The Catalina Island mountain-mahogany (Cercocarpus traskiae) is thought to be one of the rarest shrubs in the continental United States. It grows naturally only in one gully system on the south side of the sland. Early monitoring revealed that this plant was not successfully reproducing, and several individuals were fenced to exclude browsing animals. This resulted in improved regeneration for these individuals. In 1999, the entire gully was fenced against all introduced herbivores, enclosing 112 acres.
Each summer, Conservancy biologists visit the gully to assess the health and growth patterns of the individuals. Only 6 of these are pure Cercocarpus traskiae. Five individuals are hybrids meaning genetically they are a combination of Cercocarpus trakiae and Cercocarpus betuloides blancheae. The genetics of the 3 remaining individuals has not been tested so it is unknown if they are pure or hybrids.
The monitoring consists of measuring the diameter of the shrub, the amount of flower/fruit production, canopy dimensions, and overall health. Associated species and any fungus or insect damage is also noted. A search is conducted in the vicinity of each shrub for new seedlings. All seedlings and saplings are marked and tracked by recording height and vigor.