ENVIRONMENTAL-FACTORS INFLUENCING THE DISTRIBUTION OF THE LICHENS LOBARIA-OREGANA AND LOBARIA-PULMONARIA

Lobaria oregana (Tuck) Mull. Arg. and L. pulmonaria (L.) Hoffm. are pa rapatric in western North America. However, L. pulmonaria is more wide ly distributed than L. oregana; in western Oregon, L. pulmonaria occur s in the Willamette Valley and forests of the Cascades and Coast Range s, while L. oregana is largely restricted to the mountain forests. To determine whether distribution patterns are related to differential en vironmental tolerances, we examined responses to hear and desiccation and growth responses of transplanted thalli. Heat tolerances were test ed by exposing thalli (air-dry or moist) to temperatures ranging from 24-40 degrees C (3 degrees C intervals) and 25-60 degrees C (5 degrees C intervals) for 1 hr. Sensitivity was assessed by measuring electric al conductivity of deionized water in which thalli were immersed, whic h 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 C ascade Mountains. Intraspecific differences in desiccation tolerance d epended on the environment from which thalli were collected and were a s great as interspecific differences. Thus, differences in distributio n between the two species do not appear to be due simply to differenti al heat or desiccation tolerances. Lobaria oregana from upper canopies in the Cascades grew more slowly than L. pulmonaria from lower tree t runks in the Willamette Valley when both were transplanted to the Will amette Valley for 18 weeks. However, survival of the two species did n ot differ 9 weeks after transplanting to the Willamette Valley.