Ecological site group description

Provisional. A provisional ecological site description has undergone quality control and quality assurance review. It contains a working state and transition model and enough information to identify the ecological site.

Physiography

This ESG is found on fluviomarine terraces and hills on slopes from 5-50% and elevations generally under 1000 ft in LRU L.

Climate

The average annual precipitation in this MLRA is 23 to 98 inches (585 to 2,490 millimeters), increasing with elevation inland. Most of the rainfall occurs as low-intensity, Pacific frontal storms. Precipitation is evenly distributed throughout fall, winter, and spring, but summers are dry. Snowfall is rare along the coast, but snow accumulates at the higher elevations directly inland. Fog is a significant variable that defines this MLRA from other similar MLRAs. Summer fog frequency values of greater than 35% are strongly correlated to the extent of coast redwood distribution, which is a primary indicator species in this MLRA. Nightime fog is approximately twice as common as daytime fog and seasonally, it reaches its peak frequency in early August, with the greatest occurrence of fog from June through September (Johnstone and Dawson 2010). The average annual temperature is 49 to 59 degrees F (10 to 15 degrees C). The freeze-free period averages 300 days and ranges from 230 to 365 days, decreasing inland as elevation increases.

The Fort Bragg/Fort Ross Terraces form an elevated coastal plain that has less relief (200-800 feet) than the adjacent low elevation mountains of LRU K. Monthly and annual temperature variations are minimal and summer fog is common.

Soil features

This ESG is found on isomesic, well-drained soils that are derived from alluvium derived from sedimentary rocks. They are fine-loamy, Typic Tropohumults that have good water-holding capacity, have high runoff and slow permeability and are slightly acidic.

A representative soil for this site is the Empire soils within Mendocino County.

Vegetation dynamics

This provisional ecological site concept attempts to describe the coast redwood-Douglas-fir dominated slopes that can be found within this LRU. This concept is primarily supported through literature and available information from the Mendocino County Survey. This provisional ecological site concept covers the mountains within close proximity to the coast and at the lower elevations that spend longer periods within the summer coastal fog. Future work will need to be done to better understand the soil and site characteristics that drive the vegetation expression for this provisional ecological site concept.

Abiotic Factors

Sequoia sempervirens (coast redwood) and Pseudotsuga menzeisii (Douglas-fir) forests in this LRU dominate the more well-drained, less acidic soils of LRU L that are solidly within the coastal fog influence, especially during the summer months. Although coast redwood and Douglas-fir can grow on a variety of soils, the soils are found at elevations below 1,000 feet between the ocean and the first main north-south ridge. Where frequent heavy summer fog is intercepted by a tree canopy, a significant amount of moisture is added to the soil. Soils have water available for plant growth most or all of the year, and average soil temperatures at a depth of 20 inches vary by less than 5 degrees C between summer and winter.

Coast redwood attains a height of 395 ft (~120 m), and an age of at least 2200 years. Roots are shallow without a taproot. Trees begin bearing cones by 5 to 15 years of age and seed production is generally high, however seed viability is low. Wind and gravity disperse the seeds, with most falling within 395-400 ft of the parent tree. Seedling establishment is best on moist soil lacking litter but can occur on duff or logs. Plants are moderately shade tolerant, but they grow faster in higher light levels if soil moisture is present (MCV 2018).

Douglas-fir is a large, coniferous, evergreen tree. Adapted to a moist, mild climate, it grows bigger and more rapidly than the inland variety. Trees 5 to 6 feet (150-180 cm) in diameter (150-180 cm) and 250 feet (76 m) or more in height are common in old-growth stands. These trees commonly live more than 500 years and occasionally more than 1,000 years. Old individuals typically have a narrow, cylindric crown beginning 65 to 130 feet (20-40 m) above a branch-free bole. It often takes 77 years for the bole to be clear to a height of 17 feet (5 m) and 107 years to be clear to a height of 33 feet (10 m). In wet coastal forests, nearly every surface of old-growth Douglas-fir in this ecological site is often covered by epiphytic mosses and lichens (Uchytil, 1991). This tree's rooting habit is not particularly deep. The roots of young Douglas-fir tend to be shallower than roots of many of the same aged conifers like ponderosa pine, sugar pine, or incense-cedar. Some roots are commonly found in organic soil layers or near the mineral soil surface.

This ecological site is dominated by a multi-tiered canopy of conifers, with coast redwood making up more than 50% of the stands basal area and Douglas-fir and other hardwoods accounting for between 30-50%. Pacific rhododendron and tanoak readily establish after disturbance and may dominate the overstory for several years post-disturbance. Fallen logs are an essential part of this ecological site, providing significant habitat for wildlife species and conifer recruits. Conifer recruitment on the bare mineral soil is rare, due to the thick litter layer and organic surface soil and is therefore relegated only to areas of surface soil disturbance from mass wasting, logging practices, wind throw, and recreation trails.

Primary Disturbances

Fire is the principal disturbance agent in both young-growth and old-growth stands. Lightning-ignited fires occur in this zone with fair regularity, however, Native American burning is thought to have also played a major role with fires set in areas adjacent to redwood forest burning into the redwood zone (Veirs, 1996). Natural fire intervals ranged from 500 to 600 years on the coast, 150 to 200 years on intermediate sites, and 50 years or less on inland sites. The northern range of redwoods evolved within a low to moderate natural disturbance regime (Veirs, 1979). The mean fire interval is quite variable, depending on environmental site conditions. Old-growth stands show evidence of three or more severe fires each century, and the distribution of fires appears as a natural pattern of several short intervals between fires followed by one or more long interval (Stuart 1987, Jacobs et al. 1985).The co-dominance of Douglas-fir and hardwoods in this provisional ecological site concept indicates a more regular occurrence of fires and disturbance, since Douglas-fir would only persist in this type of forest if there were adequate openings and mineral soils periodically exposed to facilitate regeneration and canopy recruitment. Fire scars are abundant throughout old-growth stands and are evidence of this fire history. Previous harvesting and the use of fire to treat logging slash in this area has also changed species composition on many formerly redwood-dominated sites (Noss et al, 2000).

Both redwood and tanoak can re-sprout following fire (Veirs, 1996). After fire, redwood may sprout from the root crown or from dormant buds located under the bark of the bole and branches (Noss, 2000), while tanoak typically only sprouts from the root collar. The sprouting ability of redwood is most vigorous in younger stands and decreases with age, while the ability to survive fire increases with age as its fibrous bark thickens. Frequent fire reduces tanoak’s sprouting ability and also tends to keep understories open (Arno, 2002). Fire exclusion would allow for the gradual increase of tanoak in the understory (McMurray, 1989). Surface fires likely modified the tree species composition by favoring the thicker-barked redwood and killing Notholithocarpus densiflorus (tanoak). Fires also expose the mineral-rich soil and reduce competition from other plants, thereby increasing the establishment of Douglas-fir (Veirs, 1979, Agee, 1993). Tanoak seedlings and sapling-sized stems are often top-killed by surface fire, though larger stems may survive with only basal wounding (Tappeiner, 1984).

A moderate fire could lead towards a mosaic in regeneration patterns an uneven-aged structure. Patches of trees would be killed leaving others slightly damaged or unharmed. Douglas-fir regeneration would be favored in the large gaps that are created following a moderate fire, potentially leading to a larger proportion of Douglas-fir to redwood for several centuries (Agee, 1993). Without these gaps caused by fire, Douglas-fir regeneration is unsuccessful, and with continued lack of disturbance it may slowly be replaced by redwood as the dominant canopy species (Veirs, 1979, 1996).

Fires will also alter the composition of shrubs and forbs in the understory community. Vaccinium ovatum (evergreen huckleberry) is a common species in both moist and dry Douglas-fir and redwood environments. It is normally a fire-dependent shrub species, but little is known concerning it's adaptation to fire under low to moderate fire return intervals (Tirmenstein, 1990). Following a fire, evergreen huckleberry will often re-sprout and recover rapidly. Rhododendron macrophyllum (Pacific rhododendron) is considered sensitive to fire. Following a surface fire, it may reestablish seedlings by sprouting from the root crown or stem base (Crane, 1990). After a disturbance such as fire, a decrease in plant cover is common, and will be followed by a gradual increase in cover over time.

Another important disturbance for this redwood ecological site is damage from winter storms that can cause top breakage and blowdowns. This breakage may kill individual or groups of trees and create small openings from windfall (Noss, 2000). This would likely favor the establishment of redwood and other shade tolerant conifers.

Significant disturbance to this ecological site would occur if there are climatic changes great enough to impact the amount of fog influence this ecological site experiences on a yearly basis. Coast redwoods reliance on fog is crucial to its survival and without the moisture available in the summer from the daily blanket of fog, redwoods may begin to die out and Douglas-fir would begin replacing those redwood stands. Well established redwoods may persist where access to water is still available (concave depressions, valley bottoms, etc.) until removed by fire or other types of human disturbance.

Coast redwood is one of the signature trees of California, with 95% of its range existing within the state. Years of logging have left significantly lower amounts of the original forest (Sawyer et al. 2000b). Old-growth stands exist mainly in protected areas including parks, experimental forests, and private reserves. Asexual regeneration is prolific and many stands of younger trees exist, but many areas are on the third cycle of regeneration with collateral impacts of erosion, streambed siltation, and alteration to watershed and wildlife values. Residential development is an increasing concern.

References and Citations:

Agee, James. (1996). Fire Ecology of Pacific Northwest Forests. The Bark Beetles, Fuels, and Fire Bibliography.

Barbour, M., Keeler-Wolf, T., & Schoenherr, A. A. (Eds.). 2007. Terrestrial vegetation of California. Univ of California Press.

Burgess, S. S. O., & Dawson, T. E. 2004. The contribution of fog to the water relations of Sequoia sempervirens (D. Don): foliar uptake and prevention of dehydration. Plant, cell & environment, 27(8), 1023-1034.

Franklin. J.F. & C.T. Dyrness. 1973. Natural vegetation of Oregon and Washington. United States Department of Agriculture, Forest Service, General Technical Report PNW-8. p. 417.

Fryer, Janet L. 2008. Notholithocarpus densiflorus. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: www.fs.usda.gov/database/feis/plants/tree/notden/all.html / [2024, January 9].

Greenlee, J.M. and J.H. Langenheim. 1990. Historic Fire Regimes and Their Relation to Vegetation Patterns in the Monterey Bay Area of California. American Midland Naturalist, vol 124: 239-253.

Griffith, Randy Scott. 1992. Picea sitchensis. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: https://www.fs.usda.gov/database/feis/plants/tree/picsit/all.html [2024, January 9].

Griffith, Randy Scott. 1992. Sequoia sempervirens. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: https://www.fs.usda.gov/database/feis/plants/tree/seqsem/all.html [2024, January 9].

Jacobs, Diana F., D.W. Cole, and J.R. McBride. 1985. Fire History and Perpetuation of Natural Coast Redwood Ecosystems, Journal of Forestry, Volume 83, Issue 8: 494–497. https://doi.org/10.1093/jof/83.8.494

Johnstone, J. A., & Dawson, T. E. 2010. Climatic context and ecological implications of summer fog decline in the coast redwood region. Proceedings of the National Academy of Sciences, 107(10), 4533-4538.

Koopman, M, D. DellaSala, P. Mantgem, B. Blom, J. Teraoka, R. Shearer, D. LaFever, and J. Seney. 2014. Managing an Ancient Ecosystem for the Modern World: Coast Redwoods and Climate Change. RedwoodsManuscript20141016 (climatewise.org). Accesse 9 Jan. 2024.

Munster, J., & Harden, J. W. 2002. Physical data of soil profiles formed on Late Quaternary marine terraces near Santa Cruz, California (No. 2002-316). US Geological Survey.

Noss, R.F. 1999. The Redwood Forest History, Ecology, and Conservation of the Coast Redwoods. Save the Redwood League. 366 pages.

Painter, Elizabeth L. “Threats to the California Flora: Ungulate Grazers and Browsers.” Madroño, vol. 42, no. 2, 1995, pp. 180–88. JSTOR, http://www.jstor.org/stable/41425065. Accessed 9 Jan. 2024.

Stuart, J.D. 1987. Fire history of an old-growth forest of Sequoia sempervirens (Taxodiaceae) forest in Humboldt Redwoods State Park, California. Madroño 34(2):128-141.

Tirmenstein, D. 1990. Vaccinium ovatum. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: https://www.fs.usda.gov/database/feis/plants/shrub/vacova/all.html [2024, January 9].

Uchytil, Ronald J. 1991. Pseudotsuga menziesii var. menziesii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: https://www.fs.usda.gov/database/feis/plants/tree/psemenm/all.html [2024, January 9].

Varner, J.M. and E.S. Jules. 2016. The Enigmatic Fire Regime of Coast Redwood Forests and Why it Matters. Proceedings of the Coast Redwood Science Symposium, Sequoia Conference Center, Eureka, CA. pp. 15-18.

Veirs, S. D. 1996. Ecology of the coast redwood. In J. LeBlanc (technical coordinator) Proceedings of the conference on coast redwood forest ecology and management (pp. 9-12).

Zinke, Paul J. 1977. Mineral cycling in fire-type ecosystems. In: Mooney, Harold A.; Conrad, C. Eugene, technical coordinators. Proc. of the symposium on the environmental consequences of fire and fuel management in Mediterranean ecosystems; 1977 August 1-5; Palo Alto, CA. Gen. Tech. Rep. WO-3. Washington, DC: U.S. Department of Agriculture, Forest Service: 85-94.

Major Land Resource Area

MLRA 004B
Coastal Redwood Belt

Stage

Provisional

Contributors

Kendra Moseley