Prairie Described

invasive species

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Note: The scientific names for the plant species are taken from the Jepson Manual of Vascular Plants of California, Second Edition (Baldwin et al. 2012).

Invasive Holcus lanatus

Although velvet grass can be beautiful, this non-native perennial invades coastal prairies and forms solid stands that eliminate other plant species. Photo by J. Coleman.

bulletInvasive Annual Grasses

bulletInvasive Perennial Grasses

bulletInvasive Forbs

bulletInvasive Animals

Common invasive annual grasses of coastal prairie

Wild Oat (Avena fatua) and Slender Wild Oat (Avena barbata) - non-native

wild oats dominating a grassland

Wild oats (Avena) in Marin coastal grassland. Photo by D. Immel-Jeffery 2010.

Grass Family (Poaceae)

Wild Oat:

bulletIs an annual native to Eurasia and North Africa.

Wild Oat Ecology

bulletSpecies Interactions: The success of Avena lies in its superior competitive ability:

  • It has a dense root system. The total root length of a single Avena plant can be from 54.3 miles long to, most likely, twice that long (Pavlychenko 1937; Dittmer 1937).
  • It produces allelopathic compounds, chemicals that inhibit the growth of other adjacent plant species.
  • It has long-lived seeds that can survive for as long as 10 years in the soil (Whitson 2002).
  • Pavlychenko (1937) found that, although Avena is a superior competitor when established, it is relatively slow to develop seminal roots in the early growth stages (as compared to cultivated cereal crops wheat, rye and barley).
One crown root of wild oats (Avena) separated from the root system.

One crown root of wild oats (Avena) separated from the root system. The length of the main root is 63 inches (5.25 ft, 1.6 m). The combined length of its branches is 4.5 miles. The total root length of a single Avena plant can be from 54.3 miles long to, most likely, twice that long. Figure from Pavlychenko (1937).

More Fun Facts About Wild Oats

bulletAvena is Latin for “oat.”

bulletThe cultivated oat (Avena sativa, also naturalized in California) is thought to be derived from  wild oats (Avena fatua) by early humans (Baum and Smith 2011).

bulletWild oats were either introduced accidentally or as forage for cattle during the Mission Period (1769-1824) and have been widespread in California grasslands since that time (Hendry 1931).



Rattlesnake Grass, Large Quaking Grass (Briza maxima) - non-native

grassy hilltops

Florets of rattlesnake grass with visiting bee. Photo by Jim Coleman 2010.

Grass Family (Poaceae)

Rattlesnake Grass:

bulletIs a widespread annual.

bulletCan be dominant in grasslands in California and southern Oregon (California Invasive Plants Council).

bulletIs native to southern Europe.

Fun Facts About Rattlesnake Grass

bulletRattlesnake grass may be the earliest grass cultivated for ornamental rather than edible purposes (Snow, N. Utah State University c2001-2002).

bulletRattlesnake grass escaped from gardens into the wild (Jepson c1902-1943).

bulletA lower stature, more delicate species, small quaking grass (Briza minor) is more widely distributed occurring in several states and  in many habitats.

grassy hilltops

Large Rattlesnake Grass (Briza maxima). courtesy of Robert W. Freckmann Herbarium, University of Wisconsin-Stevens Point http://wisplants.uwsp.edu/
photographers.html
. Accessed 2010 Nov 5.



Ripgut Brome (Bromus diandrus) - non-native

line drawing of ripgut brome influorescense

Ripgut brome (Bromus diandrus). Illustration courtesy of USDA-NRCS PLANTS Database / Hitchcock, A.S. (rev. A. Chase). 1950. Manual of the grasses of the United States. USDA Miscellaneous Publication No. 200. Washington, DC.

Grass Family (Poaceae)

Ripgut brome (Bromus diandrus) is a non-native annual.

Ripgut Brome:

bulletIs native in Southern and Western Europe.

bulletAlong with red brome (Bromus madritensis), can be dominant in grasslands in California and other western States (California Invasive Plants Council 2011a; Minnich 2008). 

Ripgut Brome Ecology

Life History:

  • The long rough needle-like awns aid in dispersal.
  • Seeds can be dispersed long distances by wind and water and by sticking to animals and people (California Invasive Plants Council 2011a).

bulletFire: Ripgut brome has been implicated as one of many non-native grasses that have increased fire frequency in forests and shrublands, sometimes converting them to grasslands (Cal IPC). 

Fun Facts About Ripgut Brome

bulletRipgut brome was introduced to California sometime around 1860.

bulletThe needle-like awns can injure animals by penetrating their eyes, nose and mouth parts.

bulletRip-gut brome sometimes looks a lot like the native purple needle grass. To tell the difference, hold a floret by the tips of the needle-like awns and run your finger along the awn toward the base of the floret. Purple needle grass is smooth while rip-gut brome has barbs that feel quite rough and catch on your fingertips.



Soft Brome (Bromus hordeaceus) - non-native

line drawing of soft brome

Soft brome (Bromus hordeaceus). Illustration courtesy of USDA-NRCS PLANTS Database / Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. 3 vols. Charles Scribner's Sons, New York. Vol. 1: 278.

Grass Family (Poaceae)

Soft Brome:

bullet Is native to Eurasia.

bullet Has naturalized on all continents except Antarctica.

bulletSoft brome is abundant in coastal prairies (CPEFS 2010).

Soft Brome Ecology

bulletGrazing: Soft brome was introduced as a forage species, although there are conflicting accounts of its nutritive value and palatability.

bulletLife History:

  • The seeds are short-lived (Howard 1998).
  • Bromus seeds readily germinate under mulch layers. Therefore the plant litter accumulation that occurs in the absence of fire and grazing tends to increase Bromus populations at the expense of native annuals and perennials whose germination is suppressed by litter (Heady 1988).

bulletSpecies Interactions: Soft brome threatens rare grassland species because it can outcompete them in the areas of infertile and serpentine soils that act as refuges for many rare plants (California Invasive Plants Council 2011b).

Fun Facts About Soft Brome

bulletSoft Brome Is more abundant in the Mediterranean areas of California than in its native range in Mediterranean Europe (Howard 1998). 

bulletBromus hordeaceus was previously called Bromus mollis and is also known by the common name soft chess.



Mouse barley, foxtail barley, hare barley, farmers foxtail (Hordeum murinum) - non-native

grassy hilltops

Hordeum murinum, 24 Mar 2008, along railroad tracks, Tempe, Arizona. Miwasatoshi, Wikimedia Commons.

Grass Family (Poaceae)

Mouse Barley:

bulletIs native to Eurasia

bulletNow occurs in every county in California (Calflora 2010).

Mouse Barley Ecology

bulletLife History: A common weed in disturbed sites in its native Eurasia, Mediterranean barley’s origins are thought to be around seasides, sandy riverbanks, and animal watering holes (Utah State University c2001-2002).

bulletSpecies Interactions: The Kashaya Pomo, Ohlone, and the Mendocino Indians made use of this introduced annual grass by harvesting and eating the seeds of Hordeum murinum (Bocek 1984; Chesnut 1902; Goodrich, et al. 1980).

More Fun Facts About Mouse Barley

bulletMore common than Mediterranean barley (H. marinum), this annual from Eurasia may have been brought by the Spanish settlers in California (California Invasive Plants Council).



A couple more.....

Mediterranean barley (Hordeum marinum subsp. gussoneanum) - non-native

bulletMediterranean barley (Hordeum marinum Huds. subsp. gussoneanum) is an introduced annual from Eurasia. Although similar to mouse barley (H. murinum), it is less abundant in coastal prairies and in California as a whole.

Purple false brome (Brachypodium distachyon)

bulletWiry culms, sparse foliage, and stiff-awned seed heads make purple false brome poor forage for livestock (Crampton 1974:77).

bulletThis introduced annual grass is considered a model organism for research because of its small genome, short lifecycle & stature, is self-fertile and because it is closely related to the major grain crops (wheat, corn, etc.) (http://www.brachypodium.org/).



COMMON InVASIVE PERENNIAL GRASSES of Coastal Prairie

Italian ryegrass (Festuca perennis, formerly Lolium perenne) - non-native

line drawing of Lolium perenne

Lolium perenne  ssp multiflorum. USDA-NRCS PLANTS Database / Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. 3 vols. Charles Scribner's Sons, New York. Vol. 1: 282.

Grass Family (Poaceae)

Italian ryegrass is a European annual or short-lived perennial tufted grass.

Italian Ryegrass:

  • Is found in wetlands, grasslands, and disturbed sites (Holloran, et al. 2004).
  • Is now common in coastal prairies.

Italian Ryegrass Ecology

bulletLife History: Seeds germinate readily leaving few in the seed bank (Holloran, et al. 2004).

bulletSpecies Interactions: The plants leave a thick layer of dead leaf litter on the soil each season which can inhibit the germination of other species. 

bulletDrought: Roots can extend 3 or more feet into the soil on dry sites (Holloran, et al. 2004).

Fun Facts About Italian Rye Grass

bulletItalian ryegrass was cultivated in Italy from at least the 13th and 14th centuries (Carey 1995).

bulletItalian ryegrass often escapes into grasslands from cultivation where it is grown as livestock forage and as a turf grass (California Invasive Plants Council).

bulletIt was for many years the most commonly used species for erosion control in the coastal areas of California (Carey 1995).

bulletIncreased soil fertility from nitrogen deposition in auto exhaust has been linked to the increase of Italian ryegrass in serpentine grasslands—grasslands  with harsh, nutrient poor soils that often are refuges for native plants—in the San Francisco Bay area (Harrison and Viers 2007:154).

bulletTaxonomic Note: Perennial ryegrass (formerly Lolium perenne) and annual ryegrass (formerly Lolium multiflorum) were considered as separate species in the First Edition of the Jepson Manual (Hickman 1993). Some authors considered them both as subspecies of Lolium perenne (L. perenne ssp. multiflorum and L. perenne ssp. perenne). The Second Edition of the Jepson Manual (2012), moves them from the genus Lolium to the genus Festuca and combines them into a single species: Festuca perennis. The authors note that what was once thought to be the differentiating feature--awned or awnless florets--can often be found on the same plant. Annual ryegrass is described as having bristle-like awns on lemma tip (a lemma is the lower of two bracts that subtend the floret) while perennial ryegrass is awnless. It may be that the perennial or annual habit relates to the availability of summer water, with the plant acting as a perennial when water is available. Regardless, the plants are found in coastal prairie habitats.



Sweet vernal grass (Anthoxanthum odoratum) - non-native

Grass family (Poaceae)

grassy hilltops

Sweet vernal grass (Anthoxanthum odoratum) at Point Reyes National Seashore. Photo © 2010 National Park Service.

bulletSweet vernal grass is a tufted perennial grass.

Sweet Vernal Grass:

bulletIs native to Europe.

bulletIs widespread in the United States and other temperate climates (University of California 2009).

bulletIs distributed from Santa Barbara through Del Norte Counties and common in coastal grasslands in northern California.

Fun Facts About Sweet Vernal Grass

bulletThis species escaped from cultivation as a meadow grass.

bulletIt is named for its sweet vanilla-like odor from a chemical compound called coumarin, that has a bitter taste and, in large quantities, can cause hemorrhaging in cattle (University of California 2009).



Common velvet grass (Holcus lanatus) - non-native

grassy hilltops

Velvet grass (Holcus lanatus). USDA-NRCS PLANTS Database / Hitchcock, A.S. (rev. A. Chase). 1950. Manual of the grasses of the United States. USDA Miscellaneous Publication No. 200. Washington, DC.

Grass family (Poaceae)

Common Velvet Grass:

bulletIs dominant in many of California’s coastal prairies (Sawyer, et al. 2009).

Common Velvet Grass Ecology

bulletDrought: Holcus lanatus and other non-native perennials have the ability to use summer fog to extend its growing season much like California’s native perennials (Corbin, et al. 2005).

bulletGrazing

  • Holcus lanatus is cultivated for forage and hay (Jepson Manual 2012).
  • Livestock do not prefer the soft velvety foliage but will graze it before the seed stalks appear” (Sampson et al. 1951)
  • Tule elk at Point Reyes National Park graze on Holcus lanatus from August to December, during which time it comprises from 15 to 41 % of their diet (Grogan & Barrett, 1995).
  • Holcus has more protein than perennial ryegrass, a common forage species often planted by ranchers. Harrington and others (2006) found that Holcus had 295g per kg of dry matter of crude protein compared to 232g/kg for ryegrass.

bulletLife History: Viable seeds can persist in the seed bank 5 to not more than 20 years (Bond et al. 2007).

bulletSpecies Interactions:

  • Holcus lanatus impalatability to sow bugs, also introduced, leads to increased litter accumulation in grasslands (Bastow, et al. 2008).
  • Sampson and others (1951) suggest that Holcus lanatus is an early successional plant that is “often replaced by more desirable forage species when ranges are grazed conservatively.”
  • Velvet grass seed is abundant and has become a "key" food for California quail (Callipepla californica) (Gucker 2008).
  • Holcus lanatus is not resistant to trampling and populations can be decreased by heavy, sustained trampling (Bond et al. 2007).

Fun Facts About Common Velvet Grass

bulletHolcus lanatus probably originated on the Iberian Peninsula in Europe (Jacques, 1974).

bulletHolcus lanatus was introduced from Europe and already widespread in North America by 1800 (Utah State University c2001-2002).

bulletHolcus lanatus is cultivated for forage and hay (Jepson Manual 2012).

bullet With the arrival of invasive perennial grasses, such as common velvet grass, coastal prairies may be undergoing the most significant change in species composition since the arrival of Europeans (Corbin, et al. 2005).

bulletThe Coastal Prairie Enhancement Feasibility Study and others are working to find ways to control Holcus lanatus. Seedlings can be pulled easily, but mature plants develop dense fibrous roots that bind the soil and make removal difficult. The easiest time to pull adults is in late summer when the plants go dormant (Kathleen Kraft, personal communication). Mowing treatments are effective in controlling seed production but can stimulate spread through tillers. For information on controlling Holcus lanatus see the Cal-IPC (California Invasive Plants Council) website and the Weed Workers Handbook (Holloran, et al. 2004).

bulletHolcus mollis (creeping velvet grass) is a rhizomatous grass that is also introduced from Europe, sometimes sold as an ornamental, and is a problem weed in prairie remnants and oak savannahs in the Pacific Northwest (Utah State University c2001-2002). There is one specimen on file for Sonoma County (collected on Bayflat Road, Bodega Bay in 1990) and three for Marin County (1969, above Tomales Bay; 1974,near Marshall on Hwy 1; 1977, Point Reyes south of Inverness)according to the Consortium of California Herbaria. However, the species is not listed in the Marin Flora (Howell et al. 1997).



Hairy oat grass, poverty Grass, hairy wallaby grass (Rytidosperma penicillatum, formerly Danthonia pilosa) - non-native

grassy hilltops

Hairy oat grass flowers (Rytidosperma penicillatum, formerly Danthonia pilosa). Photo by Jose Hernandez @ USDA-NRCS PLANTS Database.

Grass Family (Poaceae)

Hairy oat grass is an introduced perennial bunchgrass.

Hairy Oatgrass:

bulletIs native to Australia.

Hairy Oat Grass Ecology

Grazing: This perennial bunch grass is considered of economic importance as animal forage in Australia and in New Zealand (USDA GRIN (Germplasm Resources Information Network, cited 15 Oct 2010).

Fun Fact About Hairy Oat Grass

bulletIntroduced and grown experimentally in California and in several other states, hairy oa tgrass is now considered a troublesome pest in coastal areas of California and southwestern Oregon (Jepson Interchange. Cited 15 Oct 2010 ).


Andean tussock grass (Stipa manicata, formerly Nassella manicata) - non-native, recent invader


grassy hilltops

Andean tussock grass north of Jenner. Photo by D. Immel-Jeffery 2010.

Grass Family (Poaceae)

Tropical Needlegrass:

bulletIs native to Ecuador, Chile, Argentina, and Uruguay.

bulletIs established in Sonoma, Monterey and Calaveras counties in California (USDA NRCS 2010; Utah State University c2001-2002).

Fun Facts About Tropical Needlegrass

bulletIt was introduced and established in California in areas associated with sheep grazing. It was misidentified as N. formicarum in the Jepson Manual (1993).

bulletAndean tussock grass resembles the California native purple needlegrass (Stipa pulchra, formerly Nassella pulchra), but has shorter florets and more developed crowns  (Utah State University c2001-2002). 

bulletOther scientific names previously used for this species include: Stipa manicata, Nasella formicarum.


 
Common invasive forbs of coastal prairie

Italian thistle (Carduus pycnocephalus) - non-native

grassy hilltops

Carduus pycnocephalus, Korbblütler (Asteraceae) - Italien/Italia/Italy: Friuli-Venezia Giulia, Prov. Trieste, Sistiana, Rilkeweg/Sentiero Rilke, 23 May 2008,Franz Xaver, Wikimedia Commons.

Sunflower family (Asteraceae)

Italian Thistle

bulletIs an annual native to the Mediterranean regions of Eurasia and northern Africa (Bossard, et al. 2000).

Italian Thistle Ecology

bulletDrought: It is thought that drought favors an increase in Italian thistle, but there seemed to be a substantial increase in thistle colonies along the Marin and Sonoma coasts during the high rainfall growing season beginning winter 2009 through spring 2010  (Brendan O’Neill, personal communication 2010). However, the wet winter of 2009-2010 followed three years of unusually low rainfall in California.

bulletLife History:

  • A single plant can produce 20,000 seeds (Bossard, et al. 2000). 
  • Seeds germinate readily with fall rains and are quick to colonize areas where vegetation has been removed, such as after fire or in pastures that have been overgrazed and excessively trampled (California Department of Food and Agriculture. Accessed 2010 Oct 24).

bulletSpecies Interactions:

  • Italian thistle is a poor competitor with established perennial plants (California Department of Food and Agriculture. Accessed 2010 Oct 24).
  • The plants grow from basal rosettes of leaves that cover the ground blocking the growth of other species (Bossard, et al. 2000). 

Fun Facts About Italian Thistle

bulletThis species was accidentally introduced into California between 1912 to 1930 (Bossard, et al. 2000).



Burclover (Medicago polymorpha) - non-native

grassy hilltops Medicago polymorpha (habit and flowers). Maui, Kula. 8 March 2007. Plants of Hawaii, Image 070308-5270 from http://www.hear.org/starr/
plants/images/image/ ?q=070308-5270; Forest & Kim Starr

Pea Family (Fabaceae)

Burclover has a clover-like leaf with three leaflets and yellow pea-like flowers, but it is not a true clover (Trifolium).

Burclover:

bulletIs an annual native to the Mediterranean region.

Burclover Ecology

bulletLife History: The spirally coiled bur-like fruits stick to animal fur and to the socks and shoes of humans who help to spread the seeds.

bulletDrought: Jepson (1922, as Medicago hispida) says of burclover, “By cattlemen the plant is prized as a dry season stock feed, since the burs are produced in great quantity and are highly nutritious; it also furnishes a green pasturage in the rainy season. This is a rare instance of an aggressive immigrant herb having a high economic value.”

grassy hilltops

The spiny spiral-shaped seed pod of California burclover (Medicago polymorpha) Photo courtesy of Tracey Slotta @ USDA-NRCS PLANTS Database

Fun Facts About Burclover

bulletMedicago polymorpha is so widespread in California that its common name in the Jepson Manual is California Burclover (Isley 1993).

bullet Burclover was most likely brought into California in the wool of sheep accompanying the Spanish Missionaries (Hendry 1931; Jepson c1902-1943).


Common, rough or hairy cat’s ear, false dandelion (Hypochaeris radicata)

grassy hilltops

Hypochaeris radicata. USDA-NRCS PLANTS Database / Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. Vol. 3: 309.

Sunflower Family (Asteraceae)

Cat's Ear is a perennial dandelion-like forb.

Cat's Ear:

bulletIs widespread in coastal terrace prairie.

bulletCan be one of the more dominant species in coastal terrace prairie (Warner, P. 2003).

Cat's Ear Ecology

bulletGrazing and Fire: Cat's ear can resprout when cut, grazed or burned (Warner 2003).

bulletLife History: perennial that produces many seeds annually.

It  has a thick fleshy tap root in which it stores energy to resprout.

bulletSpecies Interactions:

  • The plants basal leaves, arranged in a rosette, spread over the soil obstructing other plants from growing around it.
  • Maria Copa: leaves eaten with salt (57).


hairy hawkbit (Leontodon saxatilis, formerly Leontodon taraxacoides) - non-native

grassy hilltops

Leontodon saxatilis in flower along northern Sonoma County coast. Photo by D. Immel-Jeffery 28 June 2010.

Sunflower Family (Asteraceae)

This dandelion-like plant (Leontodon means “lion’s tooth”) looks and behaves very much like hairy cat’s ear (Hypochaeris radicata). It is prevalent in the coastal prairies that are nearest to the ocean.

Introduced from Europe, there are two subspecies in California: L. saxatilis subsp. longirostris and L. saxatilis subsp. saxatilis. Both occur in disturbed areas.



English plantain (Plantago lanceolata) - non-native

close up of influorescence of english plantain

Ribwort plantain, English plantain, or narrowleaf plantain (Plantago lanceolata) in Fredericia, Denmark.17 September 2009. Anneli Salo. Wilimedia Commons.

Plantain family (Plantaginaceae)

English Plantain:

Is native to Europe.

Is wildly successful in cismontane California.

English Plantain Ecology

Species Interaction:

  • Tom Smith, Bodega Miwok, told Elizabeth Kelly that Plantago lanceolata, called súgui-kole, or just kole, was used for house thatching by placing the root end up (Kelly 1996).
  • Tom Smith added that after the Spanish came, the women saved and planted the seeds by scattering them on the ground.

  • Plantain (P. major, also native to Europe ) was used medicinally by several groups in Mexico, Baja, and New Mexico (Timbrook 2007), but Tom Smith does not mention any medicinal use by the Bodega Miwok.
  • Chesnut writes that the Mendocino Indians did not use the plant although it covered the valley and that it was grazed only sparingly by cattle.


Red-stem filaree, red-stem stork’s bill (Erodium cicutarium) - non-native

grassy hilltops

Erodium cicutarium, 14 May 2005, Darkone, Wikimedia Commons

Geranium family (Geranaceae)

Red-Stem Filaree:

bulletIs native to Mediterranean region (Mensing and Byrne 1999).

Red-Stem Filaree Ecology

bulletLife History:

  • The barbed corkscrew-like awns on the fruits can launch seeds up to a half meter from the plant.
  • The awns bury the seeds by drilling into the ground as they wind and unwind with changes in humidity (Evangelista et al 2011).

Fun Facts About Red-Stem Filaree

bulletRed-stem filaree may have been one of the earliest weeds introduced into California. Native to the Mediterranean region, it was probably first brought to Baja California in the 1750s and moved north with the pre-Mission Spanish explorers, its barbed corkscrew-like seeds stow-a-ways in the fur of livestock and as a contaminant in feed  (Mensing and Byrne 1999).

bulletThere are only two native Erodium species in California in the Jepson Manual (Hickman 1993). Erodium macrophylla, the only native Erodium that occurs in coastal prairies was recently reassigned to a new genus as California macrophylla being segregated from Erodium on morphological, molecular data. The genus is named for the California Floristic Province (Jepson Interchange for California Floristics. Accessed 14 Nov 2012).

grassy hilltops

Red-stem filaree (Erodium cicutarium) seeds showing cork-screw dispersal feature of seeds. . Photo courtesy of Steve Hurst @ USDA-NRCS PLANTS Database .




Animal invaders of coastal prairie

The most visible animal invaders in coastal prairies are feral pigs (see below). However, exotic animals of all sizes have found a home in coastal prairie. Even the smallest of introduced species can have big effects on community structure and composition.

Feral pigs and wild boars (Sus scrofa)

"Pigs' effects may typify the complicated events to be expected when an ecosystem's regime of disturbance is significantly altered."

Peter Kotanen 1995

grassy hilltops

Left: Wild boar Kiel, Germany. 12 April 2008. Volker. G. Wikimedia Commons: http://commons
.wikimedia.org/wiki/File:Wildschwein_12.4.2008
_117.jpg

Right: Male pig at a farm in England. 27 August 2008. Amanda Slater. Wikimedia Commons: http://commons.wikimedia.org/wiki/File:
Gloucester_Old_Spot_Boar,_England.jpg

Pig Family (Suidae)

The Wild Boar/Feral Pig crosses of California have the typical large heads, and tusks (males) of their wild ancestors, but show a range of patterns in black, brown and white more typical of domestic pigs.

Wild Boar:

bulletIs native to northern and central Europe, the Mediterranean region and Asia south to Indonesia.

bulletWere established in California in the 1800s around coastal Spanish settlements and
expanded over the last century by hunting introductions of wild boar, domestic pig releases, and natural dispersal (Sweitzer and Van Vuren 2009).

bulletOccupy a wide range of habitats, including grasslands; their range is largely coincident with oak woodlands in California due to their dependence on acorns and cover (Sweitzer and Van Vuren 2009, Massei and Gunov 2004).

Feral Pig Ecology:

bulletSoil Disturbance:

  • Rooting, which occurs at an average depth of 5-15 cm, can cause 80-95% reduction in herbaceous cover, cause the severe reductions or local extinction in some plants and animals, and reduce the density of seedlings by 1.5 to 6 times (Massei and Gunov 2004).
  • In areas of high pig density, rooting can occur at least once per year on 74 to 80% of the soil surface and cause increased erosion on steep slopes, and nutrient leachng (Ca, P, Zn, Cu, and Mg) (Singer 1982). Although in a 4-year pig exclosure study in California grassland, Cushman et al. (2004) found no evidence that pig disturbances affected nitrogen mineralization rates or soil moisture availability.
  • Areas that have been rooted by Wild Boar show greater rates of organic matter decomposition, and can create more vigorous growth in plants that survive (Massei and Gunov 2004).
  • Wild Boars may serve as a dispersal agent for some plants. Seeds can pass through their digestive tract unharmed, and they have been shown to disperse seeds of invasive plants (Massei and Gunov 2004).

Species Interactions:

  • Pig rooting may enhance colonization by non-native grasses and forbs. Based on the results of 4-year pig exclosure study in California grassland, Cushman et al. (2004) hypothesized that clearing by pigs provided greater opportunities for colonization and reduced intensity of competition for non-native plants.
  • Pig rooting may also prevent the colonization of grasslands by shrubs and trees: pig rooting significantly decreases colonization by oak seedlings in the understory of oak woodlands (Sweizer and Van Vuren 2009).
  • Plants comprise 80% to 90% of the diet of wild boar. Pigs spend most of their time rooting for tubers, roots, bulbs and often eat fruit, fungi, and acorns (Massei and Genov 2004). Their rooting can cause 80-95% reduction in herbaceous cover and declines in preferred species (Massei and Gunov 2004).
  • Animals are found in 97% of pig stomachs sampled and comprise 2-11% of the diet volume. Invertebrates, such as insect larvae, earthworms, and snails are regularly consumed. Seven years after removal of feral pigs, the total density of microarthropods in a forest nearly doubled and biomass increased by 2.5 times. Impacts to small vertebrates consumed, such as carcasses, small rodents, reptiles, amphibians, and fish, have also been found for ground-nesting birds, surface-tunnelling rodents, and small insectivores (Massei and Gunov 2004).
  • Where large carnivores are present, wild boar invariably appear in their diet and
    sometimes are one of the most important prey. Golden eagles (Aquila chrysaetos)
    recolonized the California Channel Islands with availability of pigs as prey and subsequently started to prey heavily on the native island fox (Urocyon littoralis), causing drastic declines.

Fun Facts About Wild Boars

bulletBetween the 1960s and mid 1990s, Wild Boar populations expanded from about 10 coastal counties to over 50 coastal counties in California. As of 1996, 25% of the total land area of California was occupied by Wild Boars and they were most abundant in the central and north-coast regions (Waithman et al. 1999).

bulletWild boars have the highest reproductive rates among ungulates and, in areas with abundant food supply, are capable of 150% annual increases in population size (Massie and Genov 2004).

bulletThe extent of rooting and the density of Wild Boar populations are directly correlated (Massei and Genov 2004).



Sow bugs (Porcellio scaber) - non-native

grassy hilltops Common rough woodlouse (Prcellio scaber). 23 May 2009. Acélan. Wikimedia Commons

Sowbugs are crustaceans (order Isopoda) that consume plant debris.

Sow Bugs:

bulletAre native to western Europe.

Sow Bugs Ecology

bulletSpecies Interaction:

  • Sow bugs are an important detritivore in coastal grasslands  (Bastow, et al. 2008).
  • The impalatability of Holcus lanatus to sow bugs leads to increased litter accumulation in coastal prairies (Bastow, et al. 2008).

Fun Facts About Sow Bugs

bulletSowbugs have been present in California for over a century (Bastow, et al. 2008).

bulletIt is not known if there were native terrestrial isopods in California prior to European contact.



Slugs and snails

Introduced slugs and snails are major pests in California croplands. Slugs and snails eat seeds, leaves, and other plant parts and can consume and kill seedlings. Researchers are just beginning to discover that slugs and snails can have large effects on wildland plant communities (Maze 2009; Strauss, et al. 2009). California has a rich variety of native slugs and snails.

An introduced gray field slug (Deroceras reticulatum) retreating back into the ground after destroying the seed leaves of a newly germinated showy Indian clover. Photo by D. Immel-Jeffery.