Crossosoma 34(2), Fall-Winter 2008 
72 
Xanthomendoza oregana (Gyeln.) Sochting, Karnefelt & Kondr. - Corticolous, 
saxicolous, terricolous. Green Mountain, Nash 41475 (ASU). 
Xanthoria ascendens S. Kondr. - Corticolous. Green Mountain, Nash 41378 
(ASU); the Gangplanks, Nash 41091 (ASU). 
Xanthoria Candelaria (L.) Th. Fries - Corticolous, saxicolous. Trail to Caldwell 
Point, Knudsen 6729 (UCR); Green Mountain, Knudsen 6687 (UCR), Nash 
41415B (ASU); Harris Point Nash 41169A (ASU); S side of Prince Island, 
Crayton (ASU). 
Xanthoria pollinarioides L. Lindblom & D M. Wright - Corticolous. Caliche 
Forest, Marsh 7959B (ASU); San Miguel Hill, Nash 41197 (ASU). 
CONCLUSIONS 
The total diversity number of 141 lichen species is fewer than should be 
expected, representing less than 10 per cent of the total taxa currently reported 
from California (Tucker & Ryan 2006). The fog and maritime conditions of 
the Channel Islands, creating high relative humidity, are ideal for many species 
of lichen. Though further field work and herbarium studies will increase these 
numbers, I believe the total number will still be fewer than occurred on San 
Miguel Island before sheep ranching began in the 1850s. 
The sheep ranchers probably depleted the island of large chaparral shrubs 
by using them for firewood, and sheep grazing would have destroyed many 
shrub seedlings. Junak et al. (1995) described similar loss of woody vegetation 
on neighboring Santa Rosa Island due to combined effects of fires and grazing. 
These effects would have reduced or eliminated shrub substrates and may even 
have caused the extirpation of some shrubs. This habitat loss is reflected in the 
subsistence of some lichen species, such as several Lecanora , only on fence 
posts, though they normally occur on the wood of maritime chaparral and oaks. 
The same habitat loss would have caused the disappearance of some corticolous 
species and many others are relatively rare now. 
Due to depleted seed banks, soil loss, and other long-term effects of grazing, the 
maritime chaparral will probably never come back. We are not even sure what 
species and genera were there before the 1850s. 
The stripping of the island’s vegetation and destruction of biological crusts by sheep 
eventually led to serious wind erosion. This would have caused the extirpation 
