California prairies

California Prairies and Exotic-Dominated Annual Grasslands

California grasslands are probably the single most drastically human-altered vegetation in the State

At the present time, these grasslands are:

dominated by exotic, annual grass species, most originating from the Mediterranean borderlands. Examples:
- Avena (oats)
- Bromus (brome)
- Hordeum (barley)
- Lolium or Festuca (oats)
- Triticum (wheat)
These accidental introductions were accompanied by equally accidental introductions of exotic forbs. Examples:
- Erodium (heron's bill)
- Taraxacum (dandelions)
- Sonchus (sow thistle/dandelion)
- Salsola (tumbleweed)
- Convolvulus (bindweed)
- Marrubium (horehound)
- Centaurea (star thistle)
- Carduus (Italian and plumeless thistles) Cirsium vulgare (bull thistle)

Many of these species were brought here accidentally by the Spanish and, later, Americans

Seeds were brought in on the coats of animals (California's mission and rancho economies were dominated by cattle grazing and their slaughter for the hides and tallow trade with New England ships (the American industrial age started with production of leather goods, candles, and fuel oil, and California was the raw material source)
Grazing animals schlepped seeds around in their coats and distributed them by rolling (to scratch itches) and walking around
Many species were deliberately introduced, grasses as forage (such as Phalaris aquatica or Harding grass), forbs as honey sources (such as Centaurea or star thistles), and spices (such as Foeniculum or fennel, and mustards, Brassica and Hirschfeldia)

Many of the newcomer species are annuals that blast through their life cycles in a short period, reproduce prodigiously, and die, leaving great masses of dry litter behind

This is a great adaptation, not only to Califoria's summer drought, but to fire
The dry litter alters fire régimes, making fire more frequent
The exotics don't "care" since they're already dead

Native species, including CSS shrubs and native California perennials, are also adapted to drought and fire

The problem is that the native species are not as well adapted as these annuals to the new conditions created by the annuals, particularly the increase in fire frequency these light, flashy fuels encourage
This is one mechanism maintaining the type conversion from CSS to grass
Type conversion is long-term or permanent change in ground cover that is self-sustaining: The plants belonging to the original ground cover community are unable to reëstablish in the local microclimatic and soil conditions that support the new community

Adding to the problem, the exotic invasives are themselves subject to invasion by exotics even MORE invasive than they are!

So, annual exotic grassland is readily invaded by mustards, fennel, several thistle species
These are capable of creating huge amounts of biomass that dry out at season's end, which amplifies the fire risk
Some are capable of allelopathy, or chemical warfare, suppressing both annual grasses and CSS shrubs

Many native California grass species are perennial and at a disadvantage against pyrogenic annuals, so they are very scarce in the heart of the grasslands but may sometimes be seen on the edges, sometimes in association with CSS vanguard species, such as coyotebrush (Baccharis pilularis)

California grassland is in worse shape than CSS, having lost perhaps 97 or 98% of its original extent, with who knows what impacts on native fauna

There are conservancies up and down the State trying to restore California grasslands

These often feature clearing and replanting with such species as Stipa pulchra (purple needlegrass), Muhlenbergia spp. (deergrasses), Elymus condensatus (giant California rye)
This clearance may be problematic, according to research done by the CSULB Biogeography Lab group
- Clearing is often done by plowing or scraping the surface
- This substantial mechanical disturbance tends to discourage reëstablishment of CSS species
- We're not quite sure why this is, but there's some support for the idea that mechanical overturn can disrupt and even destroy subsurface symbioses between CSS plant roots and a number of fungal species (arbuscular mycorrhizæ)
These restoration efforts are generally not too successful, exotics reïnvading and displacing the natives to the perimeter

And this brings us to the emerging central issue: We have no real idea what these grasslands looked like before the Spanish explored and set up shop here!

Much of our notion of the original California grassland is based on the work of Frederick Clements, a famous ecologist active from around 1910 to 1945. He's the guy who elaborated a succession model: That Clements.
- Succession is a fairly orderly and predictable change in the plant communities that cover a given site once it is exposed or after it has been disturbed by fire, flood, windstorms, human clearing.
- As each community or sere establishes, it alters the environmental conditions at the site that may make reproduction tougher on that plant community, and these alterations may actually make the site more hospitable to a different group of plants that then replaces it.
- This process of establishment, alteration, decline of one group, and replacement by another group goes on until it finally reaches a climax condition. A climax community marks the establishment of a community that alters things in such a way as to promote its own reproductive success. That means it maintains a stable equilibrium through long reaches of time and that equilibrium reflects local climate and soil conditions.
- The correspondence between climatic and edaphic (soil) conditions was believed to be so close that you can actually use the climax community to retrodict what the climate and edaphic conditions are.
- Clements did a lot of field work in California, and he thought that succession before the arrival of Europeans would produce a climax community in the California grasslands dominated by perennial bunch grasses in areas of semi-arid climate and deep valley soils.
- He focussed on the perennial bunchgrasses, because it was perennial bunchgrasses in the grasslands that were often the natives, while the annual grasses were usually intoduced exotic species.
- He also commented that he would find the native perennial bunchgrasses (e.g., Stipa pulchra) on the periphery of the grasslands up where they bordered on CSS or chaparral or oak parks. He also noted finding them in disturbed areas, such as along railroad tracks, fencelines, and road shoulders. He thought that that "off to the side" distribution implied that the native grasses had surrendered their core habitat to the annuals and then clung to life displaced to the margins of the exotics' environmental envelopes and almost past their own. He saw this as a relict distribution, a mere remnant of their original dominant distribution.
- This idea of a perennial bunchgrass dominated climax community has dominated a lot of the work conservancies undertake to heal the grasslands, and it informs how they frame what they want to restore to and the palettes of species they are trying to establish. Many folks even get annoyed when a native CSS shrub, Baccharis pilularis, starts invading their plantings and displacing the native grasses they fight so hard to restore. Our own work in the Biogeography Lab suggests that Baccharis pilularis is a vanguard plant that acts as a nursemaid species facilitating the reëstablishment of CSS on lands type-converted to annual exotic grassland, rather than an annoying invader of a carefully reconstructed native California grassland.
The trouble is: We don't know if Clements' perennial grasses, in fact, are what dominated California prairies!
Richard Minnich (yes, that Richard Minnich from the great "firefight" with Jon Keeley about the original fire régime in chaparral) and a few other researchers are now wondering if there was any such thing as a perennial bunchgrass dominated grassland.
- They're wondering if the vegetation that once occupied grasslands now might have been a mix of forbs, geophytes, low shrubs and subshrubs, and a few perennial bunchgrasses and maybe even some annual grasses (there are native California annual grasses, such as orcutt grass, Orcuttia californica, alkali barley, Hordeum depressum, and small fescue, Festuca microstachys). So it may have been a mixed prairie or steppe rather than a bunch gassland.
- This suspicion is based on analysis of diaries and travel notes of the early Spanish expeditions to explore California. They often comment on the vegetation and, in areas now covered with annual grassland, they describe fields of wildflowers (forbs and geophytes) in addition to grasses. Close examination of these many historical commentaries does not support the image of a perennial bunch grassland.
- This is a very different vision of the past California grassland landscape and, if they're right, it's no wonder the conservation and restoration efforts fail. They may be trying to bring us back to the wrong past, a romanticized representation of the prairies rooted more in reverence for a classic ecologist than to whatever was actually there. Testing a variety of plantings based on a wider array of inspirations might make a feasible experimental approach to figuring out what is possible in California prairie restoration.
- It is important to evaluate the kinds of animal species that hung out in whatever these prairies were and whether they can be introduced, too. Vegetation restoration is as much about restoring ecological functioning and native animal habitat as it is about restoring the look of the pre-Spanish vegetation.

GEOG/ES&P 330

California Ecosystems