Transcript 1 - Defining Invasive Weeds Ecology and Biology

Invasive Weeds;
Are They Really
Special & Unusual?
Weed Definitions
• Plant out of place
– Weed Science Society of America
• A plant that interferes with the
management objectives of a parcel of
land at a given time
– Weeds of the West
• A plant whose virtues have yet to be
discovered
– Emerson, ~ 1870
Anthropocentric Nature
of Weeds
• Definitions centered around humans
– not entirely bad
• Humans evolved on earth
• Humans use natural resources
• Weeds inhibit efficient use of natural
resources
H.G. Baker – Ideal Weed
• 1974. The evolution of weeds.
Ann. Rev. Ecol. and Sys. 5:1-24.
1. Germination requirements fulfilled many environments
2. Discontinuous germination (internally controlled) &
great longevity of seed
3. Rapid growth thru vegetative stage to flowering
4. Continuous seed production as long as conditions permit
5. Self-compatible but not completely autogamous or
apomictic
6. When cross-pollinated, unspecified visitors or wind
7. Very high seed output favorable environments
H.G. Baker – Ideal Weed
• 1974. The evolution of weeds.
Ann. Rev. Ecol. and Sys. 5:1-24.
8. Produces some seed under wide range environmental
conditions; tolerant and plastic
9. Adaptations for short- and long-distance dispersal
10. If perennial, has vigorous vegetative reproduction or
regeneration from fragments
11. If perennial, brittle, so not easily pulled from soil
12. Has ability to compete interspecifically by special
means (rosettes, choking growth, allelochemicals)
Weeds as Strategists
• 2 basic external factors limit amount
of plant material in any environment:
– Stress
– Disturbance
Selection Pressure - Extremes
of Stress & Disturbance
Stress
High
Low
Disturbance
High:
Low:
Death
Ruderals
Stress
Competitors
tolerators
Weeds as Strategists - Extremes
of Stress & Disturbance
• 3 possible strategies
– Stress tolerators
– Competitors
– Ruderals
• Weeds as competitive ruderals
– disturbance precludes strict competitors
– no severe disturbance precludes ruderals
– meadows, seasonal grasslands, rangeland
subject to seasonal disturbance, floodplains,
lake & ditch margins, arable lands
Why Are Alien
Plants Troublesome?
• Noxious weeds primarily of foreign
origin
– Required by law to manage
• Biotic pressures left at weed origin
– plant/plant & animal/plant interactions
• Abiotic pressure ‘new home’
insufficient;
– populations increase exponentially
So What’s
the Big Deal?
• National Invasive Species Council:
– “Society pays a great price for invasive
species – costs measured not just in
dollars, but also in unemployment,
damaged goods and equipment, power
failures, food and water shortages,
environmental degradation, increased
rates and severity of natural disasters,
disease epidemics and even lost lives.”
Invasive Species Impacts
• Anthropocentric:
– interfere with land mgmt objective
•
•
•
•
interfere with ag production
harmful to human health
impede movement of water
………
Invasive Species
Impacts
• Natural:
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–
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cause population declines native spp.
cause native spp. extinctions
cause shifts predator-prey dynamics
alter ecosystem function
decrease ecosystem complexity
………
Invasive Spp. Impacts
• Economic:
– can involve anthropocentric and/or
natural effects
What Plants Should
Society Manage?
• No debate list:
–
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–
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leafy spurge
Canada thistle
knapweeds
downy brome
purple loosestrife
salt cedar
toadflaxes
Kudzu
• Debated plants:
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–
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–
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damesrocket
blue flax
smooth brome
crested wheatgrass
Kentucky bluegrass
………
How Can Society End Debate
Fairly and Objectively?
• Stop all importations
• Assess each spp. thru rigorous
science
• Use invasiveness elsewhere as
indicator
• Adopt view of neighbors
• Objective screens and flow charts
Perception
to Cause Harm
• Richardson et al. 2000.
Naturalization and invasion of alien
plants: concepts and definitions.
Diversity and Distributions 6:93-107
– definitions & communication may be a
heart of problem
• use of naturalization and invasive
interchangeably
Naturalization/Invasion
Process
• Plants must overcome various barriers:
– Introduction
• overcome geographical barrier
– Naturalization
• abiotic & biotic barriers to survival surmounted and
various barriers to reproduction overcome (selfsustaining)
– Invasion
• overcome dispersal barriers to produce reproductive
offspring distant from intro site
Definitions
• Alien plant
– result of intentional or unintentional
intro due to human activity
• Casual alien plant
– alien plant that may flourish or
reproduce occasionally
• do not form self-replacing populations
• rely on repeated intros for persistence
Definitions
• Naturalized plant
– alien plant that reproduces consistently
and sustains populations over many life
cycles without direct intervention by
humans (or in spite of humans)
• often recruit offspring freely, close to
parents
• do not necessarily invade natural, seminatural, or human-made ecosystems
Definitions
• Invasive plant:
– naturalized plant that produces
reproductive offspring, often in large
numbers, at considerable distances from
parent
• > 100 m < 5yr by seed
• > 6m/3 yr by vegetative reproduction
Definitions
• Weeds:
– plants, not necessarily aliens, that grow
in sites where not wanted and usually
have detectable economic or
environmental effects
– Environmental weeds:
• alien plants that invade natural areas
• usually adversely affect native biodiversity
and ecosystem functioning
Definitions
• Transformers:
– subset of invasive plants that change
character, condition, form, or nature of
ecosystems over substantial area
relative to extent of that ecosystem
• “bad boys” of the plant world
• approximately 10% of invasive plants fall into
this category
Excessive use of Resources:
- Salt cedar and water
Donors of limited resources:
- nitrogen fixers;
- yellow sweetclover
Fire promoters/suppressors:
- downy brome increase fire
frequency & intensity
Suppressors:
Russian knapweed allelopathy
Litter accumulators:
Perennial pepperweed
Salt accumulators/redistributors:
Tamarisk salt uptake & exudation
Transformation Examples
•
•
•
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Sand stabilizers
Erosion promoters
Sediment stabilizers
…
The Perfect Ranking System?
• Does not exist
– too many differing perspectives
• We need objective approach however!
– Reichard screen plants not yet here
• Dr. Sarah Reichard, University of Washington
– IFAS screen (adapted) for plants already present
• Drs. Randall Stocker, Allison Fox, Univ. Florida
– Australian screen
• Dr. John Virtue
– NatureServe
• Invasive plants assessment program
– Colorado has adopted & adapted CALIPC screen
What Plants Should
Society Manage?
• Weed mgmt is expensive!
• Choose battles carefully!
• Manage only those weeds that
cause economic and
environmental harm
– environmental
weeds/transformers
National Invasive Species Council
• Invasive Species Advisory Committee:
– Beck et al. 2008. Invasive species
defined in a policy context:
Recommendations from the federal
Invasive Species Advisory Committee
Invasive Plant Science and Management
1(4):414-421.
• Clarified definition Executive Order 13112
– What do we mean and what do we not mean
Colorado State University
Weed Science