Resilience of a Subalpine Ecosystem in the Southern Rocky Mountains to Past
Changes in Hydroclimate and Disturbance Regimes
Thomas Minckley
Bryan Shuman
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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
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1200 year long stream-flow reconstructions from tree rings for the Colorado River at Lees Ferry (Meko et al. 2007, GRL 34, L10705)
Drought as a norm
AGU 2011 3 Minckley et al. 2012, Ecol Mono. In press
Pribyl and Shuman, in review
The Past as a Proxy
• Functionally the past
allows for an evaluation
of how western forests
may respond to
drought in the future.
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Little Windy Hill Pond, 2008
• What was the response
of subalpine forests to
prolonged drought in
the past?
• If a response occurs,
how do forests recover
in structure?
The Past as a Proxy
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Little Windy Hill Pond, 2008
• We hypothesize that
regional forest
remained resilient in
context of hydroclimate
pushes
– Broad climatic tolerance
– Non-steady state
landscapes of pioneer
species
The Past as a Proxy
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Little Windy Hill Pond, 2008
• Little Windy Hill Pond
– 2980 m asl
– 2.2 ha lake
– 10.7 ha watershed
– Contiguous Forest
• (not at ecotone)
The Past as a Proxy
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Little Windy Hill Pond, 2008
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Vegetation History
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• Rapid transitions in vegetation record
– 10.7 ka
– 10.2 ka
– 8.4 ka
– 7.2 ka
– 1.5 ka
• Periods of low lake level
– Prior to 10.7 ka
– 7.3 – 5.2 ka
– 3.7 – 2.5 ka
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Forest responses over the last 8000 years
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Drought Response Fire Response
Minckley and Shriver, J. Fire Ecology 2011
• 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 mid-
elevation forests
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