RESTORATION OF MARITIME FORESTS: EVALUATING LIMITING FACTORS OF QUERCUS VIRGINIANA (LIVE OAK) REGENERATION
thesisposted on 17.01.2019, 00:43 by Emily C. ThyroffEmily C. Thyroff
Maritime forests are a critical interface between ocean and terrestrial ecosystems, providing important ecosystem services and functions. Along the U.S. southern Atlantic coast, maritime forests are dominated by Quercus virginiana. Maritime forests and Q. virginiana have been heavily impacted by conversion to agriculture, residential development, and pine stands. Southern pine beetle outbreaks have led to salvage and thinning silvicultural treatments of pine stands which offer an opportunity to restore more complex maritime forests. This research project is comprised of two experiments which allowed me to study the performance of planted Q. virginiana seedlings in response to (1) animal browse, (2) competing vegetation, and (3) varying overstory pine canopies. For both experiments, one-year-old bareroot seedlings were planted as split-plot experimental designs. The first experiment evaluated control of deer browse (fenced and not fenced whole plots) and competing vegetation (0, 1, and 2-yr vegetation control subplots) as independent variables. Overall seedling survival was 60% after two years. There was a significant interaction between deer browse and competing vegetation for seedling height, diameter, crown width, and lateral branches. Seedlings were larger for all response parameters when fenced with vegetation control. Vegetation control significantly improved seedling performance only in fenced plots, indicating a shift in pressure from herbivory to competition when deer were excluded. Foliar nitrogen (N) was significantly greater in fenced plots than non-fenced plots and in 2-yr vegetation control subplots than non-weeded subplots. The second experiment evaluated varying pine overstories (clearcut, heavy thin, light thin, and no thin whole plots) and competing vegetation control (0 and 2-yr vegetation control subplots). Overall seedling survival was 78% after one growing season, with clearcut plots at the greatest survival (83%) and no thin at the lowest (72%). Seedling growth and foliar nitrogen were significantly greater in clearcut plots followed by the heavy thin, light thin, and no thin plots. Vegetation control consistently promoted seedling height, but was only beneficial to diameter and crown width in clearcut/heavy thin plots. Q. virginiana seedlings demonstrated plasticity in their ability to acclimate to the varying microclimates created by silvicultural treatments, as demonstrated by light response curves, stomatal density, and specific leaf area. These results highlight the importance of fencing to remove deer browse, introducing light in the understory, and further improving seedling performance by removing competing vegetation.