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The Natural History of Big SurCalifornia Natural History Guides, 57
By Paul Henson Donald J. Usner
The University of California PressCopyright © 1993 Regents of the University of California
All right reserved.
Chapter OneRedwood Forest
If there is one tree that most non-Californians identify with this state, it is certainly the coast redwood (Sequoia sempervirens) (fig. 77). These giant trees, famous for their size and longevity, form dark, primordial groves in moist valleys and canyons, and large ferns and a lush understory suggest a different, earlier time. Big Sur is the southern stronghold of California's redwood forest, and the species reaches its southern distributional limit about 2.5 km (1.5 mi) from the Salmon Creek drainage in southern Big Sur. From this point, the redwood forest stretches north 725 km (450 mi) just across the California-Oregon border. The trees grow in the narrow belt of fog that hugs the California coast and are rarely found more than 48-64 km (30-40 mi) inland from the Pacific.
Redwoods have not always been restricted to this foggy belt of maritime California. Fossil evidence indicates that these trees and related plants were once widespread throughout the northern hemisphere, including Greenland, Europe, and Asia, about 50 million years ago. Climatic conditions then, even in the far north, were similar to the mildtemperatures and high humidity seen today along the northern Pacific coast. In fact, a closely related species once thought to be extinct and known only from the fossil record was discovered in a remote area of China. However, due to the changing climate, says botanist Robert Ornduff, the coast redwood "should be considered a species that is on the way out in an evolutionary sense."
The redwood's distribution in Big Sur reflects this trend and is more patchy than that of the redwood forests to the north. The trees usually occupy the steep coastal canyons where summer fog is channeled. They have been recorded growing at elevations as high as 1100 m (3600 ft) and occur less frequently on the north-facing slopes of the interior valleys.
The redwood is a water-loving species and is thus restricted to areas of ample moisture. Many of the creeks flowing through the redwood-filled canyons dry up during the summer, but the summer fog supplies important supplementary moisture to the trees. The fog not only lowers temperature and increases humidity, but it also condenses on the flat needles of the redwoods and falls to the ground as fog drip. Studies in northern California have found that fog drip can add as much as 26 cm (10 in.) of precipitation to the annual total in redwood forests.
Differences in temperature and moisture are also evident within the redwood's range along the coast from Oregon to Big Sur. The warmer and drier climate of Big Sur is probably responsible for the smaller size of Big Sur's redwoods, both as individuals and the forest in general. The redwoods in Big Sur, as large as some of them are, do not come near the size of the northern redwoods of Humboldt and Del Norte counties. Those giants may be the tallest trees in the world, the largest reaching 112 m (367 ft) in height (some Australian eucalyptus trees may be as tall or taller). The largest redwoods in Big Sur are 61 m (200 ft) tall and are found in the canyons and valleys on the coastal flank of the mountains, such as along the Little Sur and Big Sur rivers and in Partington, McWay, Big Creek, and Palo Colorado canyons. To the south, the trees become noticeably smaller.
If the basic requirements of humidity and soil conditions are met, however, redwoods are extremely vigorous and competitive plants. They are not only the tallest of trees but are also some of the oldest, living longer than 2000 years. Black scars reaching far up the trees' trunks attest to their enduring many fires over the years. Their bark is fire resistant and can be as thick as 30 cm (12 in.), while their wood lacks the flammable pitch and resins that allow many other conifers to burn quickly during a blaze. Redwoods also resist disease and wood-boring insects, thus the lumber is preferred where insect and rot damage is a problem.
What remains of a tree that does succumb to a disaster, such as fire or logging, does not always die but often sprouts from its roots or stump in a process known as stump sprouting. The branches of a fallen tree or dormant buds grow straight up and send out new roots, becoming new trees as the parent log decays. Rings of younger trees often surround burned or logged stumps and are the shoots of those parent trees. As the young trees grow, the ring enlarges and these trees develop their own rings. The identity of the original ring is lost as the process is repeated. Redwoods most often reproduce this way, vegetatively, rather than sexually with their seed-bearing cones.
Fire-resistence, stump-sprouting, and the subsequent rapid growth of young trees are several important ways in which redwoods shape and dominate their environment. Most of the hardwood trees competing for space with the redwoods, such as the tanoak (Lithocarpus densiflorus) and California bay, are less tolerant of fire and have a slower growth rate. These trees, although they can also stump sprout, are quickly outgrown by the redwoods and are eventually forced to live in the shade. Shading of the forest floor inhibits the growth of tree seedlings, and the deep layer of duff-organic material dropped by the trees-raises the soil acidity and also discourages competitive growth.
Another adaptation of redwoods is their ability to withstand the flooding and silting that periodically occur in their canyon bottom habitat. Often after a severe summer fire, the following winter's rains wash soil and debris off the denuded slopes and into the redwood-filled canyons. Much of this soil is deposited in the flatter portions of the redwood groves, and in one storm several feet of mud and silt can bury the bases of the redwoods. In McWay Canyon at Julia Pfeiffer-Burns State Park, for example, the grove above the parking area was silted to a depth of several feet in the winter following the Rat Creek fire of 1985. Several tributaries of the Big Sur River channeled mudflows into the Big Sur Valley in 1972 and inundated redwoods there.
Redwoods lack tap roots and have an extremely shallow root system. They instead develop a wide root horizon close to the surface. After burial by a mudflow, new redwood roots grow from the old root system toward the surface and out from the buried portion of the trunk. A new shallow root system is then established, and the old one, now well buried, is abandoned. Bay, tanoak, and other trees, in contrast, are often killed by silt deposition. Geologist Lionel Jackson excavated ancient redwood root horizons in Pfeiffer-Big Sur State Park to establish patterns terns of mudflows over time. By reading the patterns of root growth, he found that severe mudflows probably occurred in the park area at least three times between the years 1370 and 1700.
Some common understory plants such as redwood sorrel (Oxalis oregana) (fig. 78) have also adapted to this cycle. When submerged by silt, they grow vertical shoots up through the layer and eventually reclaim their former habitat.
Types of Big Sur Redwood Forest and Related Plants
Table 7 lists the trees and understory plants most commonly found in the Big Sur Redwood forest. Redwood forests can be divided into three main phases for a more accurate description: pure redwood, redwood-riparian, and redwood-mixed hardwood. The latter two types are essentially zones of overlap between redwood forest, riparian woodland, and mixed hardwood forest; these phases are widespread and consistent. Differences in exposure to wind and sunlight, availability of water, varying soil types, elevation differences, and disturbance history all play a part in shaping the composition of each phase.
Pure Redwood Forest Many of Big Sur's coastal canyons, such as Partington Canyon and the Big Sur River valley, contain stands of pure redwood forest. These groves are not usually located directly along a large stream or river because sunlight can reach the forest floor through the open stream corridor. Instead, they are found on the moist, north-facing slopes of dark canyons or in small stream flats and protected bowls.
In its purest form, this forest is characterized by a lack of plant diversity. Here the redwoods so thoroughly dominate that often nothing else can grow, not even the shade-tolerant sword fern (Polystichum munitum) (fig. 79) and redwood sorrel. The ground, nearly bare of understory, is covered with a duff layer several inches thick. The canopy overhead systematically filters out most of the direct sunlight, and the relative humidity and temperature are kept remarkably constant.
The pure redwood forest contains some of the most magnificent and oldest redwoods, but sometimes a dense grove of young redwoods of uniform stature and age can also form a pure stand. Because the redwoods are so long lived, only severe natural or man-made disturbances can open up the forest to colonization by other plant species. On steep slopes, landslides open up patches of sunlit ground which may allow a tanoak, bay, or small shrub to move in. Fires perform the same function, but redwoods often bounce back and reclaim their territory before other species can become established.
Redwood-Riparian Forest As the name implies, the redwood-riparian forest is restricted to the canyon bottoms where streams and rivers flow. This plant community is a melding of the redwood forest and the riparian woodland. The overall plant diversity is much greater here than in the pure redwood forest. The open stream corridor allows direct sunlight to infiltrate the forest floor, and additional moisture from the stream is available to plants along the banks. The hardwoods found here include the tanoak, western sycamore, white alder (Alnus rhombifolia), bigleaf maple, and California bay. The bay and tanoak trees grow interspersed with the redwoods, while the others line the stream where water and sunlight are most readily available.
This forest often forms the picturesque scenes associated with the central California redwoods. Elegant, moisture-loving flowers such as leopard lily (Lilium pardalinum), crimson colombine (Aquilegia formosa), and Andrew's clintonia (Clintonia andrewsiana) line deep, clear pools. Elk clover (Aralia californica), western coltsfoot (Petasites palmatus), coast boykinia (Boykinia elata), horsetails (Equisetum spp.), and several ferns give the pools a lush, almost tropical look. The riparian hardwoods, the leaves of which turn yellow and orange in autumn, contrast sharply with the towering green and brown redwoods.
Just off the streambanks, this forest can have a dense and brambly understory of vines and shrubs that includes coffeeberry, poison oak, thimbleberry (Rubus parviflorus var. glutinosum), gooseberries (Ribes spp.), and California huckleberry (Vaccinium ovatum), as well as the young saplings of tanoak and bay. Depending on moisture availability, there are often many species of ferns. Sword ferns and spreading wood ferns (Dryopteris arguta) (fig. 80) are common, while wetter areas near springs have venus hair (Adiantum capillus-veneris), maidenhair (A. jordani), five-finger (A. pedatum) (fig. 81), western chain (Woodwardia fimbriata) (fig. 82), and bracken (Pteridium aquilinum var. pubescens) (fig. 83) ferns. The flowers include western Solomon's seal (Smilacena racemosa) (fig. 84), western wake robin (Trillium ovatum) (fig. 85), redwood sorrel, redwood violets (Viola sempervirens), star flower (Trientalis latifolia) (fig. 86), and fairy bells (Disporum hookeri).
Redwood-Mixed Hardwood Forest The third phase of redwood forest is redwood-mixed hardwood forest. This forest occurs on moist, north-facing slopes above the canyon bottoms where less light is available, and it represents a transition from a redwood forest to a hard-wood forest. Although conditions are drier up here, enough moisture is present for redwoods to grow with the hardwoods.
The hardwoods adapt well to growing with the taller redwoods. Along the Tanbark Trail in Partington Canyon, for example, tanoaks grow almost as tall and narrow as the accompanying redwoods. California bay displays a similar tendency, while the coast live oak and madrone sometimes grow in patchy openings in and around the redwood stands. The understory here is usually shrubbier than that of the other two phases. There are many flowers, such as milkmaids (Cardamine californica) (fig. 87), hound's tongue (Cynoglossum grande), Douglas' iris (Iris douglasiana), and California saxifrage (Saxifraga californica), and shrubs such as poison oak, California coffeeberry, and gooseberries grow thick.
The redwoods grow smaller and are less hardy near the tops of the slopes where moisture diminishes and exposure to wind and sun becomes more severe. The hardwoods, in contrast, become more numerous, and the redwoods eventually give way to a mixed hardwood or mixed evergreen forest.
Redwood Forest Animals
At first glance, the redwood forest seems quite devoid of animal life. The groves are unusually quiet. Aside from the occasional cries of the Steller's jay (Cyanocitta stelleri) (fig. 88), there is little bird chatter or insect noise. This absence is most noticeable in the pure redwood forest, where the understory has few seed-bearing plants to attract herbivores and their predators. Also, one of the most common understory plants, the redwood sorrel, is toxic to grazing animals and is avoided.
What the redwood forest lacks in diversity, however, it makes up for with a moist and stable microclimate relished by a few notable animals. The banana slug (Ariolimax columbianus ssp. stramineus) (fig. 89), for example, would perish in the hot chaparral or grassland during the heat of the summer but instead finds a suitable habitat here year-round.
This bright yellow gastropod is one of the redwood forest's most visible inhabitants. It is related to the intertidal snails described earlier in this book, but its shell has been reduced to a tiny fragment hidden in its mantle. This lack of a shell explains the banana slug's need to stay in its moist environment since the shell is used by snails to lock in body moisture during dry periods.
Shells also provide snails with a measure of protection from predators, but banana slugs have developed another strategy. Their bodies secrete chemicals that are extremely distasteful, and the slug's bright yellow coloration advertises this fact to would-be predators. Thus, they are usually left alone to graze on the vegetation and fungi littering the forest floor.
Several amphibian species also prefer the moist habitat of the redwood forest.
Excerpted from The Natural History of Big Sur by Paul Henson Donald J. Usner Copyright © 1993 by Regents of the University of California . Excerpted by permission.
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Table of ContentsIllustrations Tables Maps Acknowledgments Introduction PART I. BIG SUR NATURAL HISTORY 1. Big Sur Geology Topography Plate Tectonics Early Central California Geological History Basement Rock Assemblages Overlying Formations Faults Recent Events 2. Weather and Climate Regional Climate Local Weather Patterns 3. Big Sur Shoreline Introduction Tidal Zonation Seaweeds Common Intertidal Animals Seabirds and Shorebirds Marine Mammals 4. Big Sur Plant Communities Introduction Coastal Scrub Chaparral Redwood Forest Riparian Woodland and Freshwater Streams Big Sur Grasslands Oak Woodland Mixed Evergreen Forest 5. Fire Ecology Fire in the Santa Lucia Range Fire Behavior Effects of Fire Plant Adaptations to Fire Effects of Fire on Animals Fire Management 6. Big Sur Fauna Overview Introduction Reptiles and Amphibians Birds Terrestrial Mammals 7. Human History Introduction Natives and the Big Sur Environment Early Exploration and Settlement Highway 1 and Recent Settlers 8. Changes in the Big Sur Environment Introduction Ranching Logging Mining Offshore Oil Drilling Recreation Nonnative Plants Contents Residential Development and Roads Changes in Fauna PART II. FIELD GUIDE TO BIG SUR PUBLIC LANDS Introduction Maps of the Big Sur Area Coastal State Parks Garrapata State Park Point Sur Lighthouse Andrew Molera State Park Pfeiffer-Big Sur State Park Julia Pfeiffer-Burns State Park Los Padres National Forest: Coastal Areas Pfeiffer Beach Pacific Valley Area Los Padres National Forest: Ventana Wilderness Big Sur River Watershed Little Sur River Watershed Carmel River Watershed Arroyo Seco Watershed Cone Peak Area Salmon Creek-Villa Creek Area Maps Index
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