objective of this research is to quantify the impact of hemlock mortality on components of the forest C budget. Here we present data on soil respiration.
  
  From April to December 2019, we continued the automated measurement of soil respiration (Rsoil) we had initiated in late 2015. As was done in the past, we deployed twelve chambers at the exact same location as previous years. Six chambers were located near the Hemlock tower in an area heavily affected by the hemlock woolly adelgid; most hemlock trees in that area are either dying or dead. Six other chambers were located downstream from the Bigelow Brook weir where hemlock trees appeared healthier.
  
  Each chamber made one measurement per half hour, resulting in close to half a million valid Rsoil measurements over the duration of the study. The interruption of measurements during winter, when snow and cold conditions precluded the use of our automated systems, created gaps in data that were filled with values estimated using the relationship between Rsoil and soil temperature (Fig 1). Other gaps caused by loss of power or equipment failure during the growing season were filled the same way.
  
  There was large within-site and interannual variability in annual Rsoil totals (Fig. 2). Average annual Rsoil for each collar range from 651 to 881 g C/m2/yr at the tower site and from 886 to 1322 g C/m2/yr at the weir site.
  
  In all years, Rsoil was significantly higher at the weir (healthier) site than the tower (infested/dying) site (p < 0.001) but the difference between the two sites decreased with time (p = 0.047; Fig. 3). Site-level annual Rsoil in 2019 at the tower site (824 g C/m2/yr) was similar to that in 2018 (826 g C/m2/yr) and much higher than in 2016 (672 g C/m2/yr) and 2017 (740 g C/m2/yr). Annual Rsoil in 2019 at the weir site (1008 g C/m2/yr) was the lowest measured at that site since the beginning of the study. Previous annual totals were 1054 g C/m2/yr (2016), 1117 g C/m2/yr (2017), and 1073 g C/m2/yr (2018).
  
  Continued Rsoil measurements in future years coupled with more above- and belowground sampling of carbon stocks will help us determine temporal trends in the carbon budget of hemlock forests during and after hemlock woolly adelgid infestation.
  
  
  Figure captions:
  
  Fig. 1:
  Mean daily soil respiration at the tower (infested) and weir (healthier) sites.
  
  Fig. 2:
  Total annual soil respiration at the 12 twelve collars.
  
  Fig. 3:
  Mean annual soil respiration at the tower (infested) and weir (healthier) sites.

• Research Category: Forest-Atmosphere Exchange
  Invasive Plants, Pests & Pathogens
  Soil Carbon and Nitrogen Dynamics


• Figures:
Fig1.jpg
Fig2.JPG
Fig3.JPG