Changes in Soil Properties

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Changes in Soil Properties of Heavily Grazed
Meadows After Ten Years of Grazing Exclusion.
Hillary Talbott
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Study Sites
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Eastern Cascade Ecosystem

• Mosaic of Ponderosa Pine and Douglas Fir forest
  with common upland and riparian meadows
• Frequent fire return interval (10-24 years) and
  low-severity fire regime
• Xeric moisture regime with annual precipitation
  800mm

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Importance of Meadows

• Highly productive systems
• Important habitat
• Source of forage for wildlife
• Integral part of mosaic ecosystem
• Act as buffers and sponges

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Grazing on Forest Service Land

• Permitted use of forests since 1906
• Eastern Cascades grazed by sheep and cattle
• Meadows and open forest stands provide most of
  forage

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Heavy Grazing Effects on Soils
Consumption of vegetation
Trampling of vegetation and soils
Loss of plant cover, litter, and soil organic
matter
Soil Erosion
Increased soil compaction and disturbance
Reduced infiltration
Deteriorated soil structure
Based on Belsky Blumenthal 1997
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Meadows are being overused.
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(No Transcript)
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FF
JO
HP
MM (8km)
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Four meadow sites
Jumpoff Meadow (JO)
Fish Flats (FF)
Tyler Meadow (HP)
Minnie Meadow (MM)
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Experimental Design

• Split-plot design with 2 treatments
• -Grazing exclusion
• -Fertilizer application in fall of 92 and fall
  of 93

No grazing
Elk only
ElkCattle (Control)
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NPKS
NPS
PKS
NKS
0
50
75
100
Fertilizer Rates in kg/ha
125 150
175 200
250
N
P
K
S
125
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Meadow Properties
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Dominant Vegetation
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• After three years of grazing exclusion and two
  fertilizer applications
• Root biomass increased in all fertilized plots.
• Bulk density decreased slightly in no-grazing
  plots.

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Research Questions

• Has grazing exclusion had any effect on soil bulk
  density, hydrologic properties, or root biomass?
• Has fertilizer application affected soil bulk
  density, hydrologic properties, or root biomass
  through changes in plant productivity?

Photo courtesy of PNW research lab.
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Sampling

• Sampled NPKS fertilizer plot in each grazing
  treatment at 0 and 125kg rates
• 3 sample points per fertilizer plot

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NPKS
NPS
PKS
NKS
0
50
75
100
Fertilizer Rates in kg/ha
125 150
175 200
250
N
P
K
S
125
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Sampling

• At each sample point
• 1 permeameter reading
• 1 root biomass core
• 2 bulk density cores
• 1 SMC core
• 1 scoop for composite sample

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Saturated Hydraulic Conductivity
Root Biomass
Guelph permeameter
0-10cm
10-20 cm
20-30 cm
Photo courtesy of PNW research lab.
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Bulk Density and SMC
Gosh, drop hammers are so fun!
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Separating roots using the hydropneumatic
elutriation system.
Cleaned root samples
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Determination of Soil Moisture Characteristic
Tempe Cells Pressure Plates
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Soil Moisture Characteristic

• Van Genuchten Equation
• ? 1 m
• 1a(-?)n
• Where
• ? is relative water content
• ? is matric potential
• a and n are empirically derived constants
• m is 1/1-n

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Pore Size Distribution

• Pore size distribution
• r(-2s cos?/P)
• where
• r is the radius of largest water-filled pore
• s is the surface tension of water
• ? is the contact angle on the porous solid
• P is the absolute pressure applied

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Observed Differences

• Differences between elk only and elkcattle very
  slight.
• In JO and MM, no-grazing plots have more
  extensive gopher activity.
• Above ground biomass is greater in no-grazing
  plots.
• No-grazing plots are softer and more diggable.

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Intrinsic Permeability
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Dry Root Biomass, Top 10 cm
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Bulk Density
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Pore Size Distribution Curves
Blue ElkCattle Red Elk Only Green No
Grazing
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Thin Sections, HP
Elk Cattle
No Grazing
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What all this means

• Results point to a very slight recovery of soil
  properties.
• Meadow recovery takes place slowly.
• An increase in plant cover doesnt mean soil has
  recovered.
• Meadows with gophers show greater recovery.

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• So What?
• Carl Davis, USFS Soil Scientist

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Management Implications

• After extended heavy grazing, soil can take a
  long time to recover.
• Simple cessation of grazing is not an effective
  short-term fix.
• Repeated fertilization of meadows may be required
  to see a long term effect on recovery.
• Dont discourage gophers. They help to loosen
  the soil.

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If I knew then what I know now...

• Sample over a wider area within each exclosure.
• Take much larger root biomass samples.
• Sample when soil is more moist.
• Measure aggregate stability and soil strength.
• Think twice before using a previously designed
  experiement.

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Thanks to USDA PNW Forest Research Lab Wenatchee
National Forest Committee Dr. Paul McDaniel,
Dr. Markus Tuller, Dr. Jeff Braatne. Anita
Falen Mark Williams
Photo courtesy of PNW research lab.
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Special thanks to Jason Jimenez for heroic feats
of fieldwork!
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Any Questions?