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Plant Communities of Santa Cruz County
Much of our area's coastal prairie has been destroyed due to agriculture and development, The remaining areas have been invaded by exotic weeds such as annual fescues (Vulpia bromoides), bromes (esp. Bromus diandrus), velvet grass (Holcus lanatus), and thistles (esp. Carduus pycnocephalus). The remaining, in tact areas of coastal prairie are recognized by the patchy presence of California oatgrass (Danthonia californica) and/or wildflowers such as native bulbs (Brodiaea and Triteleia species), lupines (Lupinus nanus), self-heal (Prunellus vulgaris), and many others. The best areas to view coastal prairie are at UCSC's upper campus (Marshall Meadows), State Parks' Gray Whale Ranch, and just north of Aqo Nuevo along the coast south of Franklin Point.
PRAIRIE SIGNIFICANCE AND RECOGNITION
Somehow, despite the recent listing of California native grasslands as the eighth rarest ecosystem in the United States, the rarity of the prairie ecosystem has not been recognized and thereby continues to be lost through development or neglected by land managers . One of the difficulties facing the recognition of the rarity of grasslands is the definition of true "coastal prairie." Many land managers have recently gained a recognition of native grasses and assume that a coastal prairie consists of a few species of perennial bunchgrasses and little else. However, most natural "grassland" historically consisted of many annual and perennial forb species ("wildflowers") growing in association with relatively few native grass species. In some areas of the County, prairie habitats support as many as 250 species of native wildflowers. For Santa Cruz County, the CNPS lists 13 species of concern in their Inventory of Rare and Endangered Plants of California (1995) (see appendix A). The diversity of these prairie wildflower species, in turn, supports an even greater diversity of insect species, many of which are severely reduced in numbers (e.g., Schinia sp.- a genus of colorful diurnal noctuid moths; and solitary bees such as in the families Andrenidae and Anthophoridae) and some of which teeter on the verge of extinction (e.g., Cicindela Ohlone, Ohlone Tiger Beetle and Adela oplerella, Opler's long horned moth). Some known species have already been lost (e.g., Lytta molesta, molestan blister beetle) and, undoubtedly, others have disappeared before even being described. The reduction in numbers of plant species and numbers of populations of insects leads to a collapse in the prey base for many other species- birds, shrews, and bats, for instance.
Many people contend that meadows are artifacts of human intervention (i.e., "clearings"). This may be true of some grasslands; however, it is certainly not true of all meadows in Santa Cruz County which contain an abundance of meadow dependent species (see appendix B). It can be taken as axiomatic that a high diversity of meadow dependent species in a given meadow presupposes the meadow's long history as a stable community. It is theorized that Santa Cruz's coastal terrace prairie is the oldest, most stable ecosystem of the temperate world, dating back 600,000 years (Dr. Robert Curry, pers. comm., 1993). On the other hand, areas with few or no meadow dependent species may have been recently converted from forest or scrub.
The current technique for determining meadow diversity (i.e., seasonal botanical surveys) fails to detect species existing in the soil as seeds awaiting an improved management regime. For instance, the grassland of the City of Santa Cruz's Arana Gulch Greenbelt Land could thus have been surveyed and considered non-native and the assumption would have been made that this meadow was a human artifact. Yet, a year later, after mechanical removal of weeds, Holocarpha macradenia (Santa Cruz Tarplant, an endangered species of prairie dependent wildflower) appeared en masse along with new populations of native grass (Danthonia californica) and wildflowers (Lupinus bicolor, small-flowered lupine, Castilleja densiflora, purple owls clover) which had not been documented in recent surveys. The appearance of Plagiobothrys chorisianus (artist's popcorn flower, a CNPS list 4 plant) was a great surprise as it had not been documented on the site despite 12 years of botanical surveys.
The significance of meadowland diversity needs to be recognized by both land managers and the general public who must provide them political support for land management decisions. More people need to understand the level of crisis the prairie ecosystem faces. In the meantime, the conclusion must be that all extant coastal prairie areas should be managed to reduce weeds and thatch for as many years as it takes to allow the seedbank to express itself. In the future, standards should be developed for gathering field samples of soil and nursery growing and identifying the seedlings therein.. Only after carefully documenting the native flora should decisions be made as to the fate of the meadowland in question.
The legacy of development's impacts on the local prairie ecosystem is extensive. Nearly the entire first coastal terrace was probably prairie of around 100,000 years of age. Very few areas of this terrace remain with in tact native prairie (e.g., Franklin Point, San Mateo County; Arana Gulch, City of Santa Cruz). Much of the Pajaro valley and Watsonville and up the entire north coast of Santa Cruz has been developed in agriculture and housing. The second terrace in the City of Santa Cruz has been developed with the exception of areas of Pogonip and De Laveaga Park. Further North, large areas have been lost to row crop agriculture. The third and fourth terraces have prairie in tact in many places on the north coast. Much of the City of Scotts Valley once was prairie and has been degraded by development.
Prairie is currently protected by the County of Santa Cruz and the Coastal Commission which recognize the rarity of the habitat. However, when projects are proposed that impact prairie, destruction of the habitat is allowed through on or off site mitigation measures usually including habitat restoration. However, currently there are no proven methods of restoring prairie habitat and all such projects fall woefully short of accomplishing their goals.
It is important to note that areas of prairie habitat persist on private land zoned for agriculture. Fortunately, these areas have been used for grazing animals, not for row crops though the latter could be permitted without environmental review, a fatal flaw in the current zoning laws.
Considerations before aproving further development which destroys our remaining prairie areas are: the assessment of the acreage remaining of the community and the demonstrable efficacy of restoration practices which permit that= destruction.
The degradation of California's grasslands by the invasion of weedy exotics plants has long been recognized. A division of these weeds into three groups- perennial grasses, annual forbs and grasses, and perennial flowering plants- provides for management prioritization and strategies that help to combat their impacts.
In some native prairies the greatest threat is from perennial, introduced grasses of which five species stand out in particular: Holcus lanatus (velvet grass), Phalaris aquatica (Harding grass), Festuca arundinacea (tall fescue), Cynodon dactylon (Bermuda grass), and Pennisetum clandestinum (Kikuyu grass). These grasses, once established, can only be removed by intensive mechanical or herbicide treatment which will gravely affect native species as well. Neither grazing nor fire will eradicate these perennial species, although both methods can help in slowing their spread. On the other hand, without either management practice, these species will establish and destroy meadows. Holcus lanatus (velvet grass) has established in diverse wet meadows and mima mound prairie in the upper campus at UCSC, endangering Cicindela Ohlone (Ohlone tiger beetle) and Plagiobothrys diffusus (San Francisco popcornflower) along with many other rare or uncommon meadow species. Phalaris aquatica (Harding grass) has invaded the moist swales in the prairie at A=F1o Nuevo State Park at Franklin Point, creating large monocultural stands. I include articles on Festuca arundinacea as the threat from this weed is little understood in California but well documented elsewhere. This grass has become established on the borders of Gray Whale Ranch and throughout meadows of the UCSC campus. Cynodon dactylon (Bermuda grass) and Pennisetum clandestinum (Kikuyu grass) are invading meadows at UCSC and are present in the grasslands of Big Sur and around Elkhorn Slough. Research into the effects and invasiveness of Holcus lanatus is currently lacking and information on its effects is anecdotal.
The second largest threat to grasslands is from perennial dicots. Of these, Genista monspessulana (french broom) is the most formidable in Santa Cruz County. Broom is a major invader of grassland habitats and is well recognized by land managers as a threat to ecosystem health. At this time, through the efforts of The Wildland Restoration Team and California Department of Parks and Recreation, broom is being effectively controlled on state park land. And, luckily, Gray Whale Ranch has very little broom in its prairies at this point (Ken Moore, pers. comm., 1997). Other significant weedy dicots that are slow to spread but are now appearing in grasslands are: Foeniculum vulgare (fennel), Eucalyptus globulus (blue gum), and Acacia dealbata (green wattle). Fennel has invaded grassland and shrub areas of Santa Cruz Island to the exclusion of nearly every other species. It is now reproducing exponentially at UCSC, Pogonip, and Wilder Ranch in prairie areas. Eucalyptus has taken over many plant communities including grassland surrounding Elkhorn slough and throughout coastal Santa Cruz County. Acacia is currently invading areas of native prairie at Pogonip Open Space, one of the Greenbelt areas of the City of Santa Cruz.
Annual species of grasses and flowering plants are threats to grasslands that are, to some extent, more controllable through low cost management methods. The original invaders of native prairies, annual grasses are well known to out compete native grasses and forbs. Of equal importance is their tendency to produce large amounts of above-ground biomass that forms a thick thatch inhibiting growth and germination of native species (Menke). The worst of these species in Santa Cruz County are: Briza maxima (Rattlesnake grass), Bromus diandrus (ripgut brome), B. hordeaceus (soft chess), Avena barbata (slender oat), Hordeum murinum (foxtail), Brachypodium distachyon, and Vulpia myuros (rattail fescue). These species are ubiquitous in meadow areas of Santa Cruz County. It is important to realize that there are many species of weedy annual grasses and that the real impact is cumulative.
Annual forbs are another competitive force against native species. The most dangerous of these for our area at this time are: Carduus pycnocephalus.(Italian thistle), Hirschfeldia incana (summer mustard), Raphanus sativa (radish), and Conium maculatum (poison hemlock). Each of these species is spreading into grassland areas where management is by benign neglect. Radish, mustard, and poison hemlock produce chemicals that are strongly inhibit the growth of other species and are quickly monopolizing large areas with unknown consequences to the soil seed bank.
All of these annual species are very controllable through the use of well timed, carefully managed grazing. Grazing animals reduce non-native seed production and thatch while creating the kind of disturbance with which the prairie has evolved (see following section on disturbance). In all the cases where there is a healthy, diverse prairie remaining in Santa Cruz County, there are grazing animals. Without the use of grazing and fire, the control of all weeds becomes impossible on the scale that it is needed.
THE IMPORTANCE OF FIRE
When timed correctly (Howe, 1994), prescribed fire can be used to mimic the historical role of fire while increasing meadow diversity through weed control and reduction of thatch. The role of fire in prairie ecosystems has been well documented as maintaining diversity and structure of the community. The suppression of fire directly threatens grassland communities by allowing invasion of these areas by shrubs and trees.
Although fire may not have been a common occurrence prior to the human occupation of the last approximately 10,000 years, it previously occurred in infrequent but catastrophic episodes. These fires, along with herds of large herbivores that became extinct in the late Pleistocene could have been a key factor in maintaining and perhaps extending areas of meadow coverage . To allow live oak woodland to invade meadowlands (as is currently the policy at Wilder Ranch) is to allow the replacement of a rare habitat by a more locally common one and, thereby, the loss of structural, functional, and species level biodiversity.
The use of prescribed fire has been shown to be effective in maintaining grassland health. Well timed fire reduces thatch , while reducing the seed output of non-native species. Research at the Jepson Prairie Preserve (near Davis, California) has shown increases in native species abundance with a corollary reduction in weedy , non-native species after fire. Locally, prescribed burning by the California Department of Parks and Recreation at Franklin Point and by the California Department of Forestry at UCSC has apparently slowed the invasion of velvet grass and many other weedy species. An accidental fire at Arana Gulch Greenbelt above the Santa Cruz Yacht Harbor has contributed to the recovery of an important population of Holocarpha macradenia (Santa Cruz Tarplant) and other prairie plants.
That there is a conflict between oak preservation and grassland preservation is evident and predictable. Trees are often the beneficiaries of plant conservation efforts in similar ways to lions getting attention while rare snail darters and flower-loving flies get scorn and ridicule. Public agencies and CNPS should work together in the future to educate the public about the importance of prairie habitat and its management requirements.
The two aspects of prescribed fire that have failed are: 1) an inability to reverse the invasion of trees and shrubs into the edges of meadows, as burning along ecotones is prohibited in the interest of safety, and 2) the extent of fires is often small because of limited resources, leaving large areas neglected.
LACK OF DISTURBANCE
As previously discussed, the majority of prairie plant diversity rests in the annual wildflowers. All of these species are, to some extent, disturbance dependent. That is, without soil disturbance and, especially, thatch removal they fail to germinate. Examples of listed species that occur in Santa Cruz County meadows include: Trifolium buckwestiorum (Santa Cruz Clover), T. grayi (Gray's Clover), Plagiobothrys chorisianus (Artist's popcornflower), Plagiobothrys diffusus (San Francisco Popcornflower), and Holocarpha macradenia (Santa Cruz Tarplant). Historically, soil disturbance and thatch removal occurred in conjunction with large herbivores which became extinct in the late Pleistocene.
Locally, these species owe their existence to grazing, trail side soil disturbance, and other human induced disturbances. Without such disturbance, the native annuals retreat to tiny refugia of very shallow soil too poor and dry to support weeds. In Santa Cruz County, areas where there are remaining populations of diverse wildflowers are as follows (with disturbance type in parentheses): Bombay Corporation Lands, Westside Santa Cruz (grazing), Younger Ranch and lower UCSC, Westside Santa Cruz (grazing, roads, trails), Marshall Meadows, upper UCSC campus (trails, fire), Watsonville Airport (light tractor discing, mowing), Glenwood Grasslands, Scotts Valley (grazing, trails), and Swanton Road Grasslands (grazing). Areas where many wildflower species (including rare species) have disappeared after the cessation of grazing are: Pogonip Greenbelt Area, City of Santa Cruz; areas at UCSC campus; areas of Glenwood Grasslands- west of Glenwood Drive, near Scotts Valley; and Arana Gulch Greenbelt Land, City of Santa Cruz.
The sciences of island biogeography and conservation biology have enlightened us to some of the effects of habitat fragmentation including the increased possibility of local, regional, and global extinctions and the increased susceptibility of areas to weed invasion.
Smaller, more fragmented habitats make species more susceptible to extinctions as each individual area of habitat loses species due to catastrophic disturbance. A lack of adequate corridors then decreases the chances of recolonization by the locally extinct organisms from adjacent habitat, and slowly species lose the overall regional and global numbers they need to survive.
With local prairie habitat fragmentation, the long term preservation of sensitive, meadow dependent plant species becomes problematic. Climate fluctuations require plants to be able to shift the placement of their populations to areas of varying moisture or sun exposure. For their long term survival, species need to be able to maintain large enough populations to have a broad genetic base with which to adapt to changing situations. Habitat areas need to be close enough together for seeds to be spread by the many seed dispersal agents: ants, birds, wind, and mammals. The dispersal of these seeds allows for recolonization of species into unoccupied habitat and for the transfer of genetic information important to their adaptation to changing conditions. Restoration science may never progress to a point where managers can restore even a single species of plant into the wild for the long term, making it imperative that plant species be given every opportunity to disperse and multiply on their own.
Another impact of the fragmentation of prairie habitat is the loss of insect diversity. Fragmented, small meadows may not contain enough individuals of various plant species to support pollinators. Therefore, in a deadly circle, both plant and insect species spiral towards extinction without the space and population numbers to support healthy populations. For other insects, larval host plants may not be in enough abundance to support large, healthy populations. While we flirt with the precipitous decline of thirteen plant species in the prairies of Santa Cruz County, we must realize that the decline of these species may cause the extinction of 130 species of insects. The viablility of these insects' populations may already be more endangered than the plants themselves due to a large part to the widely spaced, fragmented nature of the plant populations.
Fragmented prairie habitat is also more vulnerable to weed invasion. Small meadows have more edge exposed to roadways, trails, and other sources of weed introduction. Weeds can then invade to occupy a large proportion of fragmented meadows in a relatively short period of time. These areas are also harder to manage with fire or grazing to reduce weed pressure.
With the north coast of Santa Cruz County and its contiguous prairie habitat, there is a golden opportunity to plan for the long term survival of meadow dependent species through the preservation and management of contiguous and expansive existing prairies.
Erosion also affects most ecosystems in our area. Gully erosion is a common phenomenon on the deep, high shrink-swell soils of the marine terraces. Currently, large gullies are consuming areas of grassland and coastal scrub in and around Wilder Ranch. The cause of these gullies is generally accepted as being accelerated runoff due to soil compaction and development. Some gullies may have begun during the widespread disturbance of forest clear cutting and road building during the limestone quarrying era of the nineteenth and early twentieth century. Current technology to stop gully expansion includes large, deeply seated check dams used in conjunction with swales to channel runoff into adjoining sub watersheds. This is a very expensive and potentially ineffective treatment. A serious look by qualified soil scientists and erosion control experts at erosion potential due to long term, human impacts related to increased trail use through our fragile prairies is in order. Because of the importance of foot trails to the Ohlone Tiger Beetle and annual wildflower species, the establishment of more diffused trail systems should be stressed rather than concentration of traffic on single trails.
(common names)American kestrel
California ground squirrel
Ohlone tiger beetle
oxeye satyr butterfly