Wilson, Chester , Fagen, Justin , Ludwig, Josh , Ralles, Steve .
Demographic and spatial structure in stands of Rhamnus cathartica.
Rhamnus cathartica (common buckthorn) was introduced into the Midwest for hedgerows and as an ornamental, but has escaped cultivation and become a serious pest in woodlands and savannas of the region. We investigated the demographic and spatial structure of a typical stand found in an unlogged upland oak woodland in St. Paul, MN, to determine whether the stand had reached a demographic equilibrium and to what extent it is still dependent upon seeds introduced from nearby cultivated plants. We mapped and measured allĀ individuals found within a 20m X 20m plot located at least 20m from the margins of the woodland. The 1117 individuals were grouped into stage classes based on height. Size distributions were compared with expected curves for stable and growing populations. Spatial autocorrelation and nearest neighbor analysis were used to describe spatial distributional patterns within the stand. Nearest neighbor analysis indicates that each age class is aggregated, with smaller size classes having the highest aggregation. Mature trees display a random spatial pattern. A cumulative frequency distribution of individuals within size classes showed a reverse J-shape indicating the strong possibility of constant recruitment and consistent with a stable population, as opposed to one experiencing sporadic recruitment. Younger age classes seem distributed randomly with respect to the mature trees. Preliminary analysis of the life table suggests that the population is growing slowly. While the local population is stable it still seems dependent upon outside seed sources, at least from the margins of the woodland.
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1 - Universitiy of St. Thomas, Department of Biology, St. Paul, MN, 55105, USA
Presentation Type: Oral Paper:Papers for Topics
Location: 551A/Convention Center
Date: Wednesday, August 4th, 2010
Time: 11:15 AM