Invasive Species Biology and Ecology

Celastrus orbiculatus (Oriental bittersweet)

Stacey Leicht (University of Connecticut) compares the invasive Oriental bittersweet (Celastrus orbiculatus) with the native American bittersweet (C. scandens). The invasive bittersweet has been on the rise in New England, while it appears that the native bittersweet is declining. The purpose of this research is to determine whether the invasive bittersweet is directly affecting the native, or if there are other explanations for the native’s apparent decline. She has conducted a study in a common garden setting to determine the effects that light, soil, density and the availability of stakes to climb on have on the invasive and native bittersweets. Using the results of this research in conjunction with research on the habitat preferences of these two species, the attributes of the invasive that make it so successful will be determined. For further information you can email Stacey at: sleichtyoung@usgs.gov

Cytisus scoparius (Scotch broom)

Roslyn Selsky (University of Connecticut) performed a case study of the possible New England invasive, Cytisus scoparius (Scotch broom). C. scoparius is a shrub in the pea family (Fabaceae) that is classified as invasive in similar habitats in Australia, New Zealand and the west coast of the United States. It has drawn attention in New England as a possible invasive due to its spread on Cape Cod and the surrounding islands, but its ecology and current invasive status in these locations lack proper documentation. To determine if C. scoparius is invasive in New England, Roz visited these locations to conduct field studies on its population structure and seed viability. She then conducted greenhouse studies on C. scoparius’s germination and growth requirements to determine its success as a possible invasive.
The results of this research suggests that C. scoparius is not currently invasive in New England. This conclusion is supported by the presence of B. villosus (a seed eating beetle) and the low temperatures of New England, which seems to be keeping the population of C. scoparius in check. However, increased disturbance, continued introduction and the possible effects of global warming may promote the future spread of C. scoparius across the landscape of New England. For further information you can email Roslyn at: roslyn.selsky@po.state.ct.us

Impatiens glandulifera (Ornamental jewelweed)

Nava Tabak (University of Connecticut) is researching the invasive potential of the annual jewelweed Impatiens glandulifera in New England. This species is native to the Himalayan region and considered invasive in several European countries, but currently has a limited distribution in New England. A seedling transplant experiment was designed to determine the microhabitat needs of this riparian weed, specifically soil moisture and light levels. Several greenhouse germination experiments are also aimed at defining microhabitat needs, as well as comparing desiccation tolerance of the seeds of Impatiens glandulifera with its native congeners , I. capensis and I. pallida . Nava has also updated the distribution information for Impatiens glandulifera in New England. For further information you can email Nava at: tabak@bard.edu

Cynanchum louiseae and Cynanchum rossicum

Bob Capers (University of Connecticut and The connecticut Agricultural Experiment Station Department of Soil & Water) is investigating the ecology and reproductive biology of Cynanchum louiseae and C. rossicum (Swallow_worts), looking specifically at the prevalence and ecological consequences of selfing and polyembryony. For further information you can email Bob at: Robert.Capers@po.state.ct.us

Invasive plant fruit dispersal

Nancy LaFleur (University of Connecticut) is investigating how woody, fruit-producing, invasive plants are spread by frugivorous birds. To date, she has focused on one invasive fruit-eater, the European starling, and three invasive plants: autumn olive, Asiatic bittersweet and multiflora rose. Nancy has investigated bird preferences for these particular invasive fruits, and is in the process of expanding her work to determine how far starlings move their seeds. In the future she hopes to investigate historical links between populations of invasive plants and frugivorous birds, and to construct a model that explores how disperser effectiveness influences the ability of a plant to spread. For further information you can email Nancy at: Nancy.Lafleur@uconn.edu

Predictive Distribution Modeling

IPANE has supported several lines of research on predictive distribution modeling. Predictive distribution models are aimed at enhancing early detection and effective management capabilities, as well as identifying environmental factors that are important in determining the distributions of various invasive species.

Melissa Woelfel (University of Connecticut) used General Linear Models to make predictions of the distributions of Berberis thunbergii, Celastrus orbiculatus, Elaeagnus umbellata, and Rosa multiflora in New England. She used IPANE locality data for this purpose, and both climate variables and land use/ land cover variables as predictors.

Stacey Leicht has used Bayesian regression models to examine the potential distribution of Celastrus orbiculatus in New England. This statistical approach allowed for the input of information from the species' native range (China) into the model, along with climatic explanatory variables.

Nava Tabak has compared Bayesian regression models to GARP (Genetic Algorithm for Rule set Production) models for predicting the potential spread of Impatiens glandulifera in New England. A native distribution (Himalayan region) and data sets from Europe (where the species is invasive) were used along with an updated distribution for New England. The performance of different climate layers as predictive variables for distributions in Europe was examined, and insights are now applied to New England models.

Invasive Plants and Land Use History

Eric Mosher (University of Connecticut) investigated the relationship between land use history and the distribution of a suite of six invasive woody plants (Berberis thunbergii, Celastrus orbiculatus, Elaeagnus umbellata, Euonymus alata, Lonicera morrowii, and Rosa multiflora). Using aerial photography from 1934, 1951, 1970 and 1991, Eric constructed a set of geo-referenced aerial mosaic images for the Meshomasic forest region of central Connecticut. By digitizing and then comparing the land use and land cover features from each period of time, it is possible to create spatially and temporally explicit polygons that indicate areas of land use change.
Eric sampled over 600 sites in the summer and fall of 2003.  A statistically significant hierarchy of woody invasion was evident from the results.  Recently abandoned agricultural fields had the greatest incidence and abundance of woody invasive plants, followed by agricultural fields that had reverted to forest, which were followed by residential/commercial areas, which in turn were followed by areas that had not undergone a change in land-use during the study period.  Regression modeling demonstrated that land-use history, canopy closure levels and distance from the nearest vegetation edge were the most predictive variables for woody plant invasion.  Berberis thunbergii was the woody invasive most associated with older post-agricultural land-use scenarios, whereas Celastrus orbiculatus was the most strongly associated with residential/commercial land-uses and anthropogenic disturbances.