Drought Impacts on Southwest PinyonJuniper Woodlands

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Drought Impacts on Southwest Pinyon-Juniper
Woodlands
Michael Clifford1 Neil Cobb1, Monique Rocca2 ,
Robert Delph1, and Paulette Ford3 1Northern
Arizona University,2Colorado State University,
3USDA Forest Service Rocky Mountain Research
Station, Albuquerque, NM .
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PCM - 20th Century ExperimentsForcings Combined
Natural-Anthropogenic and Natural Only
Observed
Natural Only
Meehl et al. (2004)
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Area of Drought Mortality on Colorado Plateau
Pinyon
Ponderosa
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2003 Pinyon and Ponderosa damage
Damage (sq km) Pinyon / Ponderosa Arizona
40917.95 / 26354.98 Utah 7368.45 /
112.91 Colorado 31766.57 / 7853.64 New Mexico
30444.96 / 2594.48
Lisa Floyd
New Mexico Study Area
Other Regional Study Sites
PJ Mortality
JFSP Study Areas
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2004 Pinyon and Ponderosa damage
Damage (sq km) Pinyon / Ponderosa Arizona 533.40
/ 2198.28 Utah 6696.69 / 202.33 Colorado
23529.12 / 1543.81 New Mexico 4957.82 / 2317.97
Lisa Floyd
New Mexico Study Area
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2005 Pinyon and Ponderosa damage
Damage (sq km) Pinyon / Ponderosa Arizona 190.23
/ 364.41 Utah 521.79 / 3.63 Colorado 1295.62 /
2564.18 New Mexico 57.25 / 971.10
Lisa Floyd
New Mexico Study Area
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Causes Consequences of Drought/Bark Beetle
Outbreaks on PJ Woodlands
Mortality Promoting Factors Tree Density
Altered Stand Structure Fire Regimes Age
Distribution Species Fuel Loads
Community Responses Herbaceous Plants
Invasives (Cheatgrass) Ground-Dwelling
Arthropods
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Intensive Study sites
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Mortality Promoting Factors Tree Density
Paradigms

• Tree densities are unnaturally high due to
  historic
• fire suppression grazing

• Tree densities represent unhealthy systems that
• predispose trees to mortality

Negron and Wilson (2003) Tree density
positively correlated with early drought
mortality (1997-98) in PJ Woodlands
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Mortality patterns in piñon-juniper woodlands in
Colorado, New Mexico and Arizona Does increasing
stand density increase tree mortality? (In
Submission Western Journal of Applied Forestry)
M. Lisa Floyd, Neil Cobb, Dustin Hanna, Robert
Delph, Michael Clifford, and Paulette Ford
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Pinyon-Juniper Woodlands need to be thinned to
reduce susceptibility to Drought/Bark Beetles
Not Supported
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Altered Stand Structure Fire Regimes P-J
Stand Structure Fuel Loads
Stand Structure Document change in age structure
and species composition
Fire Behavior Models Parameterize fire behavior
models with fuel loads and show variability at
the stand-, landscape-, and regional scales.
Refined Models will be used to forecast long-term
changes in forest structure and fire regimes that
will result from the recent drought
Suggest Effective Strategies for achieving
desired future conditions, and help design
treatment prescriptions for individual management
units
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Change in Pinyon Stand Structure
Total number of Pinyons
0.1-2.5
gt30.1
5.1-7.5
2.6-5.0
7.6-10.0
12.6-15.0
10.1-12.5
17.6-20.0
20.1-22.5
22.6-25.0
25.1-27.5
27.6-30.0
15.1-17.5
Basal Diameter (cm)
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Change in Stand Structure
Total number of Pinyons and Junipers
Basal Diameter (cm)
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North
South
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(From Arizona)
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Drought Effects on Fire Behavior

• Changes in fuel structure
• short term (1st year) widespread tree mortality
  ? sudden increase in available canopy fuels
• medium term (next several years) rearrangement
  of fuels ? from the canopy to the ground
• Stand Factors affecting Torching
• Canopy Base Height
• Fuel Loads
• Canopy Cover
• Stand Factors affecting Crowning
• Canopy Cover (Canopy Bulk Density)

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Modeling Mortality Impact on Fire Behavior in PJ
Woodlands
High Mortality Crowning Index
Low Mortality Crowning Index
Low Mortality Torch Index
High Mortality Torch Index
Fire Carries
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Community Responses Herbaceous Plants
Invasive Species Ground-Dwelling Arthropods
Tree Mortality
Water Nutrients
Herbaceous native exotic plant abundance and
diversity
Disturbance
Open Habitats
Microhabitats
Ground-dwelling Arthropod abundance and diversity
Habitat Complexity
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Ground-Dwelling Arthropods

16 Indicator Species

No Difference in Abundance

No Difference in Diversity
(Overall Weak Response)
Other Herbaceous Plants

10 Indicator Species

No Difference in Forbs

No Difference in Cheatgrass
(Overall Weak Response)
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Predicted Ecological Changes over Time
Fuels
Arthropods
Relative Change
Herbaceous
Time (Years)
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Conclusions
Tree Density not associated with rates of
mortality
Stand Structure greatly altered in north
central New Mexico, older piñons removed
Fire Model suggests torching greater in mortality
sites
Herbaceous plants ground-dwelling arthropods
show weak responses
Funded by the USFS Rocky Mountain Research
Station, Albuquerque NM
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DIREnet Projects (Papers and Proposals)
Characterizing the Spatiotemporal Progression of
Vegetation Die-Off Induced by Drought in the US
Southwest
Kamel Didan, The University of Arizona (8 PIs, 8
Institutions)
Do Extreme Droughts Act as Genetic and
Physiological Bottlenecks in Water-Limited
Systems?
Kiona Ogle, University of Wyoming (6
Investigators, 5 Institutions)
Implications of Regional Scale Tree Die off for
Land Surface Atmosphere feedbacks Consequences
of Climate Change
David Breshears, University of Arizona(5
Investigators, 5 Institutions)
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2002
2003
Lisa Floyd
New Mexico Study Area
Other Regional Study Sites
PJ Mortality
JFSP Study Areas