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Treto, Victoria

Geology

2023

M.S.

Timber harvests in the northeastern United States are integral to its economy but shifts in land management, biotic stresses, and nutrient limitations are diminishing forest productivity levels. The effects of harvesting severity and repeated harvests result in net losses of base cation nutrients which decreases woody biomass, potentially as much as 20%. Calcium (Ca) serves to regulate critical processes linked to tree growth and ecosystem health, but it is the quickest depleting base cation from northeastern forest soils. As a result, the quantification of nutrient-bearing minerals in forest soils is fundamental in predicting long-term sustainability of wood production. Further, the determination of the weathering processes responsible for unlocking nutrients in soils allows us to identify more sustainable management practices in these forests. The objectives of this thesis are: (1) to characterize the cumulative effects of parent material composition and ecosystem aging on Ca mineral nutrient dynamics in forested ecosystems and (2) ascertain mechanisms driving inorganic Ca nutrient availability. By identifying and quantifying parent material-driven primary mineral nutrient pools in soils and examining the micromorphological weathering pathways of important Ca-bearing phases, we investigated key mechanisms impacting inorganic Ca-release kinetics in northeastern forest soils. Three forests with an extensive record of management and uneven-aged harvest regimes were studied. At each forest site, soil samples were characterized to determine Ca nutrient states. Apatite, calcite, and anorthite powders were weathered in-situ for 1 year at a 30 cm depth. Physical and chemical mineral grain surface transformations were determined by SEM/EDS differential analysis between fresh and weathered mineral surfaces. Soil chemical analysis revealed a strong parent material control on nutrient states across sites. In-situ weathering suggested soil acidity, and parent material sourcing governed Ca mineral weathering processes and intensity. The development of abiotic alterations like etch pitting and neoprecipitates, as well as biotic features such as hyphal colonization of the mineral surface reflected differences in soil chemical composition. Our results also suggested that maturing stands supported by soils formed from Ca-deficient glacial till sources, and whose soil bears relatively lesser P content, are more reliant on inorganic Ca nutrient sources. This research confirmed that micro-scale observations on the nature and intensity of weathering of discrete minerals are adapted to the determination of macro-scale controlling factors for nutrient dynamics in forest soil. The combination of abiotic and biotic weathering processes and site-specific expressions suggests that forests atop soils derived from Ca-deficient parent material more intensely exploit inorganic sources of Ca and could benefit from Ca-amendments, like highly Ca-available lime or ash, to ensure optimized soil nutrient states for sustainable forest productivity