Environmental Factors Influencing the Distribution of the Lichens Lobaria oregana and L. pulmonaria

Lobaria oregana (Tuck.) Müll. Arg. and L. pulmonaria (L.) Hoffm. are parapatric in western North America. However, L. pulmonaria is more widely distributed than L. oregana; in western Oregon, L. pulmonaria occurs in the Willamette Valley and forests of the Cascades and Coast Ranges, while L. oregana is largely restricted to the mountain forests. To determine whether distribution patterns are related to differential environmental tolerances, we examined responses to heat and desiccation and growth responses of transplanted thalli. Heat tolerances were tested by exposing 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 of deionized water in which thalli were immersed, which reflects membrane damage. Heat tolerances of the two species did not differ. Lobaria pulmonaria from the Willamette Valley was apparently less desiccation tolerant than L. oregana from upper canopies in the Cascade Mountains. Intraspecific differences in desiccation tolerance depended on the environment from which thalli were collected and were as great as interspecific differences. Thus, differences in distribution between the two species do not appear to be due simply to differential heat or desiccation tolerances. Lobaria oregana from upper canopies in the Cascades grew more slowly than L. pulmonaria from lower tree trunks in the Willamette 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.