Allozyme variation of bishop pine associated with pygmy-forest soils in northern California

Two races of bishop pine (Pinusmuricata D. Don) meet in a narrow contact zone near sea level along the Sonoma County coast, northern California. The races previously were identified by foliar ("blue" in north, "green" in south), monoterpene, and allozyme differences. Disjunct stands of blue bishop pine were observed at higher elevations along a ridge south of the contact zone on patches of infertile pygmy-forest soils. Green bishop pine grew on fertile soils 0.5 km from the pygmy-forest patches. The frequency of trees with blue foliage in pygmy-forest stands was 0.73-0.86. One ridgetop stand south of the contact zone on fertile soils also had blue foliage. Allozyme differences at 7 of 46 loci distinguished blue and green races on different soils. Ridgetop blue and green stands were clearly related allozymically to lower elevation blue and green races in the same region. Selection for tolerance to soil conditions in the pygmy forest appears to maintain blue bishop pine in ridgetop pygmy forests.