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A shrub is a low-growing woody plant that branches out from the base. On the Bull Creek Nature Preserve, shrubs are found growing within the understory of woodland areas as well as scattered across savannah habitats. Shrubs provide forage for browsing animals, such as white-tailed deer, seeds and fruit for birds, and habitat or cover for many species, including nesting sites for the endangered black-capped vireo.

Along the trail, shrubs (and plants in general) are an excellent place to look for insects and spiders. Insects rely upon plants to provide habitat as well as food (i.e. leaves, sap, bark). While most insects feed on a wide range of plant species, some are adapted to feed only on a specific species. For instance, the Monarch caterpillar feeds exclusively on milkweed. Plants also provide a surface for insects to lay eggs upon and shelter from insectivorous predators like songbirds. Some insects, such as the walking stick and the cloudless sulphur, are specially adapted to mimic the twigs and leaves of plants as a defense mechanism.

Two rare native shrubs found in the BCP are among the 27 species of concern (species that are in jeopardy but have not been listed as endangered or threatened) protected by the Balcones Canyonlands Conservation Plan. Canyon mock orange and Texabama croton are endemics, meaning that they only occur in a certain limited area. Canyon mock orange is a small, deciduous shrub with white flowers that grows on limestone rock outcrops. Texabama croton is a semi-evergreen shrub, which will keep its leaves during mild winters. Texabama croton has leaves with a silvery underside and pale yellow-green flowers. It grows on forested limestone slopes, forming large colonies and often dominating the shrub layer.