An overwintering site must not only contain the right tree species, with branches at the appropriate height and correct orientation, but must also provide correct groundcover, so that monarchs may find insulated pockets of habitat during storms. Additionally, it should contain branches that are buffered from coastal winds, patches of sunshine within which monarchs can warm themselves, adequate moisture to allow monarchs to hydrate, and adequate nectar sources, so monarchs can maintain the energy resources required to survive until the next breeding season.
There are four documented monarch groves on lands managed by the U.S. Forest Service in the Los Padres National Forest in southern California. Xerces Society staff surveyed the overwintering sites and trained Forest Service employees to monitor monarch overwintering sites on Forest Service lands. In addition to surveying the four documented sites, they searched for undocumented monarch groves within the forest and developed a site-specific land management plan to ensure that these sites are not damaged by future activities.
The Xerces Society is collaborating with a leading monarch habitat specialist, Stuart Weiss (of the Creekside Center for Earth Observation, Menlo Park, CA), to develop a handbook for management and maintenance of western monarch overwintering sites. An additional management plan developed by Weiss for the Monarch Grove Sanctuary is available online here.