BCCER Habitats

Terrestrial habitats in the Big Chico Creek Ecological Reserve are extremely varied. Plant assemblages may change abruptly at the junction between two geologic substrates or at the edge of a past disturbance event such as fire or human clearing. More commonly, they grade slowly into one another as aspects of the microhabitat (slope, exposure, elevation, soil moisture, soil depth) change. In a particular transect, blue oaks in a savanna may gradually get denser until at some arbitrary point the habitat would be classified as a woodland, then a few interior live oaks will be mixed in, then more live oaks and a few canyon oaks. Gradually the canyon oaks will come to dominate, and other species (ponderosa pine, big-leaf maple, black oak, incense cedar) will be mixed in and the vegetation will be dense enough to be classified as forest. Because of these ubiquitous spatial gradients, a fine-scale vegetation map is impractical for making any reserve-wide decisions. Below the BCCER vegetation types are grouped into broad-spectrum categories with the caveat that each category represents an artificial segment of the total vegetation gradient. These categories are: grassland, wet meadow, riparian, valley oak savanna/woodland, blue oak savanna/woodland, mixed woodland/forest, chaparral, and chaparral/savanna.

Grasslands (50 acres; 1.3% of the Reserve) are open meadows, devoid of woody vegetation except for widely scattered shrubs or small trees and dominated by grasses and forbs. Most meadows are dominated by non-native annuals) such as wild oats, rip-gut brome, annual ryegrass, yellow-star thistle, filaree species, and rose clover. A few native grasses and many spring-blooming native forbs are present. Some of the reserve grasslands exist where soils are too shallow to support trees and shrubs. Others are the result of human disturbance and will be replaced by woody vegetation in the absence of disturbance.

Wet Meadows (4 acres; 0.1% of the Reserve) are uncommon and small, usually less than an acre in size. Soils are water-saturated close to the water source and grade to barely damp at the margins. Vegetation consists of native sedges, rushes, and forbs with the non-native dallisgrass often dominating. Clumps of deer grass and/or rush are also common near the margins. Many wet meadows have been degraded by down-cutting by their small drainage streams.

Riparian zones (61 acres; 1.5% of the Reserve) are found in the floodplain of Big Chico Creek as well as some tributaries ; and spring seeps. They contain a wide diversity of both woody and herbaceous plants including alders, willows, sycamores, spice bush, button-willow, California grape, deer grass, ferns, sedges and forbs such as umbrella plant and creek orchid. The invasive Spanish broom, edible fig, and Himalayan blackberry are common in some parts and are being removed as part of the vegetation management plan.

In the Blue oak savanna/woodland (348 acres; 8.8% of the Reserve) the blue oak trees grade from scattered to dense enough to form a closed canopy. Foothill pines may be scattered in or co-equal with the blue oaks. The groundcover is mostly herbaceous, containing most of the same species as the grasslands, but usually including more native perennial grasses, particularly purple needle grass, blue wild-rye, and California brome. Forbes such as lupines and irises are sometimes common. Miner's lettuce is often abundant under the trees. Some scattered shrubs are present, particularly red berry and skunkbrush.

Valley oak savanna/woodland (335 acres; 8.5% of the Reserve) is generally found next to open meadows or the riparian strip in the bottom of the canyon, but can also be found on some terraces far above the creek. Some valley oak savanna/woodland seems to be seasonally wet enough to exclude most other woody species. Ground cover in these wetter areas is dominated by sedges, rushes, and annual ryegrass. Drier areas with valley oaks are being invaded by brush and canyon oak and probably owe their existance to periodic disturbance.The understory is similar to that of blue oak woodland, but is usually brushier, containing poison oak, coffeeberry and skunkbrush . In some areas blue oaks, black oaks and big-leaved maples may be mixed with the valley oaks.

The Mixed woodland/forest (1156 acres; 29.3% of the Reserve) category is the most diverse assemblage. In the densest parts it includes overstory species of canyon oak, black oak, big-leaved maple, with emergent foothill pine, ponderosa pine, incense cedar, and douglas fir. An understory layer may be formed of juveniles of canyon oak, live oak, big-leaved maple, or incense cedar as well as and many of the typical chaparral shrubs, particularly coffeeberry, deerbrush, poison oak, and toyon. On more exposed slopes, it grades to a open-canopy woodland of canyon oaks, interior live oaks and blue oaks. Steep north facing slopes may be dominated by maple and Douglas fir. Ground cover varies from sparce to dense, usually including a number of forbs and the native grasses California and Torrey's melic, woodland brome, and blue wild-rye, with abundant ferns and mosses in moister areas. At a finer scale (1-3 acres), the forest is often dominated by one or two species but these patches quickly grade into different dominants and the entire gradient can often be encountered within a few tens of meters. Although much of the diversity of this habitat correlates with topography and geology, a great deal is due to past history of disturbance, particularly by fire.

Extensive stands of Chaparral (625 acres; 15.8% of the Reserve) are found in a few places, particularly on the Musty Buck Ridge toward the northern part of the reserve. These are almost impenetrable thickets of many species of shrubs including scrub, live, and Brewer's oak, buck brush, deer brush, mountain mahogany, poison oak, California bay, manzanita, toyon, honeysuckle and others. Foothill pines are common emergents in slightly less dense areas. Ground cover is relatively limited when the shrubs are mature, but many forbs and grasses show up after a fire. Most areas of chaparral will gradually convert to evergreen oak forest or foothill pine forest if not disturbed periodically (usually by fire).

Banded chaparral/savanna: (1377 acres; 34.9% of the Reserve) Large areas in the western part of the Reserve are vegetated by varying-width bands of chaparral interspersed with bands of savanna or grassland. (This banding is imposed by the underlying layers of substrate in the Tuscan Formation.) The chaparral bands have characteristic chaparral plants and the savanna bands are similar to blue oak savanna except for having relatively more foothill pines. Soils are very shallow; rock outcrops and surface rocks are common.

Rock Fields (<1% of the Reserve) In many areas there are exposed bedrock or large boulders. The exposed rock serves as substrate for lichins, mosses and spike mosses. Cracks or depressions with a bit of soil may support ferns or members of the stonecrop family and areas where very thin soil covers the rock will support tiny annual plants.

The following table lists the plant series described in "A Manual of California Vegetation" by John O. Sawyer and Todd Keeler-Wolf (1995) that fall into each general vegetation category. A map of plant series in the reserve is currently under development.

Vegetation Category

Sawyer/Keeler-Wolf Series

Grasslands

California annual grassland series

Wet Meadows

spikerush series

Riparian

California sycamore series
white alder series

Blue oak savanna/woodland

blue oak series

Valley oak woodland

valley oak series

Mixed woodland/forest

foothill pine series
ponderosa pine series
black oak series
canyon live oak series
Douglas fir series
incense cedar series
interior live oak series

Chaparral

wedgeleaf ceanothus series
whiteleaf manzanita series
interior live oak shrub series
deerbrush series

Banded chaparral/savanna

wedgeleaf ceanothus series
whiteleaf manzanita series
interior live oak shrub series
deerbrush series
foothill pine series
blue oak series
California annual grassland series