Geographic distribution of rare plants on public lands within the Red Mountain Study Area and a study of the population dynamics and reproductive biology of McDonald's rock-cress, Arabis mcdonaldiana Eastwood

The geographic distributions of Arabis mcdonaldiana, Eriogonum kelloggii, Sedum laxum ssp. Eastwoodiae and Silene campanulata were mapped and a total of thirty-seven new localities were recorded for these taxa in the vicinity of Red Mountain. In addition, a more indepth [sic] study of the population dynamics of Arabis mcdonaldiana was undertaken, with a series of thirty 5 square meter permanent plots located at random within the Red Mountain Study Area. Arabis was observed to maintain relatively stable mean population densities and canopy coverage values over the three years of the study, and artificial crossing and bagging experiments determined it to be a self compatible facultative outcrosser, with two species of bumble bee (Bombus caliginosus and B. edwardsii) the principal pollinating agents. Although silique predation by rodents and other animals may be periodically significant, Arabis' relatively long life appears to buffer the species against short term lapses in reproductive effectiveness. All observations indicate that Arabis mcdonaldiana is restricted to Huse Soils and appears to share habitat requirements with Erigonum kelloggii and Ceanothus pumilus. The continued survival of Arabis mcdonaldiana, as well as that of the other three species of geographically restricted plants requires the reclassification of the Red Mountain Area as critical habitat essential for the long term maintenance of these species populations.