The Burning of Cuyamaca Rancho State Park
Cuyamaca Rancho State Park after Cedar Fire showing major burn areas Photo by Barbara Barnes
Fire is an important disturbance agent in the Southern California landscape and plays an important role in the maintenance and composition of its mixed conifer forests, such as those found in Cuyamaca Rancho State Park (CRSP). Fire benefits these forests by preparing the soil for seed growth by clearing underbrush and adding nutrients through ash, and by eliminating dense thickets of small trees, thus maintaining a healthy density of large pine trees. Many of the tree species found in the mixed conifer forest are adapted to or even require fire to reproduce.
The natural fire regime of mixed conifer forests has been estimated using both fire records and fire scar methods. Estimates range from a 4 to 30 year fire interval (number of years between two successive fire events at a specific site or an area of a specified size). These frequent fires are thought to have been low intensity, surface burns that had minimal effect on large trees. This type of fire regime created an open, park-like forest dominated by large pine trees and a grassy forest floor.
Historic Photo from USDA Forest Service
Despite some debate over the length of historic fire regimes, most fire ecologists agree the intervals under current fire suppression (1900’s to present) are much longer than they were historically.
Since the early 1900’s humans have changed the natural fire regime across the western United States by excluding and suppressing fire. As a result, the amount of time that passes between fires has gotten longer and longer. Fire exclusion has allowed the persistence of shade-tolerant species (species that can live in shade and do not need direct sunlight) that would otherwise be rare in a mixed conifer forest with a fire regime of frequent surface fires. These species, such as incense cedar and white fir, form a second layer of trees below the uppermost canopy in mixed conifer forests of the west, including the forests of Southern California. The resulting increase in tree density and abundance of available fuels elevates the potential for large, stand-replacing crown fires (fires that kill all above-ground biomass) which otherwise may not occur naturally in this habitat. These thickets of shade-tolerant species act as ‘ladder-fuels’, carrying fire from the ground up into the canopy of the tallest trees and causing a crown fire. Stand-replacing fires result in the mortality of even large, fire-tolerant trees (trees adapted to live through fires). The Cedar Fire of 2003 was a stand-replacing, crown fire. This catastrophic fire is the largest mapped fire in California history.
Middle Peak after Cedar Fire (March, 2004) Photo by Dr. Janet Franklin
Prior to October 2003, much of CRSP had not burned since at least 1911 (when fire records were first kept) due to a policy of fire suppression in the Park. The Cedar Fire burned through the mixed conifer forests of the Park in a high severity stand-replacing fire, burning through the tops of the trees and causing high levels of tree mortality, especially among the conifers.
Dead Conifers on West Mesa after Cedar Fire (May, 2004) Photo by Heather Karnes-Schmalbach
The fire occurred under extreme weather conditions and was spread into the forest by the surrounding chaparral habitat and fanned by strong, westerly winds.
Tree Species of the Mixed Conifer Forest of Cuyamaca Rancho State Park
Coulter pine. Coulter pine occurs throughout the mountain ranges of California and into Mexico. It is a native evergreen conifer that lives up to 100 years of age. It attains a height of 30 to 83 feet and a diameter 12 to 31 inches. The bark is thick and roughly furrowed and the crown is pyramidal like a typical christmas tree. Needles occur in groups of three and are 6 to 12 inches long. The massive, spiny cones (9 to 15 inches long) are the heaviest of any pine. Coulter pine displays variation in degree of cone serotiny (cones that open with fire). Not every Coulter pine cone is serotinous. There are some trees with no serotinous cones and some with all serotinous cones and everything in between. Serotiny is prevalent in Coulter pines occurring withing chaparral or oak woodland. Cones of Coulter pine in these communities typically do not open until heated by fire. Consequently, the bulk of Coulter pine regeneration in these communities occurs after fire. Coulter pine ecotypes associated with coast live oak, however, typically bear cones that open at maturity or shortly thereafter. Coulter pine seedling development is best in mineral soil in open areas; such conditions are created by fire.
Photos By Michael Simpson
Coulter pine cone Coulter pine seedling next to cone opened by Cedar Fire
Jeffery pine. Jeffrey pine extends north into southwestern Oregon, across the Sierra Nevada into western Nevada, and south to the mountains of San Diego and into northern Baja California. Jeffrey pine may live 400 to 500 years and can attain immense size. The species typically grows 4 to 6 feet in diameter and 170 to 200 feet in height. The bark is deeply furrowed with hard scales that look like plates of bark. Needles are in bundles of three and are 7.5 to 11 inches long. Jeffrey pines are classified as being moderately resistant to fire. It's thick, corky bark withstands high temperatures and it's tall, erect trunk is free of lower limbs allowing a surface fire to pass through without igniting the canopy. Jeffrey pine seedlings have also adapted to reproducing well on bare mineral soil created by fire.
Jeffery Pine Tree and cone Photos By Michael Simpson
Ponderosa pine. Ponderosa pine ranges from southern British Columbia south through the mountains of Washington, Oregon, and California. San Diego marks the southern most extent of its range. Like the other pines previously mentioned, Ponderosa pine has the potential for achieving large dimensions. Diameters of 30 to 50 inches and heights of 90 to 130 feet are common. Trees often reach ages of 300 to 600 years. Needles are typically in bundles of three. They are 5 to 10 inches long and form tufts at the end of each branch. Cones are oval and 3 to 6 inches long. The trunk is typically straight, and like Jeffrey pine is clear of lower branches at maturity. The bark of mature trees is composed of broad, irregular scaly-plates that fit together like jigsaw puzzle pieces. Ponderosa pine has evolved with a thick bark and open crown structure that allows it to survive most fires. Other fire adaptations include deep roots and high needle moisture content. Seedlings prefer the mineral-soil seedbeds created by fire. Fire also shapes the composition of Ponderosa pine stands. In the late 1800's stands exhibited open park like appearances with large, healthy trees and relatively few understory trees. Fire suppression, however, has allowed the unnatural buildup of forest fuels that has increased the occurrence of stand-replacing fires. Over the last 100 years of fire suppression, Ponderosa pine stands have been replaced by shade-tolerant stands of shade tolerant species (incense cedar and white fir).
Ponderosa Pine tree and cone Photos By Michael Simpson
Incense cedar. Incense cedar is generally found from Oregon, southward through the mountain ranges of California to ranges in Baja, California. Incense cedar is most common in the Sierra Nevada, occurring individually or in small groups. Incense cedar forms a more dense and narrow crown than the pines above. Instead of the typical pine needles it has flattened branchlets with green overlapping scales. Cones are small (0.8 to 1.5 inches), and hang from the tip of the branch. Bark on mature trees is dark brown, fibrous, and deeply and irregularly furrowed. In the Coast Ranges and southern California, the largest trees generally are from 60 to 80 feet tall and 36 to 48 inches in diameter. Incense cedar is a long-lived species and large trees are often over 500 years old. Unlike many pine species, Incense cedar is highly susceptible to fire. Seedlings have very flammable bark and foliage, and are usually totally consumed by fire. More mature trees have a thicker basal bark (up to 6 inches) that adequately protects them from low intensity ground fires but not from higher intensity burns.
Incense Cedar tree and bark Photos By Michael Simpson
White fir. White fir is very widespread throughout the Western U.S. It is a large, native, coniferous tree. Mature white fir trees in the central Sierra Nevada are 140 to 180 feet tall, and 40 to 80 inches in diameter, but may grow larger. White fir may reach ages of 300-400 years. Bark on young trunks is smooth and gray, becoming thick, hard and deeply furrowed into scaly ridges with age. The crown of young trees is symmetrical and sharp-pointed, becoming rounded at the top in mature trees. White fir branches are short and stout, with needles 1.2 to 2.8 inches long and generally curved upward. Seedlings and saplings are thin-barked and are highly susceptible to fire damage and mortality. Additionally, young trees have low-growing branches that can easily ignite from burning undergrowth, providing a fuel ladder into the crown. Consequently, young white fir are usually killed by even low-intensity, surface fires. As trees mature and bark thickens, they become more resistant to fire. However, the tendency to retain some low branches makes is susceptable to mortality by fire. Exposed mineral soil seedbeds created by fire favor initial seedling establishment in white fir, but seedling survival is better in partial shade. Therefore, seedlings establish soon after fire if a canopy remains, but may take several years to establish if the canopy has been removed.
White Fir tree and needles Photos By Michael Simpson
Coastal live oak. Coast live oak occurs in California from Mendocino County south into northern Mexico. Coast live oak is a native, drought-resistant, evergreen tree, ranging in height from 19 to 82 feet and from 1 to 4 feet in diameter. The bark of young trees is smooth but with age, it develops deep furrows and ridges. Its open crowns are broad and dense, with foliage often reaching the ground. Coast live oak stands are typically from 40 to 110 years old although, individual trees may live over 250 years. Coast live oak seedlings and saplings may be top-killed (above-ground portion killed) by low- to moderate-severity fire, and severe fire kills trees of this size. Because of their thick bark, mature trees have high fire survival rates, even with severe fire. Coast live oak sprouts from the trunk, branches, and/or root crown after fire. Light-severity surface fire has little effect on mature coast live oak. Coast live oak recovers rapidly from moderate-severity fire however, severely burned crowns, trunks, and root crowns may require several years to sprout. A tree may appear dead a whole year after a fire, but may still be alive and resprout.
Photo By Michael Simpson Photo by Linnea Spears
Coast Live Oak leaves Coast Live Oak resprouts from base of tree after Cedar Fire
Canyon live oak. Canyon live oak grows from southwestern Oregon to southern California and the mountains of Mexico. It is the most widely distributed of all California oaks. Canyon live oak is a rounded, spreading, evergreen which grows as a large shrub or small-to-large tree. Height commonly ranges from 15 to 70 feet, with an average maximum diameter of 2.5 to 5.0 feet. It is typically long-lived, and many plants can live to 250 or 300 years of age. Young bark is smooth, scaly, and pale gray in color. Furrows develop in stems greater than 3 inches in diameter, and the outer bark of older trunks develop variable strips. The leathery, oblong leaves of canyon live oak are green and glossy above, but golden-yellow below. Above ground foliage of canyon live oak is sensitive to fire, and this plant is generally top-killed by fires of even relatively low intensity. The bark is relatively thin and offers little protection when compared with other species of oak. Belowground portions of canyon live oak generally survive even when the plant is top-killed by fire. Acorns of canyon live oak are sensitive to heat and are generally destroyed by fire. Canyon live oak generally sprouts prolifically after fire from the subsurface root crown. Where sprouting occurs, recovery of canyon live oak is generally rapid. In some areas, sprouts are capable of reaching 3 to 6 feet in height within only four years after fire. Conditions created by fire are not generally conducive to the germination of acorns, and most oaks seldom establish through seed after fire.
Photo By Michael Simpson Photo by Linnea Spears
Canyon Live Oak leaves and acorns Canyon Live Oak resprouts from base after Cedar Fire
Black oak. California black oak is distributed along foothills and lower mountains of California and southern Oregon, reaching its southern most extent in San Diego County. Unlike the previous two oaks, California black oak is a deciduous tree (loses its leaves each fall). It typically grows from 30 to 80 feet in height and from 1 to 4.5 feet in diameter. Trunks are often forked, and usually decayed and hollow in older trees. The bark is thin and smooth in young trees, becoming moderately thick, deeply fissured, and platy with age. Acorns are relatively large in this species, from 1 to 1.2 inches long. The deeply lobed leaves are very distincitve and an easy way to tell this oak apart from the others. California black oak can live up to 500 years of age but is fire sensitive. The outer bark chars readily, and the tree suffers heat damage even where bark is thick. All trees in a stand are usually top-killed following crown fire regardless of size, and complete kill is common after such fire in smaller trees. Complete kill is also common when individual trees or clumps of trees are surrounded by adjoining brush. Spring fire, which corresponds to the active growing season, results in greater tissue damage than fire in other seasons. Within a few weeks following fire, most surviving trees sprout from the root crown and undamaged portions of the trunk. Fire prepares an ideal seedbed, and seedlings establish in the first postfire growing season.
Photo by Linnea Spears
Black Oak seedling found in Cuyamaca after Cedar Fire (May, 2004)
Current Fire Recovery Study
In a current study, sponsored by California State Parks, Linnea Spears, a graduate student in the Biology Department at San Diego State University (advised by Dr. Janet Franklin), is investigating patterns of tree mortality and vegetative recovery following the Cedar Fire in the mixed conifer forests of CRSP. The study site is in the West Mesa area of the Park. The preliminary results from the first year of the study describe the tree mortality experienced from the fire and also show signs the forest is recovering.
Unfortunately for people who loved the mixed conifer forests of CRSP, most of the conifer trees died in the fire (95% conifer mortality). Most of the oaks, however, survived (only 14% oak mortality). Survival, in the case of the oaks, refers to any resprouting (new foliage growth from base or trunk) observed. Almost all of the oak trees were top-killed (most of the branches were removed or killed by the fire) like the conifers. As discussed above in the species descriptions, oaks can respond to fire by resprouting. Most conifer species cannot resprout and either depend on their thick bark and other adaptations to protect them from fire, or respond by producing many seedlings. Unfortunately for the pines, very few pine seedlings were found in the study area (less than 350). But this does not mean the end for the pine trees of CRSP, there are a few patches of unburned trees that could recolonize burnt areas and with all the rain in the 2004-2005 winter season, more seedlings may appear in the second year of the study.
Along with the resprouting oaks, there were many resprouting chaparral shrub species, many shrub seedlings (most abundant is Ceanothus leucodermis), and lots of beautiful wildflowers. Another positive result, only 9 non-native (e.g. exotic invasive) species were recorded in the study area. These 9 non-natives make up a small percentage of the total cover (8.1% cover) and density (5.7% of species counted) of the recovering understory vegetation.
Recovering chaparral area of West Mesa after Cedar Fire (May, 2004) Photo by Linnea Spears
Time and its interactions are important to consider in a recovering ecosystem. While a mixed conifer forest may not recover for many years in CRSP, it is becoming replaced by oak woodland and chaparral, whose species are recovering in the burned areas already. To those who remember Cuyumaca Rancho State Park prior to the fires of October 2003, it may look different for many years to come, but it will still be beautiful.
Recovering forested area of West Mesa after Cedar Fire (May, 2004) Photo by Linnea Spears
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