The influence of disturbance on the demography of the rare pine barren gentian (Gentiana autumnalis) in New Jersey
Wild fire suppression in the New Jersey Pine Barrens has limited the habitat available for early successional plant species through most of the region. In the place of natural disturbance, low intensity prescription burns and roadside mows have been used to reduce the encroachment of vegetation and reduce fuel load. While these land management practices are often used in the New Jersey Pine Barrens, little is known of the effects these anthropogenic disturbances have on rare plant populations. We used the rare, early successional Pine Barren gentian (Gentiana autumnalis) to examine demographic variations in disturbed (prescription burned and mowed sites) and undisturbed (no disturbance in 5+ years) sites. We used a repeated measure design over three successive years (2011-2013) to monitor the demography of G. autumnalis in both disturbed and undisturbed sites. We compared plant densities, insect visitation, seed set, mycorrhizal colonization and population growth projections in disturbed and undisturbed sites. What is learned by studying this species in varying land management practices can then be used to better manage other rare, early successional plant species in pine barren habitats.
We found that plant density, insect visitation and seed set were all significantly greater in disturbed sites than undisturbed sites. Previously undisturbed sites where disturbance was introduced experienced increased density, flowering percentage and patch areal size. Additionally, the greatest levels of arbuscular mycorrhizal fungi colonization and insect visitation were measured in disturbed sites. While mowing during the growing season, succession, and seed predation by moths remain potential threats, some management practices conducted after the growing season improved the viability of G. autumnalis patches. A better understanding of how disturbance can be employed to facilitate a positive response in rare plant communities, will be critical for rare plant conservation in disturbance-dependant ecosystems such as the New Jersey Pine Barrens.