Exotic Plant Management in California Annual Grasslands

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TABLE 22.1Most Common Non-native Invasive Species in California Valley and Foothill Grasslands, Including their GrowthForm and Cal-IPC ClassificationCommon name Scientific name Family Growth habit Cal-IPC categoryFennel Foeniculum vulgare Apiaceae Perennial HighItalian thistle Carduus pycnocephalus Asteraceae Winter annual ModerateSlenderflower thistle Carduus tenuiflorus Asteraceae Winter annual LimitedWoolly distaff thistle Carthamus lanatus Asteraceae Winter annual Moderate alertPurple starthistle Centaurea calcitrapa Asteraceae Annual to perennial ModerateMalta starthistle (tocalote) Centaurea melitensis Asteraceae Winter annual ModerateYellow starthistle Centaurea solstitialis Asteraceae Winter annual HighSquarrose knapweed Centaurea virgata var. Asteraceae Perennial ModeratesquarrosaRush skeletonweed Chondrilla juncea Asteraceae Biennial ModerateBull thistle Cirsium vulgare Asteraceae Biennial ModerateArtichoke thistle Cynara cardunculus Asteraceae Perennial ModerateSmooth catsear Hypochaeris glabra Asteraceae Winter annual LimitedCommon catsear Hypochaeris radicata Asteraceae Winter annual ModerateScotch thistle Onopordum acanthium Asteraceae Biennial HighBristly oxtongue Picris echioides Asteraceae Annual or biennial LimitedTansy ragwort Senecio jacobaea Asteraceae Biennial LimitedBlessed milk thistle Silybum marianum Asteraceae Winter annual LimitedDyer’s woad Isatis tinctoria Brassicaceae Biennial ModerateCalifornia burclover Medicago polymorpha Fabaceae Winter annual LimitedRose clover Trifolium hirtum Fabaceae Winter annual ModerateBroadleaf filaree Erodium botrys Geraniaceae Winter annual Not listedShortfruited filaree Erodium brachycarpum Geraniaceae Winter annual Not listedRedstem filaree Erodium cicutarium Geraniaceae Winter annual LimitedCommon St. Johnswort Hypericum perforatum Hypericaceae Perennial ModerateBarb goatgrass Aegilops triuncialis Poaceae Winter annual HighSilver hairgrass Aira caryophyllea Poaceae Winter annual Not listedSlender oat Avena barbata Poaceae Winter annual ModerateWild oat Avena fatua Poaceae Winter annual ModerateBig quakinggrass Briza maxima Poaceae Winter annual LimitedLittle quakinggrass Briza minor Poaceae Winter annual Not listedRipgut brome Bromus diandrus Poaceae Winter annual ModerateSoft brome Bromus hordeaceus Poaceae Winter annual LimitedRed brome Bromus madritensis Poaceae Winter annual Highssp. rubensDowny brome (cheatgrass) Bromus tectorum Poaceae Winter annual HighHedgehog dogtailgrass Cynosurus echinatus Poaceae Winter annual ModerateOrchardgrass Dactylis glomerata Poaceae Perennial LowTall fescue Festuca arundinacea Poaceae Perennial ModerateMediterranean barley Hordeum marinum Poaceae Winter annual ModerateHare, smooth and Hordeum murinum Poaceae Winter annual Moderatewall barleyItalian ryegrass Lolium multiflorum Poaceae Winter annual ModerateMedusahead Taeniatherum Poaceae Winter annual Highcaput-medusaeSquirreltail fescue Vulpia bromoides Poaceae Winter annual Not listedRattail fescue Vulpia myuros Poaceae Winter annual ModerateBellardia Bellaria trixago Scrophulariaceae Winter annual Limitedor biennial
FIGURE 22.1 Close-ups of flowerheads of two common invasive Centaurea species in California.Left: C. melitensis (tocalote or Malta starthistle). Right: C. solstitialis (yellow starthistle). Note that thespines on C. solstitialis are approximately twice the length of those found on C. melitensis.invasive plants in California’s valley grasslands, the two mostcommon species are yellow starthistle and medusahead (seeFigures 22.1, 22.2). Downy brome, despite its widespreadwestern impact, has caused significant problems only in thenortheastern (Modoc Plateau) part of the state, so it will notbe discussed further here.ImpactsInvasive non-native plants in California grasslands can havesignificant ecological and economic impacts. Although amore thorough treatment of ecological impacts can be foundin Chapter 6, a number of key impacts will be discussed here.Since the California grasslands have historically played amajor role in livestock production, weed impacts have oftenbeen strongly associated with that industry. Impacts includeinterference with grazing practices; reductions in forageproductivity or quality; increased costs of managing and producinglivestock; reduced animal weight gains; reduced qualityof meat, milk, wool, and hides; and livestock poisoning.Medusahead, for example, is of low value because of its highsilica content (George 1992). This reduces the forage qualityand makes it less palatable to livestock and wildlife comparedto other forage grasses. In areas heavily infested withmedusahead, livestock carrying capacity can be reduced byas much as 75 to 80% (Major et al. 1960; Hironaka 1961;George 1992). One of the more recent animal issues to cometo light is the impact of many invasive plants on the horseindustry, especially where small acreage development isoccurring. Invasive forbs such as yellow starthistle, Russianknapweed, houndstongue, and tansy ragwort can result inpoisoning and death to horses when consumed at high levels(Cordy 1954).Direct impacts of grassland weeds on humans and qualityof life include increased allergens in the air, sickness ordeath from inadvertent consumption of poisonous plants,damage to recreational equipment, and injury or discomfortfrom physical contact with spiny thistles such as milk thistleand yellow starthistle or abrasive parts such as the awnsof ripgut brome (Bromus diandrus). With increased use ofgrasslands for recreational activity, including hiking andbiking, direct impacts on humans are now much moreprevalent (DiTomaso 2000).In addition to impacts on humans and animals, many invasiveplants may alter ecosystem structure and functionalprocesses, including hydrologic, fire, and nutrient cycles. Structuralchanges in invaded plant communities typically causereduced native species richness and diversity and changes incanopy structure (Belcher and Wilson 1989; Parmenter andMacMahon 1983; Rikard and Cline 1980; Wallace et al. 1992).In one study reported on by DeLoach (1991), the number ofplant species present in California grasslands increased by 35%following biological control of common St. Johnswort (Hypericumperforatum). When large scale conversions of vegetationallife history strategies and phenology occur, the potential forfunctional changes to hydrology, nutrient, and fire cycles probablyincreases. This has been observed with the late-maturing,deeply rooted forb yellow starthistle when it invades the earlymaturing,shallow-rooted annual grass communities. Yellowstarthistle has been shown to deplete soil moisture reservesand alter water cycles in annual grasslands (Enloe et al. 2005).This could cause large annual economic losses in water conservationcosts in California. In Siskiyou County, for example,it was estimated that the potential water loss due to yellowstarthistle would be more than 100,000 m 3 , or 26,400,000gallons, per year (Enloe 2002). The depletion of soil moistureEXOTIC PLANT MANAGEMENT 283
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Page 13 and 14: grassland fires (Sweet 2005). For p
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Exotic Plant Management in California Annual Grasslands

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