Weeds and Exotics

Dandelion

What is a weed?

• a plant in the wrong place

• a plant out of place

• a plant whose virtues are yet to be discovered

• one person’s weed is another person’s herbarium specimen

What is an exotic?

• Exotic or alien species are species that are not native the area in question – i.e. an exotic in Illinois would be a species that did not occur here naturally and was somehow introduced to Illinois by human activity

Norway maple and orchard grass – exotic in Illinois, native to Eurasia

Black locust and osage-orange – exotic in Illinois, native to North America

Exotic Species

• Conservation biologists typically call introduced species “exotic species” - species which live outside their natural range

• Botanists typically refer to exotic plants as alien species

• Other terms you may see include biological invaders, introduced species, invasive species, non-indigenous species, non-native species (my preferred term)

What is a weed?

• In general, we consider weeds to be exotic or alien plants which have somehow become problem plants –

• Problem plants typically have the following two characteristics –

• 1) the plant has achieved a threshold level of abundance, and

• 2) someone is concerned about the plant

Perspectives on Weeds

• There appear to be three dominant perspectives on weeds: agricultural-ranching, suburban, and ecological.

Agricultural-Ranching Perspective

• The agricultural perspective considers any plant a weed if it competes with crops for the available nutrients and moisture in a field. Such plants can lower crop yield or cause crop failure.

• The ranching perspective considers any plant a weed if it presents a threat to livestock or reduces the quality of forage that is otherwise available.

Suburban Perspective

• The suburban perspective considers any plant a weed if it invades the lawns and gardens of suburban homeowners and other managed landscapes of mainstream society, which includes the lawns and gardens of banks, schools, churches, malls, government buildings, industrial parks, etc.

Suburban Perspective

The ideal plant of the managed landscape in suburbia has the following characteristics:

1) It is often an introduced species that is poorly adapted to the surrounding environment. 2) It is a sterile hybrid or patented cultivar. 3) It is difficult to maintain and often short-lived.4) It doesn't spread readily to places where it doesn't belong. 5) It has obvious aesthetic or culinary properties.6) It has to be purchased at a store or through a catalog (although heirloom plants may be passed from one gardener to another).

Suburban Perspective

• The weediness of a plant is defined by the absence of the preceding characteristics. Thus, suburbia considers any plant a weed that is well-adapted to its environment, prone to reproduce itself and spread, requires little or no effort to maintain, and has no obvious aesthetic or culinary properties.

Ecological perspective

• One ecological perspective considers any plant a weed if it is a pioneer species that thrives in a degraded habitat with a history of disturbance through human agency. Such weeds may be native or introduced.

• There are also superweeds that have the capacity to invade high quality natural areas. Superweeds are usually introduced plants with few natural enemies in the area of invasion. Some ecologists are only concerned with superweeds.

Fireweed (Epilobium angustifolium) in London post bombing

Another way to think about weeds

Problem invasive species Not native to ecosystem.Increase and spread in ecosystem, offspring easily dispersed.Lead to decline in native species via negative interactions such as competition, predation or parasitism.Cause changes in ecosystem properties such as hydrology, nutrient cycles, energy flow, fire regime.Tolerant of human disturbance regimes.

Problem native species Native to ecosystem.Effects are ecologically similar to problem invasive species.Frequently they are edge species tolerant of human disturbance.

Another way to think about weedsNon-problem native species Native to ecosystem.

Populations exhibit minor fluctuations in size and distribution.Presence enhances other native species.Maintain ecosystem properties.Frequently sensitive to human disturbance regimes.

Non-problem non-native species Not native to ecosystem.Reproduce and survive in ecosystem.Populations exhibit minor fluctuations in size and distribution.Presence at least is not leading to decline in native species abundance or distribution.Do not lead to changes in ecosystem properties.Have potential to become problematic as climate changes.

Alfalfa (Medicago sativa) – good crop or weed?

Problem Plants

• Perennial herbs – many examples are found in wetlands like purple loosestrife and grasslands like Canada Thistle and our woods like garlic mustard (a biennial)

Perennial Herb Problems

Purple Loosestrife Garlic Mustard

Perennial Herb Problems

Canada thistle – Cirsium arvense

Field of Canada Thistle

Problem Plants

• Perennial grasses – replace native grasses in grazed rangeland and pose a serious fire risk to native trees in forest ecosystems. Perennial grasses pose a double fire hazard: 1) they produce much greater bulk of flammable material than was produced by native plants and thus lead to more intense fires, and 2) the timing of their flammability is different than native plants so that fires occur at times of the year for which native plants are not adapted – Smooth Brome and Reed Canary Grass (Phalaris arundinacea)

Perennial Grass Problems

Smooth Brome Phalaris arundinacea

Problem Plants

• Vines – Serious pests in woods and disturbed habitat – field bindweed and kudzu

Vine Problems

Field Bindweed Kudzu

Problem Plants

• Shrubs – Very serious problems in most climates – often become severe problems in areas where native vegetation has been overgrazed – multiflora rose

Shrub Problems

Multiflora Rose

Problem Plants

• Trees – trees are potentially disastrous for nature conservation and watershed management. Often invasive trees do well in disturbed, edge habitat and become the canopy dominants, out-competing native trees – among our problem trees are autumn olive (small, almost a shrub), black locust, tree-of-heaven

Tree Problems

Autumn Olive Black Locust Tree of Heaven

Illinois Noxious Weed Act

Section 220.10 Duty of Every Persona) It shall be the duty of every person to

control the spread of and to eradicate all noxious weeds on lands owned or controlled by him in the State of Illinois.

b) All noxious weeds shall be controlled or eradicated by methods approved and adopted pursuant to the Act and these rules.

Illinois Noxious Weeds

• Section 220.60 Noxious Weeds• The following plants within the

sovereign territory of the State of Illinois are designated and declared noxious weeds:

• a) Marihuana (Cannabis sativa L.);• b) Giant Ragweed (Ambrosia

trifida L.) within the corporate limits of cities, villages, and incorporated towns;

• c) Common Ragweed (Ambrosia artemisiifolia L.) within the corporate limits of cities, villages, and incorporated towns;

• d) Canada Thistle (Cirsium arvense);

• e) Perennial Sowthistle (Sonchus arvensis);

• f) Musk Thistle (Carduus nutans);• g) Perennial members of the

sorghum genus, including johnsongrass (Sorghum halepense), sorghum almum, and other johnsongrass X sorghum crosses with rhizomes; and

• h) Kudzu (Pueraria labata).• (Source: Amended at 26 Ill. Reg.

14644, effective September 23, 2002)

Cannabis sativa

Giant Ragweed

Common Ragweed

Canada Thistle

Perennial Sowthistle

Musk or Nodding Thistle

Johnson Grass

Kudzu

Are weeds of some positive value?

1) Some weedy species are pioneers of degraded landscapes where the soil is worn-out or nearly destroyed. Such weedy species are necessary to the healing process of the landscape, as their decaying organic matter improves the quality of the soil and the sets the stage for the succession of non-weedy plants – alfalfa, red clover

Red Clover

Are weeds of some positive value?

2) Some weedy species are pioneers of disturbed landscapes where the soil is high quality, but exposed to erosion by wind and water. Such weedy species quickly cover the exposed soil and prevent erosion from occurring until they are replaced by non-weedy plants – annual ryegrass

Annual Ryegrass

Are weeds of some positive value?

3) Weedy plants are often important sources of food and cover to various kinds of wildlife, including mammals, birds, and insects. For example, the caterpillars of Papilio polyxenes asterias (Black Swallowtail butterfly) feed on Daucus carota (Wild Carrot) and Pastinaca sativa (Wild Parsnip).

Wild Carrot and Wild Parsnip

Black Swallowtail

European goldfinch on Canada thistle

Autumn olive along roadside

Autumn olive fruits

Are weeds of some positive value?

4) Weedy plants are potentially important sources of food, medicines, herbicides, and other products to modern society. For example, our major food crops are almost all weeds in terms of being exotic species for the Midwest and some of them such as apples can survive outside of cultivation. A powerful herbicide has been derived from Centaurea biebersteinii (Spotted Knapweed), while the fiber of Cannabis sativa (Marijuana) can be used to make paper, rope, or clothing.

Spotted Knapweed

Cannabis/Hemp Fibers

Cannabis/Hemp Fibers