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 ecological site group is generally found on ridges, knobs, and the upper elevation slopes within the forested areas of LRU I. This site is generally found above 800 ft. but can be lower near the southern end of the LRU. The primary factors that maintain these sites in either coastal prairies, coyotebrush shrublands, and Douglas-fir and/or redwoods are related to time without fire, the skeletal soils, and seed source availability.

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 low mountains of the Northern Franciscan Redwood Forest, LRU I, lie entirely within the coastal fog zone and are characteristically covered by fog-dependent coast redwoods and Douglas-fir. Historically, unbroken redwood forests occurred and moderated local climate by trapping coastal fog and producing shade. The combination of shade, root competition, young soils with a deep organic debris layer on the soil surface, occasional fire, and silting by floods limits the number of plant species that occur here.

Soil features

Although the soils of this provisional site concept are highly varied, they all share the common variable of loamy-skeletal soils in their control section, higher soil organic content in the soil rooting zone and loamy soil textures that provide good growing conditions and annual production.

Representative soils include Devilshole, Flintrock, and Forhaux. They are all pachic and include thermic, mesic and isomesic soil temperature regimes. These soils are all well drained with high runoff and slow permeability.

Vegetation dynamics

This provisional ecological site concept attempts to describe the various complicated areas of coastal prairie in this LRU. They exist in a patchy dynamic of perennial and annual grasses and forbs, coyotebrush shrublands, and Douglas-fir and/or redwood forests. These prairie complexes relied heavily on hundreds of years of Native American burning to maintain their dominance in an area that provided no limitations to on the growing conditions for trees that would have overtaken many of these prairies without the fires to burn them back. This concept lumps many of the unique prairie expressions into one large concept, due to limited soil mapping that successfully parses out the differences between these types and focuses primarily on the primary abiotic factors and ecological dynamics that maintain and/or alter these vegetative communities. The extent of this ecological site concept stretches primarily along the inner coastal mountain portions of LRU I. This provisional ecological site concept covers a wide variety of coastal prairie dynamics and expressions that will need to be further refined to better represent dynamics on a smaller, more ecologically specific scale.

Primary Disturbances

The primary disturbance to this ecological site concept is fire that keeps the woody species that are actively encroaching the site from establishing, allowing these grasslands to maintain the competitive advantage. When summer fog is less prevalent, tree and shrub encroachment will slow and years when summer fog is very consistent tree and shrub encroachment may be quite rapid.

Historically, prairies within the North Coast region were thought to have been dominated by native perennial bunchgrasses and numerous associated forbs. Native Americans utilized the prairies for food and cultural materials. Regular burning stimulated the growth of grasses and eliminated invading shrubs and trees, thereby attracting wildlife. The use of fire for over 5,000 years by Native Americans created a system in equilibrium that controlled the vegetative structure and composition.

With the advent of European settlements, changing land use practices significantly altered the vegetation. In the 1800s cattle and sheep grazing became widespread. Increased grazing pressure from domestic livestock and range seeding reduced the native perennials and increased the population of introduced perennials and forbs. More studies are needed to understand grazing and native plant interactions. Shifts in the annual plant community caused by grazing are difficult to document. Certain species will increase with favorable weather and grazing conditions.

Non-native grasses often outcompete natives for water, nutrients and growing space. Arrhenatherum elatius (tall oatgrass), an introduced perennial within these prairies, is considered an invasive exotic. One study indicates that early season burning may be more effective in eliminating flowers and developing seeds of tall oatgrass prior to their dispersal. However, spring burning has a negative effect on some of the native perennials, like Danthonia californica (California oatgrass). Fall burning has slowed the advance of tall oatgrass within parts of this LRU.

Prescribed burning may favor one species over another. Recent studies indicate that periodic fire may favor perennial species by reducing litter cover and eliminating other plant competition, however it may also increase the production of non-natives and exotic forbs. Long term studies are lacking to evaluate the interaction of prescribed fire, climate, and grazing on both natives and non-native species.

Historically, there was very little overlap between the prairie, oak and conifer systems within much of this LRU. Fire exclusion in the last century has allowed for the encroachment of shrubs, and in some cases trees, into the prairies. Roads established for harvesting purposes left exposed cut and fill slopes that were rapidly invaded by Douglas-fir. Invasion of prairie and oak woodland by conifers has led to conversion to forest in a very short period of time.

Major Land Resource Area

MLRA 004B
Coastal Redwood Belt

Stage

Provisional

Contributors

Kendra Moseley