Glen Canyon Park - Future Management of Glen Canyon Park

Future Management of Glen Canyon Park

The city government of San Francisco mandated the development of management plans for all the "natural areas" under the city's control, and this process culminated in release of the Significant Natural Resources Areas Management Plan in February 2006. The plan favors the re-establishment of native species and species diversity in the city's parks. Some aspects of the plan have been controversial. For example, the plan envisions the removal of some large, mature trees (often eucalpytus, which was imported from Australia) to favor smaller native plants. The plan also includes new restrictions on recreational use of the park, such as the closure of some trails and of some areas for rock climbing, and prohibitions against unleashed dogs.

In Glen Canyon Park, about 20 mature eucalpytus trees were removed in 2004 as part of an effort to increase the diversity of species living along Islais Creek. The plan envisions the removal of an additional 120 trees (of the total of 6000 trees in the park) to further improve the creek, to increase the extent of the park's grasslands, and to promote forest understory plants. The plan also seeks to restore some open-water areas along the creek, which is presently nearly totally obscured by the willow thickets. The change in the creek would be established both by re-planting sections of the creek's banks with different plants and by the introduction of "scouring" structures.

Glen Canyon Park formerly supported populations of two rare species: the "vulnerable" San Francisco forktailed damselfly and the "endangered" Mission blue butterfly. The plan proposes changes in the management of the park that would promote self-sustaining populations of these insects. The damselfly population in the park was studied by John Hafernik and his colleagues in the 1980s prior to its local extinction; they re-introduced a population of these damselflies in 1996 that persisted for two seasons. The damselflies need open water habitat, which has proven difficult to maintain.

There has been a declining population of Mission blue butterflies at the nearly contiguous Twin Peaks Natural Area; while park employees logged about 150 butterflies in the 1980s, only four were found between 2001 and 2007. A reintroduction was done in April 2009. Reintroduction may also be possible in Glen Canyon Park. Here the main issue appears to be re-establishing the native plant "silver bush lupine", whose leaves are the larval food of these butterflies. A substantial fraction of Glen Canyon Park is now covered by non-native species including eucalyptus forest (17 acres), French broom (6 acres), and field mustard, but no specific proposal for re-introduction of the lupine was included in the Management Plan.