Ecological dynamics

This ecological site occupies marine terraces around Trinidad, CA and Crescent City, CA and is largely contained with the coastal fog belt. Because of its proximity to coast and flat terrain, this site has been heavily managed for agriculture, timber production, and residential construction.

Sitka spruce (Picea sitchensis) is the dominant tree species occupying a thin band along the north coast of California and extending north to the coast of British Columbia (Franklin and Dyrness 1973). This site is found adjacent to the coast and receives high inputs of sea salt spray, a condition that limits the establishment and growth of certain conifer species. Sitka spruce has a high tolerance for salt spray, while salt-laden winds can dehydrate and damage redwood (Sequoia sempervirens) (Zinke 1988). Inland from the effect of the marine air, redwood is commonly found and can dominate the overstory. The range of redwood is largely influenced by coastal fog, which ameliorates the effects of solar radiation on conifer transpiration rates (Daniel 1942). Fog is a critical source of water in the summer months for redwood, which has high transpiration rates. This ecological site straddles the boundary of this salt-laden marine influence, so both Sitka spruce and redwood occupy the site. Red alder (Alnus rubra) is a common associate species on this site and can dominate the site in an early seral stage.

This ecological site has developed with a low natural disturbance regime. Mean fire intervals for the area may be around 10 years but with low intensity (Brown and Swetnam 1993). The close proximity to the coastal zone has caused this site to evolve with small to moderate disturbances from wind events. Winter windstorms can cause broken tops and windthrow. Repeated disturbance by wind is evidenced by a hummocky ground appearance caused by fallen trees and root wads (Agee, 1993). Pioneer species such as native shrubs and nitrogen-fixing red alder may quickly colonize windthrow gaps. . In the Sitka spruce coastal zone following logging, dense shrub communities can arise, and nurse logs are important for spruce regeneration (Franklin and Dyrness 1979). Salmonberry (Rubus spectabilis), salal (Gaultheria shallon), and bracken fern (Pteridium aquilinum) may become very dense following a disturbance and can potentially form large brushfields (Tirmenstien 1989, Crane 1990). These species can reproduce vegetatively following timber harvesting or fire. Though these brush species are most prevalent in early to mid-seral successional stages, they persist in the openings of mature stands.

Human interactions with the coast landscape have left a significant mark on this ecological site. Much of this ecological site is currently in pastureland and residential use between Crescent City and Smith River in Del Norte County. Historical photos indicate European settlers cleared terrace land around Trinidad for agriculture in order to provision the growing port (Trinidad Museum). Established before the towns around Humboldt Bay, Trinidad was a bustling port servicing miners coming down from the Klamath Mountains and ships loaded with goods headed up the Oregon Coast or down to San Francisco Bay.

Further evidence for land clearing and an open coastal prairie landscape is indicated by the dense even-aged stands of Sitka spruce now occupying much of the Trinidad headlands. Older open grown wolf trees can also be seen in the area indicating a more open pasture landscape. Sitka spruce can rapidly invade adjacent coastal prairies after cessation of burning, grazing, or tilling (Franklin and Dyrness 1973). If land clearing and stump removal did occur, redwood regeneration may be slow to infill onto the site. Historically, land clearings would have been occupied by native perennial and annual grasses and forbs with deliberate plantings of other species for forage and cultivation. Current cleared areas of this site are now dominated by both native and non-native species.

This ecological site occupies young marine terraces near Trinidad and Crescent City. The marine terrace sequence around Trinidad demonstrates the fluctuations of sea level and tectonic uplift over the past 400,000 years. Six distinct marine terraces are identified in this area, the sediments of which we deposited during times of higher sea level (Woodward-Clyde Consultants). The youngest emergent terrace, Patrick’s Point terrace, is found closest to the coast, and subsequently older terraces are found further east and at higher elevation. The oldest and highest terrace (Maple Stump) is found furthest east and exhibits the most soil development (Stephens 1982). Local eolian and colluvial deposits overlie the marine sediments on older terraces (Stephens 1982), which in the case of the A Line terrace (Savagecreek soils) influences water drainage and vegetation patterns distinct from the other terraces. The Patrick’s Point terrace, upon which this ecological site is found, likely formed about 82,000 years ago during the last interglacial period (Rust). Marine terraces in the vicinity of Crescent City suggest similar deposition during sea level high stands, with the formation of the terrace upon which this ecological site is found occurring approximately 80,000 years ago (Lorenz and Kelsey 1999). The recent formation of these terraces suggests a limitation to the amount of pedogenesis that has yet occurred in these young sediments.

The effects of climate change on species distribution and viability need to be considered in this age of rapidly changed climate regimes. The western United States is already experiencing an increase in tree mortality across all tree cohort age classes, likely due to regional warming and water deficits (van Mantgem et al 2009). These forest structure changes may cause species to migrate to higher elevations, as much as 500-1000m, as temperatures increase in lower elevations (Urban et al 1993). Climate models project many different climate regimes for the north coast of California. One model predicts a warmer, wetter climate regime in which redwood may be able to expand into canyon live-oak-madrone and chaparral systems (Lenihan et al 2003). Climate change and its effects on vegetation patterns should be considered along with historical perspectives in these ecological sites.