Influence of land management on the demography of the Pine Barren gentian (Gentiana autumnalis) in New Jersey

Ryan R. Rebozo

doi:10.17918/etd-7201

Gentiana autumnalis L. (Pine Barren gentian) is a rare early-successional, fall flowering perennial that occurs in the New Jersey Pine Barrens. My study (2011-2013) focused on the influence of management practices on G. autumnalis demography, site conditions, and pollination. I used a repeated measures design to census select G. autumnalis populations that were mowed, prescribed burned, or left unmanaged for a minimum of six years. Sites that were actively managed either by mowing or prescribed burning typically had greater gentian densities, higher percentage of flowering individuals, greater fruit seed set, and mycorrhizal root colonization in Gentiana autumnalis than unmanaged sites. Actively managed sites also had fewer woody plant species, and greater canopy openness. Insect visitation rate to the flowers of G. autumnalis was negatively correlated with heteropecific inflorescence density. Visitors from the family Syrphidae accounted for the greatest percentage of visits to gentian flowers, yet total Bombus visitation explained the greatest variation in fruit seed set of all insect visitors. Total site visitation was greatest in actively managed sites and was positively correlated with fruit seed set. As the number of flowering plants increased in managed sites, average fruit seed set increased in spite of lower individual flower visitation rates, suggesting an allee effect on female fitness. Gentiana autumnalis populations responded positively within two to six months of introduced management in terms of gentian density, percentage of flowering individuals, and average seed set per fruit. Plants added to the population after management were adult, often flowering individuals which suggests this species can remain dormant below ground for at least one year. The percentage of flowering plants at recently managed sites reverted back to pre-management levels 14-20 months after disturbance, suggesting that populations of G. autumnalis may benefit from repeated management. Threats to G. autumnalis include fire suppression, disturbance (e.g., mowing) during the flowering season, deer herbivory, and seed and fruit damage from caterpillar infestation. It is recommended that management practices aimed at the conservation of G. autumnalis focus on maintaining open-site conditions that promote the increased flowering and seedling recruitment that are essential for the long term viability of populations. Site management should be scheduled prior to the beginning of the growth period in April, or after seed set in late November in order to avoid negative impacts to G. autumnalis growth and reproduction. Maintenance of early-successional habitat will also benefit associate plant species, facilitate positive interactions with mycorrhizal fungi, and attract insect pollinators. My study is the first to examine the effects of disturbance on the life history and demography of G. autumnalis in New Jersey, and will be essential for how to best manage this enigmatic species that is symbolic of the New Jersey Pine Barrens.

Influence of land management on the demography of the Pine Barren gentian (Gentiana autumnalis) in New Jersey

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Influence of land management on the demography of the Pine Barren gentian (Gentiana autumnalis) in New Jersey

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