The significant natural resources of Nockamixon State Park include a diverse geology including a feature classified as an outstanding scenic geologic feature of Pennsylvania. Outcrops of Brunswick Formation siltstone, Lockatong argillite, and diabase can be observed within the park. The park provides habitat for 7 species of vascular plants classified as endangered, threatened, vulnerable, or undetermined by the Pennsylvania Natural Heritage Program and four additional watch list species. Breeding populations of 2 PNHP-listed animals, redbelly turtle and great blue heron, are also known from the park. Mature forest communities occur primarily on diabase geology to the north of the lake and on steep slopes elsewhere. Canadian hemlock, which was formerly a dominant species in hemlock, white pine, red oak, mixed hardwood forests on the south side of the lake, is dying due to infestations of hemlock woolly adelgid and elongate hemlock scale. Its loss threatens not only this forest community, but also the large stand of Canada yew it contains. The bulk of the land supports successional communities that have developed on former farm fields. In time secondary succession will restore forest cover to these areas, however the process of succession has been slowed by the presence of dense stands of invasive, non-native shrubs such as multiflora rose and autumn olive. Native deciduous trees have overtopped the early successional shrubs in some areas, in others it will take longer. Rose rosette disease, which is present on multiflora rose throughout the park, may allow trees such as red maple and ash to penetrate the shrub thicket more quickly. Conifer plantations are also a prominent feature of the landscape; they too will eventually be invaded by native deciduous trees, a process that has already begun in some areas. The inventory recorded 501 species of vascular plants, 32 lichens, 24 species of reptiles and amphibians and 267 species of birds, of which 83 species breed in the park. Recommendations address ongoing monitoring needs, the protection of intact mature forest communities from fragmentation or other sources of disturbance, and control of localized colonies of invasive species.