Download Centaurea maculosa

Spotted knapweed
Taxonomy
• Family: Asteracea – Aster
family
• Genus: Centaurea L. –
knapweed
• Species: Centaurea
biebersteinii DC.
• Synonyms:
• Acosta maculosa auct. non
Holub
• Centaurea maculosa auct.
non Lam.
• Centaurea stoebe L. ssp.
micranthos (Gugler) Hayek
• Common name:
Spotted knapweed
Integrated Taxanomic Information
System (ITIS)
Species description
• Biennial or short-lived
perennial with deep tap
root.
• Juvenile plants and overwintering adults are in the
rosette form.
• Small plants have one
unbranched stem with
one flower head, large
plants have multiple
stems and as many as
100 flower heads.
• Mature plants grow to
height of between 15 &
122 cm (6” – 4’).
Species description
• Flower heads are 5 to 10
mm long and can occur
singly or in clusters at
branch tips.
• Each head bears stiff,
black tipped bracts
giving the plant its
“spotted” appearance.
Species description
• Seeds are 2.5 mm long.
• Seeds are oval, black or
brown, with pale vertical
lines.
• Each seed has a short
bristly pappus about half
the length of the seed.
Biology
• Pollinated primarily by flies and bees; self compatible.
• Each plant usually produces between 400 and 900
seeds; seed production is highly dependant on annual
precipitation.
• Plants in irrigated fields produced as many as 25,263
seeds.
• Rarely produces rhizomes; population growth dependent
almost solely on seed.
Biology
•
•
•
Three seed-germination types produced by parent
plant:
1) Non-dormant seed germinates regardless of light.
2) Seed with dormancy set by far red light.
3) Dormant seed that does not germinate until buried
with soil.
Dormant seeds readily accrue in seed bank; seeds
viable as long as 8 years.
Germinate over a range of soil depths, water content,
and temperature.
Biology
• Seeds germinate
between late March and
June of each year.
Earliest plants to
germinate have the
highest survival.
• Seedlings have tap root
as long as 80 cm after
two months of growth.
• Seedling mortality is
highly variable from year
to year (precipitation), but
averages about 12%.
Biology
• Juvenile and mature
plants spend winter as a
rosette.
• Rosette mortality has
been reported as high as
48% and was attributed
to root grazing by weevils
and underground rodents.
• Adult spotted knapweed
flower 1-3 years over
lifetime.
• Plants as old as 12 years
have been documented.
Geographic Range: Native
• Central Europe and east
to central Russia,
Caucasia, and western
Siberia.
• Found in elevations
ranging from 578 to 3,040
m.
• Found in precipitation
zones from 20 to 200 cm
annually.
Spotted knapweed
in Romania
Geographic Range: North America
• Introduced as
contaminants in alfalfa
and soil used as ship
ballast.
• First recorded in Victoria,
British Columbia in 1893.
• Since spread to virtually
every Canadian province
and nearly every state in
the US.
Geographic Range: United States
•
•
•
•
Limited to San Juan Islands, WA, until 1920.
1920-1960: spread to 20 counties in Pacific Northwest.
1960-1980: spread to 48 counties.
1980-present: spread to nearly every state including
every county in Washington, Idaho, Montana, and
Wyoming.
• Nevada:
Preferred habitats: everywhere!
What makes it invasive?
1)
2)
3)
4)
5)
6)
7)
8)
9)
Vacant niche
Allelopathy
Atmospheric CO2 / global climate change
Resource availability / Competition
Microevolutionary change
Escape from biotic constraints??
Biodiversity
Disturbance / land use
Anthropogenic
What makes it invasive?
Allelopathy
• According to Weir et al. (2003), a study as early as 1832
hypothesized that allelopathy could be responsible for
spotted knapweeds success.
• Fletcher and Renney (1963) were first to extract
substances with allelopathic potential from leaves, stem,
and roots.
• Since 1963 numerouse studies have isolated chemicals
such as cnicin, (±) –catechin, and numerous
polyacetylenes (Stevens 1986, Kelsey and Locken 1987,
Locken and Kelsey 1987, Bais et al. 2002 and 2003, and
others).
What makes it invasive?
Allelopathy
• Ridenour and Callaway
(2001) showed that
spotted knapweed has
negative effects on
biomass of roots and
shoots of Festuca
idahoensis which are
ameliorated by activated
charcoal.
What makes it invasive?
Allelopathy
• Bais et al. (2003) reported that a mixture of (+)-catechin
and (-)-catechin was present in root exudates of spotted
knapweed.
• Further studies showed that (-)-catechin was solely
responsible for phytotoxic activity, whereas (+)-catechin
provided antimicrobial properties.
• (-)–catechin inhibits root growth and germination in field
soils of two North American grasses (Festuca idahoensis
and Koeleria micrantha), “by triggering a wave of
reactive oxygen species initiated at the root meristem,
which leads to a Ca2+ signaling cascade triggering
genome-wide changes in gene expression and ultimately
death of the root system”.
What makes it invasive?
1)
2)
3)
4)
5)
6)
7)
8)
9)
Vacant niche
Allelopathy
Resource availability / Competition
Atmospheric CO2 / global climate change
Microevolutionary change
Escape from biotic constraints
Biodiversity
Disturbance / land use
Anthropogenic
What makes it invasive?
Competition / Resource availability
• Callaway et al. (2004)
showed that the presence
of arbuscular mycorrhizae
can significantly alter the
competitive balance
between spotted
knapweed and native
grasses / forbs.
+ +
AMF helps (+) SK
or hinders (-) SK
-
-
What makes it invasive?
Competition / Resource availability
• Numerous studies have determined how spotted
knapweed and various other native species respond to
manipulations of limiting resources such as nitrogen,
phosphorus, and water (Story et al. 1989, Herron et al.
2001, Blicker et al. 2002, Olson et al. 2003, Blicker et al.
2003, Sperber et al. 2003, and Hook et al. 2004).
What makes it invasive?
Competition / Resource availability
• In a glasshouse studies, Blicker et al. (2002, 2003)
studied water & N use of spotted knapweed in
comparison with three native grasses.
– Spotted knapweed did not have the greatest WUE.
– Spotted knapweed did not use the most water.
– Spotted knapweed did not have the greatest NUE.
– Spotted knapweed did not use the most nitrogen.
What makes it invasive?
Competition / Resource availability
• Herron et al. (2001) hypothesized that removal of
nitrogen and phosphorus from soil would shift
competitive balance to native bluebunch wheatgrass.
– Without nutrient manipulation, spotted knapweed had
higher N uptake and biomass.
– When N was removed from soil, the competitive
balance shifted to bluebunch wheatgrass.
– Phosphorus removal had no effect.
What makes it invasive?
Competition / Resource availability
• Spotted knapweed is probably a better competitor for
nitrogen when N levels are high.
• Probably not a better competitor for phosphorus.
• Does not use water efficiently; deep tap root
• Arbuscular mycorrhizae can have a positive or negative
effect on competition between spotted knapweed and
native species.
• Callaway and Ridenour (2004) hypothesized that there
could be a connection between allelopathy and
competition for resources.
What makes it invasive?
1)
2)
3)
4)
5)
6)
7)
8)
9)
Vacant niche
Allelopathy
Resource availability / Competition
Atmospheric CO2 / global climate change
Microevolutionary change
Escape from biotic constraints
Biodiversity
Disturbance / land use
Anthropogenic
What makes it invasive?
Atmospheric CO2 / global climate change
• Ziska (2003) showed that
leaf area significantly
increased with each step
increase in CO2.
• Leaf, stem, and root
weight, as well as overall
biomass also increased
significantly with each
step increase in CO2.
Future
Current
Pre-industrial
What makes it invasive?
1)
2)
3)
4)
5)
6)
7)
8)
9)
Vacant niche
Allelopathy
Resource availability / Competition
Atmospheric CO2 / global climate change
Microevolutionary change
Escape from biotic constraints
Biodiversity
Disturbance / land use
Anthropogenic
What makes it invasive?
Biodiversity
• Ortega and Pearson (2005) studied bluebunch
wheatgrass grassland types with spotted knapweed
present at high and low densities in western Montana.
• “impacts of strong invaders, such as C. maculosa, on
native diversity may be evident even at low levels of
invasion… biotic resistance may not be a significant
force in the real world”.
What makes it invasive?
1)
2)
3)
4)
5)
6)
7)
8)
9)
Vacant niche
Allelopathy
Resource availability / Competition
Atmospheric CO2 / global climate change
Microevolutionary change
Escape from biotic constraints
Biodiversity
Disturbance / land use
Anthropogenic
What makes it invasive?
Disturbance / Land Use
• Spotted knapweed
densities are highly
correlated with the
degree of soil
disturbance.
• Because spotted
knapweed reproduces
entirely by seed,
disturbed soil allows for
rapid establishment and
spread.
What makes it invasive?
1)
2)
3)
4)
5)
6)
7)
8)
9)
Vacant niche
Allelopathy
Resource availability / Competition
Atmospheric CO2 / global climate change
Microevolutionary change
Escape from biotic constraints
Biodiversity
Disturbance / land use
Anthropogenic
Impacts
• Ecological
– Spotted knapweed monocultures eliminate
native species.
– Can severely reduce wildlife forage.
– Alters biogeochemical cycling by increasing
surface water runoff and stream sediment
yield.
Impacts
• Economic
– Reduction in quality and yield of livestock
forage.
– Does have some nutritional value early in the
spring and is used by sheep, goats, and
cattle.
– Bucher (1984) claimed a loss of $156 million
per year due to a 63% decline in forage in
Montana.
– Reduces desirability of recreational areas.
Impacts
• Social
– Rural economy and lifestyle can be severely
affected by large infestations.
– Recreation opportunities can be limited by
large infestations.
Management
• Inventory and
mapping are critical to
proper management.
• Remote sensing has
been effective tool for
mapping spotted
knapweed.
Management
• Prevention
– Prevention of spotted knapweed to adjacent
rangelands is most cost effective method.
– Seed dispersal can be limited by driving on
designated roads.
– Grazing livestock in newly establishing areas
early in spring.
– Minimizing all soil disturbances; spotted
knapweed is usually first invader on disturbed
sites.
Control: Biological Control
• Numerous natural
enemies have been
approved as biological
control agents.
Bio-control Agents
Cyphocleonus spp.
Agapeta spp. (root boring moth)
(root boring/gall weevil)
Urophora spp. (seedhead fly)
Sphenoptera spp. (root beetle)
Urophora spp. (seedhead fly)
Control: Biological Control
• Numerous natural
enemies have been
approved as biological
control agents.
• Marginal success at best
for all agents.
• Seed production has
been dramatically
decreased in some
cases, but not enough to
significantly decrease
infestation.
Control
• Burning
• Single low intensity fire may elicit positive response of
spotted knapweed.
• Repeated annual summer burns before seeds
develop has reduced populations 5-90%
• Grazing
• Spotted knapweed can tolerate severe defoliation
related to grazing.
• Repeated annual grazing in the spring during the
rosette stage can reduce populations.
Control
• Herbicides
• Picloram, clopyralid, dicamba, and 2,4-D provide
effective control on spotted knapweed. Timing for
best control varies depending on herbicide.
• Picloram provided nearly 100% control of spotted
knapweed over 8 year span.
• Mowing
• Long-term mowing effects not known.
• Longest study of three years concluded that it
provided partial control if done at the flowering stage.
Eradication
• Little hope of eradication throughout all of
introduced range.
• Best course of action is for regional land
managers to form a comprehensive
management plan that includes mapping,
prevention methods, and multiple control
methods.
Summary
• Key biological characteristics
– Allelopathic
– Usually out-competes natives for nitrogen
– Thrives in disturbed sites
• Control strategies
– Grazing/fire to reduce seed production
– Chemicals can work; picloram had best results
– Manipulate soil N to low levels where natives outcompete