Resilience of a Subalpine
Ecosystem in the Southern
Rocky Mountains to Past
Changes in Hydroclimate and
Disturbance Regimes
Thomas Minckley
Bryan Shuman
AGU 2011
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Drought as a norm
• The decade of 2002-2011
was the warmest since
1850
• Prolonged droughts
are likely more normal,
than anomalous
1200 year long stream-flow reconstructions from tree rings
for the Colorado River at Lees Ferry (Meko et al. 2007, GRL
34, L10705)
AGU 2011
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Drought as a norm
AGU 2011
Pribyl and Shuman, in review
Minckley et al. 2012, Ecol Mono. In press
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The Past as a Proxy
• Functionally the past
allows for an evaluation
of how western forests
may respond to
drought in the future.
Little Windy Hill Pond, 2008
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The Past as a Proxy
• What was the response
of subalpine forests to
prolonged drought in
the past?
• If a response occurs,
how do forests recover
in structure?
AGU 2011
Little Windy Hill Pond, 2008
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The Past as a Proxy
• We hypothesize that
regional forest
remained resilient in
context of hydroclimate
pushes
– Broad climatic tolerance
– Non-steady state
landscapes of pioneer
species
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Little Windy Hill Pond, 2008
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The Past as a Proxy
• Little Windy Hill Pond
–
–
–
–
2980 m asl
2.2 ha lake
10.7 ha watershed
Contiguous Forest
• (not at ecotone)
Little Windy Hill Pond, 2008
AGU 2011
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Vegetation History
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• Rapid transitions in
vegetation record
• Periods of low lake level
– 10.7 ka
– Prior to 10.7 ka
– 10.2 ka
– 7.3 – 5.2 ka
– 8.4 ka
– 3.7 – 2.5 ka
– 7.2 ka
– 1.5 ka
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Forest responses over the last 8000 years
Fire Response
Drought Response
Minckley and Shriver, J. Fire Ecology 2011
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• Summary of changes
– Largest magnitude
change was Holocene
transition
• Increased water levels
• Increased fire frequency
– Fire more frequent in
relatively wet periods
– Vegetation change not
strongly correlated with
hydrologic transitions
– Succession process
observed in fire free
intervals
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State Space Diagram modified from Turner et al.’s (1993) and Webb (1986) representing disturbance–
vegetation interactions, and incorporating concepts of climate–vegetation equilibrium
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Conclusions
• Paleoenvironmental
record provides some
context for optimism.
– While moisture
availability varied over
the last 6-8 ka,
vegetation did not
– Severe drought does not
necessarily result in
greater fire risk
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Conclusions
• Paleoenvironmental
record provides some
context for optimism.
– Prolonged droughts
(beyond management
horizons) occurred,
but in the past these
events do not appear
to have affected midelevation forests
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