PARENT SESSION
Poster Session 20: Invasive Species
Wednesday, August 10, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal
Population size structure and spatial pattern in native (Dirca palustris)and exotic ( Lonicera maackii) forest understory shrubs.
Turner, Bryan*,1, Schulz, Kurt 1, Jones, Cynthia1, 2, Vaughan, Audrey1, Hoover, Audra 1, Zasada, John3, 1 Southern Illinois University Edwardsville, Edwardsville, Illinois2 URS Corporation, Portland, Oregon3 Forest Service, North Central Forest Experiment Station, Grand Rapids, Minnesota
ABSTRACT- Eastern leatherwood (Dirca palustris L.) and Amur honeysuckle (Lonicera maackii Maxim.) represent two successful forest understory shrubs with dichotomous characteristics. Leatherwood is a slow-growing tremendously shade tolerant native shrub of eastern North America. Amur honeysuckle is an aggressive exotic species which grows quickly and is moderately shade tolerant. Leatherwood produces dry drupes that are scarcely transported by animals; the ripe seeds are apparently consumed on the spot by rodents. Honeysuckle produces an abundance of red berries that are taken by birds and dispersed. We examined leatherwood and honeysuckle in mapped plots to determine if their differing niches (leatherwood, the long persistent native and Amur honeysuckle the aggressive invader), were revealed in the size structure and spacing of individuals. We predicted large populations of seedling honeysuckle and little evidence of aggregation. We predicted smaller populations of seedling leatherwood and strong aggregation owing to limited seed dispersal. Study populations were located in the Ottawa NF, MI (leatherwood), and Madision County, IL (honeysuckle). Shrub densities ranged 700-1400 individuals ha-1 for both species, but there was no sign that the habitat was saturated. Populations of both species appeared to be increasing. In the two most mature honeysuckle populations, containing individual shrubs with more than 8 m2 canopy cover, more than 25% of individuals were juveniles with <1 m2 canopy cover. Almost no seedlings were present. The leatherwood populations showed a smaller proportion of juveniles, but more abundant seedlings, with one plot having more than half the population as seedlings <0.20 m tall. The spatial patterns of the two species are profoundly different. There is no strong pattern of aggregation in any size class of honeysuckle, and therefore no halo of offspring around mature honeysuckle. Leatherwood are aggregated and a halo of offspring is visible around mature individuals. The absence of extensive honeysuckle reproduction in comparison with leatherwood suggests its dominance in the forest understory may be declining.
Key words: invasive species, Lonicera maackii, Dirca palustris, understory shrub