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Summer Research Project 2018

  • Title: Forest succession via tree mortality and the effects on carbon storage and sequestration in Harvard Forest
  • Summer Supervisors: J. William Munger; Timothy Whitby
  • Researchers: J. William Munger
  • Project Description:

    New England forests have become a net carbon sink through historical trends of agricultural abandonment and reforestation in the past century. The Harvard Forest Environmental Measurement Site (EMS) has been precisely tracking net carbon exchange between the forest and the atmosphere by eddy flux measurements for the past 26 years to better understand the long-term trends and interannual variability of this regional carbon balance. To complement and help partition the estimates of forest CO2 exchange, carbon stocks in living tree biomass have also been measured for over 20 years. Some of the key findings of this research thus far show that Red Oak (Quercus rubra) trees are the dominant canopy species, and they have continually increased their annual rate of carbon uptake in recent years. However, as secondary succession continues, some of this carbon is returned to the atmosphere when trees die and are subsequently decomposed. Through our continuous record of tree growth, mortality, and recruitment, we have been able to identify shifts in the species composition of this maturing forest. In order to better predict how much longer forests like those at Harvard Forest will continue absorbing carbon from the atmosphere we need to understand what is driving tree mortality.
    For this upcoming summer, we will examine tree mortality in the EMS tower plots to identify spatial and temporal patterns and refine the quantification of tree mortality as a term in the forest carbon budget

    The research project will combine pre-existing datasets and new field measurements to quantify and analyze trends in tree mortality in the past 3-5 years. The REU student will assist in the full site measurement of tree diameter growth using dendrometer bands already installed on trees >10 cm diameter at breast height in 34, 10 m radius permanent plots. Any newly dead trees and standing dead trees from previous years will be re-located and cored with an increment borer. Sample cores will be processed and analyzed with dendrochronology software to determine the tree’s age when it died, as well as provide an independent measure of annual growth rate prior to mortality. Since tree mortality is a relatively rare, stochastic occurrence, we will also carry out a transect-based assessment of tree mortality to determine whether our plot-based measurements are providing a representative sample of overall forest tree mortality. To the extent possible, we will collect qualitative data to understand the ultimate cause of mortality, such as wind or lightning damage, fungal or other disease, and insect infestation. Another potential contributing mechanism toward tree decline is competition for resources from neighboring individuals. For each recently dead tree we will characterize its competitive environment by surveying neighboring trees and calculating a competition index. Other site specific parameters such as slope, aspect, and concavity of the terrain (either measured in situ or using GIS derived values) will also be incorporated into our models of tree mortality. Once the field data is collected, the REU student will carry out sample processing in the laboratory, as well as compile and analyze data in the statistical software R.

    The student will be mentored by J. William Munger, the PI for the EMS flux-tower project, and Timothy Whitby, staff researcher for the EMS project. Timothy Whitby will be the primary contact for the summer student, meeting in-person at least weekly and available by email or phone at other times. The student will be trained in all necessary field, laboratory, and statistical analysis techniques, and will be expected to work more independently as the project proceeds. A successful applicant for this position is expected to have some basic familiarity or interest in forest ecology, biogeochemical cycles, and/or climate change.

  • Readings:

    Urbanski, S., C. Barford, S. Wofsy, C. Kucharik, E. Pyle, J. Budney, K. McKain, D. Fitzjarrald, M. Czikowsky, and J. W. Munger. 2007. Factors controlling CO2 exchange on timescales from hourly to decadal at Harvard Forest. Journal of Geophysical Research: Biogeosciences 112:1–25.

    O’Donnell, F. C. 2007. Carbon Dynamics of a New England Temperate Forest Five Years After Selective Logging. Thesis, Harvard University.

    Jevon, F. 2013. The Importance of Age, Competition and Succession in Acer rubrum Decline in a Northeastern Mixed Deciduous Forest. Thesis, Harvard University.

    Das, A. J., N. L. Stephenson, and K. P. Davis. 2016. Why do trees die? Characterizing the drivers of background tree mortality. Ecology 97:2616–2627.

  • Research Category: Physiological Ecology, Population Dynamics, and Species Interactions, Large Experiments and Permanent Plot Studies, Forest-Atmosphere Exchange