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Description
Isolated reserves require careful monitoring and management in order to maintain ecological stability. This is especially true in fire-dependent ecosystems, where altered disturbance regimes can be a threat to native species adapted to natural fire regimes. Understanding the status of a population of a given species within a reserve can benefit others by acting as an indicator for the area's general ecological trajectory. I conducted a thorough census of the shrub, Ceanothus verrucosus, at Cabrillo National Monument (CABR), a small, isolated reserve located at the tip of Point Loma in San Diego, California. C. verrucosus germination is triggered by fire. Consequently, recruitment (and thereby, the population's persistence) depends on this disturbance. There has been no fire activity at CABR for over 100 years. A total of 1,249 plants were mapped and were comprised of 1,111 (89%) living individuals and 138 (11%) standing dead individuals. The shape and size of C. verrucosus individuals are highly variable. The majority of plants were mature (77%) or senescent (19%) and there was very little evidence of recent recruitment. Shrub ring analysis with formal dendrochronology techniques was conducted at the Laboratory of Tree Ring Research (LTRR) at the University of Arizona. Shrub ring analysis demonstrates that individuals can live and be reproductive much longer than expected. Surprisingly, the growth patterns differed between the samples of standing dead material and the samples cut from live shrubs. This suggests that the current growth regimes (i.e., variations in cambial activity) may be very different from 50 or 100 years ago. This research allows us to better understand this sensitive species, including the present extent of its distribution at CABR, as well as its current reproductive status. Lack of recruitment has been confirmed, and the distribution of its morphological variability is now documented. This study has also revealed new and unexpected questions about the species' growth rates. Ultimately this work provides a solid baseline for the condition of the species which may now act as the "canary in the coal mine" for the maritime chaparral plant community in the face of a changing climate.
