Birch A birch is a thin-leaved deciduous hardwood tree belonging to the genus Betula, which is part of the family Betulaceae. This family also includes alders, hazels, and hornbeams, and it is closely related to the beech-oak family Fagaceae. Related Articles: Woodland Bird SpottingRedpoll (Acanthis SPP) Species Guide: Appearance, Diet, Habitat, Behavior, Stats, And Conservation StatusGlossary: AlderSiskin (Spinus spinus) Species Guide: Appearance, Diet, Habitat, Behavior, Stats, And Conservation Status