Reducing Seed Output and Seed Viability of Cultivars: How Much Is Enough to Create a

Plant That Will Not Be Invasive?

Tiffany KnightWashington University

Jean Burns, Kay Havens, Pati Vitt, Ed Guerrant

Ornamental Plants

� Most are not native� Some become invasive� Traits that we select in our ornamentals

� adaptable to a wide range of conditions� high flower production � long flowering period � able to self seed

Invasive species

� Second largest threat to global biodiversity

Invasive species

� Second largest threat to global biodiversity

� 82% of the invasive trees and shrubs in the USA were introduced in horticulture

Japanese Barberry (Berberis thunbergii)

�one of the most destructive invasive plants in Connecticut�--Connecticut Botanical Society

A popular horticultural shrub that has become a natural area invader

�The reasons? Sheer growability� hardy to zone 4, can take sun or shade, wet or dry, and will come back strong after a beating.�

Purple loosestrife (Lythrum salicaria)

Lythrum alatum(Winged Loosestrife)

It's back! Yes, you can once again grow loosestrife and not be hounded by the eco-nazis. In fact, Lythrum alatumis native to all but 12 US states. Okay, it's not as pretty as purple loosestrife and when grown in a swamp, it's slightly more aggressive, but if you're out to clog up a waterway, it might as well be with a native plant.

Why the resistance?Japanese Barberry sales in Connecticut Alone

--$15-20 million Annually--

Why the resistance?35 Cultivars of Japanese Barberry

� Aurea� Bonanza Gold� Angel Wings� Crimson Giant� Rosy Glow

Individuals within these range from producing less than 100 to over 3000 seeds per year

�I know that some Barberries have become invasive but mine doesn't really set any seed and my plants are only 2 feet high after almost 5 years in the ground.�

A demographic approach

Seedling AdultJuvenile

Cultivar #1

λ=1.50

0.05

0.80

0.95

0.05

1000 * 0.10

A demographic approach

Seedling AdultJuvenile

Cultivar #1

λ=1.50

0.05

0.80

0.95

0.05

1000 * 0.10

Seedling AdultJuvenile

Cultivar #2

λ=1.00

0.50

0.35

0.95

0.05

50 * 0.10

A demographic approach� Many horticulturists aim to reduce the seed

output or seed viability of invasive ornamentals.

� Are cultivars with reduced seed output �safe�?

� How much does seed output have to be reduced for a plant to not be invasive (have a population growth rate <1)?

Plant invasions and matrix modelsPlant Invasive RangeLife form Selected Reference

Pinus nigra Tree New Zealand Buckley et al. 2005

Alliaria petiolata Biennial USA Davis et al. 2006

Heracleum mantegazzianum Monocarpic herb Europe Nehrbass et al. 2006

Clidemia hirta Shrub USA DeWalt 2006

Ardisia elliptica Shrub USA Koop and Horvitz 2005

Cytisus scoparius Shrub USA Parker 2000

Carduus nutans Monocarpic herb New Zealand Shea and Kelly 1998

Centaurea maculosa Perennial herb USA Emery and Gross 2005

Agropyron cristatum Perennial grass USA Hansen and Wilson 2006

Molinia caerulea Perennial grass Western Europe Jacquemyn et al. 2005

Lespedeza cuneata Perennial herb USA Schutzenhofer and Knight 2007

Dipsacus sylvestris Biennial USA Werner and Caswell 1978

Cirsium Vulgare Monocarpic herb USA Tenhumberg et al. 2007

Alliaria petiolata (Garlic mustard)A typical short-lived invasive plant

Rosette AdultSeed

SeedBank

AdultsRosette

Davis et al. 2006

Alliaria petiolata (Garlic mustard)A typical short-lived invasive plant

Rosette AdultSeed

SeedBank

AdultsRosette0.03 0.62

2.60.27

27.7

Davis et al. 2006

Alliaria petiolata (Garlic mustard)A typical short-lived invasive plant

Rosette AdultSeed

SeedBank

AdultsRosette0.03 0.62

2.60.27

27.7

λ=1.42

Davis et al. 2006

Alliaria petiolata (Garlic mustard)A typical short-lived invasive plant

Rosette AdultSeed

SeedBank

AdultsRosette0.03 0.62

2.60.27

27.7

λ=1.42

Davis et al. 2006

0.02

0.09 0.45

0.09

0.36

0 20 40 60 80 1000

0.5

1.0

1.5

2.0

2.5Po

pula

tion

grow

th ra

te (λ

)

a a a a aa

aa

aa

a

Percent reduction in seed production or viability

Reducing seed output reduces population growth of garlic mustard

0 20 40 60 80 1000

0.5

1.0

1.5

2.0

2.5Po

pula

tion

grow

th ra

te (λ

)

a a a a aa

aa

aa

a

caca

caca

caca

caca

ca

ca

ca

dd

dd

dd

dd

d

d

d

ee

ee

ee

ee

ee

e

ci ci ci ci ci cici

cici

ci

ci

pp

pp

pp

pp

pp p

ss

s

s

s

ss s s s

s Setaria faberip Polygonum perfoliatum

ci Cirsium vulgare

e Echium plantagineumd Dipsacus sylvestris

ca Carduus nutansa Alliaria petiolataSpecies

Percent reduction in seed production or viability

Short-lived invasive species

So, reduced seed output is likely to reduce population growth of short-lived species�.

�..But, what about long-lived species such as shrubs and trees?

Scotch Broom (Cytisus scoparius)

Parker 2000

Cytisus scoparius (Scotch Broom)

Parker 2000

Cytisus scoparius (Scotch Broom)

0.600.01 0.35

0.230.02

0.21

0.39

97.5

0.01 0.46

0.32

422

0.370.03

0.050.37

861

0.01

0.44

0.11

0.49

2725

0.03

0.03

0.85

Parker 2000

Cytisus scoparius (Scotch Broom)

0.600.01 0.35

0.230.02

0.21

0.39

97.5

0.01 0.46

0.32

422

0.370.03

0.050.37

861

0.01

0.44

0.11

0.49

2725

0.03

0.03

0.85

λ=1.40

Parker 2000

Cytisus scoparius (Scotch Broom)

0.600.01 0.35

0.230.02

0.21

0.39

97.5

0.01 0.46

0.32

422

0.370.03

0.050.37

861

0.01

0.44

0.11

0.49

2725

0.03

0.03

0.850.11

0.01λ=1.40

cy cy cy cy cy cy cy cy cy cycy

0 20 40 60 80 100Percent reduction in seed production or viability

0

0.5

1.0

1.5

2.0

2.5

Popu

latio

n gr

owth

rate

(λ)

Reducing seed output has minor effects on scotch broom

Long-lived invasive species

m m m m m m m mm

m

m

ce ce ce ce ce ce ce ce ce cece

a a a a a a a a a a a

cl cl cl cl cl cl cl clcl

cl

cl

cy cy cy cy cy cy cy cy cy cycy

r r r r r r r r r r r

p p p p p p p p pp

p

0 20 40 60 80 100Percent reduction in seed production or viability

0

0.5

1.0

1.5

2.0

2.5

Popu

latio

n gr

owth

rate

(λ)

r Rubus discolorp Pinus nigra

cl Clidemia hirta

a Ardesia elliptica

cy Cytisus scoparius

ce Centaurea maculosa

m Molina caerulea

Species

Reducing seed output has larger effects on the growth rate of short-lived species

m m m m m m m m mm

m

ce ce ce ce ce ce ce ce ce cece

a a a a a a a a a a a

cl cl cl cl cl cl cl cl clcl

cl

cy cy cy cy cy cy cy cy cy cycy

r r r r r r r r r r r

p p p p p p p p pp

p

0 20 40 60 80 1000

0.5

1.0

1.5

2.0

2.5

Popu

latio

n gr

owth

rate

(λ)

0 20 40 60 80 1000

0.5

1.0

1.5

2.0

2.5

Popu

latio

n gr

owth

rate

(λ)

a a a a a a aa

aa

a

caca

caca

caca

caca

caca

ca

d d d dd

dd

dd

d

d

ee

ee

ee

ee

ee

e

ci ci ci ci ci cici

cici

ci

ci

p pp p p p p

p pp p

ss

s

s

ss

s s s s

Percent reduction in seed production or viability

Short-lived species Long-lived species

A demographic approach

Seedling AdultJuvenile

Cultivar #1

λ=1.50

0.05

0.80

0.95

0.05

1000 * 0.10

Seedling AdultJuvenile

Cultivar #2

λ=1.00

0.50

0.35

0.95

0.05

50 * 0.10

Conclusions

Reductions in seed output will not necessarily result in non-invasive cultivars, particular for long-lived species

Demographic modeling can illuminate the invasive potential of different cultivars-seed output, seed viability-life history (time to reproduction)