Boreal forests occur at high elevations, particularly on the peaks of the Catskill Mountains. These forests include balsam fir (Abies balsamea), paper birch (Betula papyrifera), mountain ash (Sorbus americana), and red cherry (Prunus pensylvanica). Wild raisin (Viburnum cassinoides) and mountain holly (Ilex mucronata) are shrubs that grow in high elevation swamps, bogs, and ledgetops.