climate change and california forests malcolm north sierra nevada research center, davis, ca

Climate Change and California Forests

Malcolm NorthSierra Nevada Research Center, Davis, CA

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Greatest changes are in nighttime minima

Tahoe City1875 m

Courtesy of Hugh Safford

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HAD = Hadley Center 2 model: Very warm-wet future

PCM = Parallel Climate Model: Warm-dry future

California future climates: alternate scenarios

Source: Electrical Power Research Institute 2003

60% of climate models predict increased ppt for California in general

23% predict decrease

17% predict no change


Expansion of C4 grassland

Warming benefits broad-leaved spp at expense of needle-leaved

Loss of habitat as warming drives veg-types higher

Loss in shrubland due to increase in fire (= grassland) or higher ppt (= trees)


Vegetation Vegetation community responsescommunity responses

Historic conditions, and predictions for 2100 based on the Hadley and PCM models

Lenihan et al. 2003. Ecol Appl 12.


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Species-specific responses: species will respond based on their own physiological response and their interactions with other species. Future communities will not look

like current communities.

Chaparral and gray pine


Centennial-Scale Climate Trends HoloceneCentennial-Scale Climate Trends Holocene

MULTI-PROXY ANALYSIS

Early Holocene 10500 to 7500 YBP Warming

Mid-Holocene 7500 to 5000 YBP Warmest, Dry

Post Mid- Holocene

Transition 5000 to 3500 YBP Cooling, Wetter

Neoglacial 3500 to 2600 YBP Cool, Wet

Post-Neoglacial

Drought 2600 to 1600 YBP Intense Drought

Post-Drought Transition and Medieval

Warm Period 1600 to 650 YBP Dry but Summer Wet

Little Ice Age 650 to 150 YBP Cool Wet, Cool Dry

Recent < 150 YBP Warm, wetFrom Tausch et al. 2004

Courtesy Connie Millar

Giant Sequoia Glacial: Interglacial Dynamics

East Lk, 2863m, < 10kyr

Kings Cyn, 1000m, 20kyr

Central Valley, 54m, 26-22kyr

Mono Lk, 1950m, 10-11.5kyr

Current range,

W Sierra,

1370-2200m

Davis 1999a, Davis 1999b, Power 1998, Cole 1983

Past Climate Analogs:

Mid Holocene: (3,000 B.C.-1,500 B.C.)Wetter period: Increase in fir and cedar, relative to pine and a decrease in oak

Middle Warming Period (approx. 900-1200 A.D.):Rise in tree line but no significant vegetation shifts

Early 20th Century (1880’s-1950):Warming (recovery from little Ice Age) and wet period

Reconstruction or Pre-European Period (1800-1840)Very unusual period: end of the little Ice Age with cool, dry conditions

Historic Climate Naturally Fluctuated • Cyclically

• Nested Time Scales - Millennial - Centennial - Decadal

- Interannual • Rapid and Abrupt Transitions

Plants track climate at each scale, but respond with unexpected lags and threshold behaviors

Millar 2003

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Southern California forests: interactions of multiple stressors

Who wins?

Pollution Insects/disease Temps H2O stress Fire


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Before fire suppression (1865 on this graph), tree death and recruitment is pulsed by fire and El Nino events

North et al. 2005

Oaks were especially sensitive to temperature;

Oak species fluctuated from rare to widespread in W Sierra

Anderson & Smith, 1994

20th Century Responses: Meadow Invasion Central High Sierra Nevada Studies

Found increased colonization in diverse meadows with variable environmental, vegetative, & land-use histories

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• Mortality in the forest is now primarily driven by drought and beetles • Tree density, from fire suppression contributes to drought stress• The populations of some insects, including many bark beetles, are kept in check by cold over-wintering temperatures

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* Mortality significantly higher than expected in high density and lower in low density

No Burn Burn

Snowpack: Snowpack:

Nitrogen:

None AdditionReduction

Nitrogen: None Addition Reduction

None Control +S - S None Burn only

+ S - S

Addition + N + S + N - S+ N

Addition + N + S+ N - S+ N

What may happen to mixed-conifer understory herbs and shrubs with increasing nitrogen from air pollution, an increase

or decrease in snowpack, and with and without fire?

• Herb biomass increased in shrub dominated communities when snow pack was reduced. • Nitrogen additions unexpectedly increased herbaceous species richness.

• Fire was a more important factor in post-treatment species richness and cover than either snow pack addition or reduction.

Hurteau and North. In press.

1865 Reconstruction

Pre-treatment

Post-treatment Pre- to Post-Treatment

C Treatment: tC/ha Trees/

ha tC/ha Trees

/ha tC/ha Trees/

ha % change

Control 237 70 193 373 NA NA 0 Burn only 204 70 201 412 198 353 -1.5 Understory thin

255 73 238 428 173 232 -27.3

Understory thin and burn

215 67 217 421 144 142 -43.7

Overstory thin

215 61 204 327 89 150 -56.4

Overstory thin and burn

184 60 185 416 66 93 -64.4

What are the effects of different fuel treatments on forest carbon storage and emissions under modeled wildfire scenarios?

Hurteau and North. In review.

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Amount of carbon accumulated after 100 years without wildfire

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Amount of carbon released during prescribed burns over 100 years

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Amount of carbon accumulated after 100 years with a wildfire in 2010

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Control Burn Understory Thin Understory Thin Burn Restoration Restoration Burn 1865 1865 Burn


Amount of carbon accumulated after 100 years with a wildfire in 2050

Treatment 2100 Live Tree tC

Rx Fire tC Released

2040 Trees/ha

2050 Wildfire tC Released

Total Released(tC/ha)

2100 Carbon Budget

Control 200.5 NA 541 40.9 40.9 159.6Burn 303.2 55.9 322 19.5 75.4 227.8Understory Thin

240.6 NA 479 25.9 25.9 214.7

Understory Thin + Burn

161.6 46.5 244 15.1 61.6 100.0

Restoration 244.3 NA 241 24.0 24.0 220.3Restoration + Burn

232.3 41.9 89 12.6 54.5 177.8

1865 268.7 NA 215 16.9 16.9 251.81865 + Burn 277.4 27.3* 166 9.4 36.7 240.7

The amount of carbon (tC/ha) stored in live trees and the total amount released over the model’s 100 year run for all prescribed burns (Rx) and for the 2050 wildfire. The 2100 carbon budget is the amount of carbon stored in live trees in 2100 minus the total released in all prescribed fires and the 2050 wildfire for each of the eight treatments. The 2040 trees/ha is each treatment’s stand density in the nearest time step before the 2050 wildfire.

Control WF2050

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Conclusions:A.Forest communities are unlikely to simply move up

in elevation or latitudeB. Tree species will respond differently, making future

forest compositions difficult to predictC. Snow pack reduction may benefit herbs, but fire is

still the strongest influence on the understoryD.Bark beetles may become a real problem in high

density forests, particularly as winter and night time minimum temperatures rise

E. A preliminary FVS model suggest fuels treatments producing a low-density stand structure dominated by large fire-resistant pines may best protect carbon sinks in wildfire prone forests

climate change and california forests malcolm north sierra nevada research center, davis, ca

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