The Vegetation Classification developed
for the Napa County MCV map

(Includes only Alliances found on the Quail Ridge Reserve)

Thorne, J. H., J. A. Kennedy, J. F. Quinn, M. McCoy,
T. Keeler-Wolf and J. Menke.

(Made possible by funding from the California Department of Transportation,
the David and Lucille Packard Foundation, and the National Fish and Wildlife Foundation)

Napa County Mapping Classification

The National Vegetation Classification System (NVCS) establishes a hierarchy for vegetation cover types, with the Class, Subclass, Group and Formation levels forming the highest (coarsest) levels of the hierarchy, based on the physiognomy of the vegetation. The Alliance and the Association form the lowest (finest) levels of the hierarchy, and are based on floristic composition within a given physiognomic Formation. The Manual of California Vegetation (MCV) is the local implementation of the NVCS for California.

For mapping purposes, individual Alliances often cannot be distinguished on the base map imagery, but multiple aggregations of Alliances within a given Formation can be distinguished and mapped. The same is true at the Association level. Rather than lose vegetative resolution by mapping to the next coarsest level in the hierarchy (i.e., the Formation or the Alliance level, respectively) mappers will resort to ad hoc cover types of aggregated Alliances, here called Super Alliances, or aggregated Associations, here called Super Associations. When new plot data collection is not an integral component of the mapping project, as was the case for this first edition of the Napa vegetation map, these provisional cover types are not formally defined by quantitative cover data. In the classification below, these provisional types are preceded by NFD, for “not formally defined.” The authors are currently seeking funding for the field-based data collection needed to revise the classification and define these provisional types.

In the NVCS, each entry in the hierarchy has a unique alphanumeric code. These NVCS codes are long and unwieldy for map display of individual polygon (stand) labels. In current mapping practice, short four-digit codes are used instead. These have the advantage of compactness, but the disadvantage of being unique only to the particular map in question. The same numeric code could stand for a different cover type on a different map. They are merely codes of convenience for map labeling purposes. Note, also, that while codes in the even thousands refer to Class - Subclass entities and those in the even hundreds refer to Group - Formation entities, those with non-zero digits in the tens and ones place can refer to entities at either the Super Alliance, Alliance, Super Association or the Association level. The level of indentation provides a visual clue as to the appropriate hierarchical level for a given cover type. Note that cover types at the Super Association or Association level may occur out of strict numerical sequence.

MCV Vegetation Mapping Hierarchy

Class - Subclass (Level 1)

Group - Formation (Level 2)

Super Alliance - Alliance (Level 3)

Super Association - Association (Level 4)

NOTE: Types in bold face are discernible on the digital orthophoto quarter quad (DOQQ) black and white base map imagery or can be correlated to environments and have been mapped in the county. All hierarchical levels are shown for context. Physignomic Formations shown in boldface (n = 3) represent mapped cover types, usually for post-disturbance stands that are too early in their successional sequence to reliably map at a finer level. At the time the mapping project began, the most recent DOQQs dated from 1993. Napa County flew color imagery for DOQQ production in late April 2002. The resulting color DOQQs should be available in early 2004 for the entire county and will be used for map revision.

1200 - Xeromorphic Sclerophyll Woodlands

1222 – Interior Live Oak Alliance

Quercus wislizeni is uncommon as a sole component to a hardwood canopy. This cover type is generally found on steep northerly slopes in closed stands in the eastern portions of the county that may contain a minor component of Q. douglasii and/or Pinus sabiniana and often transitions to a mesic chaparral containing scrub Q. wislizeni ssp. frutescens, Umbellularia californica, Q. berberidifolia, Cercocarpus betuloides and Fraxinus dipetala. It is mapped only east of Lake Berryessa on north trending slopes.

1223 – Mixed Oak Alliance

Very common throughout the county, this type is mapped as several different provisional associations where at least two or more oaks, discernable on the DOQQ base map imagery, co-dominate. Lowest elevations often contain a mix of Quercus agrifolia and Q. lobata. Q. garryana may be a component to this phase, especially north of Napa. Higher elevations will always have a significant component of Q. kelloggii, with Q. chrysolepis playing an important role in steeper settings. Other hardwoods often occur in the stand as a minor component, with Acer macrophyllum occurring in more mesic settings, and Arbutus menziesii in more xeric sites. At higher elevations in open woodland settings, Q. kelloggii and Q. douglasii may occasionally mix. Conifers, especially Pinus ponderosa or Pseudotsuga menzeisii, may occur as a minor component to higher elevation stands generally below 10% relative cover.

1202 – Interior Live Oak - Blue Oak - (Foothill Pine) NFD Association

This is a common type that generally replaces type 1201 east of the Napa River watershed. This type is a provisional association of the Mixed Oak Alliance (1223) that can be reliably identified and mapped on the b&w DOQQs base maps. It is found in somewhat steeper settings than the Blue Oak Alliance (3122). Both oak species contain at least 10-15% relative cover. Pinus sabiana is often a co-dominant but with generally less than 15% relative cover.

2000 – Evergreen Needle-leaf Forests & Woodlands

2100 – Rounded Crown Forests & Woodlands (Pines & Cypress)

2104 – Foothill Pine / Mesic Non-serpentine Chaparral NFD Association

Several stands were noted in the eastern portion of the county, where Pinus sabiniana is emergent to non-serpentine chaparral or scrubby Umbellularia californica.

3000 – Deciduous Forests & Woodlands

3100 – Cold Season Deciduous Forests & Woodlands

3121 – Black Oak Alliance

This type occurs at higher elevations, especially in the Atlas Peak region, on gentle to moderate slopes trending in most directions except south. Outside of this type, Quercus kelloggii is generally mapped as a component to the mixed oak mapping unit.

3122 – Blue Oak Alliance

This type occurs occasionally on slopes just east of the Napa Valley, and extensively east of Chiles Valley to the Yolo County line. Stands vary from nearly closed to very open, where Quercus douglasii makes up at least 80-90% relative cover. The most common associate is Q. wislizeni, but other oaks may be a minor component, especially at higher elevations or in west county stands.

3123 – Valley Oak Alliance

This type is fairly common, especially in the southern portion of the county, on gentle to nearly level slopes in open settings. It is generally mapped where Quercus lobata is the primary dominant species. It mixes most often with Q. agrifolia.

This type occurs occasionally on slopes just east of the Napa Valley, and extensively east of Chiles Valley to the Yolo County line. Stands vary from nearly closed to very open, where Quercus douglasii makes up at least 80-90% relative cover. The most common associate is Q. wislizenii, but other oaks may be a minor component, especially at higher elevations or in west county.

SHRUBLAND - DWARF SHRUBLAND

4000 – Evergreen Shrubland

4300 – Sclerophyllous Shrubland Formation

Mapped in disturbed settings and post fire stands, generally less than 15 years old.

4301 – Scrub Interior Live Oak - Scrub Oak - (California Bay - California Ash - Birch Leaf Mountain Mahogany - Toyon - California Buckeye) Mesic East County NFD Super Alliance

This type occurs in dense stands, especially along the crest of the Blue Ridge, often associated with the Interior Live Oak (Forest) Alliance (1222), which occurs in slightly more mesic settings.

4321 – Chamise Alliance

Mapped frequently throughout the county on xeric slopes where Adenostoma fasciculatum makes up at least 70-80% relative cover, generally in a closed chaparral setting.

4322 – Chamise - Wedgeleaf Ceanothus Alliance

Chamise and wedgeleaf ceanothus important shrubs in canopy; black sage, California buckwheat, chaparral yucca, manzanitas, and/or scrub oak may be present. Shrubs < 3 m; canopy continuous. Ground layer sparse or absent.

6000 – Perennial Herbaceous (Graminoid - Forbs)

6400 – Semi permanently - Permanently flooded Grasslands & Forbs

6402 – (Bulrush - Cattail) Fresh Water Marsh NFD Super Alliance

Most mappable stands are found along edges of small ponds and reservoirs. It is a Super Alliance, because the separate Bulrush and Cattail Alliances can’t be distinguished on the base DOQQ imagery and may co-occur.

7000 – Annual Herbaceous (Graminoid - Forbs)

7100 – Upland Annual Grasslands & Forbs Formation

Generally mapped in stands that are somewhat more disturbed and contain a higher non-native forb component than type 7120. Also mapped in ruderal settings south of the town of Napa.

7120 – California Annual Grasslands Alliance

Mapped in settings where trees make up less than 5-10% emergent cover in fairly natural settings that have not been recently cleared.

Photo Credits: Title, Shooting Stars (Karen Mabry)