Post-fire population dynamics of Penstemon californicus

Background/Question/Methods

Prescribed fire is often used on public lands to reduce fire hazard. Burning can efficiently remove accumulated fuels, but may be detrimental to desirable species. California penstemon (Penstemon californicus) is a perennial herb endemic to the San Jacinto Mountains, San Bernardino National Forest (SBNF), California. It is considered rare by the California Native Plant Society and is a Forest Service Sensitive species. Relatively little is known about this species, including requirements for survival, regeneration or fire response.  P. californicus grows within the perimeter of a SBNF planned prescribed burn near Garner Valley. Forest managers were concerned about what measures would be required for protecting P. californicus during the burn operation. We conducted small test burns to measure fire effects on P. californicus. We randomly established 13 1-m² plots on a site where P. californicus occurred. An initial population of 52 P. californicus were measured and mapped.  A wire mesh “fire cage” was used to safely conduct experimental burns in the wildlands.  Prescribed burns were completed on: 3 plots during September 2003, 4 plots during January 2004; 6 plots remained unburned.  Weather and burning conditions were recorded. Plant survival, growth and recruitment were measured twice a year for 3 years.

Results/Conclusions

Pre-treatment average number of plants per plot was 3.3 for control, 4 for the fall burn and 4.5 for the winter burn. After 3 years the average density of P. californicus individuals increased for all treatments.  It was similar for the unburned (5.2) and fall (5.0) burned plots, but was twice that for the winter burn (10). Average plant cover was greatest in unburned plots (121 cm² cm) and smallest for the fall burn (729 cm²); the winter burn cover was intermediate (830 cm²). After 3 years all burned plot P. californicus average cover was about 65% of unburned.  Seedling recruitment was enhanced after the winter burn treatments.  Cover reduction from burning and post-fire seedling recruitment in burned plots accounts for much of the size difference. These results suggest that disturbance by fire can have a negligible to positive effect on P. californicus populations if burning occurs during the fall or winter. Disturbance and reduction of competition for resources may be important for improving this species success. Appropriately timed introduction of fire to areas presently and historically occupied by P. californicus may improve recruitment and hence survival of this rare species.