Witch Fire

Biological Impacts

Fire Map Impacts on Listed Animal and Plant Species

Fire Map Impacts on Vegitation

Upland species

Coastal sage scrub and chaparral speciesCoastal sage scrub burned in the slopes around Lake Hodges and San Pasqual Valley, the San Diego River canyon above and around El Capitan Reservoir, and in Rancho Santa Fe, Rancho Bernardo, Escondido, and northern Poway. While this community is adapted to periodic fires, disturbance from fires may facilitate infestation by non-native, invasive weeds (County of San Diego 2007). Increased fire frequency may convert coastal sage scrub habitat to grassland (Zedler et al.1983) and reduce California gnatcatcher populations (Bontrager et al. 1995b, Atwood et al. 1998). Typically, California gnatcatcher populations recover from fire within several years, the time that it takes coastal sage scrub to regenerate post-fire; however, the 2007 San Diego County census found extremely few California gnatcatcher territories had re-established after the 2003 Cedar Fire. The extent of the Witch Fire may have even longer-lasting effects on this species.

While our focus was on listed species, it is important to note that coastal cactus wrens (SSC) may have been severely impacted by the fire, which burned much of their prickly pear (Opuntia littoralis and O. oricola) and coastal cholla (O. prolifera) habitat near Lake Hodges, in Rancho Santa Fe (Lusardi Canyon), and in the San Pasqual Valley. Bontrager et al. (1995a) found that cactus wrens require cactus at least one meter high. Because cactus recovery after a fire is slow, cactus wrens may have difficulty recolonizing burned coastal sage scrub. During the 13 years after the Laguna Fires in Orange County, there was a 58 percent decline in the cactus wren population (Mitrovich and Hamilton 2006). The large unburned and lightly burned prickly pear cactus that remain north of Lake Hodges (County of San Diego 2007) may serve as refugia for this population.

San Diego thornmint is an herbaceous annual species that must regenerate from its seed bank each year. Any of the current year’s seeds that may not yet have been released from the dried, above-ground floral structures of the plant, would likely have been burned. Some heat kill of seed bank may have occurred if excess thatch or unusually large amounts of ground fuel were present, but as with most rare annuals and geophytes, the thornmint will probably recover from the effects of the fire over a period of several years if not impacted by repeat burns or post-fire remediation activities.

San Diego ambrosia is an herbaceous perennial arising from a branched system of rhizome-like roots. The aerial stems sprout in early spring after the winter rains and deteriorate in late summer when the species becomes dormant. The underground structures of this species would likely have survived the effects of the fire, and populations within the burn perimeter will probably recover. This species would be adversely impacted by fire remediation activities involving ground disturbance, or repeated mowing or grading if an area containing the population was designated as a permanent fuel break. The previously documented location of San Diego ambrosia one mile north of Lake Hodges may have been impacted by a dozer line. Monitoring should be done to assess this potential impact.

Buildup of high fuel loads in chaparral communities results in unnaturally hot fires that may kill plants and destroy the seed banks of some species. Nevin’s barberry is a stump-sprouter after wildfires, but the effects of an altered fire regime on this species are unknown. Seed production is sporadic and fertility has been observed to be low.

Encinitas baccharis is a rare California endemic with a very limited distribution, making it vulnerable to a single natural event, such as fire. Effects of fire on this species are unknown.

Gander's ragwort is an herbaceous perennial endemic, limited to California. This species grows in the understory of mature mixed chaparral, or in open areas of recently burned chaparral. There is potential for impacts to the establishment and reproduction of the species during erosion control measures. A biological monitor should be present to minimize activities to areas that the species is known to occur.

Currently known extant populations of Orcutt’s spineflower occur outside of the Witch Fire perimeter in Encinitas and Point Loma. One historic population of the spineflower was described as occurring somewhere in Rancho Santa Fe, possibly within the fire perimeter, but the exact location of this site is not known, nor is it known whether the population still exists. Orcutt’s spineflower is thought to be close to extinction. The spineflower is an herbaceous annual species that must regenerate from its seed bank each year. If any as-yet unlocated populations of the spineflower were subject to burning in the Witch Creek Fire, the seed bank may have been adversely affected if there was excess ground-level fuel present. It is impossible to predict the effect of the Witch Creek fire on the survival of the species because it is not known whether any populations were directly affected.

Montane Chaparral/Pine Forests

Dunn’s mariposa lily sprouts from a bulb and occurs in dry stony ridges and fire breaks in chaparral and yellow pine forests. In the first post-fire growing season, the plant sprouts from the corm. Ground disturbance activities should try minimizing damage to bulbs that have survived the fire underground. Avoid ground disturbing activities in areas where the species is known to occur.

Grassland species

While grassland habitat typically recovers after fires, weeds may invade where bulldozer lines disturbed the soil, causing a reduction in habitat value (County of San Diego, 2007). The golden eagle is a grassland species that also occurs in coastal sage scrub and chaparral. The severity and the extent of the burn likely impacted rodent and rabbit populations upon which golden eagles prey. Golden eagles may rebound as small and medium-sized mammal populations recover.

The Stephens’ kangaroo rat lives in underground burrows and prefers open grasslands. To determine if overall impacts to habitat occupied by this species in Rancho Guejito and Ramona were favorable, species monitoring should be done.

Vernal pool species

The Witch fire burned vernal pool habitats in Ramona, the southern portion of Rancho Guejito, and the Santa Fe Valley (County of San Diego 2007). Because vegetative litter tends to be sparse in vernal pools and San Diego fairy shrimp are currently dormant in the soil, direct impacts to this species were likely low. However, the possibility of an ash flurry flowing into the pools necessitates monitoring.

Thread-leaved brodiaea is geophytic plant species (a perennial that is propagated by buds on underground corms) that also reproduces by seed. Vernally moist grasslands and the periphery of vernal pools are the typical habitats where this species has been found. It is likely that the underground corms of this species would have survived the fire. Some reduction of the seed bank may have occurred in areas with excess grassy thatch or unusually large amounts of ground fuel.

Thread-leaved brodiaea populations will probably recover from the effects of the fire over a period of several years if not directly impacted by fire remediation activities involving ground disturbance or placement of erosion control objects on the ground surface above the underground corms.

San Diego mesa mint is a small herbaceous annual restricted to vernal pools within grasslands, chamise chaparral, and coastal sage scrub on the mesas of western San Diego County. If significant amounts of non-native grasses and other invasive species were present in vernal pools occupied by San Diego mesa mint, this could have resulted in adverse impacts to the seed bank due to the increased ground-level fuel load. All fire remediation efforts should be directed well away from both vernal pools and their watersheds for the preservation of the mesa mint, as well as other associated vernal pool plant and animal species. Occupied vernal pools should be monitored for at least two years following the fire to determine whether weed control will be necessary. The mesa mint will probably recover from the effects of the fire over a period of several years if non-natives are not allowed to proliferate and if repeated burns are avoided.