PLANT SUCCESSION ALONG THE CHUMASH TRAIL FOLLOWING THE OCTOBER 2003 FIRE

October 2003 witnessed a devastating fire in the mountains north of Simi Valley. The Chumash Trail wanders through some of the worst affected areas. What is offered here are some observation about the affect of the fire on the natural vegetation and the sequence of plant succession through the summer of 2005. It is my intent to update this description from time to time.

The Chumash Trail went through ruderal, i.e., made up primarily of Mediterranean grasses with some herbaceous species and laurel sumac, grasslands for the first few hundred yards north of the trailhead. The vegetation over the next 0.6 of a mile was dominated by a mixture of coastal sage scrub and chaparral. Above the 0.6 mile mark was mature chaparral. While the lower portions of the trail had been affected by wildfires several times during the previous 30+ years, the area above the 1.1 mile point had not burned during that period. As a result, the chaparral was dense and generally six or more feet high. The chaparral was dominated by chamise and hoary-leaved ceanothus, with a smattering of laurel sumac, toyon, sugar bush, hollyleaf cherry, deerweed, yerba santa and a few other species, especially along the upper one half mile section of the trail.

The immediate affect of the fire was to burn the entire area adjacent to the trail. Some areas of the ruderal grasslands near the bottom of the trail (but away from the trail itself) remained unburned due to aggressive fire protection efforts and the lower heat potential of burning dried grasses and annual herbaceous plants, such as mustards and sweet fennel. The coastal sage scrub/chaparral is made up of fairly low, widely spaced plants with a moderate fuel load. While the grasslands and coastal sage scrub/chaparral were burned, moderate fire temperatures did not, in general, destroy the stumps of perennial plants or the entire seed load in the upper few inches of the soil. The chaparral, especially on the north-facing steep slopes where the fuel load was greatest, burned with intense heat. As a result, the stumps of most species were entirely consumed and much of the seed reservoir in the upper layer of the soil was turned to ash. Following the fire, wind-blown ash contributed to air pollution in the valley and drifted over the trail mixed with lacquer-like crusts from the condensation of volatile hydrocarbons from perennial shrubs. Condensation of volatilized hydrocarbons driven below the surface of the soil has contributed to excessive runoff during winter rains. These hydrophobic soils have resulted in elevated rates of soil erosion and mass siltation of waterways, including of the basin behind the Las Llajas Stormwater Detention Dam. The mixture of ash and the lacquer-like crusts were highly subject to both wind and water erosion and does not densify well when trying to rebuild trails.

Vegetative re-growth during the first winter and spring following the fire was sparse at best in the chaparral and coastal sage scrub/chaparral. Re-growth in the ruderal grasslands was generally vigorous. Throughout the entire burn area liliaceae, with their bulbs well below the surface of the soil, made a spectacular showing. Four species mariposa lilies, soap plant, star lily, and blue dicks were profuse. Most yuccas also regenerated but were most common on south-facing slopes. Some annual plants began to grow, although sparsely. Chamise showed some signs of coming back through crown sprouting. A few fire poppies were noted. Surprisingly, yellow-throated phacelia were common along the top half mile of the trail where it was not noted before the fire.

The second winter and spring has witnessed a complete return of the ruderal grasslands, with all of the herbaceous species. Chamise is making a good recovery in the chamise area, as with toyon, yerba santa, hollyleaf cherry, laural sumac, sugarbush and deerweed. The santa susana tarplant, which grows primarily out of joints in massive sandstone outcroppings, has returned fully. Surprisingly, star lilies are much less common this second growing season – perhaps because they have been shaded out by chamise of annual plants. During the spring, the slopes were covered by bindweed and scarlet larkspur was profuse in wide areas. Of special note is that I cannot recall seeing even a single hoary-leaved ceanothus anywhere on the slopes. It is possible that the extreme heat in the chaparral area burned that species deeply below the ground surface, so no crown-sprouting was possible. Perhaps the hoary-leaved ceanothus will yet return if seeds survived the fire. No fire poppies were noted this spring – at least by me. Rose snapdragon is far more common and widespread along the upper half mile of the trail than before the fire. The yellow-throated phacelia first seen on the upper half mile of the trail the first year after the fire is either absent this year or much less common.

More than 10 years ago, i.e., from the late 1980s through the mid-1990s, wooly blue-curls dominated a flat at the headwaters of White Oaks Canyon – so much so that we called it the “Wooly Blue-curls Flat”. Their profusion appeared to be the results of the effect of the Halloween Fire of the early 1980s. Eventually, plant succession resulted in chamise taking over so that fewer and fewer wooly blue-curls were present. I expected that they would return following the 2003 fire. So far that has not happened. I can still hope that they might yet return in a big way. A few are present along the trail across the flat and the chamise has re-sprouted vigorously.

It will be interesting to see what the Spring and Summer of 2006 brings.

                                                                                                Mike Kuhn

8-7-05