Wilken, Dieter .
Life history traits and recovery of the endangered island endemic, Boechera [Arabis] hoffmannii (Brassicaceae).
HOFFMANN’S rock cress is a monocarp restricted to five known locations on Santa Cruz and Santa Rosa islands, California. Loss of habitat and threats to survival have included sheep grazing, feral pigs, and competition from alien grasses. Field and experimental studies over a 10-year period focused on estimating age structure, demography, breeding system, and ecological parameters determining recruitment and survival. Field studies were conducted at two populations on Santa Cruz Island, one having 40-70 reproductive plants per year, the other with 0-3 reproductive plants per year. Hoffmann’s rock cress is self-compatible and autogamous, although field observations suggest visitation by bee flies (Bombyllidae). Flowering takes place from February to April, with fruits maturing by late June. Most plants live for 3-4 years prior to flowering and produce 1500-3000 seeds, which are dispersed by gravity and wind. Less than 10% of reproductive plants survive to the following year, but generally show reduced reproductive capacity. Highest mortality among seedlings and among vegetative plants occurs during the summer of the first year following germination. Survivorship is enhanced by several factors, including shade provided by shrub canopies, proximity to cool, moist air masses during the summer, and absence of competitive herbaceous species. An understanding of life history traits and ecological distribution was used to design an experimental recovery plan initiated in 2005, although success in establishing self-sustaining populations can not be predictably evaluated for at least 3-5 years.[c.e.:srb]
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1 - Santa Barbara Botanic Garden, 1212 Mission Canyon Road, Santa Barbara, California, 93105-2199, USA
Presentation Type: Oral Paper:Papers for Topics
Date: Tuesday, August 1st, 2006
Time: 4:45 PM