IN-SITU WEATHERING OF CALCIUM-BEARING MINERALS IN UNEVEN-AGED SILVICULTURAL SYSTEMS

Supplying one-fourth of the nation’s wood volume, timber harvests in the northeastern United States are integral to its economy. However, these harvests are decreasing due to shifts in land management, biotic stresses, and nutrient limitations. The effects of harvesting severity and repeated harvests on long-term nutrient sustainability is uncertain, but net losses of base cation nutrients (e.g., calcium, magnesium, and potassium) can result in decreased woody biomass, potentially greater than 20%. 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.

By identifying and quantifying 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 a range of uneven-aged harvest regimes were leveraged. Using a root exclusion in-soil mesh bag approach, 3 grams of apatite, calcite, and anorthite 200 μm powders were weathered in place for 1 year at a depth of 30 cm. Mineral grain surface transformations were determined by SEM differential imaging between pristine and weathered minerals. Microscale textures were compared to mass balance transfer values to characterize harvest-induced Ca mineral weathering.

Initial results detail how weathering for a year contributed to limited mineral-specific surface alteration. In agreement with mineral weathering susceptibilities, calcite and albite presented more intense surface corrosion features than apatite. However, evidence of surface coatings were observed on apatite, suggesting armoring of the mineral in the tested conditions. First year results, out of our multi-year experiment, do not yet paint a clear picture of the effects of management practices on nutrient resilience across sites, but some aspects suggest that more frequent, low intensity management schemes result in lesser rates of inorganic nutrient depletion. Initial results show that harvest practices have a non-negligible effect at the microscale, suggesting that harvest protocol could be adapted to improve nutrient resilience in managed timber forest systems.