| | |
 |
|
| 
| ||
 |
|
|
|
 |
|
Wildlife, Animals, and Plants |
|
|||
|
BOTANICAL AND ECOLOGICAL CHARACTERISTICS
GENERAL BOTANICAL CHARACTERISTICS:Russian knapweed is a non-native, perennial, invasive forb that often forms dense, monotypic colonies from widely spreading horizontal roots. Roots are scaly and dark-brown to black in color, and can extend 14 square yards (12 m2) radially, and up to 23 feet (7 m) deep within 2 growing seasons ([83,86] and sources therein). Records indicate that an infestation of Russian knapweed can survive 75+ years through its root system [83]. Russian knapweed shoot development originates from root-borne buds. A patch of Russian knapweed may have 9 to 27 shoots per square foot (100-300/m2) [83]. Russian knapweed stems are thin, erect and openly branched, standing up to 3 feet (0.9 m) tall. Rosette leaves are 2 to 4 inches (5-10 cm) long and 0.4 to 1 inch (1-2.5 cm) wide. Leaves grow smaller near the tops of the stems. Flowerheads arise terminally and are 0.25 to 0.5 inch (0.6 to 1.3 cm) in diameter. Russian knapweed seeds are achenes and are oblong, 2.1 to 2.4 mm in length by 0.6 to 0.7 mm in width. Seeds are covered with many fine hairs and have a pappus on the apex ([83,86] and sources therein). Several allelopathic compounds have been isolated form Russian knapweed [29,71,72]. It is known that allelopathy plays an important role in Russian knapweed ecology and that these compounds can interfere with the growth of associated plants [41]. RAUNKIAER [54] LIFE FORM:Hemicryptophyte Geophyte REGENERATION PROCESSES:Russian knapweed reproduces by seed and by adventitious buds on horizontally spreading roots. Since Russian knapweed produces relatively few seeds and lacks effective mechanisms for seed dispersal, local infestations increase primarily by adventitious roots [61,83,86]. Breeding system: | Russian Knapweed Russian knapweed is monoecious and is an obligate outcrosser [36]. Pollination: | Russian Knapweed Russian knapweed is insect pollinated [36,83]. Seed production: A single Russian knapweed plant can produce about 1,200 seeds per year (Ivanova 1966, as cited by [83,86]). Watson [83] reported Russian knapweed seed production of about 100 seeds per plant per year along roadsides, and about 292 seeds per plant on rangeland in British Columbia, with a high ovule abortion rate. Beck [8] reports seed production of about 50 to 500 per shoot in Colorado. Flower production declines with decreasing light levels [22]. Seed dispersal: | Russian Knapweed Russian knapweed seedheads generally remain closed at maturity, and the relatively heavy seeds tend to lose the small pappus bristles at maturity; therefore, wind dispersal is an unlikely method for long-range seed dispersal [58,83]. Ballistic dispersal may be more important than wind dispersal: Mature achenes dehisce from the receptacle and usually remain in the involucre, but can be launched over distances roughly equal to the height of the plant when the involucre sways in a breeze [2]. The primary means of long-range seed dispersal is probably via contaminated hay and other seed (primarily alfalfa), or by movement of farm machinery or other vehicles [58,61]. Seed banking: | Russian Knapweed Seed banking of Russian knapweed is not reported in the literature. It is unclear how long Russian knapweed seeds can remain viable, as reports vary from 2 to 3 years (Ivanova 1966 as cited by [83]), while Andersen (1968) reported successful germination after 5 years of dry storage [17], and Selleck [66] reported successful germination of seeds after up to 9 years storage at room temperature. Germination: | Russian Knapweed Russian knapweed seeds do not germinate readily [58], and germination rarely occurs in the field [66,83]. An initial dormancy period has been observed in Russian knapweed seeds and can be broken by alternating temperatures. Russian knapweed seeds are able to germinate under a wide range of temperatures (33 to 95 degrees Fahrenheit (0.5-35 °C)) with optimum germination occurring between 68 and 86 degrees Fahrenheit (20-30 °C) ([83], and sources therein). Light is not essential for germination, but alternating light and darkness improves germination, and white light appears to stimulate germination [50]. Seedling establishment/growth: No information Asexual regeneration: | Russian Knapweed Russian knapweed reproduces primarily by vegetative means, and can spread rapidly and form dense colonies. The root system consists of the taproot, 1 to many horizontal roots, and their vertical extensions. Buds on the horizontal roots can form adventitious shoots that can grow to be independent plants ([58,83,86] and sources therein). Spread can be hastened by cultivation [58]. SITE CHARACTERISTICS:General: | Russian Knapweed Russian knapweed is commonly found along roadsides, railways, riverbanks, irrigation ditches, pastures, waste places, clearcuts, and croplands. It does not readily establish in healthy, natural habitats [17]. Because Russian knapweed regenerates primarily vegetatively, it does not spread as readily alongside roads and trails as do other knapweeds [60]. In its native lands, Russian knapweed is weedy along roads and among crops, in abandoned areas and near dwellings (Klokov and others 1963, as cited by [58]). In Washington it may grow in hayfields, pastures, grainfields and irrigation ditches, and is reportedly not a problem weed on most rangelands [58]. Elevation: | Russian Knapweed There are few reports in the literature on the elevational range of Russian knapweed. It is primarily an invader of croplands. It can be found up to 8,600-9,300 feet (2,620-2,835 m) in its native land (Klokov and others 1963, as cited by [58]), and up to 6,300 feet (1,900 m) in California [37]. It has been observed between 4,025 to 7,850 feet (1,220-2,380 m) in Utah [85]. Moisture and temperature: Watson [83] reports a typical infestation of Russian knapweed in British Columbia with annual precipitation of 9.8 inches (245 mm) and mean summer temperature of 70.5 degrees Fahrenheit (21.4 °C) [55]. Fructan metabolism in Russian knapweed gives it a competitive advantage by facilitating growth at relatively cool temperatures when soil moisture is usually most plentiful [19]. Only relative descriptions of the moisture requirements of Russian knapweed are available in the literature. Observations in southeastern Colorado suggest that stands of Russian knapweed are denser where precipitation is "lower" [30]. Similarly, while Russian knapweed is found in both irrigated and arid areas in Canada, it is more common and more competitive in "drier" regions [66,83,86]. However, it has been documented as well established under irrigated conditions [83]. In Washington, Russian knapweed is most commonly found in areas with relatively high soil moisture content such as irrigated or irrigation runoff areas; near rivers, creeks, canals, coulees, and draws; on toeslopes; in deep, fine textured soils in high precipitation zones and valley bottoms; and in poorly drained soils [59]. Russian knapweed can tolerate some flooding, but not severe drought [58]. Soils: | Russian Knapweed In its native land, Russian knapweed grows on clayey, sandy or rocky steppes and sunny meadows, on saline soils, clayey, rocky, or sandy shores of lakes and rivers, on rocky and clayey slopes of hills, and on bottomlands (Klokov and others 1963, as cited by [58]). In Washington, Russian knapweed is often found on sites with either greater effective rooting depth or greater effective moisture than adjacent areas [21], and it tolerates saline and alkaline soils [58]. Russian knapweed occurs mostly in alkaline, seasonally wet habitats in Montana [43]. Researchers in Colorado have noted that while Russian knapweed can grow on a variety of soil types, it appears to be most competitive on soils with high clay content [30,61]. Goslee and others [32] suggest that the ability of Russian knapweed to dominate on fine-textured soils while forming a persistent mixture with other species on coarse soils may be due to allelopathy, since allelopathy is likely to have more impact on fine-textured soils. Watson [83] reports that the northern limit of Russian knapweed in British Columbia is 54 °N, but that most infestations occur in the drier southern regions of British Columbia, Alberta, and Saskatchewan. SUCCESSIONAL STATUS:Watson [83] reports that Russian knapweed invades open, disturbed land and suppresses growth of surrounding plants. Goslee and others [32] suggest that because Russian knapweed produces few seeds and has poor dispersal mechanisms, it does not colonize new sites efficiently. Once established in open areas, however, it is highly competitive and spreads aggressively, often forming dense, single-species stands that can persist indefinitely [83]. Computer simulations suggest that the ability of Russian knapweed to dominate aboveground biomass in blue grama grassland is related to soil texture. Russian knapweed dominates clay soils within 30 years after establishment, will codominate with perennial grasses on clay-loam soils, but will not achieve dominance over perennial grasses on coarse-textured soils. These differences in dominance are related to differing allelopathic effects in different soil textures [32]. Russian knapweed is sensitive to decreased amounts of sunlight, does not compete well under a heavy canopy, and is weakened by dense shade [22,58,59]. Dall'Armellina and Zimdahl [22] found that the number of shoots and flowers produced by Russian knapweed in a greenhouse study was highly correlated with light level, and that shoot and root dry weight decreased with each light reduction. Leaf area increased with initial light reduction, but was reduced at the lowest light level. Disaccharide, inulin, and nitrogen concentrations also decreased in the roots of shaded plants ([83], and sources therein). SEASONAL DEVELOPMENT:Russian knapweed shoots emerge from perennial roots early in spring, shortly after soil temperatures remain above freezing. Plants form rosettes and bolt in late May to mid-June. Russian knapweed flowers from June to October in the U.S. and from July to September in Canada [83]. Seeds develop in late summer [86]. Flowering periods are given below.
Concentrations of carbohydrate reserves in the roots of Russian knapweed follow a seasonal pattern. Disaccharide reserves decreased during the spring form 6.8 to 3.6% and peaked at 8.5% at the end of the growing season. Inulin content in Russian knapweed roots was 4.3% in the spring and 11% at the end of the growing season ([83], and sources therein).
Related categories for SPECIES: Acroptilon repens | Russian Knapweed |
 |
 | |
| |
| |
| Content on this web site is provided for informational purposes only. We accept no responsibility for any loss, injury or inconvenience sustained by any person resulting from information published on this site. We encourage you to verify any critical information with the relevant authorities. | |
| |
|
About Us | Contact Us | Terms of Use | Privacy | Links Directory |
| 1Up Info All Rights reserved. Site best viewed in 800 x 600 resolution. |
