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Harvard Forest Symposium Abstract 2016

• Title: Refining estimates of local and climatic drivers of annual biomass production using tree-ring techniques
• Primary Author: Neil Pederson (Harvard Forest)
• Additional Authors: Daniel Bishop (Harvard Forest); Neil Pederson (Harvard Forest)
• Abstract:

  The application of tree rings to the terrestrial carbon cycle is still in a relative infancy. Early reconstructions were first started in the 1990s and the first tree ring-modeling comparisons reconstructing past aboveground net primary productivity (ANPP) was published as recently as 2009. There are now multiple efforts investigating the uncertainties and possibilities of using tree rings to reconstruct biomass around the globe. One effort is housed within the PalEON Project, a Paleo-Ecological Observatory Network for the northern US, and here at the Harvard Forest. To date, we have cored >1300 trees and surveyed downed woody material over ~5.6 ha over six forests from central Massachusetts to southern New Hampshire and the eastern Adirondack State Park. One of the primary goals for our lab is to refine the subseasonal variations and drivers of the terrestrial carbon cycle, a topic that has received very little attention to date in the reconstruction of ANPP using tree-ring records; we know of two studies of much fewer species than what our network contains. To this end, we are measuring and reconstructing biomass from trees with visible earlywood and latewood portions of their annual ring for the following species: Fraxinus americana, Pinus strobus, Quercus alba, Quercus montana, Quercus rubra, and Tsuga canadensis. Latewood is typically much denser than earlywood and thus relatively carbon-rich. Initially, we compared reconstructed estimates of biomass using growth increments with assumed constant wood density to estimates drawn from the splitting of the ring into earlywood-latewood components. We found that assuming constant density can lead to a small overestimation of biomass production at the tree and landscape scale in the Harvard Forest where composition and biomass is dominated by red oak (Quercus rubra). Splitting tree growth into subseasonal components can reveal much about the drivers from extreme events to years to decades. We have been able to determine independent climatic drivers of earlywood versus carbon-rich latewood for red oak, white oak (Quercus alba), and white pine (Pinus strobus) across the central and western New England region. For the Quercus species, we have initially found that earlywood is driven by prior year’s climate (mostly available moisture) and latewood is driven by current year’s climate (again, mostly available moisture). We have begun investigating the relationship of temporal autocorrelation between earlywood and latewood and how this relation might change over time. We hypothesize that this relation indicates allocation of non-structural carbon in the production of annual biomass. Early tests indicate some important differences between species. We will continue to investigate the relation of earlywood and latewood between climate and “themselves”. We are still in the infancy of refining subseasonal biomass production using tree rings. We suspect that our investigations will provide insightful lessons on the drivers, patterns, and temporal components of carbon from within trees up to the regional scale spatial and temporal components to more deeply evaluate terrestrial carbon dynamics over time.

• Research Category: Forest-Atmosphere Exchange
  Historical and Retrospective Studies
  Regional Studies