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Harvard Forest REU Symposium Abstract 2011

  • Title: A regional ragweed distribution survey: Identifying factors that predict ragweed presence
  • Author: Samuel M Safran (Middlebury College)
  • Abstract:

    Common ragweed (Ambrosia artemisiifolia) is a widely distributed annual weed and produces pollen that is the leading cause of hay fever in North America. While understanding its current distribution is important for public health, most efforts to map allergy “hot spots” today are done at a large scale that is not useful on smaller, more relevant regional levels. Additionally, since ragweed’s growth and pollen output increase at warmer temperatures, with higher atmospheric CO2 concentrations, and in disturbed habitats, there is also interest in understanding its distribution under predicted future environmental scenarios. In this study, we conducted a presence-absence survey across New York, Massachusetts, and Vermont aimed at identifying climate and land use variables influencing ragweed distribution. We used the PRISM climate layer and state-level land cover layers in GIS to identify nine climate-land cover categories in each state. By randomly selecting ten points within each category, we generated a stratified random sample of 90 sites per state. At each site, we constructed a 20 m2 plot and recorded the plant’s abundance and local land cover data. A preliminary analysis of 200 of the 270 sites using bagged Classification and Regression Tree (CART) analysis indicates strong positive correlations between observed edge habitat and ragweed presence as well as between observed forest habitat and its absence. The strongest predictor of ragweed presence was found to be distance to nearest road, a variable derived remotely with GIS. Some clear climate effects—including average precipitation and temperature during the growing season—were also shown to be highly relevant predictors of ragweed presence. This dataset will be used to test the accuracy of free and simple methods for identifying ragweed habitat, to model its distribution under current climate conditions, and to map regional allergy hotspots under future climate scenarios at a scale relevant to an individual’s exposure to pollen.

  • Research Category: Regional Studies