**Abstract**

This chapter considers herbaceous and woody plants near the 1800s era hydrocarbon extraction areas (HEAs) in Wiikwemkoong Unceded Territory (WUT) on Manitoulin Island, Lake Huron, Ontario, Canada. Plant community assessment used patterns of diversity and distribution at five field and six forest sites to assess the response of the plants to HEAs. These sites receive brine episodically from HEAs and natural seeps over the Collingwood Oil Shale Formation. This brine contains high concentrations of chloride and sodium along with total dissolved solids that exceed 100,000 mg/L. Exposure to brine is identified as the causative factor shaping plant distribution, survival, size, leaf bleaching (i.e., chlorosis), and dead branches on woody stems. These sites demonstrate an ecotone of disturbance defined by transition from natural plant community to dominance by eastern poison ivy (EPI, *Toxicodendron radicans* L.). Disturbed sites within brine drainage areas are dominated by EPI, reflecting tolerance to elevated salinity due to rhizome growth strategy. Evaluation of the plant communities and EPI allowed for preparation of a framework that can be used to guide interpretation of response of plants to drainage of brine from HEAs and natural sources beyond WUT.

**Keywords:** brine, community responses, hydrocarbon, *Toxicodendron radicans*, Manitoulin Island, Canada
