Environmental factors influencing the distribution of the lichens Lobaria oregana and L. pulmonaria

Lobaria oregana (Tuck.) Mull. Arg. and L. pulmonaria (L.) Hoffm. are parapatric inwestern North America. However, L. pulmonaria is more widely distributed than L. oregana; inwestern Oregon, L. pulmonaria occurs in the Willamette Valley and forests of the Cascades andCoast Ranges, while L. oregana is largely restricted to the mountain forests. To determine whetherdistribution patterns are related to differential environmental tolerances, we examined responses toheat and desiccation and growth responses of transplanted thalli. Heat tolerances were tested byexposing thalli (air-dry or moist) to temperatures ranging from 24-40°C (3°C intervals) and 25—60°C (5°C intervals) for 1 hr. Sensitivity was assessed by measuring electrical conductivity ofdeionizedwater in which thalli were immersed, which reflects membrane damage. Heat tolerances of the twospecies did not differ. Lobaria pulmonariafrom the Willamette Valley was apparently less desiccationtolerant than L. oregana from upper canopies in the Cascade Mountains. Intraspecific differencesin desiccation tolerance depended on the environment from which thalli were collected and were asgreat as interspecific differences. Thus, differences in distribution between the two species do notappear to be due simply to differential heat or desiccation tolerances. Lobaria oregana from uppercanopies in the Cascades grew more slowly than L. pulmonaria from lower tree trunks in theWillamette Valley when both were transplanted to the Willamette Valley for 18 weeks. However,survival of the two species did not differ 9 weeks after transplanting to the Willamette Valley.