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Spatial modeling of aboveground carbon dynamics of the U. S. central hardwood forest

Authors:

Wenchi Jin

Publication Type:
Thesis
Year of Publication:
2016
Publisher:
University of Missouri
City:
Columbia, Missouri
Secondary Title:
Department of Forestry (MU)
Type of Work:
Doctoral Thesis
Volume:
PhD
Year:
2016

Abstract

Central Hardwood Forest (CHF) is one of the largest forested biomes in the United States and its aboveground carbon dynamics have both regional and global significances. Thus, the aboveground carbon dynamics of CHF are of substantial interest to researchers, resources managers and policy makers. Among measures and fluxes of aboveground carbon dynamics, aboveground biomass and aboveground net primary production (ANPP) are the most widely used ones. Modeling has been a powerful approach to study aboveground carbon dynamics, however, it is largely unknown whether more complex process-based models could perform better at both plot and regional scales. CHF is currently a carbon sink mainly due to forest regrowth from previous disturbances, yet as forests regrow towards maturity, how long this carbon sink would persist is subject to uncertainty, and it is unclear what role in carbon sequestration the CHF would play after the current carbon sink diminishes. In addition to forest aging, aboveground carbon dynamics may be influenced by environmental factors, such as climate, CO2 concentration, and nitrogen deposition. Furthermore interactions between forest aging and environmental factors can be complex. Chapter II compared predictions of aboveground biomass by simple physiological, complex physiological, and hybrid empirical-physiological models against field data, at both plot and regional scales in the CHF at decadal interval. I found that simple physiological model provided the worst predictions at both plot and regional scales. At plot scale, predictions of aboveground biomass by complex physiological model were the most concordant with field data, suggesting that physiological processes are more influential than forest composition and structure on aboveground biomass at this spatial scale. Hybrid model provided the best predictions at regional scale, suggesting that forest composition and structure may be more influential than physiological processes on aboveground biomass at this spatial scale. Chapter III compared long-term trends of aboveground biomass of the CHF predicted by a landscape model LANDIS PRO 7.0, a hybrid empirical-physiological model LINKAGES v2.2, and a detailed physiological model ED2 under current climate from 2010 to 2300 to determine how long current carbon sink would persist, and what role in carbon sequestration the CHF would play after the current carbon sink diminishes. All models agreed that the current carbon sink would persist at least to 2100s. There were two different patterns of carbon dynamics after carbon increment diminished to zero. LINKAGES and ED both predicted prolonged periods of relatively stable carbon densities, with minor declines, until 2300. While LANDIS PRO predicted a period of carbon source between 2110s and 2260s, followed by another carbon sink period of approximately 100 years, thus a distinct carbon cycling dynamics. In Chapter IV, I used a simple physiological model PnET daily version to study effects of single factor of climate change, CO2 fertilization, nitrogen deposition, as well as all possible combination of these three environmental factors on ANPP in an ecological subsection (Current River Hills) in the CHF from 2010 to 2099. I also used a hybrid empirical-physiological model LINKAGES v2.2 to study the effect of forest aging, and combined effects of forest aging and climate change on ANPP. Predictions of the simple physiological model showed that all three future climate trajectories (CanESM2, GFDL-ESM2M, and MIROC5 under CMIP5 RCP 8.5 pathway) had negative effects on ANPP, both CO2 fertilization and nitrogen deposition had positive effects. CO2 fertilization could noticeably alleviate the negative effects of climate change on ANPP, and can boast positive effect when combined with nitrogen deposition. Combined effects of nitrogen deposition and climate change differed little from that of climate change alone. Combined effects of all three environmental factors showed relatively small change on ANPP. Predictions of the hybrid empirical-physiological model suggested that forest aging did not have significant effect on ANPP in the CHF during the 21st century as ANPP stayed relative stable. And when forest aging was combined with climate change, the stable trend of ANPP still did not show substantial change.