Crop Tree Enhancement of Green Ash (<i>Fraxinus pennsylvanica</i>) in a West Tennessee Hardwood Bottom

Crop tree enhancement is a forest management technique undertaken to maintain, enhance, and improve the species composition, growth rate, and stem quality of stands so that management objectives may be better and more quickly accomplished. In 1996, a crop tree enhancement study involving green ash (Fraxinus pennsylvanica) in a 16-year-old, naturally regenerated, mixed-species, pole-sized, bottomland hardwood stand was initiated at Ames Plantation in West TN. Treatments included a crown-touching release, a crown-touching release plus one-time fertilizer application, and a control, applied in a randomized block design with five 25-crop tree repetitions of the three treatments. Initial crop tree diameters, heights, clear bole lengths, crown dimensions, and crown classes, as determined by the crown rating system for southern hardwoods (Meadows et al. 2001), were recorded at this time. Eighteen years later in 2014, measurements were again recorded. Additionally, competing species, determined with a 10F wedge prism, and the depth to mottled soil horizons for each crop tree were recorded. Growth in diameter, height, crown length, and crown spread over the 18-year study period were calculated. Analysis of variance tested for differences in treatment response. Relationships between the depth to mottled horizons, treatment response, and block layout were examined with chisquare analysis and correlation analysis. Release and release plus fertilize treatments generally did not differ in diameter, height, crown expansion, and crown class. However, both outperformed the control treatment. Release and release plus fertilize treatments maintained a greater percentage of upper canopy green ash crop trees than the control. Crop trees of different crown classes responded to release at varying degrees, with the largest increases in diameter and crown expansion occurring in the codominant class. Releasing dominant crop trees did not yield significantly greater growth, while some intermediate trees benefitted from release. The depth to mottled horizons fluctuated across the study area, but with little relationship to crop tree growth. Competing species composition differed at varying depths to mottled horizons. Crop tree enhancement appears to be a beneficial management strategy for improving growth rates and maintaining the upper canopy status of green ash in mixed-species, bottomland hardwood stands.