Ashes To Wildflowers

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Volume 6 (Number 4) Winter 1998
 
Ashes To Wildflowers
A Promise Of Renewal Springs From Destruction
 
W.P. Armstrong, Updated 17 May 2014

Disclaimer: Although the chaparral is dominated by shrubs that are adapted to periodic brush fires, fire intervals that are too frequent can be very destructive to this plant community. Population growth, urbanization, vehicle traffic, and the introduction of alien weeds has altered the natural environment in southern California. The human impact on this ecosystem in some areas has been disastrous, particularly where slopes, ridges and canyons of prime watershed have been converted into housing developments. Not only is this urban sprawl destructive to a unique ecosystem, it poses a serious threat to residents and firefighters. In this Mediterranean climate, the fire danger is exacerbated by high temperatures, low humidity, strong, descending "Santa Ana" winds, and powerful, "tornadic" winds generated by fires.

This Article Is Dedicated To Dr. Richard J. Vogl: Friend, Colleague and
Inspirational Teacher Who Understood The Role Of Fire Long Before It
Was Truly Appreciated By Other Plant Ecologists.

     The October 2007 Witch Creek Fire San Diego County
     Witch Creek Fire Followers In Spring 2008 (5 Parts)
     The October 2003 Paradise Fire In San Diego County
     The October 2003 Cedar Fire In San Diego County
     Lightning: The Primary Cause Of Natural Forest Fires
     Images Of Lightning Bolt & Lightning Struck Pine
  1.    Brush Fire In Coastal Sage Scrub Of Southern California
  2.    See A Giant Smoke Cloud North Of Palomar College
  3.    Charred Leaves That Fell On The City Of Escondido
  4.    Rattlesnake Crawling On Ashes One Day After A Fire      
  5.    Exfoliating Boulders & Resproutings Shrub After Fire
  6.    Subterranean Lignotuber That Resprouts After Fire
  7.    Coast Live Oaks Resprout From Trunk & Upper imbs
  8.    Burned Hillside Covered With Beautiful Wildflowers
  9.    Three Species Of Spectacular Post-Burn Wildflowers
10.   Allelopathy In Calif. Coastal Sage Scrub & Chaparral
11.   Fire Seeds Of Ceanothus That Germinate After Fire
12.   Seed Cones Of Knobcone Pine That Open After Fire
13.   Seedlings Of Tecate Cypress Following A Wild Fire
14.   Seed Cones Of Lodgepole Pine That Open After Fire
15.   Combustible Resins From Douglas Fir & Pine Trees
16.   Fire Adapted Australian Shrubs (Hakea & Banksia)
17.   Coastal Sage Scrub Bordering Palomar College
18.   Summary and Conclusions
19.   References Cited

1. Brush Fire In Southern California

Imagine the following scenario: It is a warm, fall afternoon in the foothills of southern California. The air is still and dry, with only the occasional calls of wrentits and scrub jays from a nearby canyon. Suddenly, a funnel of black smoke rises from the dry brushlands. As the late afternoon breezes begin to pick up, the smoke enlarges into a billowing cloud that resembles an atomic bomb explosion. Soon the sun is blotted out by a huge mushroom cloud and the air is filled with ashes and the distant sounds of sirens and air horns. This is a brush fire out of control, a common occurrence in the parched hillsides of southern California and the beginning of one of nature's most fascinating cycles of death and renewal. In fact, this scenario was precisely replayed on October 22, 1996 in the hills of coastal sage scrub bordering the east side of Palomar College.

A fire storm in the coastal sage scrub, a common occurrence in the dry hillsides of southern California during the late summer and fall. When fanned by dry "Santa Ana" winds during the fall months, these fires pose a serious threat to residential areas. Note: This photo was actually taken by my father Paul Armstrong near Sun City (Riverside County) about 20 years ago.


2. Giant Smoke Cloud In Southern California

A billowing cloud of smoke rising from a fire storm near Palomar College in San Marcos.

San Marcos Fire (14 May 2014) looking toward Cal State San Marcos from Palomar College.

Fire Over Camp Pendleton Marine Corps Base One Day After Previous San Marcos Fire Image


3. Charred Leaves That Fell On City Of Escondodo

Scorched and charred leaves that showered down upon the City of Escondido during the raging Paradise Fire of October 2003. The fire burned canyons and chaparral-covered slopes several miles to the north, producing a huge, billowing smoke cloud that carried ash and debris thousands of feet into the sky. Leathery (sclerophyllous) leaves of oaks (Quercus) that did not disintegrate in the fire were carried upward in the rising plume of smoke. In fact, smoldering leaves became airborne embers, quickly spreading the blaze to nearby slopes. Volatile terpenes in the leaves of Eucalyptus trees (including eucalyptol and citronellal) make them especially flammable. This massive fire was fanned by dry "Santa Ana" winds blowing from east to west (toward the coast), literally converting everything in its path into ashes and rubble. A. Red gum (cf. Eucalyptus camaldulensis), a common Australian tree naturalized in canyons throughout northern San Diego County. Eucalyptus leaves contain volatile terpenes that make them very combustible. B. Scrub oak (cf. Q. x acutidens), a hybrid shrubby oak of the chaparral. Although the common scrub oak with toothed leaves listed for this region is Q. berberidifolia, it is propably Q. x acutidens. C. Coast live oak (Q. agrifolia), a common evergreen tree in canyons and river valleys.

Note: These leaves were collected in a Target® parking lot in Escondido approximately 4-5 miles from the Paradise Fire north of Escondido (including Daley Ranch, Valley Center Grade and the road to Lake Wohlford). The leaves were essentially intact because they were only scorched or charred. Many leaves from this parking lot were so badly burned (carbonized) that they literally disintegrated when handled.

In terms of urbanized habitats, California's fire storms are one of nature's most catastrophic and destructive forces. The fast-moving flames can sweep across entire hillsides in seconds, and can suddenly change direction with shifting winds. But in terms of natural vegetation, these seemingly ruthless brush fires can be very beneficial to some fire-adapted species. There are actually five climatic regions of the world with a similar regime of mild, wet winters and hot, dry summers, including California, Chile, the Cape region of South Africa, southwestern Australia, and the Mediterranean. Although they may have entirely different plant species, all of these regions have similar chaparral-like brushlands with wildfires during the late summer and fall.


4. Rattlesnake Crawling On Ashes One Day After A Fire

A red diamond-back rattlesnake (Crotalus ruber ruber) crawling through the ashes one day after a raging brush fire. Although I have the charred remains of animals, including rattlesnakes, wildfires do not kill all the animal residents of the chaparral and coastal sage scrub. Note: This photo was actually taken by my father Paul Armstrong near Sun City (Riverside County) about 20 years ago.


5. Exfoliating Boulders & Resprouting Shrubs After Fire

If you walk through the chalky gray ashes and charred remains of a lifeless shrub forest immediately following a fire, it is hard to imagine anything ever growing here again. Often the ashy soil is littered with flakes of granodiorite that split off of large boulders--proof of the intense heat of the flames. Like peeling off the layers of an onion skin, this is a major source of exfoliation of granitic formations in southern California. However, this bleak and silent setting of grays and blacks is only a temporary stage in a complex series of miraculous events in which nature will gradually restore the original vegetation.

Charred branches of chamise (Adenostoma fasciculatum) with bright green resprouts at the base. The intense heat of the fire caused the blackened granodiorite boulders to exfoliate into thin flakes.

Brush fires in southern California typically occur during the drought months of summer and fall, the so-called "fire season." The native thickets of shrubs, known as chaparral (and coastal sage scrub), are tender dry by late summer and many species are especially combustible due to their high content of volatile terpene oils and resins. The flames are sometimes fanned by brisk "Santa Ana" winds, producing a raging inferno that sweeps out of control toward the ocean. Thickets of dense, impenetrable chaparral, with masses of dead branches and leaf litter which took decades to accumulate, are recycled into rich, nutrient soil ash within minutes. With the coming of winter rains, small green sprigs of grasses and annual wildflowers begin pushing through the rain-soaked, ashy soil. Within weeks the barren gray and black slopes are transformed into velvety hills of green.


6. Subterranean Lignotubers (Basal Burls) That Resprout After Fire

By this time, green leafy branches have already developed from the bases of charred shrubs such as chamise (Adenostoma fasciculatum) and mazanita (Arctostaphylos gladulosa), having resprouted from vegetative buds in deep subterranean woody stumps called basal burls or "lignotubers." These remarkable woody structures are truly adapted to periodic brush fires and are a major factor in the survival of native shrubs in the chaparral of California.

[See the chamise lignotuber at left.]

To appreciate the tenacity of these basal burls, consider the mission mazanita (Xylococcus bicolor). In September 1993 the Palomar College Field Botany class found a small mission mazanita burl that was washed out along a dirt road north of Escondido (northeast of Palomar College). The burl had undoubtedly been exposed to the air since the heavy rains of the previous winter. We planted the burl in a test plot at the WAYNE'S WORD office and burned off the exposed branches with a small "ground fire." The staff at WAYNE'S WORD gave the burl several "simulated" rains, and within one month following the fire, new shoots began to appear from the charred stump.

Briarwood Pipe Made From A Mediterranean Basal Burl

 Briarwood pipes are made from the lignotuber (burl) of Erica
   arborea
, a Mediterranean shrub of the heath family (Ericaceae).
Like the burls of manzanita (Arctostaphylos) in the California chaparral, briarwood also resprouts from subterranean basal burls after a brush fire. Due to arid habitats and infertile, rocky soils, it usually takes about 30 years or more for a burl of five to ten pounds to form. A ten pound (4.5 kg) burl is large enough to make about one dozen pipes. Briarwood burls are composed of very dense, fire-resistant wood. The pipes can withstand the heat of burning tobacco which may exceed 700 degrees Fahrenheit. High quality briarwood also absorbs moisture from the tobacco, thus producing a drier smoke that is highly prized by pipe smokers. Compared with other hardwoods, such as hornbeam (Carpinus), beech (Fagus), chestnut (Castanea) and cherry (Prunus), briarwood does not impart an unpleasant taste to the smoke.


7. Coast Live Oaks Resprout From The Trunk & Upper Limbs

When the trunk and limbs of most tree species are completely charred by fire, they seldom recover. In southern California, coast live oaks (Quercus agrifolia) resprout from the trunk and upper limbs within three months following a fire. This is technically referred to as epicormic sprouting. It also occurs in some fire-adapted species of Eucalyptus in Australia. The thick, fire-resistant bark of these oaks provides protective heat insulation for the living cambial cells beneath the bark. Compared with other oaks, the relatively smooth-textured bark inhibits the fire from being carried up the trunk. Instead, the flames are gradually extinguished as the bark becomes blackened and charred.

Epicormic sprouting of charred coast live oak (Q. agrifolia) 4 months after the Paradise Fire.


8. Burned Hillsides Covered By Beautiful Wildflowers

One of the most amazing phenomena in nature's remarkable recovery from fire is the brilliant display of wildflowers that appears with the onset of winter and spring rains. Often the dazzling spectrum of color changes from orange to purple, yellow or blue, as one population of colorful wildflowers gradually fades and is replaced by another. Carpets of golden daisies, baby blue-eyes and white forget-me-nots give way to masses of purple lupines, penstemons and phacelias, mixed with bright orange California poppies. The profusion of blossoms is highlighted by vivid red clumps of Indian paintbrush, crimson campions and scarlet larkspurs. Blackened remains of chaparral thickets are decorated here and there with bright pink wild sweet peas and purple climbing snapdragons. Twining vines of wild cucumber often cover the burned shrubs, with large, spiny green fruits which hang like ornaments from the charred branches. In shady canyons and ravines lovely pink and white Chinese houses resemble a miniature city of tiered oriental pagodas. Many showy wildflowers develop from deep-seated bulbs and corms, often later in spring after the annuals have bloomed and gone to seed. Blue wild hyacinths and pink wild onions make their spring debut, followed by beautiful lilac and golden mariposa lilies.

Orange California poppies (Eschscholzia californica) and purple canterbury bells (Phacelia minor) cover a burned hillside. Note: Photo taken in the 1980s near Canyon Lake in Riverside County.

The scarcity of wildflowers in mature chaparral and their abundance after fire has been studied extensively in recent years. Fires generally occur once in every 10-40 years and seeds of some wildflowers may lie dormant for decades, and then germinate by the millions following fire. Unfortunately, most of the reseeding campaigns to prevent erosion include introduced mustards and weedy grasses, such as wild oats and rye grass, which compete with and crowd out our colorful native soil binders. Fire breaks down the impervious seed coat of some wildflowers and allows them to imbibe water. Other seeds will still not germinate unless tissue covering the embryonic root within the seed is removed. Heat or other biochemical factors may be involved in breaking dormancy in some seeds. Studies have shown that the burned remains of shrubs greatly stimulate the germination of certain seeds. The developing wildflowers thrive in the ash and often grow much more vigorously than in soil without ash.


9. Three Species Of Beautiful Post Burn Wildflowers

Three species of spectacular wildflowers that appear after fires in San Diego County. Left: fire poppy (Papaver californicum); center: hillside monkey flower (Mimulus brevipes), and right: scarlet larkspur (Delphinium cardinale). With sufficient winter rains, fire followers often germinate in profusion from seeds in the ashy soil following a fire from the previous year. The scarlet larkspur is a perennial that can regenerate from seeds and from well-established root systems.

For decades, fire ecologists have tried to solve the mystery of how to germinate California chaparral wildflowers in the laboratory. The secret is burying the seeds in soil for a year and then exposing them to smoke. In the October 1998 issue of Ecology, J. Keeley and C.J. Fotheringham described 25 species of chaparral wildflowers that respond not to a fire's heat but to its smoke. The actual biochemical mechanism may vary with different species, and some seeds apparently require burial in the ashy soil before sprouting. The duration of smoke exposure may also vary, and may be lethal to some seeds. Seeds of fire-followers such as golden eardrops (Dicentra chrysantha) require a 10 minute exposure to smoke, while those of whispering bells (Emmenanthe penduliflora) need just a minute of smoke.

Botanist Gilbert Voss in a dense stand of golden eardrops (Dicentra chrysantha). Photograph taken on a recently burned slope of Tecate Peak in southern San Diego County (circa 1967).

Ground pinks (Linanthus dianthiflorus) form bright pink clumps on the ash-covered slopes north of Palomar College following a brush fire.

See Photos Of Phacelias After A Chaparral Fire
  White Phacelia & Turricula After Fire in Laguna Mts
  


10. Allelopathy In The Coastal Sage Scrub & Chaparral

allelopathy (n): ah-lee-LOP-ah-thee; allelopathic (adj): ah-LEEL-ah-path-ik]

Studies conducted by Cornelius H. Muller and his graduate students during the 1970s indicate that terpene chemicals present in the resinous foliage and fallen leaves of chaparral shrubs inhibit germination of wildflower seeds, a phenomenon known as allelopathy. Fire destroys these inhibitory chemicals that have leached into the soil, and explains the abundance of wildflowers in recently burned chaparral. [I have also observed an abundance of wildflowers in areas of unburned chaparral that were cleared for avocado groves.]

Some botanists believe that allelopathy does not adequately explain the paucity of certain wildflower species in unburned coastal sage scrub and chaparral. The classic aerial photo on the cover of Science Vol. 143 (31 January 1964) shows a mosaic pattern of white lines (bare ground "halos") around purple sage (Salvia leucophylla), white sage (S. apiana) and California sagebrush (Artemisia california) in the coastal sage scrub of Santa Ynez Valley northwest of Santa Barbara.

These bare ground patterns were attributed to allelopathy by Cornelius Muller, Walter Muller and Bruce Haines in their article "Volatile Growth Inhibitors Produced by Aromatic Shrubs" (Science 143: 471-473). Later in 1964, Philip Wells argued that these patterns may have been caused by factors other than allelopathy, such as cattle trails (Science 143: 889). In 1970 Bruce Bartholomew published a plausible rodent explanation (Science 170: 1210-1212). Small rodents such as the California mouse (Peromyscus californcus) and Pacific kangaroo rat (Dipodomys agilis) hide from predators under the dense cover of shrubs. They make short forays into the surrounding grassland to nibble on seeds or new growth. They generally do not stray far so they can quickly leap back into the shrub canopy for safety. Bare zones around shrubs can thus be explained as "calculated risk terrain" where rodents have a chance to grab food without getting caught. Herbaceous growth increases significantly in "bare zones" protected from rodents.

One problem with the rodent grazing hypotheses is that grasses grow within bare zones around shrubs during wet years despite animal activity. Why don't rodents always eliminate seedlings? In complex ecosystems such as the chaparral and coastal sage scrub it seems plausible that chemical factors may also be involved; however, chemical hypotheses tested in laboratories may not apply to conditions in natural habitats. Allelopathy has clearly been documented for some plant species and perhaps it cannot be completely ruled out for chaparral and coastal sage scrub plant communities.

The alleopathy controversy has been summarized by Richard W. Halsey in his article "In Search of Allelopathy: An Eco-historical View of the Investigation of Chemical Inhibition in California Coastal Sage Scrub and Chamise Chaparral (Journal of the Torrey Botanical Society 131 (4), 2004, pp. 343-367). According to Halsey (2004): "For chaparral, it is clear innate dormancy in seeds can account for the lack of herbs under the community's canopy. The remarkable post-fire germination cycle can be explained without invoking environmentally induced chemical inhibition. Poor growing conditions under mature shrubs selected for traits postponing germination until those conditions improved, such as after fire, including higher available nutrients levels, more space and light, and lower herbivory." The previous quotation explains the abundance of wildflowers I have observed in recently cleared chaparral designated for avocado groves in San Diego County.

One of the best examples of allelopathy is the spotted knapweed (Centaurea maculosa syn. C. stoebe). This noxious European perennial weed secretes a potent allelopathic flavonoid called catechin from its roots that literally kills neighboring plants. Catechin has two mirror image forms, a positive (+) form and a negative (-) form. The +catechin is an antibiotic and antioxidant that prevents the formation of free radicals. It is present in a number of plants, including green tea (Camellia sinensis). The -catechin induces oxidation and cellular death in root cells of neighboring plants. Although the mechanism is complex, -catechin is a potent phytotoxin that causes plants to self destruct by producing free radicals as well as triggering genes that kill the cells. Cellular death may occur within an hour of exposure to catechin. See the following reference for more details: H.P. Bais, R. Vepachedu, S. Gilroy, R.M. Callaway and J.M. Vivanco. 2003. "Allelopathy and Exotic Plant Invasion: From Molecules and Genes to Species Interactions." Science 301: 1377-1380 (September 5, 2003).

In other species allelopathy has been demonstrated to play an important role in forests, influencing the composition of the vegetation and patterns of forest regeneration. The black walnut (Juglans nigra) produces the phenolic compound juglone, an allelopathic substance that interferes with the growth of certain plants. It has been shown that some plants are inhibited by juglone while others appear to be unaffected. It is well-known that Eucalyptus leaf litter and root exudates are allelopathic for certain soil microbes and plant species. The tree of heaven (Ailanthaus altissima) also produces allelopathic chemicals in its roots that inhibit the growth of many plants. More research may lead to a better understanding of the role of allelopathic substances in natural ecosystems, including California plant communities.


11. Fire Seeds Of Ceanothus That Germinate After Fire

In San Diego County, seedlings of shrubs also appear in the ashy soil after fires, particularly California lilac (Ceanothus tomentosus var. olivaceous), black sage (Salvia mellifera) and chamise (Adenostoma fasciculatum). In fact, Ceanothus tomentosus is a relatively short-lived shrub and periodic brush fires are necessary for its rejuvenation and propagation. The roots of some species of Ceanothus have nodules containing nitrogen-fixing actinomycetes. These are fliamentous, fungus-like bacteria rather than the eubacteria found in the root nodules of legumes.

Two species of California lilac (Ceanothus) in the chaparral of San Diego County. Left: C. tomentosus (var. olivaceous). Right: C. crassifolius. Seedlings of C. tomentosus commonly appear in recently burned chaparral.

Seedling of Ceanothus tomentosus var. olivaceous four months following the Paradise Fire of October 2003. Seedlings of this species commonly appear in the ashes of recently burned chaparral.

  See Illustration Of Above Ceanothus Species  


12. Seed Cones Of Knobcone Pine That Open After Fire

Several species of California cone-bearing trees, including the knobcone pine (Pinus attenuata) and bishop pine (Pinus muricata) grow in chaparral areas and have fire-adapted serotinous seed cones. These species are able to reseed themselves after fast-moving fires as their tight, woody cone scales slowly open and release seeds on the burned slopes. In fact, without fire the serotinous cones of the knobcone pine may remain closed for the life of the tree. The knobby cones are so firmly attached to the trunks of old trees, that they literally become enveloped by the expanding bark.

[Left: Photo of knobcone pine cone cluster.]

  See A Knobcone Pine Gear Shift Knob  

Without fire, cones of the knobcone pine may remain closed for 80 to 100 years or more. In fact, Mr. Wolffia (the editor of Wayne's Word) once made a gear shift knob out of a cone for his truck. After more than 30 years, the cone is still tightly closed--with its shiny varnish finish. Fire provides the ideal seedling requirements for these shade intolerant conifers, including full sunlight and ashy-mineral soil devoid of leaf litter and debris (known as "duff" in ecological circles). In addition, the fire kills off certain soil fungi that cause a fatal seedling disease known as "damping off."

There are many other cone-bearing trees throughout North America and other continents with serotinous seed cones. For example, in the Rocky Mountains and the Eastern United States are jack pine (P. banksiana), lodgepole pine (P. contorta ssp. latifolia) and Table Mountain pine (P. pungens), three species with woody seed cones that open during a fire. California cypresses (Cupressus) also produce numerous clusters of serotinous cones. Although cypresses are generally killed in a fire, their woody cones reseed the charred hillsides with a new generation of seedlings; however, fires that are too frequent can be disastrous, particularly if the cypress have not had enough time to produce mature seed cones. Throughout California, ten remarkable cypress species (or subspecies depending on the botanist) occur in isolated groves, sometimes referred to as "arboreal islands." The groves often occur in rugged sites and on poor, rocky soils where chaparral shrubs cannot compete as well. Cypresses probably once formed extensive forests in California, but during the past 20 million years, have been gradually replaced by more vigorous chaparral growth. In fact, their isolation into widely separated groves of relatively small populations has undoubtedly led to some of the subtle "racial" differences in cones, bark and foliage characteristics between disjunct populations within the same species, a phenomenon known as genetic drift.


13. Seedlings Of Tecate Cypress Following A Wild Fire

Left: A burned stand of Tecate cypress (Cupressus forbesii) on the north side of Tecate Peak in San Diego County (near the California-Mexico border). The charred serotinous cones on the branches have released thousands of seeds. Small seedlings on the ashy soil include Tecate cypress and golden ear-drops (Dicentra chrysantha). Right: Close-up view of two Tecate cypress seedlings which have sprouted in the ashy soil following the fire. A cluster of charred seed cones is also shown in the photo.

Serotinous cones of cypress trees open following fire and the seeds are scattered on ashy slopes devoid of competing chaparral vegetation. Under optimal conditions of temperature, sunlight and winter rains, the seeds germinate in the mineral-rich soil and a new generation of cypress trees grows from the ashes. Unfortunately, the fire scenario can also be devastating to cypress groves. Fires occurring too frequently over the same area can destroy a grove if they eliminate the young cypresses before they have a chance to produce sufficient seed cones. I have obseved Tecate cypress (Cupressus forbesii) and Cuyamaca cypress (C. stephensonii) 14 years old with mature seed cones. These were small cypress growing in dense thickets. I discussed this issue with botanists Paul Zedler and Jack Reveal and they concluded that the fire interval should be longer than 40 years. Fires as frequent as 25 years could probably lead to their extinction in local areas. See Armstrong, W.P. 1978. "Southern California's Vanishing Cypress." Fremontia 6 (2): 24-29.


14. Seed Cones Of Lodgepole Pine That Open After Fire

Branch of an old lodgepole pine (Pinus contorta ssp. latifolia) in Grand Teton National Park. Unlike the Sierra Nevada lodgepole pine (ssp. murrayana), the cones are truly serotinous and remain closed until they are heated by fire.

Left: Burned lodgepole pine forest in Glacier National Park about one month following the fire of summer 2003. Right: Natural reproduction of lodgepole pine forest in Yellowstone National Park fifteen years after fire of 1988. Both photos were taken in September 2003.


15. Combustible Resin From Douglas Fir & Pines

Dripping pitch from the trunk of a Douglas fir (Pseudotsuga menzeisii) in northern Montana. Conifers such as this ignite like a torch during a fire storm due to the combustible terpene oleoresins.
Abundant resin ducts throughout the trunk and branches of healthy trees is vital to survive freezing winters and to retard the invasion of bark beetle larvae. During prolonged drought conditions, stressed trees produce less resin and are more vulnerable to bark beetles. In fall of 2003, this drought stress was especially evident throughout mountainous areas of southern California where thousands of pines were dying.

Turpentines include a large group of oleoresins from gymnospermous trees. Raw or crude turpentine is essentially the sticky sap or pitch from coniferous trees. In the U.S., raw turpentine is largely derived from southeastern pines, including longleaf pine (Pinus palustris) and slash pine (P. elliotti) grown in large plantations. Crude turpentine is distilled in order to separate the volatile essential oils called "spirits" from the nonvolatile diterpene residue called rosin. Spirits of turpentine are used in thinners and other organic solvents, while rosin is used in the manufacture of varnishes and oil base paints (and for violin bows and baseball pitchers). Oil base paints also contain unsaturated drying oils, such as castor, tung and linseed oils. The settlement of North America was partially due to England's desire to rid herself of dependence on Scandinavian sources of resin, since the pitch was used to caulk ships and waterproof the rigging.

  See Slash Pines & Saw Palmetto  

According to N.T. Mirov (The Genus Pinus, Ronald Press, 1967), all species of pines, except two California species, contain terpenes in their turpentines. The exceptional species are P. jeffreyi and P. sabiniana. The turpentines of these latter two species consists almost entirely of an alkane, n-heptane, with a small mixture of fragrant aliphatic aldehydes. The aldehydes produce distinctive odors in bark fissures of jeffrey pine variously described as resembling vanilla extract, butterscotch or pineapple. Pure heptane, distilled from the resin of P. jeffreyi, was used to develop the octane scale for rating petroleum as a motor vehicle fuel. The following account comes from Conifers of California by Ronald M. Lanner (1999): During the Civil War, Union manufacturers of turpentine used pitch from ponderosa pine (P. pondersosa) because southern pine resins (incl. longleaf and slash pines) were not available from the Confederate States. Sometimes pitch from Jeffrey pine containing volatile n-heptane would get into the heated distillation vats and cause an explosion.

C7H16 (n-heptane)

  Seed Cones Of 20 Pine Species In California  


16. Fire Adapted Australian Shrubs (Halea & Banksia)

An interesting South African conifer (Widdringtonia nodiflora) that grows in dry brushlands of the Cape region is remarkably similar to our California cypresses (Cupressus). Like the serotinous seed cones of cypresses, the woody cones of widdringtonias open during a fire, but unlike our California cypress, widdringtonias also resprout after fire. This is a very unusual fire adaptation for a cone-bearing species. Although they are not conifers, beautiful flowering shrubs of the genus Banksia, a member of the Protea Family (Proteaceae) are well-adapted to wildfires in southwestern Australia. The woody, cone-like seed capsules slowly open during the heat of a fire, releasing hundreds of winged seeds on the ashy landscape. In addition, some species of Banksia resprout from subterranean lignotubers like chaparral shrubs of southern California. Banksias and widdringtonia can be seen in the Palomar College Arboretum.

Serotinous seed capsules of the Australian angiosperm Hakea petiolaris, a member of the protea family (Proteaceae). Like certain conifers of North America, the seed capsules remain closed for years and open following fire.

  See Banksia and Hakea Native To Australia  
Banksias In The Palomar College Arboretum

A recent National Geographic special on PBS (16 March 2003) mentioned a fascinating insect that is adapted to forest fires. The large family of wood-boring beetles (Buprestidae) contains thousands of species with larvae that bore under bark or into the wood of trees and shrubs. A species in the genus Melanophila lays eggs under the bark of recently burned trees. Infrared heat sensitive pits under the wings enable the female beetle to detect a distant forest fire many miles away. In fact, researchers are studying the mechanism of these infrared sensors in order to develop more sophisticated fire alert systems. The beetle flies toward the forest fire and lays her eggs in the charred bark of trees. Upon hatching, the larvae beginning boring and feeding on wood tissue beneath the bark. Recently burned forests are apparently the ideal place for melanophila beetles to lay their eggs. The remarkable life cycle of this beetle is truly dependent on forest fires.


17. Brief Description Of Coastal Sage Scrub Bordering Palomar College

Coastal Sage Scrub: The native vegetation bordering the Palomar College Arboretum is called coastal sage scrub, a unique plant community or assemblage of dominant plants that are indigenous to this region. This is a low scrubland plant community along the California coastal mountains extending south into northern Baja California. It is divided into two geographical subtypes: Northern and southern coastal sage scrub. It is characterized by low-growing, aromatic, drought-tolerant shrubs adapted to a Mediterranean climate characterized by a winter wet season followed by a prolonged summer drought. It is often referred to as "soft chaparral" because the shrubs are not as tall, woody and densely spaced or as rigid as those of true chaparral, and their leaves are not as thick, tough and leathery (sclerophyllous). Coastal sage scrub receives an average of 10 to 20 inches of annual rainfall, and is subject only rarely to frost conditions. The presence of scattered shrubs of laurel sumac (Malosma laurina) above the Arboretum indicate a relatively frost free climate. In fact, Avocado growers in southern California have used laurel sumac as an indicator of frost free areas. Coastal sage scrub generally occurs below 2,000 feet, primarily on dry, west-facing or south-facing slopes. For example, the south and west-facing slopes of Owens Peak ("P" Mountain) north of Palomar College are covered by coastal sage scrub; however, the northern slopes contain some indicator shrubs of true chaparral. Native soil in the Arboretum hillside is decomposed granite (DG) derived from the gray monzogranite bedrock. Nearby Owens Peak ("P" Mountain) is composed of Santiago Peak metavolcanic rock, a dark, fine-grained, very hard rock that dates back to the Jurassic Period, 145 million years ago, when dinosaurs walked the earth. This heavy rock is resistant to erosion and forms some of the higher topography in coastal San Diego County, including Owens Peak and nearby Double Peak in San Marcos.


Behr's Metalmark
Most of the dominant shrubs in coastal sage scrub are classified as "semi-woody," compared with scattered woody shrubs of toyon (Heteromeles arbutifolia), lemonade berry (Rhus integrifolia) and laurel sumac. Dominance refers to the percentage cover, typically measured by line intercepts (transects) placed randomly over the hillsides. By far, the dominant shrubs are California sagebrush (Artemisia californica), black sage (Salvia mellifera), bush sunflower (Encelia californica), red bush monkeyflower (Mimulus aurantiacus var. puniceus) and golden yarrow (Eriophyllum confertiflorum). Another dominant shrub called wild buckwheat (Eriogonum fasciculatum), is the primary food source for the caterpillar of Behr's metalmark (Apodemia mormo virgulti). In fact, this butterfly is an indicator of coastal sage scrub.

Shrubs of the coastal sage scrub are adapted to the long, dry summers in several ways. Remaining dormant throughout the dry season, they may lose 80% of their water. During this time they may drop many of their brittle, shriveled leaves or produce smaller leaves on secondary shoots. Root systems are generally shallow because the plants are inactive much of the time. It is relatively easy to clear away desiccated shrubs with a heavy hoe during the summer drought season, compared with well-anchored shrubs of true chaparral. The oily, resinous leaves also help to conserve vital moisture, but increase their flammability. The dominant shrubs are fire adapted with seeds that readily germinate after fire. This also includes numerous species of post burn wildflowers that bloom in profusion following the winter and spring rains. Unlike scattered laurel sumac and lemonade berry, the dominant semi-woody shrubs (Artemisia, Salvia, & Eriogonum) lack lignotubers and rely on seeds for regeneration after fire. These shrubs are vulnerable to excessive or poorly-timed fires, particularly when competing with naturalized grasses and other weedy species. The common vine throughout the coastal sage scrub called wild cucumber (Marah macrocarpus) sprouts soon after fires from a large, subterranean caudex. Under ideal natural conditions, complete recovery of coastal sage scrub after a fire is about 15 to 20 years.

The native scrub vegetation adjacent to the Palomar College Arboretum is not chaparral. It does not contain the dominant shrubs of true chaparral, such as chamise (Adenostoma fasciculatum), scrub oaks (Quercus), California lilacs (Ceanothus), mountain mahogany (Cercocarpus) and manzanitas (Arcostaphylos & Xylococcus). The latter shrubs are common in the nearby San Marcos and Merriam Mountains that border Twin Oaks Valley. Although Owens Peak near Palomar College is dominated by coastal sage scrub, two chaparral species (Adenostoma and Xylococcus) grow in the saddle on the north side of of this mountain. Our coastal sage scrub is an endangered plant community in coastal San Diego County, primarily due to the clearing of land for agriculture and housing developments. It has been estimated that less than 20% of the original extent of this vegetation may remain in southern California. Coastal sage scrub contains some seriously threatened birds, reptiles and insects, such as the coast horned lizard (Phrynosoma coronatum) and California gnatcatcher (Polioptila californica). In fact, the latter bird was documented in our local coastal sage scrub during an environmental impact study contracted to Palomar College. This plant communty has been extensively studied by wildlife biologists and numerous articles have been published about it. Governmental agencies such as the U.S. Fish & Wildlife Service and California Department of Fish & Game are well aware of its endangered status. For these reasons, it is very important to refer to our local native vegetation as coastal sage scrub and not chaparral. In a given region, the most dominant species has the greatest percent cover. One method for determining dominance is called the line intercept. This method is useful for analyzing a shrub community such as the chaparral or coastal sage scrub. A 100 foot steel tape measure is placed at random in the area to be sampled. The distance that each species overlies (or underlies) the transect line is recorded in feet to the nearest tenth. Dominance is then calculated from the following relationship: Dominance = total distance covered by a species divided by the total distance of line intercepts.

Above figure from Biology Laboratory Manual & Workbook (Fifth Edition) by W. P. Armstrong (1988).
Dominance refers to the area covered by the crown of a shrub or tree species, and is usually expressed as a percent. The shrub or tree canopy provides food, shelter and numerous niches for animal inhabitants. It supplies a layer of litter or duff to the forest floor in the form of dead branchlets and leaves. The vegetation canopy greatly modifies the understory environment by providing shade that results in cooler temperatures and less evaporation. Dense chaparral and coastal sage scrub vegetation on rugged hillsides of southern California also help to reduce excessive soil erosion due to heavy rains. Dominance may be expressed in absolute or relative values.

Absolute Dominance = total distance covered by a species divided by the total distance of line intercects x 100.

For large trees such as ponderosa pine, dominance is based on the total basal area of trunks rather than the area covered by the crown (canopy). The basal area of each trunk is measured at breast height or 4 1/2 feet from the ground. The total basal area can be determined from the density of a species. Absolute dominance is often expressed in square feet per acre rather than as a percent.

Relative Dominance = dominance value of a species divided by total dominance values of all species in study area x 100.

Other useful quantitative values include density and frequency of occurrence: Absolute Density = total number of individuals of a species divided by total area of sample.

Relative Density = Number of individuals of a species divided by total number of individuals of all species x 100.

Absolute Frequency = Number of samples in which a species occurs divided by the total number of samples x 100.

Relative Frequency = Frequency of a species divided by total frequency values for all species in study area x 100.

After calculating the relative values for dominance, density and frequency, importance values (IV) can be determined for each species in study area in order to rank the species according to their magnitude of importance. Importance value is a very useful quantitative parameter, especially when comparing the composition of vegetation from different study areas. The importance values of all species in a given study area should add up to 300.

Importance Value = Relative Dominance + Relative Density + Relative Frequency.

Coastal sage scrub in dormant, dessicated, very flammable state during early September. The leaves are dried up, shriveled and brittle. In the picture are three dominant shrubs: California sagebrush (Artemisia californica), black sage (Salvia mellifera) and wild buckwheat (Eriogonum fasciculatum).


18. Conclusion

It is difficult to generalize about the beneficial effects of fire because there are so many complex factors involved. The immediate benefits to a new generation of plant life may not be readily apparent to the casual observer. This is especially true at the time of a personal human tragedy when a houseful of happy memories has been reduced to smoldering rubble. Nonetheless, fire plays an integral role in nature's cycle and has been doing so long before people inhabited this region. With sufficient winter and spring rains these barren hillsides will again become veritable wildflower gardens with acres of colorful species. The air will once again be filled with the perfume of sweet-scented blossoms and the sound of busy, foraging bees. Plants have a remarkable tenacity in the face of fire, and through their dormant seeds and underground burls and bulbs, a new generation will gradually colonize the landscape. Perhaps one day we will fully understand the role of fire in the perpetuation of native vegetation, and the miraculous transformation of ashes to wildflowers.

The role of low ground fires and prescribed burning of forested areas by public agencies has been clearly demonstrated. Reducing the growth of understory shrubs prevents an inevitable lightning fire from being carried into the crowns of trees. This is the case in the Sierra San Pedro Martir of Baja Calfornia where fires have burned out of control for countless centuries. The lack of understory shrubs and fire-scarred trunks on old well-spaced jeffrey pines are testimonials that some trees have survived ground fires during the past century. However, fire management of chaparral in heavily populated regions of southern California is another story and the subject of a "heated controversy." This may also be related to climate change by global warming.

Without fire suppression in the Sierra San Pedro Martir, Baja California, periodic ground fires have swept through these forests of Jeffrey pine (Pinus jeffreyi) and created an open parkland devoid of dense understory vegetation. The trees have thick, fire-resistant bark and can survive repeated ground fires. This is essentially the logic behind prescribed (control) burns in Sequoia-Kings Canyon National Parks,

Prescribed (control) burn in Kings Canyon National Park

Natural periodic brush fires vs. fire suppression: Advocates of natural fire and prescribed burning maintain that properly spaced fire intervals will reduce the fuel build up in chaparral areas and lower the intensity of fire. They maintain that the primary cause of large wildfires is unnatural "fuel" build up due to many years of fire suppression efforts. Advocates of fire suppression counter with some interesting data about devastating fires that occurred less than 10 years apart. These fires were carried by invasive weedy plants and grasses that invaded the previously burned areas. Fanned by dry Santa Ana winds, low humidity and high temperatures, the fires swept over previously burned chaparral that did not have time to recover.

Witch Creek Fire of October 2007 looking south toward Escondido.

Fanned by strong Santa Ana winds with gusts up to 60 mph, the fire in the above image swept westward from Witch Creek east of Ramona to Escondido within 8 hours. The fire essentially followed canyons and hillsides along the general route of the San Dieguito River. It jumped across I-15 south of Escondido and moved into the hillsides bordering Lake Hodges. From here it raced through the hills and canyons west of Escondido on its way to the coast. The Witch Creek Fire burned almost 200,000 acres and destroyed about 1500 homes. This devastating fire followed essentially the same path as the previous devastating Cedar Fire of October 2003.

Embers from fires driven by high winds can start fires up to 1.5 miles away from the "front" of the fire. These spot-fires spread in the direction of the wind, and in turn can start new spot fires in whatever direction the wind is blowing. Everytime you hear that a fire "jumped" the I-15 freeway, this process was at work, since the concrete freeway doesn't burn. I-15 is an 8 lane freeway with a width of 400 feet, greater than the length of a football field. One house in Escondido destroyed by the Witch Fire was 2 miles from the nearest blaze, and yet it caught fire and was gutted without warning.

As Richard Halsey has stated: We need to use proven strategies, such as firesafe zoning, fire resistant construction, and appropriate defensable space. For example, large housing developments in chaparral areas with only one entrance/exit road are a disaster waiting to happen. These housing developments are a hazard to residents and to fire-fighters. In addition, the typical home has eaves that are a perfect trap for airborne embers. Under natural conditions, native chaparral plants are adapted to periodic brush fires; however, population growth, urbanization, vehicle traffic, and the introduction of alien weeds has altered the natural environment in southern California.

A summary of the fire suppression controversy is available at the following URL. It includes numerous references and field studies supporting both points of view:

The Chaparralian, October 23, 2008, Vol. 5, Issue 3, The California Chaparral Institute "Resolving
the Controversy: Why Large Wildfires in Southern California?" Available On-line at:

www.californiachaparral.com/images/Resolving_the_Controversy_Updated.pdf


19. References Cited In This Article


  1. Armstrong, W.P. 1978. "Southern California's Vanishing Cypresses." Fremontia 6 (2): 24-29.

  2. Bais,H.P., R. Vepachedu, S. Gilroy, R.M. Callaway and J.M. Vivanco. 2003. "Allelopathy and Exotic Plant Invasion: From Molecules and Genes to Species Interactions." Science 301: 1377-1380 (September 5, 2003).

  3. Bartholomew, B. 1970. "Bare Zone Between California Shrub and Grassland Communitites: The Role of Animals." Science 170: 1210-1212.

  4. Chou, C.H. and C.H. Muller. 1972. "Allelopathic Mechanisms of Arctostaphylos glandulosa var. zacaensis." American Midland Naturalist 88: 324-347.

  5. Christensen, N.L. and C.H. Muller. 1975. Effects of Fire on Factors Controlling Plant Growth in Adenostoma Chaparral." Ecological Monographs 45: 29-55.

  6. Halsey, R.W. 2005. Fire, Chaparral, and Survival in Southern California. Sunbelt Publications, Inc., PO Box 191126, San Diego, CA.

  7. Halsey, R.W. 2004. "An Eco-historical View of the Investigation of Chemical Inhibition in California Coastal Sage Scrub and Chamise Chaparral." Journal of the Torrey Botanical Society 131 (4): 343-367.

  8. Hanawalt, R.B. 1971. "Inhibition of Annual Plants by Arctostaphylos," pp. 33-38. In Biochemical Interactions Among Plants. National Academy of Sciences, Washington, D.C. 134 p.

  9. Keeley, J.E., et al. 1985. "Role of Allelopathy, Heat, and Charred Wood in the Germination of Chaparral Herbs and Suffrutescents." Journal of Ecology 73: 445-458.

  10. Lanner, R.M. 1999. Conifers of California. Cachuma Press, Los Olivos, California.

  11. Mirov, N.T. 1967. The Genus Pinus. The Ronald Press Company, New York.

  12. Muller, C.H. 1966. "The Role of Chemical Inhibition (Allelopathy) in Vegetational Composition." Bulletin of the Torrey Botanical Club 93: 332-351.

  13. Muller, C.H., R.B. Hanawalt, and J.K. McPherson. 1968. "Allelopathic Control of Herb Growth in the Fire Cycle of California Chaparral." Bulletin of the Torrey Botanical Club 95: 225-231.

  14. Muller, C.H., Muller, W.H. and B.L. Haines. 1964. "Volatile Growth Inhibitors Produced by Aromatic Shrubs." Science 143 (3605): 471-473.

  15. Stowe, L.G. 1979. "Allelopathy and its Influence on the Distribution of Plants in an Illinois Old-Field." Journal of Ecology 67 (3): 1065-1085.

  16. Wells, P.V. 1964. "Antibiosis As a Factor in Vegetation Patterns." Science 143: 889.

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