Effects of Experimental Burning on Individual Performance and Population Structure of Two Rare Plants of Northcentral Washington

Prescribed burning is used widely for ecological restoration but its consequences for rare plants are not well understood. We compared effects of experimental burning in spring and fall on survival, individual performance, and population structure of Long-sepaled globe mallow ( Iliamna longisepala (Torr.) Wiggins) and Thompson's clover ( Trifolium thompsonii (Morton)), two rare endemic forbs of eastern Washington. We sampled three populations of each species before and for 2 years after treatment. Survival of mature plants of both species was high. Trifolium seedlings that emerged after treatment showed greater survival in burned plots than in controls. For both species, changes in plant size, morphology, and reproductive allocation differed little among treatments. For Trifolium , plant density was largely unaffected by treatment, but for Iliamna , fall burning stimulated greater germination than did spring burning (although subsequent drought resulted in high mortality). Our results suggest that prescribed fire can be used with neutral or positive effects on both species. Season of burning has little influence on survival and performance of extant plants, but fall burning can increase population size in Iliamna by stimulating germination of buried seed. For Trifolium , frequent or more intense fire may be needed to reduce competition and maintain conditions for population persistence.