Date of Award
Master of Science
Natural Resource Ecology and Management
Agroforestry practices are tree-based systems (such as tree windbreaks) strategically integrated into agricultural landscapes to variously and often simultaneously produce marketable products directly while enhancing the production of other crops, and/or provide a broad array of environmental services such as carbon sequestration. Tree windbreaks have been planted extensively in the U.S. Great Plains following a large tree planting program during the Dust Bowl of the 1930’s. Windbreaks are one or multiple rows of trees and shrubs that are established for reducing wind speed. Windbreaks have been assessed for their ability to provide cellulosic bioenergy feedstock and carbon (C) sequestration opportunities. The integration of deep-rooted trees in the landscape has been assessed for enhancing carbon (C) storage and sequestration potential in biomass and in deeper soil profiles. Information on soil C storage and dynamics of trees, especially in deeper soil profile is, however, inadequate. This thesis presents a series of integrated studies to advance understanding of the impact of trees on soil organic carbon (SOC) storage and on soil physical and chemical properties. For this, the study evaluated eight tree plantings within the original Prairie States Forestry Project (PSFP) shelterbelt planting zones for representative tree species, soils, previous land use, and climate in four Northern Great Plains states North Dakota, South Dakota, Nebraska, and Kansas (ND, SD, NE, and KS, respectively). In the first study presented in Chapter 2, changes of SOC stocks and other soil properties were quantified on soil samples collected to 1.25 m beneath the tree plantings and in the adjacent farmed fields. We found that soils beneath trees had higher SOC stocks as compared to the adjacent fields. Tree plantings decreased bulk density, and enhanced soil aggregation as compared to the adjacent farmed fields. In addition, higher SOC stocks were found in the subsurface soil beneath trees and the adjacent farmed fields as compared to the surface soil thus, demonstrating the importance of studying deep SOC especially when regional C sequestration potential is being assessed. In Chapter 3, Stable C isotope-ratios technique was used to quantify the relative SOC contribution of tree C to the total SOC stocks. More tree-origin C was found in tree soils and at deeper depths indicated that tree presence promoted storage of C. Overall, trees show significant potential for the sequestration of SOC compared with the adjacent farmed-fields.
Ala Ali Khaleel
Khaleel, Ala Ali, "Soil carbon sequestration potential of tree windbreaks in the U.S. Great Plains" (2018). Graduate Theses and Dissertations. 16607.