The use of native vegetation in Xeriscaping
creates habitat for native wildlife while
reducing the risk of invasion
Greg Cronin
University 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 Process
Species Elsewhere
In Pathway
e.g. imported for trade
Introduced
Reproducing
Established
Ecological &/or
Economic impacts
Invasive
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
Invasion Steps
Species Elsewhere
×
Introduced
Established
Invasive
Options
Effective?
Prevention – exclude
species of concern
Yes
Insure no propagules
can escape
cultivation
Unlikely
Rapid response eliminate populations
while small
Unlikely – requires
surveys and funds
on hand
Mitigate damage,
control spread,
eradicate if possible
Eradication usually
impossible, control
is expensive
Reducing The Impacts
Invasion Steps
Species Elsewhere
Introduced
×
Established
Invasive
Options
Effective?
Prevention – exclude
species of concern
Yes
Insure no propagules
can escape
cultivation
Unlikely
Rapid response eliminate populations
while small
Unlikely – requires
surveys and funds
on hand
Mitigate damage,
control spread,
eradicate if possible
Eradication usually
impossible, control
is expensive
Reducing The Impacts
Invasion Steps
Species Elsewhere
Introduced
Established
×
Invasive
Options
Effective?
Prevention – exclude
species of concern
Yes
Insure no propagules
can escape
cultivation
Unlikely
Rapid response eliminate populations
while small
Unlikely – requires
surveys and funds
on hand
Mitigate damage,
control spread,
eradicate if possible
Eradication usually
impossible, control
is expensive
Reducing The Impacts
Invasion Steps
Species Elsewhere
Introduced
Established
Invasive
Options
Effective?
Prevention – exclude
species of concern
Yes
Insure no propagules
can escape
cultivation
Unlikely
Rapid response eliminate populations
while small
Unlikely – requires
surveys and funds
on hand
Mitigate damage,
control spread,
eradicate if possible
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