Plants

Vegetation at Pinnacles National Monument may be broadly grouped into five major habitat types or vegetation associations, described below. These associations result from a web of interactions amongst the various plant species and such factors as soil type, direction of exposure, slope, moisture regime and fire history. Recognizing the plants that characterize an association allows us to see the patterns of these co-occurring factors.

Chaparral
The most widespread plant community, chaparral occurs just about everywhere you look. Found on shallow or deep soils, north- or south-facing slopes, moist canyon bottoms or exposed upper ridges, eighty-two percent of the monument is covered by some type of chaparral. All chaparral associations share similar characteristics, though the species composition and structure differ in relation to environmental factors.
 
This vegetation type is composed mostly of shrubs up to two meters tall, and is adapted to grow in warm climates with little or no summer moisture, and variously wet winters. To survive and even thrive in the long hot summers, many of the plants have evolved adaptive traits such as small waxy-coated leaves, deep taproots, shrubby stature, water storage structures, and summer dormancy.

In addition, many chaparral plant species have adapted to the natural occurrence of fire. For example, seeds of some chaparral plants lie dormant in the seedbank for years before a fire stimulates them to sprout. Dependent on disturbance and seedcoat scarification for seed germination, the plants may appear suddenly after a fire, even in areas in which they have long been absent.

Chamise, with small needle-like leaves, is the dominant shrub at Pinnacles. Spikes of white flowers bloom at the tips of the branches from May through July. Chamise grows in mixes of other species, including buck brush, manzanita, holly-leaved cherry, mountain-mahogany and black sage. The composition of the chaparral varies depending on soil type and direction of exposure, amongst other factors. The many species of the annual and perennial understory also vary depending on moisture and exposure. As a general rule, dry south-facing stands have fewer species than moister north-facing stands.

Woodlands
Woodlands, the second most common association in the monument, occur from lower riparian areas to upper exposed slopes of North Chalone Peak, and are characterized by trees with annual grasses and forbs in the understory. The main woodland association at Pinnacles is the blue oak woodland, comprising 10 percent of the total vegetation cover in the monument. Gray pine, California buckeye, valley oak and live oak appear both in this and the riparian associations. In the woodland habitat type, however, these tree species are only minor components, while in riparian areas they play a more significant role. The woodland understory is a mixture of non-native grasses, perennial native grasses and a variety of annual and perennial forbs.

Riparian
This habitat type is restricted to the valley bottoms and sheltered, moist canyons of the monument. The species are deep-rooted and require more water than any of the other vegetation associations. Large deciduous and evergreen species dominate, such as sycamore, cottonwood, and California buckeye, often growing directly in small creeks and streams. Other major species include valley oak, live oak, and gray pine, as well as willow and mule fat. The understory in this community consists of shade-loving perennials with few annual species.

Grasslands
Found in most of the same areas as the rock and scree association described below, and closely related, grasslands have shallow soils that prevent the establishment of deep-rooted species. Dominant species include introduced grasses such as brome; native and non-native annuals including fiddleneck and filaree; and a variety of mostly native herbaceous perennials like lomatiums.

Though the rock and scree habitat type is the least common in the monument, its dramatic spires and rock faces inspired the establishment of Pinnacles National Monument. Named for its predominant substrate, the association is characterized by having little or no soil. This slight but important difference in soil depth largely accounts for contrasts between the vegetation of this and the grasslands habitat. Despite demanding conditions, some plants have developed the ability to flourish here. Bitter root and two-leaved onion, for example, are among the most spectacular plants in the monument, and are found in rocky areas of the High Peaks, Balconies and South Chalone Peak.

Vegetation Mapping

A vegetation map is a pictorial representation of the plant communities covering a given area of land. Groups of plant species that commonly occur together are delineated in a patch-like configuration on a map. These maps, with layers of detail such as species composition or soil type, become useful tools in understanding interactions between the biological and the physical world. Vegetation maps illuminate biological trends, such as an exotic weed taking over a native ecosystem, or the regrowth of vegetation after fire. Vegetation maps can also indicate the type of habitat where given rare plants or animals might be found, such as Pinnacles buckwheat (Eriogonum nortonii) or the San Joaquin coachwhip snake (Masticophis flagellum ruddocki). In addition to correlating the species with the habitat type, the map can reveal relationships that underlie the correlation, answering the question of why the given species is found in the habitat, or what specific characteristic of the habitat is associated with the species. For instance, in mapping valley oaks (Quercus lobata), the location of the oaks is consistently associated with fine soils on a geomorphic landform known as a Pleistocene Terrace. Information of this kind is vital for responsible management of the resources in our parks. Now, due to a national emphasis on Inventory and Monitoring within the National Park Service, Pinnacles National Monument is carrying out a two-year Vegetation Mapping Project.

Vegetation Map

The Pinnacles National Monument Vegetation Mapping Project will utilize IKONOS digital satellite imagery as a foundation for the map. Information about the vegetation, collected through extensive field sampling in 2003 and 2004, will be analyzed statistically by the University of Montana's Wildlife Spatial Analysis Lab in order to diagram the relationship between the images and the vegetation - ultimately producing a map segmented into identifiably differentiated vegetation types.

The vegetation sampling program at Pinnacles employs a method of data collection called a relevé. Relevé standards were developed by the California Native Plant Society in 1995, and require that field crews thoroughly inventory the plant species in a given area and determine the amount of cover taken up by each species. The crews also record GPS data, soil texture, topography, local site history, and photographic information for each location. Working in teams of two in 2003, the mapping crew at Pinnacles surveyed approximately 250 plots, many of which were located in chaparral, California buckwheat, and woodland vegetation communities. By June of 2004, the Pinnacles crew will have completed the roughly 650 plot surveys necessary for generating an accurate vegetation map.

Vegetation Classification

Before the map can be correctly segmented into vegetation alliances, it is necessary to classify the vegetation, meaning to be able to define repeatedly distinguishable vegetation types. This botanical classification will follow standards for sampling and analysis set forth by the National Biological Survey and the California Native Plant Society. By following standards for data collection and analysis, we will essentially "speak the same language" as other researchers, so that we can easily share information and make straightforward comparisons with vegetation classifications in other geographical areas. The final classification system will encompass a variety of vegetation types, from those abundant at Pinnacles, to those that occupy little of the Monument's 24,500 acres - as long as the vegetation types can be reliably differentiated. Some examples of vegetation types or alliances that will be visible on Pinnacles' vegetation map are listed below:

Exotic Plants

At Pinnacles National Monument, out of approximately 625 plant species, about 100 are nonnative. Several of these species are invasive, with the potential for creating serious ecological damage and detracting from the uniqueness of the monument’s native plant community. Pinnacles National Monument Weed Control Program is focused primarily on horehound (Marrubium vulgare), mustard (Hirschfeldia incana), and yellow star thistle (Centaurea solstitialis). Weed control efforts focus on these three species because of their potential for native habitat destruction. Yellow star thistle and mustard are controlled by working through a sequence of large areas on a monthly basis. Horehound is much closer to being eradicated within the monument and is controlled by monthly visits to 140 small plots. Eradication methods include hand pulling and herbicide application.                     

Yellow star thistle (Centaurea solstitialis)  
Yellow star thistle is considered one of the most invasive weeds in California by the California Exotic Pest Plant Council. It has already degraded over 25 percent of the land in California and is called “the plant that ate California”. Yellow star thistle is a summer-blooming annual in the Sunflower family and native to Eurasia. The plant is found primarily in open, disturbed areas such as road edges and stream channels, but through time moves increasingly into undisturbed locations, including meadows and riparian corridors.

Yellow star thistle produces a deep taproot, which extends below the zone of root competition of associated annual species. This allows yellow star thistle to grow well into the summer after most other annuals have dried up. Each seed head produces stiff spines, 1-3 cm long that make the plant unpalatable to wildlife and painful for park visitors. Yellow star thistle is less abundant and somewhat less widely distributed within the monument than mustard. Nonetheless, it imposes a serious long-term threat because of its ability to produce large numbers of seeds and its growth during the hot summer months.

In January 1999, an integrated pest management (IPM) action plan was drafted for managing yellow star thistle at Pinnacles. The control objective of the IPM action plan was to reduce the abundance of yellow star thistle to 5 percent of its abundance at that time by the year 2002.

Horehound (Marrubium vulgare)
Horehound is an herbaceous perennial plant native to Europe that arrived in North America as a cultivated herb. It reproduces readily by both seed and vegetative means. The seed is readily distributed by wildlife and visitors due to recurved barbs on the seed which attach to fur and clothing. It is likely that animal fur, possibly the fetlocks of horses and the fur of small animals, has transported horehound seeds at Pinnacles because horehound infestations are often located at corral sites and animal burrows. The monument staff has been successfully controlling horehound since the late 1980s.

Summer Mustard (Hirschfeldia incana)
Summer mustard is a biennial native to the Mediterranean. The plant was first established in southern coastal California and now can be found in Oregon, Idaho, Nevada, and Washington. Summer mustard grows extremely well in disturbed, open and sunny areas. In the first year of growth, the mustard plant produces a rosette; in the second year, the plant bolts, flowers, sets seed and dies. The plant blooms May through October and in late fall forms dense stands of brittle woody seed stalks. At Pinnacles, summer mustard is out-competing native plant species, encroaching on trails and the dried seed stalks are creating hazardous fuel buildup.

In December of 1998, Pinnacles received an anonymous donation to be applied to the removal of mustards. In 1999 an IPM action plan was developed and removal began in early 2000.

Wildflowers

The peak blooming season at Pinnacles is from March through May, when over 80 percent of the monument’s plants are in bloom. Depending on rainfall and temperature, flowers can begin opening as early as January and continue into June or, in a really wet year, into July. Manzanita, milkmaids, shooting stars, and Indian warriors are the most common early bloomers in January and February. By March, bush poppies and buck brush are the dominant flowering shrubs, along with forbs such as California poppies, fiddleneck, peppergrass, filaree, fiesta flower, monkeyflower, and baby blue-eyes.

In April, most of the March-blooming species are still blossoming, and such species as Johnny-jump-ups, virgin's bower, gilia, suncups, chia, black sage, pitcher sage, larkspur, and bush lupine have joined the spectacular display. A few early blooming species may still be seen in May, but center stage will be occupied by species that enjoy hotter, drier weather, such as chamise, buckwheat, clarkias, orchids, penstemons, and roses. Though late-blooming species may still be seen in early June of wet or cool years, by mid-June or early July, summer sets in and few blossoms are to be found.

Lichens

Pinnacles National Monument has an abundant and diverse lichen flora that is strikingly visible to the visitor and functionally important to the park’s ecosystem. The rock outcrops for which Pinnacles is named are a key habitat for a great diversity of the park’s lichen flora. Many of the rock surfaces appear to be painted in shades of red, orange, yellow, green, and brown due to the prolific lichen growth. These lichens undoubtedly contribute to rock weathering through chemical processes, although it is likely minor compared to other physical processes (i.e. freeze-thaw). The unique soil lichen communities found on open talus slopes in the chaparral vegetation community are crucial in stabilizing soil. The crowns and trunks of oak trees in the oak woodland communities are typically plastered with lichen, covering nearly every available surface. This dense lichen growth provides food, shelter, and camouflage for a variety of arthropod species. The long, pendulous lichens dangling from oak branches are commonly used as nesting material for birds and rodents, and occasionally as fodder for deer. In addition, lichens aid in nutrient cycling and the control of stand humidity. Finally, lichens are used as indicators of air quality, stand age, and stand continuity.

In 2003, we inventoried the lichens at Pinnacles National Monument. The primary objective of the project was to create a comprehensive lichen species list and reference collection for PINN. The secondary objectives were to 1) collect preliminary distribution and relative abundance information, 2) obtain GPS data for new occurrences of rare lichens found through inventory efforts, and 3) identify lichen species that are suitable for use in long-term monitoring programs. The results of this inventory plus all previous records bring the total number of lichens known to occur at Pinnacles National Monument to 293. It is estimated that another 40-50 species remain to be found here.

Pinnacles National Monument Lichen Checklist