Pine BarrensField Notes

Nature and science

When caterpillars removed the canopy: measuring carbon in 2007

Documented history and research · Sources compared

A defoliation outbreak became a test of how researchers measure a forest’s carbon balance when its leaves disappear.

Three years with different canopies

Kenneth Clark, Nicholas Skowronski and John Hom compared oak- and pine-dominated forests across 2005, 2006 and 2007. The first year had little defoliation. A mixed stand was partly defoliated in 2006; in 2007 an oak-dominated stand lost its canopy completely while the other stands experienced partial damage. The changing conditions supplied a before-and-during comparison. Clark, Skowronski and Hom (2010).

Their 2010 paper combined eddy-covariance measurements of carbon dioxide exchange with measurements of vegetation. The insects were identified as Lymantria dispar, now generally called spongy moth; the source uses the older common name. The study treated herbivory as an ecosystem disturbance with consequences beyond the immediate sight of bare branches. Clark, Skowronski and Hom (2010).

A model checked against measurements

A companion study by Karina Schäfer and colleagues estimated canopy carbon assimilation using sap-flow measurements through whole trees and gas exchange at different canopy levels. The researchers first evaluated the model against 2006 eddy-flux measurements. They then applied it to 2005 and to the two-to-three-week period of complete defoliation in 2007. Schäfer and colleagues, canopy assimilation model (2010).

This pairing matters because the atmosphere-facing instruments and the tree-based model approached the same forest from different directions. Neither an empty canopy photograph nor a tally of defoliated acres alone supplies a complete carbon budget. The early abstracts establish the comparison and methods, but do not supply an audited numerical estimate of the 2007 loss. Schäfer and colleagues, canopy assimilation model (2010).

Following the damaged forest into another decade

A 2024 follow-up extended carbon measurements across two decades and a later prescribed burn. At the oak-dominated stand, the 2019 burn released an estimated 1.7 metric tons of carbon per hectare. Annual net ecosystem production over the following three years exceeded the low rates recorded during the decade after severe defoliation and associated tree mortality. The authors suggested a possible restoration role for fire; the sequence alone does not isolate fire from every other influence. Clark, Skowronski and Gallagher (2024).

The same paper distinguished recovering annual productivity from repaying carbon released during a burn. At the repeatedly burned pine stand, the two-decade net carbon balance remained positive after estimated fire emissions were included. A forest could therefore resume absorbing carbon while still needing time to offset a particular disturbance’s release. Clark, Skowronski and Gallagher (2024).

Sources and research limits

The early papers are related investigations of an outbreak, not independent replications. Their abstracts establish methods; the separately inspected 2024 follow-up supplies the later carbon figures.