Appendix GV. The Great Central Valley Region

The GCV is an enormous plain with very little topographic relief. Sediments lie up to 10 km deep over the Sierra Nevada basement rock. The only major topographic feature is Sutter Buttes, an igneous outcrop rising over 600 m above the Sacramento River Valley. Soils tend to be fertile, lacking only adequate water in the south to be naturally productive. Hardpan formed beneath the surface in other areas. In spring, low lying "hogwallows" in the valley over this hardpan fills with water, forming vernal pools which often have unique flora. Soils around the flood basins and vernal pools are naturally alkaline as the water evaporates and leaves behind dissolved salts. Other vernal pools occur in the north end of the valley on volcanic soils, while terrace pools are found on ancient flood terraces on higher ground on the eastern side of the region. Rolling mounds, called "mima mounds" up to 2 m high often surround these terrace pools (Schoenherr 1992). Ancient sand dunes occur next to the Kettleman Hills along the shoreline of extinct Lake Corcoran (Norris and Webb 1990).

The arid climate favored the formation of grassland over all well-drained areas of the valley. Perennial bunchgrasses dominated, especially Nassella pulchra (Purple needlegrass, formerly Stipa pulchra). Huge freshwater marshes formed in the depressions in the Tulare Basin at the southern end of the region. Vernal pools were scattered throughout the region in small depressions over hardpans of various materials such as clay or basalt. The persistence of water later in the spring and the high salinity of the soils created a unique flora associated with these vernal pools. In the saline soils surrounding the shallow lakes and marshes, alkali scrub communities were found. Extensive riparian forests and woodlands bordered streams and rivers on the well-watered natural levees and terraces. Every one of these types has been extensively reduced and degraded throughout the valley as a result of the complex interaction of grazing, agricultural and urban development, draining of the vast wetlands, monumental modifications of the surface hydrology for flood control and irrigation, ground water pumping, controlling of fire, pesticide applications, firewood cutting, and the introduction of exotic species (Barry 1972, Katibah 1984, U. S. Fish and Wildlife Service 1978, Holland 1978).

In the mountainous and desert regions of the state, the public domain land remained basically in federal hands. In the flat, fertile Great Central Valley, however, nearly all land not already in Spanish or Mexican land grants was homesteaded in the 19th century. A mere 2% of the region that was retained in the public domain under the management of the Bureau of Land Management (BLM). Virtually all managed areas in this region were acquired by government agencies or private conservation organizations in this century. Many small to medium-sized military bases are distributed throughout the region. Greater than 90 percent of the land area is in private ownership, primarily dedicated to urban or agricultural uses. Only a small fraction of private land is managed for biodiversity protection, such as The Nature Conservancy preserves and National Audubon Society sanctuaries. Private duck clubs own the majority of remaining non-public wetlands in the Central Valley, which they manage for waterfowl habitat and sport hunting (Frayer et al. 1989). Many of these clubs struggle to remain open in the face of stiff competition for water needed to maintain the ponds in drought years.

The geometry of the Public Land Survey System and human settlement has been superimposed on the geography of natural topography and hydrology of the Great Central Valley, giving a superficial impression that the region is homogeneous, if not monotonous. However, the underlying variation in climate and soils still exert their influences to maintain significantly different habitats and species assemblages. The Delta still retains extensive wetlands. Rice fields in the north can provide wintering habitat for migratory waterfowl while the southern valley has evergreen citrus orchards. Forests still cling to the banks of rivers in the north, in stark contrast to the alkali sinks in the San Joaquin Valley where water is less plentiful. And when extreme winter precipitation does come, satellite images reveal the normally hidden shapes of Tulare Lake and other historic wetlands. Nature reserves must be distributed throughout the valley to fully protect the diversity of species and habitats.

Eighty-two status 1 and 2 managed areas were mapped for the Great Central Valley Region, covering a combined 3.1% of the entire region (Table GV-1). The 28 status 1 managed areas are dominated by 13 Nature Conservancy preserves and 13 ecological reserves of the California Department of Fish & Game. The status 2 areas include 15 USFWS national wildlife refuge units, 29 state wildlife units, 3 state park units, 2 water district tracts, 2 BLM ACEC's, and the Carrizo Plain Natural Area macropreserve managed jointly by the BLM, The Nature Conservancy, and California Department of Fish and Game. The Carrizo managed areas collectively encompass 62,852 ha of lands managed for biodiversity. Another 1.6% is other public lands managed at status level 3. As with ownership profiles, the distribution of management levels by subregion closely follow the region statistics.

Of the status 1 and 2 managed areas, only two of the BLM ACEC's are greater than 10,000 ha in size. Both are on the western edge of the San Joaquin Valley subregion. The average size is only 2,500 ha. Half of the managed areas are less than 1,000 ha, including most of the non-governmental organization preserves, state parks, and Fish & Game ecological reserves and wildlife areas. This pattern of small managed areas reflects the highly fragmented nature of the Great Central Valley, where large, contiguous blocks of habitat seldom exist.

CNDDB Code	CNDDB Community Name (Holland 1986)	CNDDB Rank	Status 1 %	Status 2 %	Status 3 %	Status 4 %	Total Mapped Distribution (km²)	Status 1+2 %
23300	Monvero Residual Dunes	S1.2	0.0	31.0	0.1	68.9	3.0	31.1
32600	Diablan Sage Scrub	S3.2	0.0	5.3	19.1	75.6	326.6	5.3
35400	Rabbitbrush Scrub	S5	0.0	0.0	32.7	67.3	2.1	0.0
36210	Valley Sink Scrub	S1.1	1.8	9.4	0.0	88.7	250.4	11.2
36220	Valley Saltbush Scrub	S2.1	0.9	11.9	6.5	80.7	1,900.7	12.8
36320	Interior Coast Range Saltbush Scrub	S2.1	1.5	16.1	8.9	73.5	27.7	17.6
37200	Chamise Chaparral	S4	0.0	0.0	0.0	100.0	1.5	0.0
37400	Semi-Desert Chaparral	S3.2	2.2	17.5	47.3	33.0	99.8	19.7
37900	Scrub Oak Chaparral	S3.3	0.0	0.0	6.8	93.2	6.3	0.0
37A00	Interior Live Oak Chaparral	S3.3	0.0	0.0	0.0	100.0	26.4	0.0
39000	Upper Sonoran Subshrub Scrub	S3.2	1.4	50.5	3.8	44.3	175.2	51.9
42110	Valley Needlegrass Grassland	S3.1	34.7	0.0	0.0	65.3	4.1	34.7
42120	Valley Sacaton Grassland	S1.1	0.0	64.7	0.0	35.3	9.1	64.7
42200	Non-native Grassland	S4	0.9	4.5	3.6	91.1	13,996.9	5.4
44110	Northern Hardpan Vernal Pool	S3.1	0.0	0.0	0.0	100.0	0.1	0.0
44120	Northern Claypan Vernal Pool	S1.1	21.3	0.0	0.0	78.7	1.6	21.3
45310	Alkali Meadow	S2.1	0.0	0.1	2.1	97.8	35.2	0.1
52200	Coastal Brackish Marsh	S2.1	0.8	17.0	1.5	79.2	266.1	17.8
52310	Cismontane Alkali Marsh	S1.1	0.0	10.7	0.0	89.3	9.3	10.7
52410	Coastal & Valley Freshwater Marsh	S2.1	0.2	40.8	0.0	59.0	449.0	41.0
61410	Great Valley Cottonwood Riparian Forest	S2.1	1.5	17.8	1.1	79.5	308.8	19.3
61420	Great Valley Mixed Riparian Forest	S2.2	5.0	13.3	1.1	80.7	41.5	18.3
61430	Great Valley Valley Oak Riparian Forest	S1.1	1.2	4.6	1.3	92.9	71.2	5.8
62100	Sycamore Alluvial Woodland	S1.1	0.0	0.0	0.0	100.0	2.3	0.0
63410	Great Valley Willow Scrub	S3.2	1.0	0.0	1.4	97.6	18.9	1.0
63420	Great Valley Mesquite Scrub	S1.1	0.0	0.3	0.0	99.7	22.6	0.3
63810	Tamarisk Scrub	S4	0.0	12.7	1.5	85.8	53.0	12.7
63820	Arrowweed Scrub	S3.3	0.0	0.0	7.4	92.6	13.4	0.0
71130	Valley Oak Woodland	S2.1	0.0	0.1	0.6	99.3	29.7	0.1
71140	Blue Oak Woodland	S3.2	0.8	2.0	3.6	93.6	317.3	2.8
71150	Interior Live Oak Woodland	S3.2	0.1	0.0	1.0	98.9	17.0	0.1
71160	Coast Live Oak Woodland	S4	0.0	0.0	12.7	87.3	0.6	0.0
71430	Juniper-Oak Cismontane Woodland	S3.2	2.1	15.5	1.2	81.2	8.0	17.6
72200	Mojavean Pinyon-Juniper Woodland	S3.2/4	0.0	0.0	46.9	53.1	24.6	0.0
	Region Total - Natural Communities						18,520
	Region Total - All Lands		0.3	2.8	1.6	95.2	58,627	3.1

We call attention to three groups of distribution by management level, including one in which types appear to be well protected. The area of mapped distribution and the proportions in each management level are given in Table GV-2.

1. Plant community types mainly on status 4 lands. Six of the 34 types have areas greater than 25 km² with more than 90% in status 4. These types include Interior Live Oak Chaparral, Non-Native Grassland, Alkali Meadow, Great Valley Valley Oak Riparian Forest, Valley Oak Woodland, and Blue Oak Woodland. The Interior Live Oak Chaparral and Blue Oak Woodland types are more common in neighboring regions and are marginal to the Great Central Valley. Non-Native Grassland is widespread and heavily altered by grazing and invasions of exotic plants. The remaining three types are all ranked as 1.1 or 2.1 by the state (California Department of Fish and Game, unpublished list, dated 4/12/91). That is, they are considered rare and very threatened by losses to agricultural and urban conversion or to degradation from grazing, water diversions, or chemical pollution. Remaining patches are often tiny remnants surrounded by disturbed lands, so that they are hardly pristine representatives. Small amounts of Sycamore Alluvial Woodland and Great Valley Willow Scrub and Mesquite Scrub occur almost exclusively on private land. Valley Sink Scrub, Valley Saltbush Scrub, and Great Valley Mixed Riparian Forest have greater than 80% in status 4. Tamarisk Scrub, also with greater than 80% in status 4, is considered an exotic community type.

2. Plant community types mainly located in unprotected areas. Six of the 34 types were mapped with areas greater than 25 km² and with less than 10% of their distribution in Status 1 or 2 areas, which are designated for conservation of native biodiversity. These include Diablan Sage Scrub, Interior Live Oak Chaparral, Alkali Meadow, Great Valley Valley Oak Riparian Forest, Valley Oak Woodland, and Blue Oak Woodland. The Interior Live Oak Chaparral and Blue Oak Woodland types are more typical of the surrounding foothill regions. Mojavean Pinyon-Juniper Woodland falls just below the size threshold, but is contiguous with similar habitat in the Central Western and Southwestern regions. This type is at the margin of its distribution in the southwestern corner of the Great Central Valley region and may have unusual floristic combinations of species.

3. Community types that appear well-protected. Two of the 34 types were mapped with areas greater than 25 km² and with more than 25% of their distribution in Level 1 areas. These include Upper Sonoran Subshrub Scrub and Coastal and Valley Freshwater Marsh. Upper Sonoran Subshrub Scrub is ranked as 3.2, or threatened, whereas Coastal and Valley Freshwater Marsh is ranked as 2.1, or very threatened.

Several other types are of concern to the state but not identified above because their management profiles fall in between those of groups 1-2 and group 3 above. Included in this group are Valley Saltbush Scrub, Interior Coast Range Saltbush Scrub, Great Valley Cottonwood Riparian Forest, and Great Valley Mixed Riparian Forest. All four types are ranked by the State, however, as either threatened or very threatened, and have suffered extreme reductions in their distributions. Similarly, Valley Needlegrass and Valley Sacaton Grassland are largely protected in BMA's although their extent is less than 25 km². Both are also ranked as very threatened. The explanation for the high proportion of status 1 and 2 land for these types is that they have been actively protected in recent years in recognition of their rarity, the biological significance, and the substantial historical losses. As the last remnants of these types, additional management action may still be needed to preserve them.