Joe DiTomaso University of California, Davis
Transcript of Joe DiTomaso University of California, Davis
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
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
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
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
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
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