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 generally found within LRU O, directly adjacent to the mountains of LRU N. This site is generally found below 1000 ft. on the low coastal plains and in the protected ravines. They are mostly confined to the protected ravines, footslopes, northerly aspects, and high stream terraces of the low-lying coastal plains and terraces where the coastal fog remains throughout the duration of the hot summers, unlike other parts of the LRU that do not experience fog throughout the summer months.

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 San Mateo Coastal Hills LRU have lower relief and elevations than the adjacent LRU N, with more coastal oak and scrub vegetation and coastal grasslands and areas of cultivation rather than the denser forest and woodland of the Santa Cruz Mountains. Pliocene sandstone and siltsone are the main rock types compared to the mix of geology in LRU N that includes older sedimentary and some igneous rocks. Marine terraces, coastal benches, and small valleys are the primary landforms. Mollisols are typical, with mostly thermic to isomesic temperature regimes. Soil moisture regimes are mostly xeric and ustic. Summer fog is common, and winters are cool and moist.

This ESG will exist primarily within the areas of LRU O that are the most moderate coastal temperatures, experiencing the least amount of heat stress during the summers within the LRU. This ESG differs from others in other LRUs due to the reduced duration and inland extent of fog and the impacts of warmer summer temperatures, given its proximity to the Southern California climatic influences.

Soil features

The soils of this provisional site concept are variable but will generally be found on fine to fine-loamy alluvial materials. The cooler, maritime temperatures and protected aspects allow for higher retention of soil moisture during the hotter summer days, and the fog influence provides key moisture to the redwood foliage and soil moisture content as well. The soils are predominantly an isomesic soil temperature, meaning the soils have a mean annual soil temperatures of 8 °C or more, but a difference between mean summer and mean winter soil temperatures of less than 5 °C at 50 cm below the surface. This limited change in soil temperatures minimizes heat stress to the vegetation growing on these soils.

Vegetation dynamics

This provisional ecological site concept attempts to describe the small remaining areas of coastal redwoods of LRU O. This concept historically would have covered many other areas within this LRU, however land use (timber harvest, conversion to agriculture, and urban development being most typical) and increases in overall temperature over the past 100 years have made it difficult for coast redwood to re-establish into much of its previous habitat, confining it down to areas that are not conducive to urban sprawl and maintain protection from late afternoon heat in the summers. The primary factors that maintain these sites in coast redwood are the fog influence and protected slopes and northerly aspects that maintain higher soil moisture during the warm periods of the summer.

Primary Disturbances

Historically, the primary disturbances in this ecological site group were lightning and cultural fires, and grazing by native grazers and livestock. Lightning-ignited fires are relatively infrequent in the California Central Coast where LRU O occurs when compared to other regions in the state. However, lightning strikes are more common in dry summer and fall months than in winter (Van Wagtendonk and Cayan 2008), and dry lightning occurs in this region with enough regularity (Kalashnikov et al. 2022) for lightning fires to play an important role in vegetation dynamics alongside Native American burning. Fires in coastal California are typically wind driven over large areas and across many different soil and vegetation types (Varner and Jules 2017). Interactions of soil, landform, inter-annual climate variability, grazing patterns and fire regimes sustain a mosaic landscape where coast redwood forest exists alongside areas of coastal scrub and meadows; and expresses in various structural development stages depending on time since fire or other minor localized disturbances such as landslides or alluvial deposits. In combination with fires and periodic droughts, native and introduced grazers also play a role in limiting woody encroachment in areas with good soils and a climate that could otherwise often support trees.

Native American practices along these coastlines included frequent burning to maintain coastal prairies or balds, and it is likely that fires in these prairies burned into redwood areas. Without very frequent fire disturbance, many grassland openings in this ESG will transition to forest. Further expansion of pre-existing openings and development of new openings for homesteading occurred in redwood forests of this ESG during the settlement period (approximately 1830-1900). Additional clearing to develop pasture and for other uses has occurred in some areas after the settlement period as well.

References & Citations:

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.

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.

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.

Kalashnikov, D. A., Abatzoglou, J. T., Nauslar, N. J., Swain, D. L., Touma, D., & Singh, D. (2022). Meteorological and geographical factors associated with dry lightning in central and northern California. Environmental Research: Climate, 1(2), 025001.

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). Accessed 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.

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.

Van Wagtendonk, J. W., & Cayan, D. R. (2008). Temporal and spatial distribution of lightning strikes in California in relation to large-scale weather patterns. Fire Ecology, 4, 34-56.

Varner, J. M., & Jules, E. S. (2017). The enigmatic fire regime of coast redwood forests and why it matters. Gen. Tech. Rep. PSW-GTR-258. Albany, CA: US Department of Agriculture, Forest Service, Pacific Southwest Research Station: 15-18, 258, 15-18.

Major Land Resource Area

MLRA 004B
Coastal Redwood Belt

Stage

Provisional

Contributors

Kendra Moseley