Transcript What makes a weed a weed?

What makes a weed a weed?
Traits associated with invasive behavior
And
Predicting invasive potential
Sutherland: Predictable weedy traits?
• Predictions:
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Vegetative reproduction
Hermaphroditic or monecious
Self-compatible
Wind-pollinated
Tolerant of high light
Tolerant of low moisture
Annuals or biennials
Perennial grasses or forbs
Armed and Toxic
Weed list sources
• Synthesis of the North American Flora (3,038 spp.)
– Weed def: “plants that generally grow in disturbed areas
where they are unwanted and unappreciated.”
• PLANTS, Invasive plants of the US (1,336 spp.)
• US Fed. and State Noxious Weed Lists (385 spp.)
• Daehler (1998) (311 spp.)
– Spp. that are “global natural area invaders”
Data Analysis
• Compared frequency of traits for:
– Weeds vs. Non-weeds
– Native vs. Exotic weeds
– Invasive vs. Non-invasive weeds
Results of Analysis
Weed
Native
Invasive
Trait
Prediction
Non-weed Exotic Non-invasive
Veg. Reproduction
More
K, P, N
K, P
NS
Breeding system Mon. or hermaph
NS
K
K, P
Compatibility
Self-compat
P, N
K
K, P, N
Pollination system
Wind
NS
K
NS
Shade tolerance
Intolerant
K, P, I
K
NS
Habitat
Non-wetland
K, P, N, I K, P, N, I
N
Lifespan
Annual or Bienn K, P, N, I
K
K, P, N
Life form
Herbaceous
Mixed
Mixed
K, P, N
Morphology
Armed
K, P, N, I
NS
NS
Toxicity
Toxic
K, P, N, I
K
N
Weeds (compared to non-weeds)
are:
• More likely to be Annual or Biennial
• Less likely to be Perennial
• More likely wetland spp., toxic, vines, and
trees
• Less likely to be forbs and sub-shrubs
• Annual and Biennial weeds more likely to
be armed
• Perennial weeds more to be shade intolerant
Exotic (compared to native)
weeds are:
• Less likely to be wetland spp. Than native
weeds.
• Still more likely to be wetland spp. Than
non-weeds.
Invasive (compared to noninvasive) exotics weeds are:
• Less likely to be forbs.
• More likely to be perennial, monoecious,
self-incompatible, shrubs, and trees.
• Above traits are related.
• Magnitude of Chi Square values suggest
that life form may be more important than
breeding system or compatibility.
Other Conclusions
• Lifespan constrains other life history traits.
Separating spp by life history makes some
characteristics non-significant.
• Habitat is a significant predictive trait for all weed
spp (native, exotic, or invasive).
• Toxicity is a sig. Life history trait for weds
independent of lifespan.
– If alleopathic: supports competitive release hyp.
– If anti-herb Defense: supports escape predation hyp.
Other Conclusions
• Agree with some of Baker’s predictions
(1965). Disagree on Veg. Reproduction,
self-incompatibility, wind pollination.
• With the exception of increased probability
of being a tree, invasive exotics differ very
little in life history from other weeds.
• There are life history traits that distinguish
weeds from non-weeds.
Sutherland: Predictable weedy traits?
• Predictions:
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Vegetative reproduction
Hermaphroditic or monecious
Self-compatible
Wind-pollinated
Tolerant of high light
Tolerant of low moisture
Annuals or biennials
Perennial grasses or forbs
Armed and Toxic
Risk Assessments
• Allow managers, horticulturalists, and
politicians to determine what plants to
permit and which to deny entry.
• Not all errors are equally important. It’s
worse to let in a pest species than keep out a
non-pest species. Minimize spp. held for
evaluation.
Comparing Australian and
Reichard systems
• AU 3 tiered scheme vs. Reichard’s decision tree
• Similar levels of success
• Use 5 kinds of criteria:
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History of invasiveness elsewhere
Relatedness to other invaders
Climatic match between home and novel ranges
Noxious and undesirable traits
Biological attributes of plant itself
4 Categories of traits associated
with weeds
• Vegetative growth and reproduction
– Contrary to findings of Sutherland
• Persistence, tolerance, and recovery
• Sexual and Asexual propagule production
and dispersal.
• Easy germination and establishment.
Risk Assessment take home message
• Fairly accurate
• Moderately tolerant of missing data
• Important variables fairly constant across
analyses and assessment methodology.
Potential responses by Botanical
gardens
• The conservation aware garden.
– Do impact and risk assessments
• The strict conservation garden.
– Do not transport organisms across natural
barriers to dispersal.
Questions for thought
• What will it take to get horticulturalists on-board?
• To what degree are traits associated with invasive
species the result of their selection vs. a random
sampling of potential invasives?
• What step could be taken to improve the accuracy
of Risk Assessments?
• Why the discrepancy over vegetative
preproduction?