Factors Influencing the Presence
or Absence of Native Plants in
Crested Wheatgrass Stands: An
Observation Study
Kirk Davies and Aleta Nafus
Agricultural Research Service
Eastern Oregon Agricultural Research Center
Burns, OR
Objectives
• Determine factors promoting native plant presence
in crested wheatgrass stands
• Determine the fate of native bunchgrasses coplanted with crested wheatgrass
Study Design
• Split into two studies:
• Study 1: Evaluate correlations between native plant
presence and explanatory factors
• Study 2: Determine abundance changes in coplanted native bunchgrasses and crested
wheatgrass
Native plant abundance in crested stands
• Sampled121 crested wheatgrass
stands
• Measurements:
o Vegetation: cover and density by
species
o Explanatory factors: topographical
features, soil characteristics, climatic
data, management, fire history,
seeding methodology, etc.
Study 1: Preliminary
Results
Study 1: Preliminary
Results
Cover Group
Mean
Min
Max
Crested wheatgrass
5.9
0.2
18.8
Sandberg bluegrass
3.3
0
13.3
Large native bunchgrass
0.4
0
10.4
Exotic annual grass
0.3
0
4.8
Perennial forb
0.3
0
7.5
Annual forb
0.2
0
2.5
Bare ground
44.0
10.2
71.0
Shrub
6.0
0
35
Study 1: Preliminary
Results
Study 1: Preliminary
Results
Management Influences
Future plans
• Subset data set to investigate
grazing management
• Further evaluate management
history
• Get more fire history data
• Regression analyses of key native
veg component
Co-planted native bunchgrasses and
crested wheatgrass after 13 years
• Study setup in 1989
• 9 blocks & 800 bunchgrasses per block
• Equal densities of crested wheatgrass and 7 native
bunchgrasses
• Densities maintained until 1998
• Self-regulate for the next 13 yrs
Co-planted results
Co-planted results
• Crested wheatgrass
increased 10-fold
• 64% of bunchgrass density
• 3 species of bunchgrass
migrated into plots
Co-planted
• Crested wheatgrass out recruits native species
o Highlights why crested wheatgrass limits exotics
o Probably makes it difficult for natives to establish
• However, all species still present
• Some species have maintained original density
• Results suggest that natives will not increase without
some control of crested.
Co-planted
• Limited to one study area
• Can’t determine causal mechanisms
• May have varied with other factors – grazing, fire,
etc.
Conclusions
• Environmental variables correlated to native plant
presence
• Working on correlations w/ management actions
• Native bunchgrass can persist with crested, but vary
by species
• However, crested wheatgrass is more successful at
recruiting
Questions?