TEMPERATE FOREST CARBON CYCLING: THE IMPORTANCE OF TREE SPECIES IN A CHANGING GLOBAL ENVIRONMENT.
Abstract: Forest carbon cycling is a political and scientific challenge. From
a policy perspective, carbon storage is important to climate mitigation, with the goal of
sequestering carbon dioxide (CO2) in forests. From a scientific perspective, the
environmental variables that control storage and loss of carbon are of central interest.
This dissertation looks at carbon cycling from both perspe... read morectives: carbon storage in live
biomass to offset emissions and the mechanisms that determine carbon loss from dead
biomass. First we compared Massachusetts' forest carbon sequestration in live biomass to
energy-sector CO2 emissions. We found that over 10% of the state's energy-sector CO2
emissions were sequestered within the state's forest and nearly half of these forests were
at risk of deforestation. From there we looked at the history of a Massachusetts forest to
see how a changing composition altered carbon storage in live and dead biomass. We found
that this forest increased in above-ground woody biomass carbon storage during the first 40
years, sequestering 3.80 Mg C/ha/yr, but sequestration decreased over the next 20 years. In
mature stands, we found that total coarse woody debris biomass in the forest was 13.52
Mg/ha and lignin was 23% of the total biomass. With the knowledge of the woody debris
composition, we then asked what would happen to this carbon pool with climate change. We
found that soil warming increased mass loss of woody debris by as much as 30%, but that
more recalcitrant and larger debris decomposed much slower. We also found that the most
lignin-rich species lost lignin the fastest. Last, we asked how a change in woody inputs to
the soil from a shifting forest composition would influence soil dynamics under current and
future environmental scenarios of warming and nitrogen deposition. We found that a shift
from recalcitrant to more labile woody inputs would only increase microbial respiration and
activity under future scenarios of warming and nitrogen addition. The research in this
dissertation suggests that forests may be able to mitigate CO2 emissions under current
forest composition and environmental scenarios, but this could shift dramatically in the
next 100 years with a changing environment.
Thesis (Ph.D.)--Tufts University, 2011.
Submitted to the Dept. of Biology.
Advisor: Colin Orians.
Committee: George Ellmore, Michael Reed, and Adrien Finzi.
Keywords: Biogeochemistry, Ecology, and Biology.read less