CLIMATE FEEDBACKS AND CARBON SEQUESTRATION WITH AFFORESTATION
SCENARIOS IN THE U.S.
Large changes in evapotranspiration (ET) and water yield are common
when trees are planted on lands that previously supported herbaceous
vegetation. Globally, one of the best tools to address the effects
of afforestation on streamflow is long-term catchment datasets. A
previous CGC working group (the “Plantations Group” in
AY03/04) synthesized data from catchment studies to assess changes
in streamflow with afforestation, and found that annual runoff decreased
consistently in afforested catchments, but that the level of decrease
varied by original vegetation type and climate, and with plantation
age.
In addition to affecting evaporative water losses and runoff locally,
afforestation could also affect climate at regional scales and thereby
affect precipitation and water use. These regional effects depend
on the location, extent, and patchiness of afforestation and operate
through changes in albedo, roughness length, and water transport properties
from soil to the atmosphere, including leaf area index, stomatal conductance,
and rooting depth. These variables influence climate because they
help determine the total amount of energy transferred between the
vegetation and the atmosphere and the fraction of that energy driving
evapotranspiration and warming of the air.
The objectives of this working group are to extend the work of the
plantations group on the effects of afforestation on streamflow to
the effects on climate, specifically by quantifying the biosphere
atmosphere feedbacks of afforestation. The group will run meso-scale
model simulations of various afforestation scenarios in the United
States using the Ocean-Land-Atmosphere Model (OLAM) – an Earth
System Model that in addition to simulating the general circulation
of the atmosphere, includes a dynamic terrestrial vegetation model
and nested grids and other approaches for increasing the resolution
and accuracy of regional simulations. Through the model simulations,
the group will estimate potential carbon sequestration rates, explore
key biophysical interactions, and quantify feedbacks from large-scale
afforestation with climate and precipitation.
The group is composed of an ecologist and an atmospheric scientist:
Robert B. Jackson, Nicholas
School of the Environment and Earth Sciences and Department of Biology,
Duke University
Roni Avissar, Civil and Environmental Engineering, Duke University
