GERMINATION AND ECOPHYSIOLOGICAL RESPONSES OF SAN BERNARDINO MOUNTAIN PLANT SPECIES

Limited gene flow and small population sizes make montane plant species, like many of the species found in the San Bernardino Mountains, vulnerable to rising temperatures and other environmental changes predicted to occur over the coming 30 years. The influence of rising temperatures on montane species was tested by conducting a germination experiment with variable temperature treatments on six representative species. The physiological responses of adult Bouteloua gracilis plants from two distinct populations grown under different temperature treatments were also investigated and compared based on net photosynthesis and growth. Germination rates for three of the six species increased with higher temperatures relative to present-day conditions while germination rates for the remaining three species did not change with higher temperatures. Species with wider geographic distributions did not produce statistically significant differences for germination rates under the different conditions. Net photosynthesis values for the San Bernardino Mountain range population of B. gracilis decreased with increasing temperature but biomass growth for this population was also highest at the warmest temperatures. These results suggest that higher temperatures alone may not negatively impact native montane plant species, and that they are capable of tolerating warmer temperatures and might even prefer them. However, warming temperatures could still lead to other challenges including increased competition between plants as species that are not cold adapted begin to migrate from lower elevations as well as the potential compounding stressors of higher ambient temperatures, reduced or changed precipitation patterns, and increased frequency of hot daily extreme temperatures.