Thesis (M.S.) University of Alaska Fairbanks, 2008"The objective of this study was to assess the effect of throughfall exclusion (1989-2005) on forest vegetation and soil in upland and floodplain landscape positions. In uplands, imposed drought reduced soil moisture at 5, 10, and 20 cm depths and increased soil C storage by slowing decomposer activity at the surface. In the drought plots, aboveground tree growth was reduced and root biomass in mineral soil was increased. In floodplains, imposed drought did not reduce soil moisture as strongly as it did in uplands, though near-surface soil C storage was still increased as a result of reduced decomposer activity. Floodplain vegetation response to imposed drought differed from that of uplands; imposed drought did not reduce aboveground tree growth but instead reduced root biomass in mineral soil. At both landscape positions, imposed drought accelerated the loss of understory vegetation. Overall, the results of the throughfall exclusion indicated that chronic soil drying is likely to increase forest C storage only in floodplains. In uplands, where soil moisture is more limited, forest C storage is not as likely to change because an increase in soil C may be offset by reduced tree growth"--Leaf iiiBonanza Creek Long-Term Ecological Research Program (funded jointly by NSF grant DEB-0423442 and USDA Forest Service Pacific Northwest Research Station grant PNW01-JV11261952-231), McIntyre-Stennis Research Program at the School of Natural Resources and Agricultural Sciences, UAF, Center for Global Change, and UAF Graduate School1. General introduction -- 2. Landscape position influences the responses of boreal forest vegetation to long-term experimental drought in Interior Alaska -- 3. Long-term (1989-2005) experimental drought increases surface soil carbon storage in an interior boreal forest -- 4. General conclusion -- 4.1. Forest soil and vegetation response to imposed drought -- 4.2. Whole-forest C balance -- 4.3. Recommendations for future research -- 4.4. References
