Responses of Northern U.S. Forests
to Environmental Change
Chapter 11: Regional Impacts of Climate Change
and Elevated CO2 on Forest Productivity
Jennifer C. Jenkins, David W. Kicklighter,
and John D. Aber
Changes in productivity of ecosystems in the Northeast in response
to increasing atmospheric CO2 and scenarios of climate change were
estimated with two ecosystem process models, PnET-II and TEM 4.0.
Models were used for this regional analysis because of complex interactions
at the ecosystem scale between CO2 response, biogeochemical cycles,
and water and energy fluxes. The two models differ in their representation
of above- and below-ground processes, in their mechanisms of response
to CO2, and in their approaches to regional parameterization. To
the extent possible, input data was consistent so that differences
in how the two models represent ecosystem processes could be considered
as an explanation of differences in results.
At the regional scale, both models predicted an increase in productivity
under climate change scenarios, with PnET-II predicting an average
increase of 37.9% and TEM 4.0 an average increase of 30.0%. There
was a large difference in model predictions for different climate
change scenarios, with both models tending to respond in a similar
way. Estimates of NPP with PnET-II showed more sensitivity to different
forest types. NPP responses in TEM 4.0 appear to be limited by temperature,
while PnET-II appears to be limited by water. Differences in model
structures and representations of response to increased CO2
contributed to variability in predictions of future productivity.
Neither model included some factors known or suspected to influence
productivity, such as transient (as opposed to stepwise) climate
change, nitrogen deposition, and past land use.
to individual climate variables from Hadley/ suplphate GCM . Within each forest type, each bar represents
the mean +/- SD for one run with one Hadley/sulphate climate variable
substituted for the equivalent VEMAP contemporary variable. "Altered"
variables are from the Hadley/sulphate GCM; all others are from
the VEMAP contemporary climate scenario, except for the "all
combined" run, in which all of the Hadley/sulphate variables
were applied at once.
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