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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