Joe DiTomaso

University of California, Davis

Avena spp. (wild oat)Lolium multiflorum

(Italian ryegrass)

Bromus hordeaceus

(soft brome)

Barb goatgrass

(Aegilops triuncialis)

Jointed goatgrass

(Aegilops cylindrica)

Red brome

(Bromus

madritensis

ssp. rubens)

Ripgut brome (Bromus diandrus)

Species Acres infested (x million)

Downy brome 56.0

Yellow starthistle 14.8

Canada thistle 7.1

Sericea lespedeza 5.5

Spotted knapweed 5.2

Musk thistle 4.7

Leafy spurge 3.7

Saltcedar 3.7

Medusahead 2.4

Perennial pepperweed 2.0

Diffuse knapweed 1.8

Russian knapweed 1.2

Cheatgrass or Downy brome

Invasive species that change the character,

condition, form or nature of a natural

ecosystem over a substantial area. These

species are considered significant

ecological threats.

From Richardson et al. 2000. Diversity and Distributions, 6:93-107

Excessive users of resources◦ Light, water, CO2 and O2

Donors of limited resources◦ nitrogen

Fire promoters and suppressors Sand stabilizers Erosion promoters Colonizers of intertidal mudflats/sediment

stabilizers Salt accumulators Litter accumulators

From Richardson et al. 2000. Diversity and Distributions, 6:93-107

Seeds

Germination

Establishment and Maturity

Soil factors

Competition

Reproduction

Seeds

Germination

Establishment and Maturity

Soil factors

Competition

Reproduction

Two basic principles to managing annuals◦ Prevent new seed production or recruitment

Reduce propagule pressure

◦ Deplete existing seed bank

Dormancy consideration

How long does the seed survive in the soil?

Cheatgrass◦ Forage source by

birds and small mammals

◦ Increased small mammal populations creates disturbance to perpetuate population

Medusahead◦ Seeds covered with

small silica barbs

◦ Animals do not like to utilize as food source

Timing

Dormancy

Moisture

Nitrogen

Seedbank longevity

Root growth

Cheatgrass◦ In arid environments,

germinates primarily in spring (once ever 5 yrs in fall)

Medusahead◦ Can also germinate

in winter and spring

Both grasses germinate in the fall with first rains.

Cheatgrass◦ Generally little

dormancy with seed ready to germinate first season

◦ Areas with summer rain some seeds can acquire afterripening dormancy

Medusahead◦ Cold temperature

related afterripening dormancy

◦ Controlled by chemical in the awn

Cheatgrass◦ To find enough

holding moisture seeds must find way into cracks or litter to germinate

Medusahead◦ Controlled by

humidity level within litter layer

Both species can be stimulated to germinate in areas with higher nitrogen or by adding nitrate

Cheatgrass◦ Most seed

germinate in first year, some survive up to 5 years

Medusahead◦ Survival generally 2 years,

but also up to 5 yrs

Low point in seedbank is in early spring after germination (typically April)

With fall germination, both species put early energy into root growth

Allows for rapid shoot growth when temperature increases in spring

Life cycle◦ Medusahead matures 2-4 weeks later

than most other annual grasses, including cheatgrass

Plasticity◦ Dense stands can have1000 plants ft2

and produce thousands of seeds

◦ Single open plant can produce hundreds of tillers and have same number of seeds

Medusahead◦ Requires more moisture than cheatgrass

◦ Prefers high clay soils

Destruction of microphytic crust (lichens, mosses and blue-green algae) increased annual grass invasion and suppressed establishment of native perennials

Medusahead◦ Prolonged dominance my reduce

mycorrhizae which favor natives

◦ Cheatgrass may act same

◦ Disfavors establishment of perennials through restoration

Moisture effects

Effects of litter accumulation

Effects of other species

Effects of grazing

Cheatgrass◦ Very competitive

with other natives for soil moisture

◦ Can resist invasion by medusahead when soil moisture is limited

◦ Leaves little moisture for medusahead to complete life cycle

Medusahead◦ Competes well with

cheatgrass when late season soil moisture remains

Cheatgrass◦ Litter does not

accumulate as decay is rapid

Medusahead◦ Litter layer 2-5 in

◦ Slow decay due to high silica content

◦ Litter prevent other plant seed from contacting soil surface

◦ Also ties up nutrients

◦ Medusahead adapted to germinating and surviving in its thatch

◦ Roots more resistant to drying and can resprout

Cheatgrass◦ Four cheatgrass

plants/ft2 can outcompete crested wheatgrass

◦ Other bunchgrasses less competitive

Medusahead◦ Squirreltail is one of

few natives that can establish in medusahead stands

Annual grasses are not as susceptible to overgrazing as perennial grasses

Seedling vigor slow in perennials so recovery favors invasive annuals

Both species self pollinated Dispersal typically by seeds falling to

ground, but some long distance dispersal on animals

Cheatgrass ◦ After fires many seeds can be killed

◦ Germinating plants can be vigorous with added nutrients

◦ Anthers exposed longer due to high vigor and increases cross-pollination

◦ Exchange of genetic material increases hybrid vigor allowing populations to more fully expand range

Salt desert habitats