Ivesia webberi

Ivesia webberi is a perennial herb known from seventeen extant occurrences in a small region of northeastern California and western Nevada in the United States. It occurs densely in some places with hundreds of thousands of individual plants, but the area it occupies is limited. Many occurrences are exposed to multiple threats including encroaching residential development, off-road vehicle use, invasive species, and fire. Nearly all occurrences are threatened by more frequent and intense fires that can cause mortality and loss of the seedbank. Invasive species, which fuel these fires, quickly recolonize after fire, outcompeting less aggressive species, like Ivesia webberi. These threats have caused some declines in the species, including the extirpation of one occurrence.

Ivesia webberi occurs in Western Nevada and eastern California, in the United States. It is known from the Upper Long Valley of the California-Nevada border, and elsewhere in Nevada, from both north and southwest of Reno (Washoe County) and from the western slope of the Pine Nut Mountains in Douglas County. In California, the species occurs in Lassen, Plumas, and Sierra Counties.

This species is currently known from nine extant populations in Washoe and Douglas Counties, Nevada, and eight extant populations in Lassen, Plumas and Sierra Counties, California.

This species is threatened by residential development (especially in the Reno area), road development and maintenance, land conversion to agricultural uses, and off-road vehicle use. Transmission line development is considered a threat at two California occurrences. Historical fire intervals were infrequent, but with the presence of invasive species, like Bromus tectorum, Poa bulbosa, and Taeniatherum caput-medusae, the frequency and severity of burns has increased due to greater fuel loads. In turn, invasive grasses that colonize after fire increase and further outcompete this small herb that thrives in low competition areas. There is also concern that more severe fires cause mortality of plants and the destruction of the seedbank. Plant and soil damage from concentrated livestock trampling is not currently a threat, at least on USFS lands, where the grazing allotments are inactive (USFWS 2014).