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GBNPSIP 2009
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Successional trajectories of >30-yearold crested wheatgrass seedings
Tom Monaco
USDA-ARS
Utah State University, Logan, Utah
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FRRL Mission Statement
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Provide an array of improved plant materials and management alternatives for sustainable stewardship of rangelands and pastures in the western U.S.
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Overview
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Historical use of crested wheatgrass. community phases. Seed bank.
Role of soil and disturbance history. Updated state‐and‐transition model.
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Historical Perspective
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Why was crested wheatgrass seeded?
Degraded shrub‐steppe rangelands
– Overgrazing
– Exotic weed invasion
– Halogeton Control Act of 1952.
Abandoned farmland
– BankHead‐Jones Land
– Soil loss and erosion
Competitive
Adapted
Long‐lived
Met practical needs
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What successional trajectories have these
ecosystems taken?
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Common assumptions ‐
• Low diversity and near monoculture, even after 50 years?
• Shrub dominated?
• Functioning as stable, naturalized shrub‐steppe?
R.E. Rosiere
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Objectives
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• Identify ‘dominant’ indicator species.
• Determine whether distinct successional phases exist.
• Identify soil and ground cover attributes related to variation in phases.
• Determine seed bank composition.
• Characterize influence of soils, disturbance history, elevation, and topography on vegetation attributes.
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Wyoming big sagebrush communities historically
seeded with crested wheatgrass
• Site selection criteria:
– Seedings greater than 30 years old. – Never burned or retreated chemically or mechanically
since establishment.
– Have similar historic grazing histories.
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Typical looking historic crested wheatgrass seeding ?
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Modified-Whittaker Plots (Stohlgren et al. 1995)
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4 ‐ plots per community
% Canopy cover Ground cover
Species richness
Diversity index
Soils ‐ 15 cm
– texture
– nitrogen, carbon, pH
• Seed Banks
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Results – indicator species
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• Communities clustered into four phases.
• Indicator species differ for phases.
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Community Phases
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1- CRESTED dominated
3 - HERB/SHRUB co-dominated
2 - HERBACEOUS dominated
4 - SHRUB dominated
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Seed banks description
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• 47 species. • 13 common species.
• Few species were normally distributed.
Mean Density
Seed m-2
# of
Communities
2303
27
Agropyron cristatum
337
32
Poa secunda
239
24
Poa bulbosa
135
19
Bromus tectorum
106
12
Descurainia sophia
84
27
Artemesia tridentata
49
21
Collinsia parviflora
45
6
Alyssum desertorum
35
8
Hackelia micrantha
22
10
Microsteris gracilis
17
5
Halogeton glomerotus
16
10
Erigeron spp.
15
5
Species
Ranunculus testiculatus
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Results ‐ Soils
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• Soil texture, chemistry, and ground cover varies among phase
• Vegetation and ground cover also varies with soil texture
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Results ‐ Disturbance history
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• Disturbance history depends on soil texture
• Combined, soils and cropping status determine vegetation of communities
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Seeded
community
state-and transition
model
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Conclusions
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• In absence of fire, herbicide, and mechanical treatments, 4 distinct community phases are possible.
• Pre‐existing soil attributes, disturbance history, and topography drive succession.
• Updated STM provides insights for management. FORAGE AND RANGE RESEARCH LABORATORY
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The Cheatgrass
Problem
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Huge problems require sound strategies
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Manage vegetation
Desired
condition
Stabilize soils
minimize disturbance
Cheatgrass dominated
adapted from Bob Nowak, UNR
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Ecologically-Based Invasive Plant Management
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Site Assessment
Causes of
change
Processes
Impacted
Utah DWR
Pickett et al. 1987
Sheley et al. 1996
Krueger-Mangold et al. 2006
Site
Availability
Disturbance
Species
Availability
Dispersal &
Seed abundance
Soil Resources
Species
Performance Competition