Ecological dynamics

This ecological site occupies a marine terrace outside Trinidad, CA and is largely contained with the coastal fog belt. This site is of limited extent and the reference plant community is inferred as the entirety of the site has been harvested. The range of redwood (Sequoia sempervirens) is largely influenced by this 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 differs from other redwood ecological sites in the region because of its poorly drained soils and their effect on vegetation composition. Site productivity of redwood is lower than that of the surrounding redwood ecological sites, as redwood is intolerant of extended periods of soil saturation. When the root zone of redwood becomes permanently saturated, the roots die for lack of oxygen and the tree dies (Veirs 1996). Shore pine (Pinus contorta spp. contorta) is able to quickly establish on this site as it competes well on nutrient poor or wet sites (Cope 1993). Plant species found on this ecological site are uniquely adapted to poorly drained conditions. Plants often found in saturated areas can be found on this site including: rush (Juncus spp.), rose spiraea (Spirea douglasii), Gentian spp., and western Labrador tea (Ledum glandulosum). Redwood is the dominant overstory tree species on this site but shore pine and Douglas-fir (Pseudotsuga menziesii) are also present.

The northern range of redwoods evolved within a low to moderate natural disturbance regime, with severe fire intervals ranging from 500 to 600 years on the coast (Veirs 1979). Fires could have historically occurred by lightning ignition or deliberate setting by Native Americans to create desirable hunting habitat (Veirs 1996). Whereas frequent surface fires on other redwood ecological sites may promote establishment of western hemlock in the understory (Veirs 1979), the poorly drained soils of this site may limit this successional shift. Redwood has the ability to resprout following fire from the root crown or from dormant buds under the bark of the bole and branches (Noss 2000). Previous harvest and the use of fire as a slash treatment can alter species composition on many sites (Noss 2000) as repeated burning can favor resprouting of redwood and hardwoods and limit the regeneration of Douglas-fir and other conifers. Shore pine is sensitive to fire, does not exceed 50 feet in height, and is short-lived (Cope 1993). However, recruitment of shore pine on this site is high and would be expected to provide for a continuously regenerating community of shore pine on this site. The limited height and longevity of shore pine could help create a subcanopy under the much longer lived and taller redwood.

Other dynamic ecological patterns include windthrow and non-native species invasion. Wind damage from winter storms can cause canopy top breakage which may kill individual trees or create windthrow gaps in the forest (Noss 2000). Pioneer species tolerant of this site’s high water table could infill into these gaps in the canopy. The close proximity of this site to residential areas provides the opportunity for non-natives such as Pampas grass (Cortaderia jubata) and Spanish heath (Erica lusitanica) to colonize the site in early seral stages. These invasive species can colonize most quickly in early seral stages and may even out-compete native conifers and shrubs. Pampas grass invasion may prevent conifer seeding establishment and may even increase fire potential (DiTomaso). After conifer establishment and canopy closure decreases light levels in the understory, invasive species may be eliminated from the site.

Species often found in marshes and along riparian areas are found prevalently on this site. Rose spiraea, rush species, and gentian species are indicative of the high water table present on this site.

California huckleberry occupies a large percentage of the understory on this site. California huckleberry is a dominant shrub species across redwood ecological sites as it can thrive in both moist and dry environments. As California huckleberry is typically a fire-dependent species, sprouting can be widespread following natural fire or site preparation treatments (Tirmenstein 1990).

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 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 this ecological site influence drainage and vegetation patterns distinct from the other terraces. The A Line terrace, upon which this ecological site is found, likely formed about 300,000 years.

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 ecological site development.