Existing invasive exotic species and the potential introduction of new invasive species pose a threat to forest biodiversity and function. The PEI National Park invasive species composite measure consists of two annual field measurements: the percentage of forest ecosystem with invasive species present (measured by proportion of 244, 441 m2 quadrats covering the forest ecosystem), and the percentage of total forest area (ha) with invasive species present. The measure includes four invasive plants and one insect: Garlic Mustard (Alliaria petiolata), Japanese Knotweed (Polygonum cuspidatum), Scots Pine (Pinus sylvestris), and Glossy Buckthorn (Frangula alnus), and Gypsy Moth (Lymantria dispar), which is measured for presence only.