• ABBREVIATION
• SYNONYMS
• NRCS PLANT CODE
• COMMON NAMES
• TAXONOMY
• LIFE FORM
• FEDERAL LEGAL STATUS
• OTHER STATUS
• AUTHORSHIP AND CITATION

ABBREVIATION:

ACHMIL

SYNONYMS:

Achillea lanulosa Nutt. [73]

NRCS PLANT CODE:

ACMI2
ACMIA
ACMIA2
ACMIB
ACMIC
ACMIG
ACMIL2
ACMIM
ACMIO

COMMON NAMES:

western yarrow
common yarrow
wooly yarrow

TAXONOMY:

The scientific name of western yarrow is Achillea millefolium L. (Asteraceae) [26,36,44,73]. There are both native and introduced phases of western yarrow in North America. Introduced and native phases differ primarily in chromosome number and are difficult to distinguish morphologically [26,73]. Native and introduced phases hybridize. The intricate pattern of morphologic, geographic, and ecologic variation within the species has frustrated all efforts to organize an intraspecific taxonomy on a circumboreal or even a strictly North American basis [26]. Most authorities do not recognize infrataxa [26,73,74]; however, Kartesz [44] recognizes the following varieties:

A. millefolium var. alpicola (Rydb.) Garrolt - common yarrow
A. millefolium var. arenicola (Heller) Nobs - common yarrow
A. millefolium var. borealis (Bong.) Farw. - boreal yarrow
A. millefolium var. californica (Pollard) Jepson - California yarrow
A. millefolium var. gigantea (Pollard) Nobs - giant yarrow
A. millefolium var. litoralis (Ehrend.) Nobs - coast yarrow
A. millefolium var. megacephala (Raup) Bolvin - largehead yarrow
A. millefolium var. occidentalis (DC.) Hyl. - western yarrow

LIFE FORM:

Forb

FEDERAL LEGAL STATUS:

No special status

OTHER STATUS:

Boreal yarrow is state-listed as a species of special concern in Maine [48].

AUTHORSHIP AND CITATION:

Aleksoff, Keith C. (1999, June). Achillea millefolium. In: Remainder of Citation

• GENERAL DISTRIBUTION
• ECOSYSTEMS
• STATES
• BLM PHYSIOGRAPHIC REGIONS
• KUCHLER PLANT ASSOCIATIONS
• SAF COVER TYPES
• SRM (RANGELAND) COVER TYPES
• HABITAT TYPES AND PLANT COMMUNITIES

GENERAL DISTRIBUTION:

Western yarrow is circumboreal. In North America, it occurs in every state, province, and in Mexico [19,33]. It is adventitious in Hawaii [62].

ECOSYSTEMS:

STATES:

BLM PHYSIOGRAPHIC REGIONS:

KUCHLER PLANT ASSOCIATIONS:

SAF COVER TYPES:

210  Interior Douglas-fir forest
216  Blue spruce
217  Aspen
218  Lodgepole pine
219  Limber pine
237  Interior ponderosa pine

SRM (RANGELAND) COVER TYPES:

HABITAT TYPES AND PLANT COMMUNITIES:

Western yarrow occurs in a variety of plant communities across its wide distribution. It is not usually a community dominant [39,54].

• IMPORTANCE TO LIVESTOCK AND WILDLIFE
• PALATABILITY
• NUTRITIONAL VALUE
• COVER VALUE
• VALUE FOR REHABILITATION OF DISTURBED SITES
• OTHER USES AND VALUES
• MANAGEMENT CONSIDERATIONS

IMPORTANCE TO LIVESTOCK AND WILDLIFE:

Western yarrow varies greatly in forage value, depending on locality and seasonal development. It is generally unpalatable, although domestic livestock and wildlife occasionally consume the flowers. Cattle and horses usually do not graze western yarrow, but bighorn sheep, pronghorn, and deer may use it. They most often graze the flowerheads. Western yarrow provides fair forage for domestic sheep and goats [24,43]. The average summer use is 20% for cattle and horses and 40% for domestic sheep and goats [58]. Western yarrow is an important food of 4- to 8-week-old sage grouse chicks [16].

Western yarrow contains volatile oils, alkaloids, and glycosides but is not generally considered a toxic plant because it is so seldom consumed by livestock. Milk from cows consuming western yarrow has a "disagreeable" flavor [64].

PALATABILITY:

The palatability of western yarrow to livestock and wildlife in several western states has been rated as follows [27]:

                     CO      MT      ND      UT      WY
Cattle              poor    poor    poor    poor    poor
Domestic sheep      fair    fair    fair    good    fair
Horses              poor    poor    poor    poor    poor
Pronghorn           ----    poor    fair    fair    fair
Elk                 ----    poor    ----    fair    fair
Mule deer           ----    poor    fair    fair    fair 
White-tailed deer   ----    poor    poor    ----    fair
Small mammals       ----    poor    ----    fair    fair
Small nongame birds ----    poor    ----    fair    poor         
Upland game birds   ----    poor    ----    fair    good
Waterfowl           ----    ----    ----    poor    poor

NUTRITIONAL VALUE:

Western yarrow is rated as poor in energy and protein content [27]. In Northern Utah, plants growing on unfavorable sites (defined by slope, exposure, and vegetation cover) were 9% higher in crude protein than plants growing on favorable sites [21]. Mean percent (+/- S.D.) monthly nutrient values and moisture content of western yarrow collected from Cold Meadows in the River of No Return Wilderness, Idaho, (1977 to 1978) were as follows [29]:

 
                June        July           Aug 
crude fiber    22(2.0)     24(1.8)       25(1.2)
crude protein  20(1.6)     17(0.3)       14(0.9)
moisture       78(5)       64(2)         58(3)
CA:P           2.7:1       4.5:1         5.1:1

COVER VALUE:

The degree to which yarrow provides cover for wildlife has 
been rated as follows [27]:

                       CO      MT      ND      UT      WY
Pronghorn             ----    ----    fair    poor    poor
Elk                   ----    ----    ----    poor    poor
Mule deer             ----    ----    fair    poor    poor
Small mammals         good    poor    ----    fair    poor
Small nongame birds   good    poor    fair    fair    poor
Upland game birds     ----    poor    ----    fair    poor
Waterfowl             ----    ----    ----    poor    poor
White-tailed deer     ----    ----    fair    ----    poor

VALUE FOR REHABILITATION OF DISTURBED SITES:

Due to its extensive system of rhizomes, western yarrow is a good soil binder [59] and has been used in erosion control projects on the Wasatch Plateau in central Utah [69]. In Massachusetts, seed-grown sod of western yarrow, along with sod of 11 other species, was transplanted onto a roadside site with shallow, infertile soil and direct exposure. After 4 years, western yarrow was one of 3 surviving species on the site [2].

OTHER USES AND VALUES:

Native Americans used tea made from western yarrow to relieve ear-, tooth-, and headaches; as an eyewash; to reduce swelling; and as a tonic or stimulant. Western yarrow varies in taste and in potency depending on where it grows and at what stage of growth it is in. The best time to collect yarrow for tea is right before the flowers are produced, using only the new succulent leaves [34]. During the Civil War, western yarrow was widely used to treat wounds and became known as "soldiers' woundwort." An ethanol extract of western yarrow has mosquito- repelling properties [67].

Western yarrow is used for summer and winter bouquets. When cut fresh and kept in water, western yarrow flavors the air with an aromatic spiciness [43,64].

MANAGEMENT CONSIDERATIONS:

Western yarrow tends to increase rapidly in disturbed areas or overgrazed rangelands, replacing more valuable forage species and crops [43]. It is often an indicator of past overstocking and excessive utilization [69]. Western yarrow tends to decrease on grazing plots once grazing has ceased [7,20]. Since rhizomes are a major means of western yarrow regeneration, starting control measures early in autumn may prevent spring growth from autumn and winter rhizome dry matter [15]. In New Zealand, barley (Hordeum vulgare) reduced rhizome and seed production in western yarrow [15]. Dicamba and mixtures with triclopyr are effective in controlling western yarrow [74].

• GENERAL BOTANICAL CHARACTERISTICS
• RAUNKIAER LIFE FORM
• REGENERATION PROCESSES
• SITE CHARACTERISTICS
• SUCCESSIONAL STATUS
• SEASONAL DEVELOPMENT

GENERAL BOTANICAL CHARACTERISTICS:

Western yarrow is a perennial forb 11 to 40 inches (30-100 cm) in height with extensive rhizomes. It has few to numerous erect stems. The basal rosette of leaves may remain green throughout the winter [43]. Plants grow in a somewhat scattered fashion and seldom form pure stands in areas larger than 5 square meters [69]. Typical European Achillea millefolium is hexaploid with flat leaves. Native forms are mostly tetraploid, with narrow leaf-segments disposed in various planes so that the leaf is 3-dimensional [33].

McLean [49] reported that in a Douglas-fir (Pseudotsuga menziesii) forest zone in British Columbia, the fibrous roots and rhizomes of yarrow grew mostly in the duff layer or between it and the mineral soil.

RAUNKIAER LIFE FORM:

Hemicryptophyte

REGENERATION PROCESSES:

Western yarrow regenerates from fragments of rhizomes and from colonization through short-distance (1-2 m) wind dispersal of seeds [15,47,61]. In disturbed soils, fragmented rhizomes regenerate shoots which can emerge from soil depths as great as 12 inches (30 cm). In undisturbed soil the rhizomes remain attached to the parent plant, forming new plants at the rhizome apices [15].

The fruit is a small achenes weighing about 0.17 mg. They are produced in large numbers. Several thousand achenes may be produced per flowering stem. The viability of freshly shed seeds exceeds 90%. Western yarrow seed showed 41% germination after 9 years in dry storage [15].

SITE CHARACTERISTICS:

Western yarrow usually occupies dry, open sites in a variety of habitats across its range including sagebrush (Artemisia spp.)-grassland, canyon bottoms, glades, roadsides, and vacant lots. It is prevalent in brushlands, quaking aspen (Populus tremuloides), open timber, and subalpine zones. It is intolerant of dense shade. It is common on thin soils and sandy gravelly loam on open flats, parks, and dry meadows [69]. The elevational distribution in several western states is as follows [19]:

Colorado: 4,000-12,000 feet (1220-3660 m)
Montana: 2,400-10,000 feet ( 730-3050 m)
Utah: 4,300-10,300 feet (1210-3040 m)
Wyoming: 4,600-11,000 feet (1400-3350 m)

SUCCESSIONAL STATUS:

Western yarrow is a pioneer species everywhere it is found [1]. It is an invader species on disturbed rangeland sites. Western yarrow also appears to be tolerant of competition but not tolerant of excessive shade. It is usually present in the earliest stages of vegetation development and persists throughout succession [42]. It dominates on overgrazed high summer ranges, where the undisturbed climax vegetation would be made up of wheatgrasses (Triticeae) [69].

SEASONAL DEVELOPMENT:

Western yarrow has a long flowering season throughout its range, 
which varies as follows [19]:

    State     Earliest     Most Frequent     Latest
                Month         Month           Month
---------------------------------------------------
     CO          May           May             Jun
     ID          Apr           May             Jun
     MT          May           May             Jun
     UT          Apr           May             Jun
     WY          May           Jun             Aug


Average dates of different growth stages at different elevations in Utah
were recorded as follows [22]:

Elev.   Flower buds  Flowers    Seeds    Seeds         Plant
(ft)    evident      in bloom   ripe     disseminated  dried
---------------------------------------------------------------
7,150   May 30       Jun 29     Sept 28  Sept 19       Oct 10
7,655   Jun 01       Jul 05     Aug 26   Sept 24       Oct 13
8,450   Jun 06       Jul 10     Sept 04  ---           Sept 25
9,000   Jun 18       Jul 15     Sept 08  Sept 29       Oct 01
10,100  Jun 25       Jul 21     Sept 20  Oct 08        Oct 08 


Average heights (cm) of plants at various dates and altitudes from
Ephraim Canyon in Utah were as follows (1925-1934) [22]:

Alt.(ft) May 1  May 15  Jun 1   Jun 15  Jul 1  Jul 15
-----------------------------------------------------
7,150    4.9    9.1     16.2    26.2    30.8   33.9
7,655    3.9    8.0     12.9    20.0    28.4   31.1
8,450    1.4    4.6      7.7    15.8    24.2   29.3
9,000    --     0.5      3.5     7.9    19.0   28.3
10,100   --     --       --      5.1    11.1   19.9


Over a 10-year period in Saskatchewan, Canada, flowering dates
were recorded for yarrow [18]:
                                                         Mean
------------First flowering date-----------  Latest date flwring
earliest date & yr  latest date & yr  mean   in flower   period
------------------  ----------------  -----  --------    ------
May 28/1946         Jun 30/1950       Jun 19 Sept 23     78 days

• FIRE ECOLOGY OR ADAPTATIONS
• POSTFIRE REGENERATION STRATEGY

FIRE ECOLOGY OR ADAPTATIONS:

The life cycle of western yarrow in grasslands is completed by the onset of the summer drought and fire season in July [6]. Following fire, regeneration is from rapid rhizome spread [72] and wind dispersal of seeds onto burned sites from adjacent unburned areas [41].

Western yarrow occurs in plant communities with a variety of fire regimes. The range of fire intervals reported for some species that dominate communities where western yarrow occurs are listed below. To learn more about the fire regimes in these communities, refer to the FEIS summary for that species, under "FIRE ECOLOGY OR ADAPTATIONS."

Community dominant        Range of fire interval (yr)
                                            
interior ponderosa pine   20-42
   (Pinus ponderosa var. scopulorum)
Rocky Mt. Douglas-fir     10-30
   (Pseudotsuga menziesii var. glauca)
quaking aspen             7-10
   (Populus tremuloides)             
rough fescue              5-10
   (Festuca altaica)       
 

POSTFIRE REGENERATION STRATEGY:

Rhizomatous herb, rhizome in soil
Initial-offsite colonizer (off-site, initial community)

• IMMEDIATE FIRE EFFECT ON PLANT
• DISCUSSION AND QUALIFICATION OF FIRE EFFECT
• PLANT RESPONSE TO FIRE
• DISCUSSION AND QUALIFICATION OF PLANT RESPONSE
• FIRE MANAGEMENT CONSIDERATIONS

IMMEDIATE FIRE EFFECT ON PLANT:

Western yarrow's rhizomes and mycorrhizae are usually only slightly damaged by fire [10,38,60], although western yarrow is susceptible to fire-kill and reduction by severe fire [51]. Western yarrow is not highly flammable. Out of 14 species commonly found in boreal forests, western yarrow has the lowest potential ignitability based on chemical characteristics measured on live stem, live leaf and dead leaf tissues. These rankings rely primarily on total ash, silica-free ash and energy content [40]. Ignitability is measured as time to ignition.

DISCUSSION AND QUALIFICATION OF FIRE EFFECT:

No entry

PLANT RESPONSE TO FIRE:

Fire results in fragmentation of western yarrow's rhizomes stimulating regeneration [15]. Cover and frequency of western yarrow generally increase 1 to 2 years after fire but not with any consistent pattern [4,13,14,32,40,56,71]. After initially increasing in cover, western yarrow may decrease to unburned levels as early as 3 years after fire [17,37,65,75]. Production doubled within 3 to 4 years postfire near Missoula, Montana [6] and other ponderosa pine/mountain grassland ecosystems [32,69]. In another study of fire effects in ponderosa pine, western yarrow increased by 0.37 stem/m in 6 years, a negligible amount [55]. Western yarrow is responsive to season of burning. Late spring burning usually reduces western yarrow [4,12,66].

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:

The initial surge of western yarrow is probably caused by 
extensive rhizome sprouting; mineral soil exposure and the 
resulting favorable seedbed; less competition from tree, 
grass and shrub cover; and nutrient release [28,53].


A burn was conducted each April for at least 24 years on a 
rough fescue(Festuca scabrella) grassland in a 
quaking aspen parkland in east-central Alberta. Average 
frequency and canopy cover for western yarrow were as
follows [3]:

            % Frequency               % Cover              
            burned  unburned         burned   unburned
            36         23                   3.0         1.1

Density and crown area of western yarrow 
(per 180,000 in²)following an August wildfire 
of moderate severity in a northeastern California range 
dominated by bitterbrush (Purshia tridentata) 
and various perennial bunchgrasses were as follows [23]:

                             Number of plants     Crown area (in²)
Unburned plots      99                             153
postfire yr 1             3                              29
postfire yr 2             9                            101
postfire yr 3           88                            531
postfire yr 4          269                           252
postfire yr 5            48                         1391

Productivity values (kg/ha) of western yarrow before and after 
a late August fire in western Wyoming quaking aspen communities 
are listed below for plots of different burn intensities [9]:

Before burning:  14 kg/ha 
After a "light" burn:  40 kg/ha 
After a "moderate" burn:  16 kg/ha 
After a "heavy" burn:  14 kg/ha

FIRE MANAGEMENT CONSIDERATIONS:

Western yarrow's good resprouting ability, high germination percentages, and competitive seedlings result in a remarkable persistence under fire disturbance. Western yarrow often appears in the first stages of succession [15,63]; however, no consistent trends relative to age of burns seem evident for the western yarrow [4,57].

Western yarrow has low ignitability, and can be used as a fire barrier, created by replacing highly flammable vegetation with species that are less likely to burn [41]. Planting less-flammable vegetation in fire-prone areas, or around property and fire-sensitive areas, may help prevent ignition or slow fire spread [40].

• CASE NAME
• SEASON/SEVERITY CLASSIFICATION
• STUDY LOCATION
• PREFIRE VEGETATIVE COMMUNITY
• TARGET SPECIES PHENOLOGICAL STATE
• SITE DESCRIPTION
• FIRE DESCRIPTION
• FIRE EFFECTS ON TARGET SPECIES

CASE NAME:

White Cap Creek, Idaho

REFERENCE:

Merrill, E. H.; Mayland, H. F.; Peek, J. M. 1980 [50]

SEASON/SEVERITY CLASSIFICATION:

late summer/moderate

STUDY LOCATION:

The fire occurred in the Upper Selway River (White Cap Creek) drainage, Idaho. The area is a portion of a fire management zone in the Selway-Bitterroot Wilderness where fires are allowed to burn under natural conditions.

PREFIRE VEGETATIVE COMMUNITY:

The fire occurred in a ponderosa pine (Pinus ponderosa) forest and adjacent montane grassland. Important understory species included western yarrow (Achillea millefollium), bluebunch wheatgrass (Pseudoroegneria spicata), arrowleaf balsamroot (Balsamorhiza sagittata), cheatgrass (Bromus tectorum), and junegrass (Koeleria macrantha).

TARGET SPECIES PHENOLOGICAL STATE:

unknown but most likely in flowering and seed ripening stages

SITE DESCRIPTION:

Aspect: south
Elevation: 3,200-4,160 feet (1000-1300 m)
Average annual precipitation: 760 mm, with peaks occurring from November to January and April to June

Soils are derived from Idaho batholith parent material consisting of decomposed granite, gneiss, and rhyolite. They are described as low in fertility, water-holding capacity, and of weak structure.

FIRE DESCRIPTION:

The fire occurred under extremely dry conditions, with relative humidity as low as 11%, maximum temperatures of 87 degrees Fahrenheit (32^oC), and winds gusting up to 27 miles/h (45 km/hr). The fire was a lightning-ignited and began 10 August, 1973, and burned for 43 days until extinguished by rain. The fire burned quickly and little ash was left.

FIRE EFFECTS ON TARGET SPECIES:

Cover and frequency of western yarrow were equal to or lower than those on unburned sites during the 1st postfire year, but by the 3rd postfire year were greater than on unburned sites:

postfire     % Cover (+/- S.D.)     % Frequency (+/- S.D.)
  year       burned   unburned      burned        unburned
--------     ------------------     ----------------------
   1          2 (2)   2 (2)         5 (4)         5 (2)
   3          12 (12) 4 (5)         11 (5)        6 (12)

Achillea millefolium: References

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Related categories for SPECIES: Achillea millefolium | Western Yarrow