The use of native vegetation in Xeriscaping creates habitat for native wildlife while

reducing the risk of invasion

Greg CroninUniversity of Colorado at Denver and Health

Sciences Center

March 8, 2007

Some Goals of Xeriscaping

• Water conservation– Less human consumption means more water for

aquatic ecosystems– Saves money

• Beautiful, fun landscaping• Wildlife Conservation

– Providing habitat for native species– Preventing the introduction of exotic species

Native to Balkans

A hybrid, but most daylilies originate in Asia. None are native to NA.

Exotic Species - What are they?• They are species that have been transplanted, usually with

human’s help, to habitats outside their normal range, regardless of political boundaries.– These include plants, animals, fungi, bacteria, protists, and viruses– Some are obvious (purple loosestrife, zebra mussels, kudzu), but

most probably go undetected (many microbes, and colonists that do not successfully invade)

– They can have beneficial (biocontrol agents) and/or negative impacts on communities. An introduced species can become a resource for some natives, or an enemy of others

– Most countries have on the order of 100's to 10,000 exotic species– Often reach nuisance abundance

• Exotic Species is the #2 reason for our current biodiversity crisis, after habitat loss

Invasion ProcessSpecies Elsewhere

Introduced

Established

Invasive

In Pathwaye.g. imported for trade

Reproducing

Ecological &/or Economic impacts

How do Exotics Occur?• Natural

– plate tectonics. Mixing of marsupial and placental mammals 3 mya

– migrations• Human-aided

– Accidentals– Waterways– Hitchhikers (on clothing or shoes)– Ballast water - zebra mussels– Wooden crates– Imported fruits, vegetables, soils– Failed quarantines

– Intentionals• Citizens/uncontrolled releases

– Released pets– Ornamental plants

• Government releases/”controlled releases”– Game fishes– Food resource (Nile perch)– Biocontrol agents

Risks Posed - Plants

• Availability of known invasives– 45% of US restricted plants available over web

• Misidentifications– 40% of Linnean names incorrect– Ambiguous common names

Effects of exotics• Allowed success of European imperialism

– Disease • Black and brown rats killed 30-40% of Europeans in 1500's• HIV• Ebola

• Costly/Economics• Costs the USA $137 billion/yr• Foot and mouth disease cost Britain $30 billion• EO 13112, National Invasive Species Council

Ecosystem Costs of Exotic Species• second most detrimental factor on biodiversity,

after habitat loss

– Species extinctions via predation– Brown tree snake wiped out 10 of 13 native birds on

Guam, 6 of 12 native lizards, and 2 of 3 native bats

– Nile perch in Lake Victoria has extirpated half of the endemic cichlid species

– Pet cats/feral cats

– Sea lamprey - destroyed 97% of lake trout in 21 years

– Effects via competition/ecosystem change: – Tamarisk/Salt Cedar

State of understanding of biological invasions(not very good)

• Paul Ehrlich “ecologists can make some powerful and wide-ranging predictions about invasions...On the other hand, ecologists cannot accurately predict the results of a single invasion or introduction event”.

• Depends on complex interactions between the species and community, which are difficult enough to understand in isolation

What percentage of colonists successfully invade?

• Over-representation of organisms that are easy to observe

• Most unsuccessful colonists go unobserved

• In biological control cases, overrepresentation of species likely to be successful

• Probably from 1-40%

What communities are susceptible to invasion?

• Islands (biologically “unsophisticated” communities)

• Early successional/Disturbed• Climactically matched with exotic’s home

habitat (global warming will result in range expansions)

• Absence of predators (islands)• Predators both make it difficult for species to

invade AND• May make it easier for some species to invade

by minimizing competition

Invasions of Nonnative Species• Most permanent form of pollution• Summary of why species invade successfully

– most invaders fail to establish– major community effects occur most often in low-diversity systems– species must have appropriate physiological and morphological

adaptations to invade successfully– invaders are more likely to become established in disturbed systems– even stable systems can be vulnerable to invasion– the greater the number of invaders and the number of invasions, the

greater the probability of successful invasions– species that have a history of prior invasions are likely to invade

successfully again

Common Invasive Species in Colorado

• European Starling• English House Sparrow• Eastern Fox Squirrel• Bull Frog• Leafy spurge• Russian knapweed• Diffuse knapweed• Spotted knapweed• Musk thistle

• Canada thistle • Field bindweed• Purple loosestrife• Perennial pepperweed• Hoary cress• Yellow toadflax• Dalmatian toadflax• Russian Olive• Salt cedar

Reducing The Impacts

Species Elsewhere

Introduced

Established

Invasive

×Invasion Steps Options

Prevention – exclude species of concern

Insure no propagules can escape cultivation

Rapid response - eliminate populations while small

Mitigate damage, control spread, eradicate if possible

Effective?

Yes

Unlikely

Unlikely – requires surveys and funds on hand

Eradication usually impossible, control is expensive

Reducing The Impacts

Species Elsewhere

Introduced

Established

Invasive

×

Invasion Steps Options

Prevention – exclude species of concern

Insure no propagules can escape cultivation

Rapid response - eliminate populations while small

Mitigate damage, control spread, eradicate if possible

Effective?

Yes

Unlikely

Unlikely – requires surveys and funds on hand

Eradication usually impossible, control is expensive

Reducing The Impacts

Species Elsewhere

Introduced

Established

Invasive×

Invasion Steps Options

Prevention – exclude species of concern

Insure no propagules can escape cultivation

Rapid response - eliminate populations while small

Mitigate damage, control spread, eradicate if possible

Effective?

Yes

Unlikely

Unlikely – requires surveys and funds on hand

Eradication usually impossible, control is expensive

Reducing The Impacts

Species Elsewhere

Introduced

Established

Invasive

Invasion Steps Options

Prevention – exclude species of concern

Insure no propagules can escape cultivation

Rapid response - eliminate populations while small

Mitigate damage, control spread, eradicate if possible

Effective?

Yes

Unlikely

Unlikely – requires surveys and funds on hand

Eradication usually impossible, control is expensive

Native Alternatives• Resources

– Colorado Native Plants Society• http://conps.org/conps.html

– Denver Botanic Gardens• http://www.botanicgardens.org/pageinpage/home.cfm

– Native Plant Master Program  (CSU)• http://www.coopext.colostate.edu/jeffco/natural/native.htm

• http://ww14.co.jefferson.co.us/coopext/slideshow.do

– National Invasive Species Information Center• http://www.invasivespeciesinfo.gov/

By promoting native vegetation,

• We provide habitat for native species– Habitat loss is the #1 cause of extinction

• We reduce the chance of introducing invasive species– Exotic species is the #2 cause of extinction

• Better safe than sorry