Impacts of Cheatgrass and
Native Grasses on Great
Basin Forb Development
Hilary Parkinson
Primary advisor:
Cathy Zabinski
Committee members:
Nancy Shaw
Bruce Maxwell
Jon Wraith
Research Objectives
1. Measure forb response to increasing
densities of B. tectorum.
2. Measure forb response to two native
grasses compared to B. tectorum.
3. Gather information on the autecology of 5
native forbs (biomass, phenology, RGR,
root mass ratios).
Field Experiment
•
Measure the effect of B. tectorum on:
1. Seedling survival
2. Biomass
•
•
Differences among forbs?
Measure soil water content with
increasing densities of B. tectorum
Forbs-Field
experiment
• Achillea millefolium
(yarrow)
• Lomatium grayi
(Grays biscuitroot)
• Eriogonum
umbellatum
(sulfur flower
buckwheat)
• Penstemon
speciosus
(royal penstemon)
Experimental Design
• 5 B. tectorum
seeding densities
• 4 forb species
• 3 complete blocks
• Water content
measured in plots
seeded at 0, 180 and
360 plants m-2
• 2 locations in Snake
River Plain: Lucky
Peak and Orchard
Impact of Cheatgrass on forb seedling
survival
•
•
•
•
Lucky Peak
By May 15, no A. millefolium plants alive in
plots seeded with densities of 360 plants m-2
No effect on E. umbellatum
Senescence of L. grayi occurred 5 weeks earlier
at the highest density of B. tectorum
Inadequate sample size for P. speciosus
Impact of Cheatgrass on forb biomass
Shoot biomass (g)
Lucky Peak
L. grayi
0.04
A
0.03
E. umbellatum
7
B
5
4
3
P. speciosus
A. millefolium
25
BC 20
C
15
0.02
2
3
0.01
1
5
0
0
1
0.00
0
100 200 300
0
10
100 200 300
0 100 200 300
-2
B. tectorum plants m
0
100 200 300
-3
0.35
-3
Soil water content (m /m )
Soil Water Content--20 cm depth with 0, 150-300 and >300 B. tectorum plants m-2
0.30
April 13
0.25
0.20
0.15
0.10
0.05
3/1/07
4/1/07
5/1/07
6/1/0
LOGR
ERUM
ACMI
PESP
Relative emergence dates
Forbs only
-2
150-300 B. tectorum m
-2
>300 B. tectorum m
May 15-B. tectorum fully
mature, harvested
Why differences among forbs
in response to B. tectorum?
Traits shared by forbs that responded better…
• Small biomass
• Early phenology
• Contrasting root morphologies
Taprooted/vertically
oriented
• Eriogonum
• Lomatium
E. umbellatum &
Lomatium
Fibrous,
laterallybranched
• Achillea
• Penstemon
P. speciosus
(& A. millefolium)
Reduced biomass and RGR of all forbs
No effect
E. umbellatum
20% reductions in RGR
P. speciosus
Elymus
B.
tectorum
elymoides
Machaeranther
a canescens
Sphaelace
a
Conclusions
– B. tectorum reduced survival of only one forb, but
only at the highest seeding level-360 B. tectorum
plants m-2
– Some native species can germinate and grow well
at low densities of B. tectorum
– Timing of B. tectorum water use and forb growth
may have favored species with early phenology
– Root morphology may be an important
characteristic to select species that grow well with
grasses
Additional information
Parkinson, H. Zabinski, C. Shaw, N. 2009. Effects of native grasses and
cheatgrass on the growth of five Great Basin forbs. Boise (ID): USDA Forest
Service Rocky Mountain Research Station. General Technical Report,
publication number pending.
Parkinson, H. Zabinski, C. Shaw, N. 2009. Growth characteristics of six forbs
selected for restoration in the Great Basin. Boise (ID): USDA Forest Service
Rocky Mountain Research Station. General Technical Report, publication
number pending.
Parkinson, H. Zabinski, C. Shaw, N. 2009. The response of four Great Basin
forbs to increasing densities of cheatgrass. Boise (ID): USDA Forest Service
Rocky Mountain Research Station. General Technical Report, publication
number pending.
Thanks to Nancy Shaw and all the crew at the Rocky Mountain Research Station.