Title: Boreal ecosystem responses to climate change
Description: The anthropogenic climate change is modifying terrestrial ecosystem structure and function, especially in boreal regions. The responses from the ecosystem will in turn affect the climate, forming a land-atmosphere feedback loop. To understand the future consequences of large-scale changes, simulation modeling is the powerful tool used in this thesis. In chapter 1, I briefly review the literature on terrestrial ecosystems under climate change to highlight the current understandings of land-atmosphere feedbacks and anticipated changes in boreal regions. In chapter 2, using an inverse modeling scheme, I estimate temperature and moisture dependencies of soil carbon decomposition in a global scale. This analysis indicates the importance of boreal regions for the global carbon budget, due to physical characteristics (i.e., low temperature and high humidity in boreal soils) and chemical recalcitrance of boreal vegetation. In chapter 3, I simulate carbon and hydrological dynamics of a boggy black spruce stand in continental Canadian boreal region, by coupling peatland biogeochemical processes to a physical land-surface model. This study emphasizes the sensitivity of peatland to climate change because of a positive feedback between soil moisture and peat depths. In chapter 4, I apply the modeling scheme in chapter 3 to a boreal fen, with a process-based model of methane emission. The sensitivity to climate change of the fen is stronger than that in the boggy stand due to the larger range of water table fluctuations.

A massive carbon loss and reduction in methane emission from the fen are observed in the simulation. In chapter 5, I reproduce the current and future patterns of forest dynamics of the central Canada, using an ecophysiology-based model. Changes in temperature moisture, fire frequency, and CO 2 concentration affect the patterns of growth, competition, and succession in the forest. In chapter 6, I analyze the significance of local ecological effects on regional tree ring patterns. In closed-canopy stands, local interactions among neighbor trees affect tree growth as strong as regional climatic variations.