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Harvard Forest Symposium Abstract 2016

• Title: Trends in 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 main objective of this research is to study changes in soil carbon stocks (soil C, root biomass) and fluxes (soil respiration) in a hemlock stand that is currently infested by the hemlock woolly adelgid, and where trees are declining in vigor and dying off. Because our team has collected similar data in the same stand (circa 2010) prior to the infestation, it gives us a rare opportunity to study soil C dynamics before, during, and after a major disturbance event. We have published two papers assessing changes in ecosystem C balance using a chronosequence approach [1]. With the infestation underway in the same location we will test whether the predictions from the chronosequence analysis hold.
  
  
  
  We deployed an automated soil respiration (Rs) system including six chambers near the Hemlock tower from October 6 to December 16, 2015 to field-test the system and collect preliminary data. Rs was measured once every 30 minutes on each collar until winter conditions forced us to take the system down. As expected, there was a strong correlation between Rs and soil temperature (Fig. 1). Average Rs per chamber during that period was very similar for the chambers located near black birch seedlings and ground cover vegetation (Fig. 2). Mean Rs was 30% lower in chambers located far from any live vegetation.
  
  
  
  In summer 2015 we also collected soil samples in six subplots in each of six plots located in two different areas in the hemlock stand: three plots south of Hemlock Hollow and three plots in the Bigelow Brook weir area. In each subplot, we collected a 10 cm × 20 cm organic horizon sample and sampled the underlying mineral soil to a depth of 30 cm in 10 cm increments. Samples were used to estimate root biomass, root C content, and soil C content. Preliminary results indicate that the top 30 cm of the mineral soil contains approximately 25% more organic C than the organic horizon (Fig. 3; OH=6170 gC m-2, mineral=7704 gC m-2). The root biomass in the first 30 cm of the mineral soil is double the amount present in the organic horizon, and at each sampling depth there is approximately the same mass of live and dead roots (Fig. 4).
  
  
  
  Six additional soil respiration chambers will be deployed from spring until fall of 2016 downstream from the Bigelow Brook weir where hemlock trees appear to be healthy. We will add to the soil respiration measurements an intensive soil sampling effort to determine the number of cores required to detect a 5-10% change in soil and root C content that is anticipated with the death of hemlock. Additional sets of soil samples will be collected in the upcoming years to study the change in C pools following hemlock die off.
  
  
  
  
  
  [1] Raymer, P. C. L., D. A. Orwig, and A. C. Finzi. 2013. Hemlock loss due to the hemlock woolly adelgid does not affect ecosystem C storage but alters its distribution. Ecosphere 4. doi: 10.1890/ES12-00362.1
  
  
  
  Finzi, A. C., P. C. L. Raymer, M.-A. Giasson, and D. A. Orwig. 2014. Net primary production and soil respiration in New England hemlock forests affected by the hemlock woolly adelgid. Ecosphere 5. doi: 10.1890/ES14-00102.1
  
  

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


• Figures:
Finzi_Hemlock_dieoff_Fig1.JPG
Finzi_Hemlock_dieoff_Fig2.jpg
Finzi_Hemlock_dieoff_Fig3.JPG
Finzi_Hemlock_dieoff_Fig4.JPG