Semester of Graduation

Summer 2020

Degree

Master of Forestry (MF)

Department

Renewable Natural Resources

Document Type

Thesis

Abstract

Ecological processes controlling transition areas of coastal wetlands between marshes (not forested) and swamps (forested) are poorly understood, despite important ecosystem services provided and strong interest in managing for ecosystem structure and function. The objective of this work was to identify how soil chemistry and stand density control individual-tree growth of the important coastal species baldcypress (Taxodium distichum (L.) Rich.) and pondcypress (Taxodium distichum var. imbricarium (Nutt.) Croom) along a coastal salinity gradient. Tree cores, soil samples, and stand density measurements were collected for sixty cypress trees at the coastal Joyce Wildlife Management Area, Louisiana, which is a former forested wetland that partially transitioned to marsh following salt-water intrusion in the 20th century. There was strong correlation between tree-ring chronologies and water levels and rainfall as expected. Soil concentrations of sea-water components (S, Na, Mg, Ca) and electrical conductivity of pore water followed the hypothesized geographic gradient across the site of higher values near the source of seawater. Concentrations of these salinity-associated components were higher at 30 cm depth than at the surface, suggesting recent flushing, but concentrations of plant nutrients (P, K, Ca, Mn) were higher at depth, suggesting concentration by plants. Unexpectedly, cypress growth efficiency—basal area increment per sapwood basal area—was not correlated to stand density or soil chemistry. A principal component analysis of tree-level growth sequences indicated that the trees living in higher salinity were proportionally less responsive to high salinity (drought) years as compared to trees further inland. Thus, trees on the forest-marsh edge, which experience the most seawater influence, apparently have some mechanism to compensate for or avoid salinity. The most likely explanation is that microhabitats such as hummocks might be critical in understanding controls on cypress growth and persistence in marginal sites such as this.

Committee Chair

Keim, Richard

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